high-performance ceramic lubricating materials

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Advances in Materials Science Research. Volume 17

Maryann C. Wythers

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ADVANCES IN MATERIALS SCIENCE RESEARCH

ADVANCES IN MATERIALS SCIENCE RESEARCH VOLUME 17

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ADVANCES IN MATERIALS SCIENCE RESEARCH

ADVANCES IN MATERIALS SCIENCE RESEARCH VOLUME 17

MARYANN C. WYTHERS EDITOR

New York


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Published by Nova Science Publishers, Inc. † New York


CONTENTS Preface Chapter 1

Chapter 2

vii Polymeric Micro and Nanoparticles as Drug Carriers and Controlled Release Devices: New Developments and Future Perspectives M. T. Chevalier, J. S. Gonzalez and V. A. Alvarez Chemical Modifications of Natural Clays: Strategies to Improve the Polymeric Matrix/Clay Compatibility Romina Ollier, Matias Lanfranconi and Vera Alvarez

Chapter 3

High-Performance Ceramic Lubricating Materials Yongsheng Zhang, Yuan Fang, Hengzhong Fan, Junjie Song, Tianchang Hu and Litian Hu

Chapter 4

Physical and Chemical Characteristics of Pincina Alginate Svetlana Motyleva, Jan Brindza, Radovan Ostrovsky and Maria Mertvicheva

Chapter 5

Chapter 6

Relaxation and Dynamics of Spin Charge Carriers in Polyaniline V. I. Krinichnyi New Polyalkenyl-Poly (Maleic-Anhydride-Styrene) Based Coupling Agents for Enhancing the Fibre/Matrix Interaction Csilla Varga

Index

1

55 83

93

109

161 207



PREFACE Materials science encompasses four classes of materials, the study of each of which may be considered a separate field: metals, ceramics, polymers and composites. This volume gathers important research from around the globe in this dynamic field including research on the outstanding contributions in the area of polymeric micro and nanoparticles as drug delivery systems; strategies to modify the inorganic clays and to make them compatible with polymeric matrices and the effect of each one; present problems of ceramic lubricating materials, and the design principle of these materials; the study of Pincina alginite and its applications; the methods of determining the composition of polarons with different mobility and their main magnetic, relaxation and dynamics parameters from effective EPR spectra and the development of glass fibre reinforced polyester composites. Chapter 1 – There are many disadvantages associated with the use of certain drugs. These are distributed in the organism according to their physical properties such as solubility, partition coefficient and charge. In consequence, drugs can reach a variety of sites where they are outside of their therapeutic range, where they are inactive, or where their action is unwanted or harmful and therefore with negative side effects. Therefore, therapeutically effective and patient-compliant drug delivery systems continuously lead researchers to design novel tools and strategies. Polymeric micro and nanoparticles are micron and submicron size entities made from a wide variety of polymers. Because of their potential ability to improve current disease therapies these micro and nanodevices are being extensively used as drug carriers and controlled release systems in the field of medicine and pharmacy. Indeed, active pharmaceutical ingredients can be encapsulated, covalently attached, or adsorbed onto such carriers. Since all the novel possibilities offered by such


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devices many methods have been developed in order to prepare micro and nanoparticles, these methods depends almost exclusively on the polymer and the drug employed. In addition, drug loading and drug release mechanisms from these particulate carriers and its biodistribution in the human organism have attracted the attention of the researchers. Among all the approaches proposed in the last years in this scenario, this chapter presents the most outstanding contributions in the area of polymeric micro and nanoparticles as drug delivery systems. Chapter 2 – Polymer/clay nanotechnology age started with Toyota‘s work about clay particles exfoliation in nylon-6, by the last 80‘s and the beginnings of the 90s. The improvements on several properties of the polymeric matrices have been improved by the addition of nanometric scale particles. The most used nanoparticles to reinforce polymeric materials are layered silicates. Their crystalline net consists of bi-dimensional layers where a central octahedral layer of either alumina or magnesia is joined to two external tetrahedrons of silica in such a way that the oxygen ions of the octahedral layer also belong to the tetrahedral layers. In order to obtain the best properties, the key point is the dispersion of the clay particles inside the polymeric matrix but the tendency of the particles to agglomerate is difficult to overcome. In addition, most of the polymers are hydrophilic and original clays are hydrophilic. In order to make them (matrix and clay) more compatible, some chemical treatment will be required. Although there are different ways to optimize the polymer/clay compatibility, the most popular method consists on converting these hydrophilic silicates to organophilic ones by performing chemical treatments of the clay. In this chapter several strategies to modify the inorganic clays and to make them more compatible with polymeric matrices are studied and the effect of each one, together with the relevant parameters, is established. Chapter 3 – With the rapid development of modern technology, various machineries have proposed changes in lubricating materials. These are geared toward improving the property of materials and allowing them to surmount severe challenges under extreme conditions (e.g., high/low temperature, special media, atmosphere, etc.) in the fields of aviation, space, nuclear energy, microelectronics, and so on. The ceramic lubricating material is a new solid lubricating material composed mainly of a ceramic matrix, reinforcing phase and solid lubricant. This ceramic lubricating material shows good performance in high temperature and corrosion resistance due to its ceramicskeleton. Moreover, the ceramic lubricating composite is the only material that can work above 1,000℃, while maintaining low density and excellent


Preface

ix

corrosion resistance. These materials are considered to be high temperature lubricating technology with the most development potential and practical value. This chapter has analyzed the research focus and present problems of ceramic lubricating materials, and then proposed the design principle of these materials. The design, preparation and performance of several typical ceramic lubricating materials were introduced. Based on these studies, the authors developed a kind of ceramic lubricating composite which has low wear, high reliability and long life, and provide theoretical guidance and technology support for the application of new ceramic materials in the fields of high technology. Chapter 4 – The study of the natural resources necessary for their rational, efficient and "intelligent" use. This is one of the most pressing issues of our time. Ore and non-ore potential of the Slovak Republic is restricted by the size of its area. Each successful result of geological research uncovering modest raw material supplies is considered to be worthy. Since 1990 the alginite bed situated in Lučenec Valley, locality of Pincina village, has been considered in the above mentioned sense. Alginite represents a rock with relatively high organic matter content which was sedimenting together with the clays in post volcanic outbursts during geological periods appropriate for algae occurrence. Alginite has a wide variety of utilization as an ecological raw material. Natural character, absence of phytotoxicity, effective economy of mining technology and ecologization of farming systems, those are the arguments for alginite to be included among such materials like zeolites and bentonites which have already achieved a possition for useful agricultural utilization. Alginite is a 3-4 million year old specifically rock as it is originated from the accumulated fresh water in the caldera of the volcano of the Pannonia Sea. It is due to a special sedimentary process. Rocks washed into the water of the crater started to flake due to the oxygen and bacteria, so the water became rich in nutrients. Being rich in minerals and organic nutrients led to the proliferation of some lower class organisms, for example green algae (Clorophyta). The algae built into their organisations the micro- and macro components that helped their existence. After perishing they got into the bottom of the lake among reductive conditions. Majority of the organic materials did not dissolve, but it mixed with the non-organic material and became Alginite. Alginite is organic and it basically consists of algae and nonorganic materials such as basalt rubble, calcipelite, dolopelite and diatomite. Our research focuses on the study of Pincina alginite. Alginity have a layered structure. Its solidity is 0,5-1,5 kg/cm2 and its consistency is 2,1-2,4 gr/cm3. Its water content is 17-35% which decreases to 4-5% under laboratory


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Maryann C. Wythers

circumstances and its volume reduced to 1,122 kg / l. By scanning electron microscopy (SEM), the peculiarities of the surface microrelief. Measured the size of the macro-and micropores. Identified floral remnants, obtained information on the safety, location and mineralization of organic matter in the algin. The method of energy dispersive spectrometry revealed that the mass fraction (%) macro is: Na (0.64), Mg (0.54), Al (13.48), Si (27,57), K (2.39), Ca (0.75). In laboratory experiments using HPLC studied the chemical composition of water and alcoholic extracts from various fractions alginite. Chapter 5 – The main results of the study of charge transfer in polyaniline modified with sulfuric, hydrochloric, camphorsulfonic, 2-acrylamido-2methyl-1-propanesulfonic and para-toluenesulfonic acids at various (9.7 – 140 GHz) wavebands EPR obtained in the Institute of Problems of Chemical Physics RAS are summarized. The methods of determining the composition of polarons with different mobility and their main magnetic, relaxation and dynamics parameters from effective EPR spectra are described. The dependences of the nature, electronic relaxation, dynamics of paramagnetic centers, and the charge transfer mechanism on the method of synthesis, the structure of the acid molecule, and the polyaniline oxidation level are shown. Chapter 6 – Although several types of fibres and matrices have appeared in the last four decades in military and aircraft applications in the weekdays glass fibre reinforced polyester composites are the most widely used among thermoset matrices since proper, satisfactory properties can be coupled with low cost by their application. Therefore, development of glass fibre reinforced polyester composites is always timely. For treating the surface of the glass fibres such polyalkenyl-poly (maleicanhydride-styrene) based coupling agents have been synthesized at the authors‘ Department which are able to improve the different mechanical properties of the polyester and vinyl ester composites by enhancing the fibre/matrix interactions. The preliminary aspect of choosing the adequate structure of the additives was to establish possibly strong interactions between the fibre and the additive and between the additive and the matrix. Furthermore, economical aspects of the production and application of the additives were also to keep in mind as the advantageous price/value ratio is also needed for possible substitution of the expensive silane based sizings applied by the glass fibre producers. So therefore, the effects of the additive treating of different forms of Eglass fibres (chopped fibre mat and woven [0/90°] fabric) both silane sized and unsized types will be dealt with. Analytical information about the additives has


Preface

xi

been collected by FT-IR and GPC measurements for determining the most possible structures of them. The minimally needed concentration and optimal impregnation times will also be shared. Moreover, the effects of the molar rate of the additional chemicals (alcohols and amines) used for creating the proper structure of the additives have also been investigated both with chopped fibre mat and woven [0/90°] fabric reinforcements. Weathering behaviour will also be detailed, exactly the effects of the additive treating on the water-uptake of the composites and on the mechanical properties either. Tensile, flexure and impact properties of the polyester and vinyl ester composites will be discussed. SEM micrographs taken of the broken surface of the composites have been used to study the fibre/matrix interactions. FT-IR technique and FT-Raman Microscopy measurements have been carried out in order to arrive at a comprehensive understanding how the structures of our newly developed coupling additives influence the fibre/matrix interface.



In: Advances in Materials Science Research … ISBN: 978-1-62948-734-2 Editor: Maryann C. Wythers © 2014 Nova Science Publishers, Inc.

Chapter 1

POLYMERIC MICRO AND NANOPARTICLES AS DRUG CARRIERS AND CONTROLLED RELEASE DEVICES: NEW DEVELOPMENTS AND FUTURE PERSPECTIVES M. T. Chevalier*, J. S. Gonzalez and V. A. Alvarez Composite Materials Group (CoMP) - Research Institute of Material Science and Technology (INTEMA), Engineering Faculty, National University of Mar del Plata, Mar del Plata, Argentina

ABSTRACT There are many disadvantages associated with the use of certain drugs. These are distributed in the organism according to their physical properties such as solubility, partition coefficient and charge. In consequence, drugs can reach a variety of sites where they are outside of their therapeutic range, where they are inactive, or where their action is unwanted or harmful and therefore with negative side effects. Therefore, therapeutically effective and patient-compliant drug delivery systems continuously lead researchers to design novel tools and strategies. Polymeric micro and nanoparticles are micron and submicron size entities made from a wide variety of polymers. Because of their potential ability to improve current disease therapies these micro and nanodevices are being extensively used as drug carriers and controlled release systems in *

Tel: 0054 220 4816600 int. 321, [email protected].


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M. T. Chevalier, J. S. Gonzalez and V. A. Alvarez the field of medicine and pharmacy. Indeed, active pharmaceutical ingredients can be encapsulated, covalently attached, or adsorbed onto such carriers. Since all the novel possibilities offered by such devices many methods have been developed in order to prepare micro and nanoparticles, these methods depends almost exclusively on the polymer and the drug employed. In addition, drug loading and drug release mechanisms from these particulate carriers and its biodistribution in the human organism have attracted the attention of the researchers. Among all the approaches proposed in the last years in this scenario, this chapter presents the most outstanding contributions in the area of polymeric micro and nanoparticles as drug delivery systems.

Keywords: Nanoparticles, drug delivery, biodistribution, targeting

INTRODUCTION Nowadays, targeted delivery of drug molecules to specific sites represents a big challenge for researchers in pharmaceutical sciences [1]. A new frontier in the field of biomedical technologies was opened by the developing of drug delivery devices such as, liposomes [2], micelles [3], dendrimers [4], micro and nanoparticles [5]. All these drug delivery systems (DDS) attempt to improve the therapeutic effect of drugs mainly by improving their biodistribution and modulating drug release [6]. Within all the drug delivery systems, nanoparticles present numerous advantages, mainly associated to their special characteristics, such as, small particle size, large surface area and huge versatility to customize and personalize their surface [7-8]. Since the term ―nano‖ has become so familiar; it is important to define it properly or state understandable criteria to call something ―nano‖ in the field of drug delivery; otherwise, confusion and misunderstanding can easily appear. In its fact sheet the FDA speaks about nanotechnology as an emerging technology that has the potential to be used in a broad array of FDA-regulated products, including medical products, foods and cosmetics (U. S Food and Drug Administration, Fact Sheet: Nanotechnology, April 2012). Nanomaterials are measured in nanometers (equal to about one-billionth of a meter) so small that they cannot be seen with a regular microscope. These nanomaterials can have different chemical, physical, or biological properties than their conventionally-scaled counterpart materials used in many products regulated by FDA. Then, even when generally the term ―nano‖ is used to refers particles with sizes between 1 to


Polymeric Micro and Nanoparticles as Drug Carriers …

3

100 nm; we cannot cling to this definition strictly since submicron particles (from 10 to 1000 nm) can also shown special properties and they are commonly referred as nanoparticles in the field of pharmaceutics and medicine. The application of nanotechnology in order to reach goals from medicine has recently been defined as ―nanomedicine‖ [9]. This is an extremely explored area of research but also nanomedicine has become clinical in the last years since the remarkable developing and production of nano-size drug delivery systems. Since 1990 regulatory entities have approved several products for clinical use and, between them, it is easy to identify different nano-devices that nanoscience has introduced us since its beginnings [10]. However, there are many unsolved problems in medicine associated mainly with the unspecific action of certain drugs used in urgent diseases and material science has become determinant to drug delivery sciences, especially to modulate and define drug release mechanisms. A wide variety of biodegradable and non biodegradable polymers have been used in drug delivery research ([11]; [8]). It has been demonstrated that active pharmacological ingredients (APIs) can be encapsulated, covalently attached, and/or adsorbed onto nano-carriers as polymeric nanoparticles in order to effectively deliver the drug to a target, improving in this way the therapeutic effect while minimizing side effects ([12] ; [13], [14]). Polymeric nanoparticles con easily overcome drug solubility difficulties, stability and specificity issues but it is important to always remember that the drug encapsulation efficiency and the release profile from polymeric nanocarriers will depend on the polymer-drug couple we are going to work with [13]. For this reason, in order to synthesize drug loaded polymeric nanoparticles, a precise previous study of each component of the desire formulation is needed [15]. How useful a nanoparticle delivery system would be depends on the bio-acceptability of the carrier polymer, which is also affected by the particle size, shape, and physicochemical properties of the polymer and the drug [13]. The election of one particular polymer will mainly rely in the therapeutic goal and, since there are plenty of polymers used nowadays in the biomedical field, the possibilities are wider every day. In this scenario, this review presents the most outstanding contributions in the area of polymeric micro and nanoparticles as drug delivery systems, including the preparation and characterization methods, biodistribution and targeting and release mechanism.


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M. T. Chevalier, J. S. Gonzalez and V. A. Alvarez

AN OVERVIEW OF DRUG DELIVERY SYSTEMS Nanotechnology is the area of science in charge of the construction of structures in the nanometer scale size; these nano-scale structures may possess unique properties that can be used to achieve specific purposes to benefit human existence [6]. Despite the fact that the new generation of drugs that have been developed as a result of genomics and proteomics have shown potency and specificity in their therapeutic action, they also have shown limitations because of their instability in the biological environment and their potential inaccessibility to the target site ([16]; [17]; [1]). Drug delivery systems can be defined as devices capable of perform mechanisms to introduce therapeutic agents into the body [16]. The ability to target and control the release of a drug are the two main requirements that and ideal drug delivery system must complies. But there are also other general objectives, drug delivery researchers attempt to develop nano-carriers capable of:      

Act as a vehicle for a wide variety of therapeutic agents. Protect drug molecules from degradation in the human organism before reaching the target site. Modulate release rate in the target site to achieve the adequate pharmacological response. Be customized in order to effectively reach the specific target in the human body. Achieving intra or extracellular drug delivery depending of the therapeutic goal. Be biocompatible and be able to biodegrade in order to be safe for human administration [16].

Several nano-devices were developed and applied to drug delivery such as nanoparticles, nanocapsules, liposomes, micelles, dendrimers and more. In this section the most relevant nano-carriers are described.



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Polymeric Nanoparticles Although nanotechnology is nowadays applied in several fields, biodegradable nanoparticles are most of all used to improve the therapeutic effect of water soluble/insoluble active pharmacological ingredients by improving its retention time, biodistribution, bioavailability, solubility and specificity ([18], [8]). The development of this kind of nanocarrier lead to a new strategy to reduce patient expenses, increase patient compliance to the treatment and decrease patient risks of toxicity [8]. Polymeric nanoparticles (Figure 1) made from biodegradable or nonbiodegradable, synthetic or natural polymers, represent one of the most relevant drug delivery vehicles nowadays due to their capability to modulate drug release effectively, improve encapsulation and bioavailability and decrease toxic side effects ([19]; [8]). There has been considerable attention relaying on the development of polymeric nanoparticles in the last decades. A wide variety of polymers [15] have been used to produce these nanodevices; like poly (D,L-lactic acid) (PLA), poly(D,L-lactic-co-glycolic acid)(PGLA) ([20]; [21]), poly-εcaprolactone (PCL) [22] and their copolymers diblocked or multiblocked with poly-ethylene glycol (PEG) ([23];[24]) between others that are going to be mention in the next sections [25].

Figure 1. Micro/nanoparticle carrying drug molecules within it matrix. (b) Micro/nanoparticle carrying drug molecules in its surface. (c) Micro/nanocapsule carrying drug molecules in its internal cavity.

Depending of the synthesis strategy these carriers can be nanoparticles, nanospheres or nanocapsules. These are three different kinds of nanodevices that will have different behavior regarding to the location of the drug molecules in the nanocarrier and to the release profile of the drug. In fact,


6


polymeric nanoparticles are able to perform a sustained drug release over a period of days and even months [16]. Nanoparticles based on PCL and PEG were synthesized and thoroughly investigated by Zamani et al. [26] and they have concluded that the prepared nanoparticles were suitable devices for drug delivery and their architecture make them good candidates for modulate drug release. In another study, Tewes et. al. [27] have described how the control of doxorubicin (DOX) polarity allows to encapsulate it inside poly (lactide-co-glycolide) (PLGA) nanoparticles formulated either by a single oil-in-water (O/W) or a double water-in-oil-in-water (W/O/W). They have indicated that the encapsulation of DOX in the nanoparticles formulated leads to increased pharmacological active ingredient entrapment efficiency and decreases the burst effect.

Liposomes Liposomes were first described by Bangham et al. in the 1960s but they were used as drug delivery system in the 1970s [19]. They are submicron microparticulate lipoidal vesicles which form spontaneously when natural or synthetic lipids are hydrated in aqueous media and as a result of this selfassembling process an aqueous volume entrapped by one or more bilayers of lipids is obtained [28]. Drug formulations with liposomes (Figure 2) have been developed with the objective of reduce side effects and improve the efficacy of the desired pharmacological response especially for a wide variety of lipophilic actives. However, there are several obstacles associated to the development of liposomal formulations such as limited physical stability of the dispersions, drug leakage and difficulties in upscaling [19]. Despite other nanocarriers such as polymeric NPs, offer some specific advantages over liposomes these lipoidal nano devices have been extensively investigated [18]. Liu et. al [29] have developed liposomes and nanoliposomes, respectively, formed both from a milk fat globule membrane (MFGM) phospholipid fraction and from soybean phospholipid prepared by thin layer dispersion and dynamic high pressure microfluidization methods. By evaluate the structure and the integrity of the liposomes during in vitro digestion as a function of time several observations were done: Liposomes synthesized from soybean were less stable than liposomes prepared from the MFGM phospholipid fraction and in general liposomes exhibited lower stability in simulated intestinal fluid (SIF) than in simulated gastric fluid (SGF). Obtained results



7

gave some information about the possible development of more stable liposomes in the gastrointestinal tract.

Figure 2. Drug loaded liposome.

Muthu et.al [30] develop liposomes which are coated with dalphatocopheryl polyethylene glycol 1000 succinate (TPGS), a PEGylated vitamin E, with docetaxel as a model drug for enhanced treatment of brain tumor in order to compare them with the nude liposomes as well as with the so-called stealth liposomes. The purpose of these liposomes was to enhanced cellular uptake and cytotoxicity of docetaxel in brain cancer cells. As a conclusion of this study Muthu et. al. [30] indicated that the prepared liposomes showed great advantages in vitro than the PEG coated liposomes.

Hydrogel Nanoparticles Hydrogel nanoparticles are outstanding drug delivery since they have unique properties as a result of combine hydrogel and nanoparticles special characteristics is for this reason that this nanodevices have gained the attention of the drug delivery researchers [31]. Hydrogels are polymeric 3D- networks


8


capable of absorb large quantities of water or biological fluids. They have an important water affinity because of the presence of hydrophilic functional groups such as amine, ether, sulfate, hydroxyl and carboxyl in the polymer chemical structure. Hydrogel nanoparticles allow high drug loading and this may be achieved without chemical reactions, as all drug nanocarriers it is expected and in several cases already shown that hydrogel nanoparticles are able to control and sustained drug release in the specific target site improving the therapeutic effect by reducing side effects [32]. Showing interesting advantages over other nanodevices polymeric hydrogel nanoparticles have been prepared from polymer of different nature. Among synthetic polymers, poly (vinyl alcohol), poly (ethylene oxide), poly (ethyleneimine), poly (vinyl pyrrolidone), and poly-N-isopropylacrylamidein have been extensively used and they have shown interesting features regarding drug delivery. According to the literature, chitosan and alginate are the most applied natural polymers to produce hydrogel nanoparticles. The drug release mechanism from the hydrogel nanoparticle will depend on the type of polymer uses as a result of three main factors; drug diffusion, hydrogel matrix swelling and chemical affinity of the couple drug/matrix [31]. Polysaccharide–PEG hybrid nanogels (CHPOA–PEGSH) crosslinked by both covalent ester bonds and physical interactions were prepared by Shimoda et al. [33] performing the reaction of a thiol-modified poly (ethylene glycol) (PEGSH) with acryloyl-modified cholesterol-bearing pullulan (CHPOA). In this study the size of the nanogel assemblies was in the range 50–150 nm. An extension of the elimination half-life of CHPOA–PEGSH nanoparticles compared with that of the nanogel. Thus, these nanoparticles can be utilized as injectable nanocarriers capable of controlled release of proteins such as cytokines over relatively long periods.

Solid Lipid Nanoparticles The poor solubility of therapeutic agents is one of the issues faced by drug delivery researchers [34]; [35]. The beginning of drug delivery systems for lipophilic drugs was in the 1960‘s when a fat emulsion was developed for parenteral nutrition, in this case drug molecules could be incorporated easily into the oil droplets [19]. However, there were disadvantages associated with this system being the main one the critical physical stability of the drug in the emulsion because of a reduction of the zeta- potential which can results in agglomeration, drug expulsion and eventually breaking of the emulsion [19].



9

Another lipid based carrier system are liposomes, first described in the 1970‘s, this drug delivery systems have shown several limitations [19] that have been discussed in previous paragraphs with more detail. Thus, in the middle of 1990‘s, as an alternative to emulsions and liposome, different research groups ([19]; [16]) has focused on nanoparticles made from solid lipid, consequently the so-called solid lipid nanoparticles (SLN) were developed ([19]; [16]). The SLN exhibits several advantages over its lipid-based predecessors such as, their good tolerability and biodegradation, improved physical stability and protection of the incorporated drug from even when we are considering labile drugs and at the same time this nano carrier minimize side effects of the pharmacological treatment [19]. SLN have been applied for targeting of drugs to the brain, and for drug delivery via parenteral, pulmonary, and dermal routes [16]. Cavalli et al. [36] have studied these nanoparticles as carriers for topical ocular delivery of tobramycin (TOB) with an average diameter below 100 nm. In that study it has been shown that compared with an equal dose of TOB administered by standard commercial eye drops, TOB-SLN produced a significantly higher TOB bioavailability in the aqueous humor. Proteins and antigens can be incorporated or adsorbed onto SLN, and further administered by parenteral routes or by alternative routes such as oral, nasal and pulmonary. Formulations using solid lipids nanoparticles improved protein stability, avoids proteolytic degradation, and modulate sustained release [19, 37]. Cyclosporine A, insulin, calcitonin and somatostatin have been incorporated into solid lipid particles and are currently under investigation [38]. Glyceryl behenate SLN loaded with vitamin A and incorporated in a hydrogel and o/w-cream was tested by Jenning et. al. [39] with respect to their influence on drug penetration into porcine skin in order to evaluate the potential application of SLN in dermatology and cosmetics. Vitamin A concentrations in the skin tissue indicated a certain drug localizing effect when SLN were compared with conventional formulations. Carrillo et al. [40] reported the use of cationic solid lipid nanoparticles developed by the technique of microemulsion, which are complexed with DNA in order to study their application as non-viral vectors in gene therapy.


10


Dendrimers Dendrimers (Figure 3) have been discovered in the early 1980‘s, they are macromolecular systems constitute by an inner core surrounded by a variable but well defined number of branches generations [16]. Nowadays dendrimers represent a very important type of drug delivery systems. The can be defined as an ubiquitous type of precisely defined polymers able to be used in several applications [41]. Dendrimers have unique characteristics including a branched layered architecture which confers them a globular structure and internal cavities that enhance sequestration; they also display a large numbers of terminal groups in their surface that leads to a potential multivalency. Because of all of these special properties dendrimers are considered as promising devices for biomedical applications and especially as drug nano-carriers [41-44]. Drugs may be physically entrapment in or of the dendritic skeleton depending on the respective size and ratio of the active pharmacological ingredient and the dendrimer.

Figure 3. Drug loaded dendrimer.

These nano-devices have been extensively studied as drug delivery systems performing either covalent or noncovalent association with the drug, in both cases multivalent sites play a crucial role [41-42, 45]. A very important feature of these drug delivery systems in that in most of the cases the drug of



11

interest is able to be derivative in order to accommodate it on the dendrimer platform [42]. Pan et al. [46] have synthesized a range of amphiphilic Janus dendrimers. This kind of dendrimers are constitute by acidic amino acid and naproxen molecules as the peripheral groups and the intention was to develop a novel potential bone-targeting dendritic drug delivery system. G. Thiagarajan et al. [47] have performed a very interesting study about the toxicity of poly(amidoamine) (PAMAM) dendrimers. They have been evaluated these nanosystems for the influence of surface functionality and size on the epithelial barrier of the gut with the goal of identifying safe carriers that can be used for oral drug delivery.

Magnetic Nanoparticles Magnetic nanoparticles have attracted the attention of the drug delivery researchers because of their intrinsic magnetic properties which enable tracking of these nanodevices through the human body for different purposes such as targeting or imaging [48-49]. The special feature of these nanoparticles is that they can vehiculize drugs and target specific organs by the application of an external magnetic field, once the nanocarrier is in the desired site of action drug release is performed. In order to achieve all this goals regarding magnetic nanoparticles, surface chemistry, charge and size are particularly important parameters to control. All these considerations improve drug bioavailability and blood circulation time [16] [50]. Magnetic nanoparticles can be made of metallic, bimetallic and superparamagnetic iron oxide which has been very studied due to its non toxic characteristics and easily modifiable surface[48]; [51]. Above all magnetic nanocarriers magnetite nanoparticles have been applied in medicine because of their inoffensive toxicity profile and good biocompatibility [17]. Magnetite nanoparticles are approved by the FDA for in vivo applications such as hyperthermia treatment, magnetic resonance imaging and drug delivery [52]; [53] Magnetite nanoparticles are able to perform targetable drug delivery and release. But in order to achieve the desired therapeutic effect a suitable drug delivery system for each specific case must be developed. A lot of different materials such as polymers have been used to functionalize magnetite nanoparticles and in this way avoid agglomeration, improve biocompatibility and reduce cytotoxicity [54]. Shen et.al [55] developed a dual-drug delivery system composed by two hydrophilic drugs, doxorubicin and verapamil, combined preliminarily with chitosan shell coated on magnetic nanoparticles


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(MNPs), followed by entrapping into the PLGA nanoparticles. The resulting nanoparticles were then functionalized with a specific tumor-targeting ligand and the final nanoparticles exhibit an average size of 144 nm. Obtained results suggest that these dual drug delivery systems may offer an approach to a less aggressive cancer therapy. Another example of the last developments involving magnetic nanoparticles is the study performed by N. Wang et al. [54] who prepared a stable drug carrier by covalently coating magnetic nanoparticles with PEOPPO-PEO block copolymer Pluronic P85. After characterization these nanoparticles were proven to be stable in several conditions which are crucial for biological applications and interestingly a temperature-responsive property that can improve drug loaded and delivery efficiency was observed due to Pluronic copolymer layer on the surface of the nanoparticles.

Polymeric Micelles Polymeric micelles are self- assemblies of block copolymers and they are very promising nano-systems for drug delivery applications [3];[56-58]. Drug carriers including polymeric nanoparticles, polymer- drug conjugates and polymeric micelles (Figure 4) have demonstrated to be useful y in nanomedicine, especially in drug delivery and novel formulations in clinical trials [10]. For instance, micellar formulations of antitumor drugs have been evaluated in preclinical and clinical trials, and the results shown that they have a potential utility [59]. Importantly, polymeric micelles comply with all the requirements of drug delivery systems and presents special features because of their unique core-shell structure. Block copolymers with amphiphilic character spontaneously assemble into polymeric micelles with a diameter of several tens of nanometers in aqueous media, as a product of these self-assemble we have an inner core which is able to accommodate hydrophobic drugs and it is surrounded by an outer shell of hydrophilic polymers. Poly(ethylene glycol)(PEG), have shown good behavior as an outer polymer, especially because its stability in the bloodstream and effective tumor accumulation after systemic administration [60]; [61];[62]. Miller et al. [63] investigate PEGylated poly-(d,l-lactic acid) (PEG-PDLLA) micelles which incorporated the hydrophobic model drug dechloro-4-iodo-fenofibrate (IFF). This system allowed for successful solubilization of the hydrophobic drug by physical incorporation into micelles. Gao et al. [64] have focused on the developments of polymeric micelles as stimuli-responsive nanocarriers.



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The function of pH-sensitive polymeric micelles is intimately related with the enhanced permeability and retention effect (EPR) and the low-pH microenvironment in cancer tissue are very interesting stimuli-responsive nanocarriers. Last findings about these kinds of polymeric micelles and their biomedical applications in cancer diagnosis and targeted therapy are reviewed.

Figure 4. Drug loaded polymeric micelle.

Clay-Polymer Nanocomposites An emerging and very interesting kind of drug delivery devices are this involving polymers and clays. Clays are widely used in the pharmaceutical industry as excipients or active substances. During the 60‘s it was observed that the oral absorption of some drugs seems to be reduced when these drugs was co-administered with intestinal adsorbents containing clays. Soon enough it was deduced that this clay influence over drugs could offer new strategies to achieve biopharmaceutical and biotechnological goals [65]. This was the starting point in the use of clays in the drug delivery field. Clays are natural occurring ionic exchangers and this is the most important feature regarding drug release [66]. The excellent performance of biodegradable polymers in drug delivery is widely known and detailed in this chapter and the fruitful synergy between polymers and clays has been early reported [67] [68].


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Polymer-clay nanocomposites (Figure 5) presents several advantages since these composites reduce the water absorption, improve the mechanical and rheological properties, and are able to modulate the drug release. These composite materials exhibit excellent properties for biomedical applications such as swelling properties, ability to film-forming, bioadhesion and cell capture properties [67].

Figure 5. Idealization of the obtaining and behavior of clay-polymer nanocomposites.

Considerable scientific production has been reported on this field: Kevadiya et. al. [67] have studied a novel combination between clays and polymers to encapsulate tamoxifen (Tmx). They evaluated intercalation of Tmx in interlayer gallery of Na+-MMT (Montmorillonite, MMT), which is further compounded with poly-(-caprolactone) for oral chemotherapy of breast cancer. That work have leaded to the conclusion that Tmx–MMT hybrid and microcomposite particles can be of considerable value in chemotherapy of malignant neoplastic disease with reduced side effects. In addition, this study clearly stated that MMT not only plays a role as a delivery matrix for drug, but also enhance delivery proficiency by the synergy achieved when the clay is coated with the polymer. Huang et al. [68] have synthesized four systems of biodegradable polymeric nanoparticles of for oral delivery of anticancer drugs with Docetaxel used as a model drug, two of them involves clay-polymer composites: the poly(lactic-co-glycolic acid)–MMT nanoparticles and the poly(lactide)–vitamin E TPGS/MMT nanoparticles. An extremely actualized, detailed and acute review of the state of art in this promising field has been done by Rodrigues et al.[69].



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POLYMERS USED FOR THE PREPARATION OF NANOPARTICLES Nano and micro particles for drug delivery can be set up from a variety of materials, including polymers, lipids, ceramics, metallic inorganic particles and carbon nanotubes, among others [70]. Polymers are the first choice to obtain drug-carriers because: Their stability and capability for high loading of many agents and their control over drug release kinetics and capability for modified their surface for attached ligands [71] [72]. An ideal polymer should be biocompatible, biodegradable with minimum toxicity, sterile and nonpyrogenic, and must have a high capacity to accommodate drugs and protect them from degradation [73] [74]. There are currently many different polymers (natural and synthetic) reported in the literature that have been evaluated for use in micro- and nano-particle based drug delivery, some of them are listed here:

Poly(ε-caprolactone) (PCL) PCL is a biodegradable, synthetic and biocompatible polymer often used in the formulation of micro and nanoparticles because: it is a low cost material, is approved by the FDA, and undergoes slow degradation in the body [75]. Some studies have even reported PCL and its copolymers as devices for drug delivery [76] [77] [78]. Micelles assembled from amphiphilic poly(ethylene glycol)/poly(ε-caprolactone) (PEG/PCL) copolymers are promised as safe and effective drug delivery systems. They offer the potential to achieve high solubility of hydrophobic drugs, long blood circulation time and effective delivery to target organs [79]. PCL can be used as polymer to prepare different types of nanocapsules presenting diverse flexibility according to the chemical nature of the core. They can modulate cutaneous drug penetration and act as physical sunscreen due to their capability of light scattering. PCL nanocapsules are versatile formulations, once they can be used in the liquid form, as well as incorporated into semi-solid or solid dosage forms [80].


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Poly(3-Hydroxybutyrate) (PHB) Poly (hydroxyalkanoates) are synthesized by a wide variety of microorganisms, have recently attracted a great deal of interest and particular attention has been focused on the use of poly(3-hydroxybutyrate) (PHB) and related copolymers as carriers for drug delivery or scaffolds in tissue engineering for their biodegradability and biocompatibility [81]. In vitro investigation of the cytotoxicity of PHB and the resulting nanoparticles show their high cytocompatibilities [82], copolymer of PHB was employed to study drug-release behaviors with promised results [83].

Poly Lactic Acid (PLA) Many PLA and poly (lactic-co-glycolic acid) (PLGA) polymer nanoparticles based drug delivery systems have been extensively investigated due to their efficacy in drug targeting and biocompatibility. PLA is a biodegradable polymers, an aliphatic ester of lactic acid, derived from renewable resources such as corn starch or sugarcanes, which has gained commercial interest due to its easy manufacture [84]. The hydrolysis of this polymer leads to metabolite monomers, lactic acid and glycolic acid, these two monomers are endogenous and easily metabolized by the body via the Krebs cycle [20]. PLA and its copolymers that contain glycolide (PLGA) have been approved by the FDA for the purpose of drug delivery [85]. PLGA nanoparticles can be used safely for oral, nasal, pulmonary, parenteral, transdermal and intra-ocular routes of administration [86]. They allow effective protection and long-term delivery of the inhaled drug and, when adequately engineered, its efficient transport to the target [87] [88]. Biodegradable microparticles of various sizes using PLA/PLGA (50:50) copolymer were also formulated [89].

Poly (Methyl Methacrylate) (PMMA) PMMA is one of the most widely explored biomedical polymer because of its biocompatibility, and recent publications have shown an increasing interest in its applications as a drug carrier [90-91].



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Poly Amino Acid (PAA) Amphiphilic polymers based on amino acids which present as either poly(L-amino acid) block copolymers or poly(L‐amino acid) backbones with hydrophobic substituents, self assemble into micelles, vesicles, nanofibres and solid nanoparticles and such self assemblies, have drug delivery capabilities [92]. Results of the diffusion assays demonstrated strongly enhanced permeation behavior of poly(acrylic acid) and papain nanoparticles owing to local mucus disruption by papain. Improved transport rates, reduction in mucus viscosity and the retarded release of hydrophilic macromolecular compounds make proteolytic enzyme functionalized nanoparticles of substantial interest for improved targeted drug delivery at mucosal surfaces [93]. Moreover, the PMMA was studied as a graft in silica nanoparticles to the aim of provide a platform to bind biomolecules and to track the movement of the nanoparticles in biological systems [94].

Poly (Alkylcyanoacrylate) (PACA) The properties inherent in PACA nanoparticles, such as biocompatibility and biodegradability of the polymer, a simple preparation process and particularly the entrapment of bioactives and the advantage of the in vivo degradation potential and its good acceptance by living tissues, made possible the in vivo delivery of many types of drugs including [95]. Research has focused on the oral route of administration, however ocular, transdermal and delivery across the blood-brain barrier have also been investigated.[96].

Poly (Butyl Cyanoacrylate) (PBCA) Has been extensively used in drug delivery systems for a variety of drugs due to its excellent biocompatibility and biodegradability. Current literature is replete with studies investigating drugs incorporation into PBCA nanoparticles [97] [98] [99].


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Polystyrene (PS) It was studied the movements of PS coated with PEG nanoparticles of various sizes and surface chemistries in fresh bovine vitreous [100]. It was also investigated uptake and biodistribution of PS nanoparticles in mice following administration to lungs via pharyngeal aspiration. The extent of uptake and lymph distribution of the model, non-degradable PS nanoparticles lends potential to pulmonary administered [101]. The in vivo study investigating the biodistribution of the PS-PEG particles after intravenous injection into rats reveals that a relationship exists between the surface density of PEG and the extent to which the particles remain in the circulation, avoiding recognition by the reticuloendothelial system [102].

Poly (Vinyl Alcohol) (PVA) Ahighly biocompatible and hydrophilic, non-toxic and inexpensive polymer, that can be easily processed [103]. PVA-based microparticles can be considered a potential efficient way to deliver anticancer drugs by systemic administration [104]. However, it is often use PVA as stabilizer in the nanoparticle preparation [105].

Hyaluronic Acid (HA) HA has emerged as a promising candidate for intracellular delivery of various therapeutic and imaging agents because of its innate ability to recognize specific cellular receptors that over expressed on diseased cells [106].

Chitosan (CH) CH is a natural and cationic polysaccharide which has been widely explored for the delivery of drugs, peptides, proteins and genes to the colon for different therapeutic applications and has attracted a great deal of attention from scientists due to its unique properties [107] However, the potential application of CS is hindered by its poor solubility in the neutral or basic pH range [108].



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Both PEG and PEO polymers are most used as coating to the purpose of increment the biocompatibility, or to bypass the normal physiological defense or for adhesion of specific drug in the surface of NPs. Poly(ethylene glycol) (PEG) Is the most used polymer and also the gold standard for stealth polymers in the emerging field of polymer-based drug delivery [109]. PEGcoated nanoparticles were also preparated to minimize muco-adhesion and showed promising results [110]. Poly(ethylene oxide) (PEO) PEO has been the most successful synthetic material used to modify the interactions of solid surfaces with biological media. This has been demonstrated for particulate carriers with either grafted PEO [111]. Moreover, it have been investigated the adsorption of PEO on bare silica nanoparticles [112] [113].

PREPARATION OF MICRO AND NANO-PARTICLES In drug delivery subject, polymeric nanoparticles involves drug nanocarriers in the range size of 10-1000 nm such as nanospheres and nanocapsules made from different kind of polymers [114-115]. In the case of nanospheres drug molecules might be attached by adsorption in the surface or entrapped within the particle since this kind of nanocarrier is a monodisperse solid matrix particle. On the other hand, nanocapsules are particles that can act as a reservoir of drug molecules since they have a cavity product of a liquid core-solid shell structure [15]. In order to select an appropriate method for manufacturing polymeric nanoparticles it is crucial to well know the nature of the polymer and the drug employed, and most importantly the therapeutic goal. Also it is required to consider all the variables that can be externally controlled in order to obtaining a good yield during nanoparticles production and an adequate biomedical behavior. These variables include the nature and solubility of the drug to be encapsulated, polymer type and concentration, its molecular weight, composition of the copolymers, drug loading concentrations, type and volume of the organic solvent, the water phase volume, pH, temperature, concentration, types of surfactants, and the mechanical speed of agitation [14].

Methods to Prepare Polymeric Nanoparticles It is possible to obtain polymeric nanoparticles using preformed polymers or by in situ polymerization of monomers [116] [14-15]. In this section most


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commonly used, laboratory and large- scale techniques using preformed polymer will be discussed.

Emulsification/Solvent Evaporation (Figure 6) This method was the first one employed to prepare polymeric nanoparticles from a preformed polymer [117]. This method consists in prepare a polymer solution in volatile, water-immiscible, organic solvent such as chlorophorm, dichloromethane or nowadays ethyl acetate since it has a better toxicity profile [118]. After this step, the drug is added and the mixture is emulsified in an outer aqueous phase using an emulsifier such as PVA and some kind of high speed homogenization such a sonication [119] to facilitate the process. In this case we would obtain a single o/w (oil/water) emulsion. By removing the organic solvent at the adequate temperature and pressure conditions [120] an aqueous nanoparticle suspension is obtained [121] [15]. Polymeric nanoparticles can be finally recollected by centrifugation, filtration, washed, and freeze dried or spray drying [14, 122].

Figure 6. Outlining of the emulsification/solvent evaporation method to prepare polymeric micro/nanoparticles.

A modification of this method can be done when instead of prepare a single o/w emulsion a double emulsion w/o/w is obtained. This alternative of the emulsification/solvent evaporation technique is very useful to incorporate hydrophobic drugs to the polymeric nanoparticles [27].



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Emulsification/Solvent evaporation method is one of the most widely used versatile technique since several strategies depending on the hydrophobicity/hydrophilicity of the polymer and the drug using single or double emulsions can be overcome. The use of these approach will result in a considerable variety of polymeric nanoparticles formulations, Rao and Geckeler [15] made a very detailed description of the different factors affecting the performance of this technique.

Salting Out Unlike emulsification/solvent evaporation this method allows to work without organic solvents or surfactants which can be hazardous [123]. The preparation method consists in use a polymer solvent which is normally totally soluble in water, commonly acetone. In this way an emulsification of the polymer solution in an aqueous phase can be performed by adding a high concentration of electrolyte (usually magnesium chloride hexahydrate) or a non–electrolyte-saturated aqueous solution containing PVA as a viscosity increasing agent as well as a stabilizer of the organic phase [14-15, 124]. An impediment for complete solubility between both phases is executed by virtue of the modification of the miscibility properties of water with other solvents when the high salt content is added. A dilution of the emulsion with a large excess of water leads to a reverse salting out effect which results on the precipitation of the polymer dissolved in the droplets of the emulsion [15]. In order to removal the acetone remaining the final emulsion can be stirred overnight at room temperature leading to the evaporation of the organic solvent or it can be also centrifugated [14]. Free PVA and electrolytes must be eliminated too before filtration, freeze drying and the final obtaining of the polymeric micro and nano-particles [125-127]. Solvent Displacement Method This method is based on the interfacial deposition of a polymer after displacement of a solvent, soluble in water, from a hydrophobic solution [128]. There are three crucial components to carry out this technique also called ―Nanoprecipitation‖: 

The polymer, which can be a synthetic, semisynthetic or natural polymer. The most widely used polymers for these method are PCL [129-131], PLA [132-133] and PLGA [134-135]. Also, some polymers are PEG copolymerized to avoid their removal by the reticular endothelial system [136].


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M. T. Chevalier, J. S. Gonzalez and V. A. Alvarez 



The polymer solvent; usually an organic solvent miscible in water and volatile enough to eliminated by evaporation such as acetone, ethanol, hexane or methylene chloride [128, 137-138]. As alternative, binary solvents blends such as acetone-water or acetone-ethanol can be utilized [139-141]. Non-solvent phase; a polymer non-solvent, usually water, or mixture of non-solvents additionated with a surfactant.

Using this technique polymeric nanoparticles are yielded by slow addition of the organic phase to the aqueous phase, or inverting this order adding the polymer non-solvent phase to the polymer solvent organic phase under moderate stirring. A well-defined and narrow size distribution obtained as a result of the rapid diffusion of the polymer solution in the non-solvent phase [15].

Spray Drying (Figure 7) Spray drying is a scalable method to obtain polymeric nanoparticles that provides the possibility to forming and drying the particle in one step [142]. It is a well-established technique used in the pharmaceutical industry for liquid substances into powders rapidly and efficiently [143-144]. Spray dying process starts when liquid feedstock is atomized into a spray of fine droplets and then brought into contact with the hot drying gas at sufficient temperature for the moisture evaporation to take place. While moisture evaporates from the droplets, the solid product is formed, and the powder is readily recovered from the drying gas [144]. The high speed of the process and the consequently short drying time enables application of this technique to temperature-sensitive products without degradation [145-146]. This mechanical method of synthesized is very versatile since it empower the control of fundamental particles properties such as, particle size, bulk density and flow properties. This could be carry out by vary equipment parameters such as, spray flow, compressed spray air flow, inlet and outlet temperatures [14]. Spray dried polymeric micro and nanoparticles are have a uniform size distribution, approximately spherical in shape, frequently hollow, and posses good flowability and a solution fast rate [147]. Even when the equipment of spray drying is sophisticated, this technique is industrially cheaper than other processes since it produces a dry powder directly from liquid reducing steps of synthesize, labor, equipment costs, space requirements and possible contamination of the product. Several drugs have been vehiculized in



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polymeric nanoparticles based formulations such as indomethacin [148], carbamazepine [149], ketoprofen [150]and albendazole [147].

Figure 7. Outlining of a spray drying equipment to produce polymeric micro/nanoparticles.

CHARACTERIZATION OF LOADED MICRO AND NANO-PARTICLES The characterization of micro and nanoparticles is of importance both in formulation development and nanotoxicological studies [151]. Characterization of micro and nanoparticles involves several aspects; among we can mention the followings.

Physicochemical Characterization The focus of interest in the characterisation of nanoparticulate drug delivery systems lies with the overall morphology, the size distribution and


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particle shape. In order to ensure the repeatability of the formulation processes and the efficacy/stability of the formed particles an exhaustive physicochemical characterization is needed [152]. Many well known studies as: X-Ray Diffraction Spectrometry (XRD), Fourier Transform Infrared Spectrometry (FTIR), Raman Spectrometry, Thermogravimetric Analyses (TGA) and Differential Scanning Calorimetric (DSC) should be carried out. Analytical electron microscopic techniques such as electron energy-loss spectroscopy or energy-dispersive X-ray spectroscopy are additional assets to determine the elemental composition of the systems, but are not yet standard tools in pharmaceutical research [153].

Surface Characterization Many techniques have been developed and used to study the surface modification of polymer nanoparticles. Surface characterization is an important analysis because modification of the nanocarrier surface properties can be utilized to increase the residence time in the blood [154].The efficiency of surface modification can be measured either by estimating the surface charge, density of the functional groups or an increase in surface hydrophilicity. The two principal methods used to this purpose are: zeta potential determination and X-ray photoelectron spectroscopy [155]. Zeta potential (ζ): Consists in determining of the nanoparticles via the mobility of charged particles monitored by an electrical potential. Depending on the polymer and the surface modification, the zeta potential values may be positive, neutral or negative [155]. Photo electron spectroscopy (XPS): soft Xrays have the advantage to make use of the element-selectivity, where it is shown that the optical constants of nanoscopic matter differ from those of the macroscopic solids. For applied research, the surface sensitivity of coincidence approaches should be exploited, so that properties of ligands and surface reactions occurring on nanoparticles can be studied in large detail [156].

Particle Size and Particle Size Distribution Minor deviations, for instance, in particle size/shape, surface charge or aggregation tendency, may play a significant role in their behavior in the body. The very small size of the nanoparticles imposes extra demands for the



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characterization techniques [152]. The most common techniques used for size and/or shape determination are:

Electron Microscopy Morphological analyses are most frequently performed by TEM (transmission electron microscopy), although SEM (scanning electron microscopy) or FESEM ( field emission scanning electron microscopy) can likewise be employed [157]. High-resolution TEM provides detailed information about nanocrystals; both surface and planar defects can be visualised with great accuracy. Nanoparticulate samples can be deposited on the grid as a drop that is left to dry before analysis. If samples are prone to aggregation, aerosol deposition should be employed to produce specimen of well-dispersed, isolated particles. [153]. Classical TEM and SEM techniques often have to be adapted for an accurate analysis of formulation morphology, particularly in case of hydrated colloidal systems. Specific techniques such as environmental scanning microscopy or cryo preparation are required for their exploration. Environmental scanning microscopy allows the observation of hydrated samples in their original state. The main limitation of this technique is the comparatively low resolution compared to TEM and SEM [153]. Cryoelectron microscopy preserves the microstructure of hydrated biological specimens in vitreous ice, and it is a technique that was continually improved and adapted tone tasks [153]. As well known from other applications, detailed 3D structures of investigated objects can be obtained by tomography techniques. Electron tomography is an extension of traditional TEM and the data are accordingly collected by means of a TEM [158]. In the process, a beam of electrons is passed through the sample at incremental degrees of rotation around the centre of the target sample. Information is collected and used to assemble a 3D image [153] [159]. Current resolutions of electron tomography systems are in the 5– 20nm range, suitable for examining supra-molecular multi-protein and lipid based structures, although not the secondary and tertiary structure of an individual protein or polypeptide [160]. Dynamic Light Scattering A wide range of nanomaterials can be characterizing using dynamic light scattering (DLS), including metals, metal oxides, and carbon-based materials, in water and cell culture media [161]. This technique provides information about size, shape, and flexibility of particles as well as offering insight concerning the nature of the interactions between particles and their


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environments [162]. DLS analyzes the velocity distribution of particle movement by measuring dynamic fluctuations of light scattering intensity caused by the Brownian motion of the particle. This technique yields a hydrodynamic radius, or diameter, to be calculated via the Stokes-Einstein equation from the aforementioned measurements [161] to a wide variety of systems including solids, gels, membrane vesicles and colloidal dispersions [163]. Ultrasound spectrometry is a new technology which works in optically opaque, concentrated dispersions, has a large dynamic range of 10 nm - 1 mm that can be obtained in an only one measurement, and it can be used as a spectroscopic technique for the characterization of materials. There are many different sorts of ultrasound spectrometer but one widely used commercial apparatus uses a continuous ultrasound signal that forms a standing wave in the sample whose amplitude is measured by moving the transducers through it [164]. After each measurement at a given frequency, the frequency is changed to make another measurement; a full spectrum and particle size distribution can take 2–3 min to acquire. It is important to remove bubbles that interfere with the measurement and to carefully control temperature [164].

BIODISTRIBUTION AND TARGETING OF POLYMERIC MICRO AND NANO-PARTICLES Localize the release of very potent, and sometimes toxic, drugs acutely and only in the specific site of action is probably the main goal of drug delivery. Controlling the release of a drug both spatially and temporally is the key to reduce undesirable side effects [165] which nowadays represents one of the most challenging issues of our time. An increase in the comfort of the patient and quality of life would be the results of developing systems capable of reach this main goal [166]. According to this, high therapeutic index and corresponding clinical success of any drug delivery device is determined by pharmacological and toxicological parameters that must be taking into account during the process of designing the nano-carrier. Blood circulation residence, maximal tolerated dose, and desired selectivity are the most important factor to rely on [167].



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Opsonization (Figure 8) To finally achieve the goals of nanomedicine a drug delivery system must be stable in the bloodstream long enough to recognize and reach its specific site of action [166]. Nevertheless, the phenomenon of opsonization represents a threat for our nanocarriers of drugs. By definition, opsonization is the process by which an alien particle or organism is covered with opsonin proteins, promoting aggregation and highlighting it for macrophages. After this, phagocytic cells engulfing and dispose of these strange materials from the bloodstream. The synergy of these two process results on the main clearance mechanism for the removal of undesirable agents in the human organism [166]; [168]; [169];[154];[170]. Most of opsonized particles are cleared by a receptor-mediated mechanism almost immediately due to the high concentration of phagocytic cells in the liver and spleen, or alternately they are excreted [170].

Figure 8. Scheme of micro/nanoparticles phagocytosis as a result of the opsonins surface attachment.

Consequently, unprotected nanoparticles are easily removed from the bloodstream by the macrophages of the reticuloendothelial system, also known as the mononuclear phagocytic system. These macrophages are typically from the liver, or Kupfer cells, and they recognize the opsonins bound to the surface of the nanoparticles [171]. Thus, opsonins are any component of the blood serum that enhances phagocytosis of nanoparticulate drug delivery devices by checking them off for an immune response. As a result of this process, nanoparticulate drug delivery systems are eliminated from the bloodstream within seconds of intravenous administration, making them unsuccessful as site-specific drug delivery devices [172]. Phagocytes are not capable of


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destroy polymeric nanoparticles and for this reason sequestration in the mononuclear phagocytic system, organs take place. If the polymer used is nonbiodegradable, then accumulation of particles in these organs probably will lead to non safe levels of toxicity [173]; [174];[166].

Surface Modification: Aiming to Reach Long-Circulation Nanoparticles (Figure 9) In order to improve the blood circulation half- life of nanoparticles several methods of camouflaging or masking them from the reticuloendothelial system (RES) have been developed [172]; [175]. Surface functionalization can overcome the most important limiting factor for long-circulating nano-devices: protein absorption. In accordance with this, the most relevant strategy to interfere with the binding of opsonin proteins and consequently avoid the mononuclear phagocytic system is making use of surface treatments [166]. The main objective is increase blood residence and accumulation in the adequate tissues for the treatment of a specific disease; numerous approaches to reach this goal have been developed. Furthermore, nanoparticles surface customizing can enable target tissues or specific cell surface antigens with a targeting specific ligands such as antibody/antibody fragment, peptide, aptamer or small molecules [167]. It is well known that hydrophilic polymers, especially PEG, can be associated to the surface of nanoparticles and provide them steric stabilization and ―stealth‖ properties such as prevention of protein absorption [176]. PEG-containing surface treatments for nano drug containers seem to represent one of the most promising strategies and show the lowest occurrence of harmful effects in vivo [166].

Figure 9. Unfunctionalized micro/nanoparticle is marked by opsonins (a). PEG coated micro/nanoparticle avoid opsonins recognition (b).



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In order to achieve a significant prolongation in blood circulation Sheng et al. [177] have developed a combinatorial design, covalent attachment of PEG to PLA and physical adsorption of water-soluble chitosan (WSC) to particle surface and have studied its behavior in vitro and in vivo, aiming to modify the surface of PLA nanoparticles. It was found that the synergistic action of PEG and WSC strongly decrease the macrophage uptake and increase the blood residence, or circulation half-life with concomitant reduced liver sequestration. It is well established that positively charged polymeric nanoparticles have a higher rate of cell uptake compared to neutral or negatively charged formulations. Positively charged DDS surface are also expected to have a high nonspecific internalization rate and short blood circulation half-life, thus neutral or negatively charged nanoparticles present low rate of nonspecific cellular uptake and a decreased plasma protein association [167]. However, Xu et al. [178] have investigated the effects of the surface charges on the in vitro macrophage cellular uptake and in vivo blood clearance and biodistribution of the hemoglobin-loaded PEG–PLA–PEG nanoparticles, the in vivo assays have been indicated that cationic nanoparticles mainly accumulate in liver, lung and spleen and that they have shown a longer half-life in bloodstream than anionic nanoparticles. Parveen and Sahoo [179] have developed and characterized PLGA nanoparticles coated with chitosan/PEG aiming to encapsulate hydrophobic drugs (paclitaxel), and also avoid the phagocytic uptake by reducing opsonization in order to increase the bioavailability of the drug. They have reported that these nanoparticles exhibit remarkable prolongation in blood circulation, as well as reduced macrophage uptake, with only a small amount of the nanoparticles accumulated in the liver, when compared to noncoated nanoparticles.

The EPR Effect: Passive Targeting of Polymeric Nanoparticles (Figure 10) In 1986 Matsumura and Maeda reported a phenomenon that will revolutionize antitumor therapy [180]: the EPR effect. After this first report, this special feature exhibit by solid tumors was described and validated in more detail by Maeda et al.[181-184]. It was shown that most solid tumors presents an abnormal vascular architecture compared with normal tissues, which leads to the production of large amount of several vascular permeability factors. As a result of these phenomenon solid tumors posses enhanced vascular permeability that enable the rapid growth of tumor tissues since they


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sufficient supply of nutrients and oxygen. In other words, this unique anatomical–pathophysiological nature of tumor blood vessels enhanced capability for the uptake of particulate systems such as drug carriers [185]. Researchers have indicated that tumor vasculature is hyperpermeable and selectively takes up macromolecules and colloidal carriers of diameter up to 600 nm. According to this, if a drug delivery system could overcome biological obstacles (such as opsonization and posterior removal by reticuloendothelial system) and finally reach tumor mass, it will remain inside the tumor for a longer time releasing the drug either outside of tumor cells or internalized by the cell and release the drug in the cytoplasm [186] [181]. Among the various factors influencing the EPR effect, the most important is having a molecular size larger than 40 kDa. Nevertheless, this requirement is not sufficient since surface charge and hydrofobicity also affects the possible occurrence of the EPR effect. Like this, a lot of issues regarding EPR effect are discussed by Maeda et al. [181] in an historical review.

Figure 10. Outlining of the enhanced permeability and retention effect.

Polymeric nanoparticles containing anticancer agents can be delivered to solid tumors taking advantage of the EPR effect. For instance, PLGA is a widely used polymer in drug delivery. These nanocarriers extravasate through the tumor vasculature, delivering pharmaceutical active ingredients into the cells by the enhanced permeability and retention effect, thereby increasing their therapeutic effect [187]. Xin et al. [188]have proposed Angiopepconjugated PEG-PCL nanoparticles (ANG-PEG-NP) as a dual targeting drug delivery system for glioma treatment and evaluated the availability and safety



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of ANG-PEG-NP, penetration, distribution, and accumulation into 3D glioma tumor spheroid. This unique phenomenon which lead drug delivery nano-vehicles (cutoff size of >400 nm) to preferentially accumulate and diffuse in tumor tissues, has resulted in the concept of passive targeting of nanoparticles to tumors through the ―enhanced permeability and retention‖ (EPR) effect. Polymeric nanoparticles are used as ones of the most preferred drug delivery system especially because of the passive tumor-targeting they exhibit [189].

Active Targeting of Nanoparticles (Figure 11) This kind of active targeting mechanism takes advantage of highly specific interactions between the targeting ligand and certain tissues or cells in the human organism to increase the accumulation of nanoparticles [190-191]. In order to achieve this, attached ligands such as antibodies, engineered antibody fragments, proteins, peptides, small molecules, and aptamers to the nanodevices surface is needed. The use of this strategy to reach biological targets has attracted the attention of drug delivery researchers because customizing the surface of nano-particles overcome selectivity and specificity issues [167].

Figure 11. Surface customizing of micro/nanoparticles to reach active targeting within others biomedical goals.

Rituxan (target, CD20-positive B-cells for the treatment of non-Hodgkin‘s lymphoma and rheumatoid arthritis), Herceptin (target, HER-2-overexpressing breast cancer cells), Erbitux (target, epidermal growth factor receptor (EGFR) for the treatment of colorectal cancer), Iressa (target, EGFR for the treatment of non-small cell lung cancer and metastatic breast cancer), and Avastin


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(target, vascular epidermal growth factor (VEGF) for the treatment of metastatic colorectal, non-small lung, and breast cancers) are examples of FDA-approved antibodies in clinical use nowadays [192] [193]. Drug delivery nano-devices surface can also be modified with proteins, including antibodies or antibody fragments and various other targeting ligands which result in an increased specificity and binding affinity. Nanoparticles made from cyclodextran and containing transferrin targeting ligand showed enhanced intracellular accumulation in a human tumor xenograft mouse model [194]. But while active targeting with proteins have lead to positive results in several cases, a surface customizing with small molecules may also be convenient. For instance, cell surface membrane lectins have been shown to be over expressed on the surface of numerous cancer cells and folic acid or sugar molecules have been widely used [167] Another successful specific ligands and very used in clinical applications are aptamers since they are able to fold into unique structures capable of binding to specific targets with high affinity and specificity [195]. As can be seen, active targeting represents a valuable strategy in drug delivery science to increasing the concentration of a drug in the specific site for treatment, and in this way improves therapeutic action.

Size Effect: Micro Vs Nano- Particles One of the most evident differences between micro and nano-particles is the difference in surface area and volume ratio and many other extra differences are a consequence for that [189, 196]. It has been studied that in the case of larger particles there is a major probability of lose payload during formulation than smaller ones. Additionally, drug efflux will be faster from smaller particles than for larger ones. Thus, size affects almost every aspect of particle function including degradation, flow properties, clearance and uptake mechanisms [197] [198]. The size has a marked effect on particle distribution throughout the body. Drug delivery literature usually highlight the advantages of nanoparticles over microparticles such as relatively higher intracellular uptake compared [199200]. It is well established in the literature that nanoparticles larger than 200 nm are likely to mechanically filtered in the spleen, but it is important to consider that smaller than 100 nm leave the blood vessels through fenestrations in the endothelial lining [13] [197]. Meanwhile, microparticles usually posses a size from 1 to 5 µm, because of its size they are typically removed by the reticuloendothelial system, whereas larger microparticles are typically trapped in the capillary beds. Always depending on the



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administration method, particles larger than 500 nm can be phagocytosed by macrophages and smaller particles can be endocytosed by phagocytic or nonphagocytic cells [197]. For instance, internalization by targeted nonphagocytic cells could be desirable, thus, as can be seen different strategies can emerge from the size influence in the behavior of particles. Not all the phenomenon associated with nanoparticle size are entirely negative or entirely positive. Broadly talking about particle size; not too large and not too small may keep as in safe field, however it is always necessary executed the pertinent design depending on the administration and the therapeutic goal. In the last years several studies about size dependence on micro and nano particles performance for drug delivery ([189];[201]) was reported.

Particle Shape: A New Parameter to Design DDS? Indeed, particle shape also has a strong impact on drug carrier‘s performance. The exact role of particle shape in drug delivery is still in discussion but there is evidence enough to say that, at least, particle shape, along with size and chemistry, is certainly a key parameter in the designing of a drug delivery devices [197]. Non- spherical, biodegradable particles for drug delivery have been fabricated and the fact that this kind of synthesize is possible open the door for a future study of particle shape influence in drug delivery devices performance. In other words, the goal of researchers working on this field could be uncovering the effect of shape in degradation, transport, targeting, internalization and possibly other areas of drug delivery [197]. One of the properties of a nanocarriers affected by particle shape is their degradation and drug release, and this was reported several years ago [202]. The goal of many sustained release devices, which is to get zero-order release profile, was achieved with a hemi-spherical particle that only allowed degradation on the face. Interestingly, non-spherical particles that have areas of different thicknesses, the shape of the particle will be always changing over time and this results unique degradation profiles as a dependence of surface area and diameter [203] [204]. Several methods for producing non-spherical particles have been reported ([205]; [206]; [207]) and some interesting analysis about this new parameter over polymeric nano-particles have been done too [189]. With this new concept of involving particle shape in drug delivery, since non-spherical particles have two or more different length it will be needed a redefinition of ―particle size‖ [197]. The influence of shape on biological


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interactions is not as clear as degradation process, but there is evidence that indicates that could be a intimate relation between phagocytosis and particle shape and between orientation of non-spherical particles and cellular uptake [197].

RELEASE MECHANISMS The term ―release mechanism‖ can be defined as a description of the way in which drug molecules are transported from their matrix to the outer media [208], and as a description of the process or event that determines the velocity of release. In general, drug delivery vehicles are nano-systems composed by a pharmacological active ingredient aimed to be trapped and a matrix (a polymer in the case of polymeric nanoparticles) that severely act as its vehicle. Physicochemical properties of both drug molecules and the matrix will determine the release profile of the drug from polymeric nanoparticles [18, 209-210]. These properties will result in the physical state of the drug within the matrix and parameters controlling matrix hydration and/or degradation which are directly associated with the most importantly feature of a nanodevice: the mode of drug attachment and/or encapsulation (e.g. surface adsorption, dispersion homogeneity of drug molecules in the polymer matrix, covalent conjugation) [13]. Release mechanism of polymeric nanoparticles can be modulated by the molecular weight of the polymer used following this relation between molecular weight and drug release rate: higher the molecular weight of polymer slower will be drug release [211]. When the drug is weakly bound to the surface of the polymeric nanoparticles rapid drug release occurs by desorption [13]. If the drug is monodispersed within the polymer matrix, the release occurs by diffusion if the encapsulated drug is in crystalline form since the drug is first dissolved locally and then diffuses out [13]. Also the release can take place by erosion of the matrix, or as a combination of both mechanisms. Erosion can occur both by homogeneous degradation rates throughout the matrix or by degradation only at the surface which leads to heterogeneous degradation [13]. There are another factors that affects degradation mainly because they influence matrix hydratation, between them it is important to mention the hydrophobicity /hydrophilicity character, polymer molecular weight distribution, crystallinity,



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melting and glass transition temperature, polymer blends and also possible polymer treatment before the synthesize of the nanoparticles [13]. Within all polymers used to synthesize nanoparticles for drug delivery, PCL is one of the most outstanding regarding biomedical applications and this is related with its adequate biodegradation and drug release. It is well-known that PCL crystallinity and surface hydrophobicity dependent on the molecular weight are the reasons of its biodegradation in two defined steps: random nonenzymatic cleavage and enzymatic fragmentation [212-214]). Drug release from PCL nanoparticles will be affected by the specific properties of the drug. Lipophilic drugs generally distribute uniformly in the matrix while hydrophilic drugs tend to move thought the interface and stay adsorbed in the surface [215]. The degradation mechanism of a polymer in any formulation alters or influences drug release profile. It have been studied that in the case of PCL diffusion is the only option for lipophilic drugs to release from the matrix and particularly drugs with a high lipophilic character that present resistance to diffuse release by enzymatic erosion take place. Hydrophilic drugs are released by desorption and faster [216]. It is evident how polymer degradation mechanisms in biological environment in association with the specific drug properties define release mechanisms. PLGA is maybe one of the most frequently used biodegradable polymer in drug delivery. Drug release from PLGA nanoparticles can occur by three possible mechanisms [217]: (i) transport through water-filled pores, (ii) transport through the polymer, and (iii) due to dissolution of the encapsulating polymer (which does not require drug transport). Fredenberg et al. [217] explain this in a very acute and detailed review about the mechanisms of drug release in poly(lactic-co-glycolic acid)-based drug delivery systems.

FINAL REMARKS AND FUTURE PERSPECTIVES Urgent diseases such as cancer keep researchers looking for new alternative treatments that can achieve the therapeutic effect and leads to patient welfare.


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Drug delivery science as the most important branch of nanomedicine seems to be an inexhaustible source of new strategies and within them polymeric nanoparticles have exceeded other type of drug delivery devices showing each day more promising performance. Of course there is a lot of work to do since limitations continue appearing, especially when it comes to clinical application of drug delivery developments. In vivo studies need to be done and reported in pos of a better understanding of the complex interactions between drug delivery devices, in this case polymeric nanoparticles, and human organism. It is interesting to remark an emerging topic discussed in the present chapter closed related with the development of polymeric nanoparticles that can offer new alternatives in the design of drug delivery systems: polymerclay composites materials. These materials deserve further study since they probably exhibit new drug degradation profile and targeting versatility corresponding to the synergy of their components.

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Chapter 2

CHEMICAL MODIFICATIONS OF NATURAL CLAYS: STRATEGIES TO IMPROVE THE POLYMERIC MATRIX/CLAY COMPATIBILITY Romina Ollier*, Matias Lanfranconi and Vera Alvarez Composite Materials Group (CoMP), Research Institute of Material Science and Technology (INTEMA), Engineering Faculty, National University of Mar del Plata, Mar del Plata, Argentina

ABSTRACT Polymer/clay nanotechnology age started with Toyota‘s work about clay particles exfoliation in nylon-6, by the last 80‘s and the beginnings of the 90s. The improvements on several properties of the polymeric matrices have been improved by the addition of nanometric scale particles. The most used nanoparticles to reinforce polymeric materials are layered silicates. Their crystalline net consists of bi-dimensional layers where a central octahedral layer of either alumina or magnesia is joined to two external tetrahedrons of silica in such a way that the oxygen ions of the octahedral layer also belong to the tetrahedral layers. In order to obtain the best properties, the key point is the dispersion of the clay particles inside the polymeric matrix but the tendency of the particles to * Composite Materials Group (CoMP), Research Institute of Material Science and Technology (INTEMA), Engineering Faculty, National University of Mar del Plata, Solís 7575 (B7608FDQ) Mar del Plata, Argentina. [email protected], Tel: 54-223-4816600 ext. 321.


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Romina Ollier, Matias Lanfranconi and Vera Alvarez agglomerate is difficult to overcome. In addition, most of the polymers are hydrophilic and original clays are hydrophilic. In order to make them (matrix and clay) more compatible, some chemical treatment will be required. Although there are different ways to optimize the polymer/clay compatibility, the most popular method consists on converting these hydrophilic silicates to organophilic ones by performing chemical treatments of the clay. In this chapter several strategies to modify the inorganic clays and to make them more compatible with polymeric matrices are studied and the effect of each one, together with the relevant parameters, is established.

Keywords: Organo-clays, compatibility

chemical

modification,

nanocomposites,

1. INTRODUCTION Composite materials represent an increasingly important field in the polymer industry. Conventionally, many different kinds of fillers have been used in the form of particles, fibers or plate-shaped particles in the micrometer size range to provide an improvement of the properties of the neat polymer, for instance carbon black, calcium carbonate, glass fibres and mica. However, high filler loadings are required to achieve the desired improvements and, thus, problems in processing of the composite material may appear. Other important drawbacks of conventionally filled or reinforced polymeric materials are the weight increase, brittleness and opacity (Alexandre et al. 2000; Fischer et al. 2003). Polymeric nanocomposites are a new class of materials, for which at least one dimensions of the dispersed particles, is in the nanometer range. Their dimensions typically range from 1 to 100 nm. They represent an interesting alternative to conventional polymer composites because of their unique properties, synthesis and processing methods. Among all the potential nanofillers studied in the past decades, clays occupy an important position because they are easily available on all the continents with relatively low cost. Nanoclays belong to the family of phyllosilicates, also called layered silicates. Phyllosilicates consist of two-dimensional layers where a central octahedral sheet of alumina is fused to two external silica tetrahedrons, so that the oxygen ions of the octahedral sheet share also the tetrahedral sheets (Pavlidou and Papaspyridesb 2008).


Chemical Modifications of Natural Clays

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Polymers with small quantities of nanometric-sized clay particles have shown improvements in many properties such as thermal stability, module, flammability, permeability, conductivity, and also increased their biocompatibility and biodegradability. The high aspect ratio of the nano-scale layered silicate and their dispersion in the polymer plays a key role in these improvements (Yılmaz et al 2011). Nanoclay particles are generally agglomerated as a result of their high surface energy, therefore the disaggregation of nanoparticle agglomerates before or during composites processing proves to be a key point in obtaining an optimal dispersion (Rong et al. 2006). The modification of smectitic clays with different molecules has been extensible investigated (Cao et. al., 2005; Lee et. al., 2005; Kooli, 2009; Kozaka and Domka, 2009; Avalos et. al., 2009; Onal and Sarikaya, 2008a; Onal and Sarikaya, 2008b; Yapar, 2009). There are in the literature different studies related with the modifications of clay and other attending to clay based materials using mainly quaternary salts. On the other hand, a diversity of silanes and other organic functional groups that contain organic groups were introduced into the clay in order to functionalize it. Furthermore, organoclays were also obtained by the removal of the exchangeable cations from the clay structure functionalizing it with appropriate organic molecule. (Lee and Tiwari, 2012). This chapter will be focused on the state of art treatments that allow clays to disperse in polymer matrices as well as on the most significant findings in the polymer/clay nanocomposites field considering thermoplastic and thermoset matrices.

2. CLASSIFICATION OF LAYERED SILICATE FILLERS The general structure, with a small number of exceptions, consists of sheets arranged in structural layers. Each individual layer is formed by 2, 3 or 4 sheets which are formed either by tetrahedral, T, [SiO4]4or by octahedral, O,[AlO3(OH)3]6. All the clay minerals are composed either of TO or of TOT layers. The TO and TOT layers are also called ‗‗1:1‘‘ and ‗‗2:1‘‘ types because one octahedral sheet is linked to one tetrahedral sheet, or sandwiched between two tetrahedral sheets, respectively. The interiors of T and O have low quantities of metal cations and their apices are occupied by oxygen from which some are connected with protons (as OH-); all elements are arranged to form a hexagonal network with each sheet.


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Romina Ollier, Matias Lanfranconi and Vera Alvarez The crystalline clay minerals are mainly classified into seven groups: i. ii. iii. iv. v. vi. vii.

kaolinite and serpentine group: 2 sheet phyllosilicates, T:O = 1:1; charge of the two-sheet layer (unit cell): 0 e/uc; micas group: 3 sheet phyllosilicates, T:O = 2:1 ; charge of the threesheet layer (unit cell): ≤2 e/uc; vermiculite group: expanding threesheet phyllosilicates, T:O = 2:1; charge of the three-sheet layer (unit cell):1.2 to 1.8 e/uc; smectites group: expanding three-sheet phyllosilicates, T:O = 2:l; charge of the three-sheet layer (unit cell): 0.5 to 1.2 e/uc; pyrophyllite and talc group: nonswelling three-sheet phyllosilicates, T:O = 2:1; charge of the three-sheet layer: 0 e/uc; chlorites group: four-sheet silicates, T:O:O = 2:1:1; charge of the four-sheet layer: 1.1 to 3.3 e/uc; palygorskite and sepiolite group: layer-fibrous structure with tendency to organize themselves to form stacks with a regular van der Waals gap between them, called an ‗interlayer.

Among these groups, only kaolinite, smectite and sepiolite are the most widespread frequently used in clay polymer nanocomposite studies. Specially, the smectites (between one of the most famous is the montmorillonite) are the main choice in the preparation of polymer based nanocomposites. Their crystal lattice consists of two-dimensional layers where a central O sheet of alumina or magnesia is fused to two external silica T sheets so that the oxygen ions of the octahedral sheet do also belong to the T sheets (Figure 1).

Figure 1. Structure of a 2:1 layered silicate.



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The thickness of a layer is around 1 nm whereas the lateral dimensions are in the range from 300 Å to several microns or even larger depending on the particular silicate, the source of the clay and the method of preparation. Therefore, the aspect ratio of these layers is really high (Alexandre and Dubois, 2000). The layers are organized in the form of stacks with a regular Van der Waals gap between them denominated interlayer or gallery. In the octahedral sheet, isomorphic substitution within the layers may occur; i.e. high charge cations are substituted by cations with a charge lower by one, for instance Al+3 is replaced by Mg+2 or by Fe+2, or Mg+2 by Li+. Similarly in the tetrahedral sheet, Si+4 is substituted essentially by Al+3. Thus, the layers become negatively charged and this is counterbalanced by hydrated alkali or alkaline cations (Na+, Ca+2) situated in the interlayer (Bergaya et. al., 2012). As the forces that hold the stacks together are relatively weak, the intercalation of small molecules between the layers is easy. So, added to their low cost, the rich intercalation chemistry of these clays allows them to be chemically modified and to make them compatible with polymeric matrices. This is illustrated in Figure 2.

Figure 2. Illustrative representation of chemical modification of smectites and compatibilization with a polymer matrix.

3. FUNDAMENTALS OF POLYMER/CLAY SCIENCE Natural clays are very abundant and clay deposits are spread all over the world (North Africa, Europe, Russia, China, USA, South America). Hence,


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Romina Ollier, Matias Lanfranconi and Vera Alvarez

they are available in big quantities and most deposits are commercialized. Between smectites, montmorillonite, have been extensively used to prepare organoclays (Betega et.al., 2008) due to its exceptional properties: high cation exchange capacity, swelling behavior, adsorption properties and large surface area. Nevertheless, other clays such as hectorite (Vougaris and Petridis, 2002), synthetic fluoro-hectorite (Gorassi et al., 2003), sepiollite (Akyüz and Akyüz, 2003) and synthetic micas (Tamura and Nakazawa, 1996, Klapyta et al., 2001, Chang et al., 2003 and Klapyta et al., 2003) have been used to prepare nanocomposites. Two different types of polymer/clay nanocomposite structures (Figure 3) can be obtained, namely intercalated, where polymer chains intercalate between the layers resulting in finite expansion, and exfoliated nanocomposites where silicate layers are completely delaminated in the polymer matrix (Pavlidou and Papaspyridesb 2008; Ray and Bousima 2005).

Figure 3. Schematic illustration the morphologies of polymer/clay composites.

XRD (X-Ray Diffraction) is the most common technique used to analyze the nanocomposite structure; by monitoring the position, shape, and intensity of the basal reflections from the distributed silicate layers, the nanocomposite structure (intercalated or exfoliated) may be identified. Although that technique offers a simple method to determine the average interlayer spacing of the silicate layers in the intercalated nanocomposites, it is not able to determine the spatial distribution of the silicate layers and the homogeneity of the nanocomposites, namely the simultaneous occurrence of both intercalated and exfoliated structures and, so that, it is necessary to used other techniques, mainly Transmission Electron Microscopy (TEM) that allows a qualitative



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evaluation of the internal structure and spatial distribution of the various phases. Other techniques like Small Angle X-Ray Scattering (SAXS) or Wide Angle X-Ray Scattering (WAXS) provide information about the dispersion and orientation of the clay platelets in the polymer matrix, as well as other structural features in polymer/clay nanocomposites. Both morphologies (intercalated and exfoliated) result in an important enhancement in range of properties compared with the neat polymer (Ray and Okamoto, 2003) such as mechanical properties (Okada et. al., 1990), thermal stability (Kojima et.al., 1993; Zilg et. al., 1999), and flame retardant properties (Ke et. al., 1999) are among the properties affected by the addition of a few weight percentages of nanomaterials. However, since improvements in many properties depend on the degree of dispersion of the nanoparticles, exfoliated nanocomposites is generally the target of many nanocomposite studies. Modifying clay minerals with various surfactants is the most widely used physical method to prepare inorganic/organic hybrid materials and accordingly clay mineral–polymer nanocomposites (Ray and Okamoto, 2003).

Figure 4. Importance of clay functionalization and processing of the composite material.


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Polymer-clay nanocomposites have been mainly prepared by three different routes: in situ polymerization, solution polymerization, and melt intercalation. The first method used to synthesize polymer/clay nanocomposites was the in-situ polymerization of polyamide 6 (Okada et. al., 1990). The obtained nanocomposites displayed improved mechanical, thermal and barrier properties (Kojima et.al., 1993). Other nanocomposites prepared by the same technique were based on polyurethanes (Zilg et. al., 1999) and polyethylene terephthalate (Ke et. al., 1999) and they showed increased tensile properties (both strength and modulus). The in situ intercalative polymerization method was used to prepare thermoset-clay nanocomposites based on: phenol (Lan et. al., 1995); epoxy (Lee and Jang, 1998) and unsaturated polyester (UPE) resins (Suh et. al., 2000). In that method, the polymer chains are intercalated between clay layers and then it proceeds by a crosslinking reaction. Other key factors, that determine the clay dispersion inside the matrix, and, so that, the final properties are the processing parameters. Both factors, the compatibility between the matrix and the clay as well as the processing technique with the corresponding parameters are responsible of the dispersion and distribution of the clay inside the polymeric matrix (Figure 4). Dennis et al. (2001) have demonstrated the importance of both the chemistry of the clay surface and how the clay was melt blended with the thermoplastic. So many factors will determine whether an intercalated or exfoliated nanocomposite is formed or not, including the type of polymer matrix, the clay and its organic modifier, the preparation technique and processing parameters.

4. CHEMICAL TREATMENTS Most of polymers are hydrophobic in nature and, so that, the hydrophilic Na+ cations of the interlaminar spaces of clay should be exchanged by organic cations (Xi et. al., 2004). Thus, modified clays posses lower energy at the surface and are more compatible with hydrophobic polymers, which are then able to ingress inside the galleries, always under appropriate processing conditions (Picard et. al., 2007; Drown et. al., 2007). The synthesis of organoclays is based on the mechanisms of the reactions that the clay minerals can have with the organic compounds. The surface treatment of clay minerals has received great interests, for example, ion exchange of the inorganic cations with organic cations usually with quaternary



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ammonium or alkylphosphonium compounds can dramatically alter the surface properties. Hence, the interlayer cations can be exchanged by various types of organic cations. Grafting reactions, i.e., forming covalent bonds between reactive surface groups and organic species are important steps to hydrophobise the surface of many clay mineral particles. Only the 2:1 clay minerals that provide the silanol and aluminol groups on the edge surface react with organic agent by grafting reactions (Bergaya et al., 2006).

a. Purification of Clays Commercial clay materials are often raw clays so they usually contain a variety of impurities, for example carbonates, cristobalite, feldspars, quartz, organic matter, iron hydroxides among others (Bergaya et al 2012). Clay minerals obtained from the same deposit may show some variability in the properties in different parts of the deposit. They differ by their composition and the nature of the impurities. In consequence, for certain applications, purified clay minerals are required, so a previous purification step must be performed. The purification of clays by sedimentation isolates the smectite portion and produces highly pure MMT with improved properties such as high CEC and high thermal stability (Leite et. al., 2010).

b. Activation of Clays Activated clay is usually of bentonite origin, which has been treated to improve its ability to absorb. This treatment was studied from several years because the catalytic properties of clays are affected by chemical composition, structure, and pretreatment conditions (Auer and Hofmann, 1993; Ravichandran et at., 1996). That kind of properties can be really enhanced by means of an acid treatment and/or pillaring methods (Auer and Hofmann, 1993; Ravichandran et al., 1996; Upadhya et al., 1996; Chitnis and Sharma, 1997; Clark et al., 1997). There are different works in the field of acid attack. Several authors (Novák and Číčel, 1978; Komadel et al., 1990; Ravichandran and Sivasankar, 1997; Madejová et al., 1998; Pálková et al., 2003) have investigated the effects of hydrochloric acid on the structure of smectites. One possibility is to use sulphuric acid (H2SO4); the goal of that treatment is to enlarge a high specific surface area but retaining the ability to absorb organic molecules and layered morphology (Steudal et. al., 2009). They have


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demonstrated that the treatment produces dissolution of the octahedral cations and that the decrease of the layer charge reduced cation exchange capacity and increased the specific surface area. Nevertheless, the material is still able to incorporate large organic cations. Edge attack also took place and octahedral sheet as well as protons blocked the formation of a three-dimensional structure.

c. Ion Exchange Reactions A relatively simple industrial treatment enables the exchange of any of the interlaminar cations by a desirable cation (Lee et. al., 2012). In addition, these cations could provide functional groups that eventually can react with the polymer matrix or initiate a polymerization reaction, improving the strength of the interface between the inorganic platelet and the polymer matrix (Frost et al. 2007). The technique consists in the exchange interlayer cations of the clay mineral by quaternary cations from a salt, the most common used salts are quaternary alkylammonium ones whose are cationic surfactants and they are synthesized by complete alkylation of ammonia or amines. The surfactant then enters the interlayer spaces mainly by replacing the initial inorganic cations and electrostatic force is the main linkage between the modifier and the clay platelets (Lagaly, 1981) (Figure 5). It is important to note that the intercalation with a cationic surfactant not only changes the properties of the clay surface from hydrophilic to hydrophobic but also leads to a significant augment the interlaminar spacing. The cationic exchange using alkylammonium salts has been studied by several authors (Kornmann et al., 2001, Le Pluart et al., 2002, Lee et al., 2005, Edwards et al., 2005, He et al., 2005 and Zhu et al., 2005). Generally, an aqueous dispersion of the clay is mixed with a solution of the cationic surfactant in a defined ratio (Figure 6). After equilibration under stirring at a specific temperature, the mixture is filtered and washed several times to remove the nonadsorbed surfactant molecules and their counterions. In order to produce an effective modification, it is important to determine the amount of bonded surfactants (Le Pluart et al., 2002, Osman et al., 2003 and Xi et al., 2005), and to select the quantity of organic salts to be used in the modification, it is necessary to know the CEC (cation exchange capacity) of the clay that can be determined by several methods (Chapman, 1965, Fraser and Russel, 1969, Gillman and Sumpter, 1986, Kitsopoulos, 1999, Madeira et al., 2003 and Czimerova et al., 2006, Bergaya et al., 2006). Thus, the CEC is simply defined as the number of cationic charges retained by a fixed mass of



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the clay mineral sample, generally either 1 or 100 g, so it is commonly expressed as (meq/g) or (meq/100 g). This parameter of clay minerals determinates the degree of adsorption of organic surfactant by electrostatic interaction, so it represents the maximum amount of cations that can be retained electrostatically by the clay.

Figure 5. Illustration of the cationic exchange process.

Figure 6. Schematic representation of the cation exchange steps.


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Another relevant factor on getting high purity organic modified clay is the washing (Vázquez et. al., 2008) being the effect of the process dependent on the incorporated alkyl chain length. The time and temperature used during the exchange process are also meaningful variables to increase the amount of surfactant incorporated to the clay. In addition, depending on the functionality, packing density, and length of the alkyl tail of organic modifiers, the organoclay may be designed to optimize the compatibility with a given polymer (Xie et al 2001). It can be generally said that the longer the surfactant chain length and the higher the charge density of the clay, the further separation of the clay layers will be caused due to the fact that both of these parameters contribute to increasing the volume occupied by the surfactant molecules in the interlaminar space. Modifications are performed by exchanging the inorganic cations of the clay with quaternary salts, calculating the mass of organic cation and clay by using the following equation (Upson and Burns, 2006):

M c  f .CEC. X .PMc.103

(1)

where: Mc is the mass of organic cation (g); f is the fraction of CEC (cation exchange capacity, meq/g clay) satisfied by the organic cation; X is the mass of clay (g); and PMc is the molecular weight of the organic cation (g/mol). Thermal properties of organoclays play an important role in the subsequent processing and stability of nanocomposites. Thermogravimetric Analysis (TGA) allows comparing the thermal stability of clays. It is generally carried out in air atmosphere in order to determine both, the degradation temperature of the clays and the real content of organic modifier that has been incorporated after the exchange reaction. The reduced thermal stability of alkylammonium treated organoclays and the processing instability of some polymers in the presence of nano-dispersed clay have provoked the studies related with improved organophillic clays which could be useful in the preparation of thermoplastic/clay nanocomposites that require high melt-processing temperatures or long residence times under high shear and for thermoset/clay nanocomposites with high cure temperatures or large reaction enthalpies whose could degrade the traditional clay modifiers (Gilman et. al., 2002). Such problems have been reported, for instance, at high processing temperatures above 200 ºC in the melt processing of polyamides (PA6 and PA66), poly (ethylene terephthalate), and polycarbonate. Thermal degradation during processing can initiate/catalyze



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polymer degradation mechanisms and also to different undesirable effects during processing and in the final nanocomposite. Hence, many research works have been developed in orden to synthesize thermally stable organoclays based on stibonium, phosphonium, or imidazolium surfactants (Gilman et. al. 2002; Wang and Wilkie et. al. 2003; Patel et. al. 2007; Hedley et. al. 2007; Avalos et. al. 2009). Phosphonium salts behave differently than their ammonium counterparts because of the greater steric tolerance of the phosphorus atom and the participation of its low-lying d-orbitals in the processes of making and breaking chemical bonds (Xie et. al. 2002). Calderon et. al. (2008) prepared organoclays with water soluble phosphonium surfactants by traditional cation exchange reactions. An alternative procedure (two phase reaction) was used to prepare organoclays with water insoluble salts as well. Abdallah and Yilmazer (2013) recently reported different surface modifications of purified MMT with two phosphonium surfactants (tetraoctyl phosphonium bromide and benzyltriphenyl phosphonium chloride) resulting in thermally stable organoclays, which overcame the thermal degradation problem of conventional organoclays when used with PA66 during compounding and processing. The extent of improvement depended on the structure of the phosphonium surfactants. Saitoh et. al. (2011) designed and prepared various organoclays modified with different functional groups to improve the dispersibility in an epoxy matrix and to accelerate the curing of the resin. Tris(4-phenoxyphenyl)phosphine, carboxydecyltris(4-phenoxyphenyl) phosphonium bromide, 10-hydroxydecyltris(4- phenoxyphenyl)phosphonium bromide, hexyltris(4-phenoxyphenyl)phosphonium bromide, dodecyltris(4phenoxyphenyl)phosphonium bromide, and octadecyltris(4-phenoxyphenyl) phosphonium bromide were synthesized. They found that the organic modifiers of organoclays influenced various properties on epoxy/clay nanocomposites. It was confirmed that the dispersibility of the organoclay and thermal properties of the nanocomposites were improved by incorporating carboxyl-phosphonium modified MMT. Goswami et. al. (2012) synthesized and characterized a series of imidazolium salts with various functionalities and substituent chain length and performed organic modifications of natural clays with them. Six different imidazolium surfactants were synthesized by reacting 1,2-dimethylimidazole or 1-decyl-2-methylimidazole with 11-bromoundecenoic acid, 11-bromo-1undecenol, or 1-bromodecane. The thermal stabilities of the imidazoliumfunctionalized clays were found to be much greater than those of the neat organic salts. This increase was attributed mainly to the removal of the halide


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that catalyzes the decomposition process. Moreover, stability did not depend on the functional group present on the imidazolium surfactants or the position of the substituent on the ring.

d. Modification with Biomolecules The clays may be modified with various biomolecules such as proteins, enzymes, amino acids, or peptides. Protonated natural functionalized α-amino acids have a similar chemical structure compared with conventional modifiers of alkylammonium cations. It is known that amino acids are biological chiral resources and they have gathered much interest due to their biocompatibility, biodegradability, and their possibility of targeting for cleaving by different enzymes. Amino acids present a significant low toxicity and various possible structures in comparison with chemically synthetic modifiers (Katti et al. 2005; Parbhakar et al 2007). For example, Mallakpour et. al. (2011 and 2013) have reported modifying a sodium montmorillonite (Cloisite Na+, Southern Clay Products Inc., Texas, USA) with different -natural positively charged amino acids such as L-alanine, L-valine, L-leucine, L-isoleucine, Lphenylalanine, and L-methionine. The modification reaction consisted of an ion exchange process of the sodium cations of the protonated amino acid clay (Figure 7).

Figure 7. Clay platelets intercalated with protonated amino acids.

The exchange process was conducted in aqueous solution at 60 °C for 6 hours with continuous mechanical stirring. They have shown form the XRD patterns and TGA thermograms that the amino acids were mainly intercalated into MMT layers effectively and to less extent adsorbed on its surface. The



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amino acids resulted in the increase of the interlayer distance, and conferred to modified montmorillonite organophilicity properties, biocompatibility and biodegradability. They have also shown, from TGA analysis (Xi et al., 2007; Zhou et al., 2009) that the intercalation was lower for aromatic than for aliphatic amino acid surfactants relating this result with the fact that the aliphatic chain posses‘ smaller molecular volume being more easily intercalated MMT interlayer. It is important to note that these clays are attractive as starting materials to be used as fillers in the preparation of various products with biopolymers. As they are not harmful to human health, they may have curative properties and are sometimes used in pharmaceutical formulations (Bergaya et al). Sarier et al (2010) synthesized sodium montmorillonite modified with salts of fatty acids. In their work, they used the sodium salts of octadecanoic acid and dodecanoic acid and a sodium montmorillonite. The modification reaction was conducted in aqueous solution with the addition of the sodium salt of 4-dodecilbencenosulfanílico as a surfactant to allow fatty acid emulsion and dispersion of the clay particles in the colloidal mixture. The exchange reaction was conducted at 80 ° C for 2 hours, with continuous mechanical stirring. The electron transmission microscopy (TEM) showed that the modified montmorillonite fatty acids were well dispersed and sandwiched in the interlamellar spaces or adsorbed on the surface of the clay. As a result of the modification, the interlayer distance increased significantly. To examine the applicability of the modified montmorillonite in the preparation of nanocomposites, a mass equivalent to 2 wt.% of montmorillonite was incorporated in a mixture of 1, 3 propanediol and 4-methyl-m-phenylene diisocyanate to produce a polyurethane foam rigid by in situ polymerization. This process resulted in the efficient dispersion of modified clay in the polyurethane foam. The nanocomposite obtained had a significant increase in thermal stability compared with the polyurethane control.

e. Silylation Reactions Silylation of clay mineral surfaces has attracted much attention (He et.al., 2013) because silylated products exhibit properties suitable for many applications in materials science (Carrado, 2000; Herrera et al., 2004; LeBaron et al., 1999; Okada and Usuki, 2006; Ray and Okamoto, 2003) and environmental engineering (Le Pluart et al., 2002; Prado et al., 2005).


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The silylation method consists on covalently bonding the silane molecules to the clay platelets. The covalent bond is produced from a condensation reaction of the reactive hydroxyl groups of the clay, located at the edges of the platelets and structural defects, with the hydroxyl groups generated from the hydrolysis of an alkoxysilane. Then in the nanocomposite, the organosilane acts as a bridge between the clay and the polymeric matrix, providing silanol to condensate with M-OH on the clay surfaces and giving special functional groups that can be able to react with the matrix improving the final properties of the material (Katsarava and Yakov, 1992; LeBaron et al., 1999; Herrera et al., 2004; Rong et al., 2006; Zhou et. al., 2007; Kiliaris and Papaspyrides, 2010). It has been demonstrated that a successful silylation strongly depends on the reactivity of clay mineral surfaces (He et. al., 2013). Montmotillonites and bentonites are swelling clays and, for that kind of smectites, the silane can be easily intercalated into the interlayer space; being the external and internal surfaces silylated under standard conditions (room temperature, without pretreatments) (He et al., 2005; Shen et al., 2007, 2009). Trialkoxysilanes, alkylchlorosilanes and alkylsilazanes can be used to modify the filler surface due to their ability to readily undergo hydrolysis and condensation reactions (Beari et al. 2001). In addition, the organic groups, represented as R in Figure 8, may contain functionalities able to react with monomers or pre-polymers and they are useful to prepare nanocomposites in which some polymer chains are covalently bonded to the clay surface (Bauer et al. 2003). Thus, these chemical bonds between the inorganic and organic components are of great importance to assure a proper delamination of the individual silicate layers in polymeric matrices. This method provides covalent bond between organic components and clay minerals that produce a durable immobilization of the organic moieties in the silylated products (da Fonseca and Airoldi, 2003; LeBaron et al., 1999; Takahashi and Kuroda, 2011), and prevents their leaching into the surrounding solutions. The reaction between -OH groups of the organosilanes and the clay can occur at three different sites (Piscitelli et. al., 2003): in the space between the platelets, on the outer surface of the platelet, or on the edges thereof. However, the reactions which involve edge –OH groups do not increase the interlayer distance; i.e. they are not useful for intercalation, but they can be used to enhance platelet compatibility with the host polymer. The successful grafting does not necessary increase the interlayer spacing (Park, 2004; Daniel et al., 2008; Herrera et al., 2004, 2005) suggesting that the broken edges of clay are



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the most reactive sites for silane grafting. Whereas in the case of cation exchange reactions the maximum interlaminar spacing can be directly correlated to the length of the surfactant alkyl chain length (Lagaly, 1981; Zhu et al., 2003); there exists no relationship between the organic chain length and the basal spacing of the silylated clays.

Figure 8. Schematic representation of silylation reactions.

On the other hand, it has been proved that the quantity of grafted silane can be greatly enlarged by the acid activation of clays (Shen et al., 2009), this feature could be related with the increment of reactive sites generated through acid treatment (Breen et al., 1995, 1997; He et al., 2002). Di Gianni et al. (2008) have studied the silylation reaction of a sodium montmorillonite (Cloisite Na +, Southern Clay Products, USA) with glycidylpropyl triethoxy silane (GPTS, Aldrich). The reaction was carried out at 80 °C for 4 hours in an ethanol / water (75:25) using a large excess of the silane with respect to the mass of clay. After the reaction, the product was filtered, washed with ethanol and dried at 80 °C. The modified montmorillonite was incorporated in a cyclo-aliphatic epoxy monomer (3, 4-epoxycyclohexylmethyl 3, 4'-epoxycyclohexylcarboxylate; Cytec) and dispersed in an ultrasonic bath for 8 hours at room temperature. The mixture was photopolymerized with UV light. Because the GPTS organic chain contains in an epoxy ring, this may be copolymerized with the monomer during the


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formation of the thermosetting matrix. Transmission electron micrographs (TEM) of the obtained nanocomposites showed a mixed intercalatedexfoliated hybrid structure. The obtained films showed optical transparency, and improved thermal and mechanical properties compared to the net epoxy matrix. Meanwhile, Piscitelli et. al. (2003) have studied the effect of chain length on the organic alkoxysilane silylation grade and on the interlamellar spacing of sodium montmorillonite. They have used three alkoxysilanes with different chain length: 3-aminopropyltriethoxysilane (A1100), N-(2-aminoethyl)-3aminopropyl trimethoxysilane (A1120), and 3 - [2 - (2-aminoethylamino) ethylamino] propyl-trimethoxysilane (A1130). They have found that the degree of silylation increased as a function of the length of the organic chain, with the overall concentration of the silane, and with the increase of temperature. On the other hand, the interlaminar spacing increased with the concentration of the silane and the reaction temperature, but unexpectedly that parameter (d001) decreased with increasing length of the organic chain. This behavior was explained in terms of the marked tendency of A1120 and A1130 aminosilanes to interact between themselves by intermolecular bonds and the hydrogen bond type and hydrophobic interactions due to the presence of one or two-NH groups in organic chains. The silylation reaction and the microstructure developed in the interlaminar space strongly depend on the nature of the used clay. This conclusion was drawn by He et. al. (2005) who have studied the silylation reaction between 3-aminopropyltriethoxysilane and two clays of different nature: a synthetic fluorohectorita (SOMASIF ME100, CO-OP Chemical Co., Japan), and a natural montmorillonite (Optigel-757, Nanofil, Süd-Chemie Co., Germany). They concluded that the silylation reaction takes place in these systems basically in two steps: first, the silane molecules intercalated into the interlaminar space of the clay, and then passes the condensation reaction between silane molecules and the surface of the sheets of clay. In natural montmorillonite silane molecules adopted a bilayer-type arrangement parallel, whereas in the arrangement adopted fluorohectorita synthetic mono-parallel. The bilayer-type arrangement parallel in natural montmorillonite, resulted in increased interlaminar spacing and different properties of the arrangement surface monolayer. Another feature that influences the silylation reaction is alkoxysilane functionality. Herrera et al. (2005) have studied the silylation reaction of Laponite RD (synthetic hectorite one of Rockwood Additives Ltd., UK) with two different functional alkoxysilanes: methacryloxypropyl dimethyl methoxy



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silane (monofunctional) and methacryloxypropyl trimethoxysilane (trifunctional). They have found that while the trifunctional silane condensation polysiloxane oligomers resulted interspersed between the clay platelets, with a marked increase in the interlaminar spacing, the monofunctional silane produce a silane monolayer generated on clay surface, with much less effect on the interlaminar spacing. The study of physicochemical properties of the silylated laponite showed that while the monofunctional silane produced no significant effects on the properties of the clay, the trifunctional silane resulted in a decrease of porosity, a sharp increase in the interlaminar distance and greater hydrophobicity.

f. Alternative Modifiers Malucelli et al. (2007) have reported the modification of organic-modified montmorillonite with different polybutadienes maleinized. The reaction was conducted in various organic solvents. In nonpolar solvents (such as nheptane) the modification reaction was very slow, while increasing the polarity of the solvent is favored modification process. The solvent which led to the best results was the 2, 2-dimethoxyethane. The final composition corresponds to about 25 per each ring succinic butadiene experienced a marked increase in the interlaminar distance. The modified clay was dispersed in a cycloaliphatic epoxy monomer (3,4-epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexane carboxylate), which was then cured with UV light. The structures obtained showed intercalated nanocomposites or cuasiexfoliadas. The best results were obtained with a maleinised polybutadiene of MW = 5000 and 7.5repeat units in the oligomer chain. Liao et al. (2010) have studied the intercalation reaction of amidopolyoxyalkylenes in two different ionic clays: a double layer of anionic (MgAl LDH, Showa Chemicals) and a sodium montmorillonite (Nanocor Co.). They found that the intercalation process led to a marked increase in the interlaminar distance: from 7.8 to 63 Å in the anionic clay (LDH), and from 12.4 to 51 Å in the montmorillonite.

CONCLUSION Clay minerals present a rich intercalation chemistry which allows the properties of the polymer/clay nanocomposites to be enhanced in many


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different ways. Their physico-chemical properties along with their potentially low production costs make them useful for a broad range of applications. However, although these materials have been known for many years, there is still much work to be done to develop polymer/clay nanocomposites with enlarged dispersions and well-exfoliated morphologies that ensure the desired final properties (mechanical, thermal, barrier, etc) of the final material. In order to meet that objective, efforts should be done in two different areas: the development of new chemical modifications of the clay and the optimization of the processing conditions of the composite material. Specially, research efforts are now focused in the possibility of functionalizing the nanoclays with tailored modifications in order to develop materials with specific functional properties for applications such as drug release, sensors, functional coatings, in biomedicine, electronics, aeronautics and energy devices.

ACKNOWLEDGMENTS The authors would like to acknowledge the financial support of the National Research Council of Argentina (CONICET), National University of Mar del Plata (UNMdP) and the National Agency of Scientific and Technologic Promotion (ANPCyT), Fonarsec FSNano004.

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Chapter 3

HIGH-PERFORMANCE CERAMIC LUBRICATING MATERIALS Yongsheng Zhang, Yuan Fang, Hengzhong Fan, Junjie Song, Tianchang Hu and Litian Hu State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, China

ABSTRACT With the rapid development of modern technology, various machineries have proposed changes in lubricating materials. These are geared toward improving the property of materials and allowing them to surmount severe challenges under extreme conditions (e.g., high/low temperature, special media, atmosphere, etc.) in the fields of aviation, space, nuclear energy, microelectronics, and so on. The ceramic lubricating material is a new solid lubricating material composed mainly of a ceramic matrix, reinforcing phase and solid lubricant. This ceramic lubricating material shows good performance in high temperature and corrosion resistance due to its ceramic-skeleton. Moreover, the ceramic lubricating composite is the only material that can work above 1,000℃, while maintaining low density and excellent corrosion resistance. These materials are considered to be high temperature lubricating technology with the most development potential and practical value. This chapter has 

Corresponding author: E-mail: [email protected].


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Yongsheng Zhang, Yuan Fang, Hengzhong Fan et al. analyzed the research focus and present problems of ceramic lubricating materials, and then proposed the design principle of these materials. The design, preparation and performance of several typical ceramic lubricating materials were introduced. Based on these studies, we developed a kind of ceramic lubricating composite which has low wear, high reliability and long life, and provide theoretical guidance and technology support for the application of new ceramic materials in the fields of high technology.

1. INTRODUCTION Lubrication problems are the common problems of motive machinery. There are all kinds of lubrication problems in the space, ground mechanical equipment and large aircraft carrier. Moreover, high performance lubricating materials are the key to assuring the mechanical system runs in high precision and more stability. With the rapid development of modern technology, various machineries have proposed changes in lubricating materials. These are geared toward improving the property of materials and allowing them to surmount severe challenges under extreme conditions (e.g., high/low temperature, special media, atmosphere, etc.) in the fields of aviation, space, nuclear energy, microelectronics, and so on. In recent years, various types of aerospace engines and space vehicles have developed very urgent requirements for high-temperature lubrication technology. The lubricating materials corresponding to the required conditions in these fields must be capable of working in corrosive environments and high temperatures above 1,000℃ for a long time. However, the conventional solid lubricating material cannot satisfy these application requirements [1]. Lubricating materials are currently facing a series challenge. Ceramic materials are considered to be potential candidates for hightemperature tribological applications because of their excellent properties, such as high temperature resistance, low specific density, high hardness and anti-oxidation. Unfortunately, the friction coefficient and wear rate of ceramics are very high under dry sliding, which limit their application in the areas of high-temperature lubrication. According to the basic theory of tribology, it is necessary to have a low-shear-strength film on the surface of ceramics to reduce both the coefficients of friction and the wear rates of the materials. To minimizes the friction coefficient and subsequent energy losses, researchers tried to introduce a self-lubricating mechanism in the ceramiccomposites.


High-Performance Ceramic Lubricating Materials

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The ceramic self-lubricating composite is a new solid lubricating material composed mainly of a ceramic matrix, reinforcing phase, and solid lubricant. This self-lubricating material shows good performance in high temperature and corrosion resistance due to its ceramic-skeleton. The solid lubricant can be used to improve the tribology performance of materials, demonstrating excellent self-lubricating properties in a wide range of temperatures [2-4]. Moreover, the ceramic lubricating composite is the only material that can work above 1,000℃, while maintaining low density and excellent corrosion resistance. However, subsequent studies have shown that these composites are homogenous in terms of mechanical and tribological properties. Thus, the strength of ceramics and the lubrication of solid lubricants cannot be fully utilized. In addition, because the continuity of ceramic phases is destroyed by the layered structural solid lubricant phase, the mechanical property of this type of material is reduced. Therefore, the design and fabrication of the composites must be geared toward improving both mechanical and tribological properties, which is also the focus of the ceramic lubricating materials [5,6]. Based on the above background, some new design methods to achieve the integration of structure and lubricating function in ceramic were proposed. On this basis, we developed a kind of ceramic lubricating composite which has low wear, high reliability and long life, and provide theoretical guidance and technology support for the application of new ceramic materials in the fields of high technology.

2. PREPARATION AND TRIBOLOGICAL PROPERTIES OF ZIRCONIA/ALUMINA NANOCOMPOSITES WITH CONTROLLABLE GRAIN SIZE Ceramic-based nanocomposites are highly attractive materials due to their exceptional properties. Nanocomposites have a new material design concept and significantly improved strength has been achieved with moderate enhancement in fracture toughness. The microstructure of nanocomposites is constructed by dispersing second-phase nano-size particles within the matrix grains and on the grain boundaries. Thermal expansion mismatch between the matrix and second-phase particles produces a marked improvement in mechanical properties such as fracture strength, fracture toughness, creep resistance, thermal shock resistance [2]. In addition, ceramic nanocomposites have more excellent wear resistance than traditional micro-ceramics [7].


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Yongsheng Zhang, Yuan Fang, Hengzhong Fan et al.

Therefore, ceramic lubricating materials based on nanostructured are considered to have a great application prospect. By controlling the sintering temperature properly, Y-TZP/Al2O3 nanocomposites with controlled grain size (100~500 nm) were prepared by hot-pressing using the powders with different grain size [8]. Based on the design of tribology, we developed a kind of ceramic lubricating composite which has low wear and friction coefficient. In the temperature range of 25~200℃, the friction coefficient and wear rate of YTZP/Al2O3/MoS2 composite were less than 0.2 and 5×10-6mm3/Nm, respectively. Moreover, the friction coefficient of Y-TZP/Al2O3/MoS2 composite can maintain less than 0.5 at 600℃. For the Y-TZP/Al2O3/CaF2-Ag and Y-TZP/Al2O3/CaF2-Graphite composites, the friction coefficients were less than 0.45 in the temperature range of 25~800℃, which could be attributed to the presence of graphite, Ag and CaF2. The variation of friction coefficient of friction pairs of YTZP/Al2O3/CaF2-Graphite and Si3N4 ceramic with temperatures is showed in Figure 1(a).The friction coefficient was about 0.23 at room temperature and 0.28 at 200℃, which could be attributed to the presence of graphite. As the temperature increased above 300℃, the friction coefficient remained around 0.32~0.45, and that was because CaF2 act at high temperatures to reduce the friction coefficient. As a consequence, it is the synergistic effect of graphite and CaF2 which offer excellent tribological properties for the Y-TZP/Al2O3 over a broad temperature from room temperature to 800℃. Figure 1(b) shows the typical curves of friction coefficients of friction pairs of YTZP/Al2O3/CaF2-Graphite and C-SiC composite. One can see that the friction coefficients of the composites are steady at room temperature and 800℃ after the run-in period. It can also be seen from Figure 1(a) and (b) that the friction pairs of Y-TZP/Al2O3/CaF2-Graphite and C-SiC composite has lower friction coefficient than Y-TZP/Al2O3/CaF2-Graphite and Si3N4 pairs. In addition, on the basis of Y-TZP/Al2O3 nanoceramics, metal molybdenum was developed to generate Y-TZP/Al2O3/Mo nanocomposites, which are compounded by nano-sized ZrO2-Y2O3-Al2O3 and micro-sized molybdenum powder as raw material [9]. There are mixed-structures composed of intra-type, inter-type and nano/nano type in Y-TZP/Al2O3/Mo ceramic-metal nanocomposites, which results in high fracture toughness. The metal molybdenum improves evidently the tribological characteristics of Y-TZP/Al2O3 nanoceramics. The friction coefficient of the material can reach the minimum value of 0.48, which is 0.38 lower than the Y-TZP/Al2O3



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monoliths. A reduced friction coefficient of composite was gained that attributed to the formation of friction induced oxide layer during hightemperature friction process [2]. 1.0 0.9

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Time(S) Figure 1. The variation of friction coefficient with temperature (a) and sliding time (b).


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3. TRIBOLOGY DESIGN AND FABRICATION OF HIGH-PERFORMANCE ZIRCONIA AND ALUMINA LAMINATED COMPOSITES Lamination is one of the new strategies to enhance the mechanical properties of ceramics. Recent studies have shown that the laminated ceramic composites could significantly improve the bending strength and fracture toughness compared with monolithic ceramics. Nevertheless, there is only few literature on the lubricating properties of ceramic laminated composites. Therefore, making self-lubrication laminated ceramic composites with high strength and fracture toughness has a promising potential. Firstly, we prepared a series of layer structural composite materials with composition of Al2O3 and ZrO2(3Y). On this basis, we developed a kind of structural and lubricatingfunctional integration ceramic composite materials. The Al2O3/Al2O3–ZrO2(3Y) laminated composites were prepared with different starting powders. The particle size and the size distribution of starting powders significantly affect the microstructure and mechanical properties of the laminated composites. The laminated composites with the best mechanical properties and microstructure, which use the micro/nano-sized powders as starting powders, the bending strength is about 740 MPa. In addition, the bending strength in the parallel direction of 436 MPa can be achieved, which indicate that the composites with good bonding strength [10,11]. Figure 2 shows the optical photos of the laminated nanocomposites. It can be seen from Figure 2 that the laminated materials have obvious layered structure with a distinct boundary. In addition, ultrafine grained ZrO2(3Y)/ZrO2(3Y)-Al2O3 ceramic with layered structure was prepared using synthesized nano-powder as raw materials. There are mixed-effects composed of residual stress and phase transformation toughening in ZrO2(3Y)/ZrO2(3Y)-Al2O3 layered nanocomposites, which results in excellent mechanical properties. The highest bending strength of 968 MPa can be achieved for this material with a ZrO2(3Y) mass fraction of 15%, thickness ratio of 1:1 and the thickness of 80 μm, which is 1.4 times larger than the monolithic ZrO2(3Y)-Al2O3 ceramics. On the basis of laminated composites, three-dimensional-compositelubricating-structure (TDCLS) was developed on the surface of this material to improve its tribological property. Laser micromachining was used to form pictured structure on the surface of nano-ceramics (Figure 3), and solid lubricants were deposited on the surface of pictured nano-ceramics by surface



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deposition method. Under the collaborative lubrication of regular patterns themselves and solid lubricants, TDCLS are formed on the surface of ceramics in order to realize the structural-functional integration of nano-ceramic materials.

Figure 2. The optical photos of the laminated composites.

This TDCLS structure shows a very low friction coefficient of 0.15 nearly 5 times smaller than the traditional Al2O3 ceramics under the same experimental conditions and friction couple pair. This mainly because the TDCLS can provide a continuous and uniform lubricating film during friction process that reduces the coefficient of friction.

Figure 3. 3D photograph of textured surface of nanocomposites.

Complying with the design principle of structural-functional integration of advanced composites, ZrO2 and Al2O3 lubricating materials with laminatedgraded structure were successfully prepared by layer-by-layer pressing and


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hot-pressing sintering [1,6]. The schematic of the laminated-gradient structure ceramics are given in Figure 4.

Figure 4. Schematic of the laminated-gradient structure composites.

The laminated-gradient structure ceramics not only showed excellent tribological properties, it also maintained good mechanical performance, which realized the structural lubricating-functional integration of ceramic composites. In the temperature range of 25~800°C, the friction coefficients of these composite were less than 0.6, which were about half of that of monolithic Al2O3 and ZrO2 ceramics under the same experimental conditions and friction couple pair. The bending strength, fracture energy and fracture toughness of materials were 3~10 times higher than that of traditional Al2O3 and ZrO2 ceramics lubricating material. For Al2O3 lubricating material with laminated-graded structure, the bending strength of 348 MPa, which was five times higher than that of traditional Al2O3 ceramics lubricating material, reached the same level as the properties of general Al2O3 ceramics. These excellent tribological and mechanical properties indicate that the composite materials can have numerous high-technology applications as a structural material. Meanwhile, there is uneven distribution of residual stress in the materials, which have important impact on the mechanical property of the materials. The variation of p causes the change of the residual stress generated from the thermal mismatch, and further influences the mechanical property of the materials. The residual stress can reach a higher level by controlling the



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gradient exponent of materials, which realize the optimization of the material properties.

ACKNOWLEDGMENTS The authors acknowledge financial support from the National Natural Science Foundation of China (51175493), the Program of the Light of the Chinese Academy of Sciences in China‘s Western Region (2010), and the China National Science and Technology Program of 973 (2011CB706603).

REFERENCES [1]

[2]

[3] [4]

[5] [6]

[7] [8] [9]

Qi YE, Zhang YS, Fang Y, Hu LT. Design and preparation of highperformance alumina functional graded self-lubricated ceramic composites. Compos Part B-Eng 2013;48:145. Zhang YS, Hu LT, Chen JM, Liu WM. Lubrication behavior of YTZP/Al2O3/Mo nanocomposites at high temperature. Wear 2010;268:1091. Liu HW, Xue QJ. The tribological properties of TZP-graphite selflubricating ceramics. Wear 1996; 198(1-2):143. Jin Y, Kato K, Umehara N. Further investigation on the tribological behavior of Al2O3-20Ag20CaF2 composite at 650℃. Tribo Lett 1999; 6:225. Qi YE, Zhang YS, Hu LT. High-temperature self-lubricated properties of Al2O3/Mo laminated composites. Wear 2012; 280:1. Fang Y, Zhang YS, Song JJ, Fan HZ, Hu LT. Design and fabrication of laminated–graded zirconia self-lubricating composites. Mater. Des. 2013;49:421. Zhang YS, Chen JM, Hu LT. Progress on Tribological Investigation of Ceramic-based Nanocomposites. Tribology 2005; 26(3): 284. Fang Y, Zhang YS and Hu LT. Preparation of crystal-controlled YTZP/Al2O3 nanocomposites. Mater. Sci. 2012; 30(4):348. Zhang YS, Hu LT, Chen JM, Liu WM. Fabrication and mechanical property of Y-TZP/Al2O3/Mo ceramic-metal nanocomposites. J. Chin. Ceram. Soc. 2009; 37(8):1398.


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[10] Qi YE, Zhang YS, Hu LT. Microstructure and bending strength of Al2O3/Al2O3–ZrO2(3Y) laminated nanocomposites. J. Chin. Ceram. Soc. 2011; 39(2):228. [11] Qi YE, Zhang YS, Hu LT. Preparation and properties optimization of Al2O3/Al2O3–ZrO2 laminated nanocomposites. J. Mater. Eng. 2013; 2:17.



Chapter 4

PHYSICAL AND CHEMICAL CHARACTERISTICS OF PINCINA ALGINATE Svetlana Motyleva,1, Jan Brindza,2,† Radovan Ostrovsky2 and Maria Mertvicheva1 1

All-Russian Breeding and Technological Institute of Horticulture and Nursery RAAS, Moskow, Russia 2 Slovak University of Agriculture, Nitra, Slovakia

ABSTRACT The study of the natural resources necessary for their rational, efficient and "intelligent" use. This is one of the most pressing issues of our time. Ore and non-ore potential of the Slovak Republic is restricted by the size of its area. Each successful result of geological research uncovering modest raw material supplies is considered to be worthy. Since 1990 the alginite bed situated in Lučenec Valley, locality of Pincina village, has been considered in the above mentioned sense. Alginite represents a rock with relatively high organic matter content which was sedimenting together with the clays in post - volcanic outbursts during geological periods appropriate for algae occurrence. Alginite has a wide 

Svetlana Motyleva: All-Russian Breeding and Technological Institute of Horticulture and Nursery RAAS, Moskow, 115598, Russia, E-mail: [email protected]. † Jan Brindza: Slovak University of Agriculture, 949 76 Nitra, E-mail: [email protected].


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Svetlana Motyleva, Jan Brindza, Radovan Ostrovsky et al. variety of utilization as an ecological raw material. Natural character, absence of phytotoxicity, effective economy of mining technology and ecologization of farming systems, those are the arguments for alginite to be included among such materials like zeolites and bentonites which have already achieved a possition for useful agricultural utilization. Alginite is a 3-4 million year old specifically rock as it is originated from the accumulated fresh water in the caldera of the volcano of the Pannonia Sea. It is due to a special sedimentary process. Rocks washed into the water of the crater started to flake due to the oxygen and bacteria, so the water became rich in nutrients. Being rich in minerals and organic nutrients led to the proliferation of some lower class organisms, for example green algae (Clorophyta). The algae built into their organisations the micro- and macro components that helped their existence. After perishing they got into the bottom of the lake among reductive conditions. Majority of the organic materials did not dissolve, but it mixed with the non-organic material and became Alginite. Alginite is organic and it basically consists of algae and non-organic materials such as basalt rubble, calcipelite, dolopelite and diatomite. Our research focuses on the study of Pincina alginite. Alginity have a layered structure. Its solidity is 0,5-1,5 kg/cm2 and its consistency is 2,12,4 gr/cm3. Its water content is 17-35% which decreases to 4-5% under laboratory circumstances and its volume reduced to 1,122 kg / l. By scanning electron microscopy (SEM), the peculiarities of the surface microrelief. Measured the size of the macro-and micropores. Identified floral remnants, obtained information on the safety, location and mineralization of organic matter in the algin. The method of energy dispersive spectrometry revealed that the mass fraction (%) macro is: Na (0.64), Mg (0.54), Al (13.48), Si (27,57), K (2.39), Ca (0.75). In laboratory experiments using HPLC studied the chemical composition of water and alcoholic extracts from various fractions alginite.

Keywords: Alginite, physical and chemical characteristics, scanning electron microscopy, local energetic dispersion spectrometry, high performance liquid chromatography

INTRODUCTION Alginite is a 3-4 million year old specifically rock as it is originated from the accumulated fresh water in the caldera of the volcano of the Pannonia Sea. It is due to a special sedimentary process. Rocks washed into the water of the crater started to flake due to the oxygen and bacteria, so the water became rich in nutrients.


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Being rich in minerals and organic nutrients led to the proliferation of some lower class organisms, for example green algae (Clorophyta). The algae built into their organisations the micro- and macro components that helped their existence. After perishing they got into the bottom of the lake among reductive conditions. Majority of the organic materials did not dissolve, but it mixed with the non-organic material and became Alginite. Alginite is organic and it basically consists of algae and non-organic materials such as basalt rubble, calcipelite, dolopelite and diatomite (Solti 2008, Vass 1998). Alginite is available in the given composition only in the Carpathian-basin (in Hungary and Slovakia). It is only mined in Pula and Gérce, in Hungary and in Pincina in Slovakia. The two mines owe 120 million tons of Alginite from which 90 million tons can be exploited (Hajós, 1976; Solti, 1986; Solti et al., 1988, Vass 1998, Hartyáni et al., 2000; Pápay, 2001). The exploration of the basalt maars infill in Southern Slovakia resulted by finding of two non-metalic deposits: the diatomite deposit near Jelšovec and the alginite deposit near Pinciná, both deposits are close to the town of Lučenec, center of Novohrad county. The maars belong to Podrečany basalt formation, Pontian (Upper Miocene) in age. The deposits originaded in the maar-lakes after the termination of the freatomagmatic eruptions. The Jelšovec maar-lake was inhabited by AlgaeDiatomaceae, meanwhile the Pincina maar was inhabited by Algae of the taxa Botriococcus braunii Kütz. On the botoom of the Jelšovec lake, there the diatomite, in Pincina lake the alginite came to existence. Alginite deposit near Pinciná infills a smaller maar (760x930 m). Its maximal thickness is of 45 m, the cover thickness varies from 4 m to 7 m (Vass 1998). The maars are generally characterised by a subsided crater floor, which forms during and after the phreatomagmatic eruptions due to collapse and subsidence of country rocks and pyroclastic deposits in a funnel-shaped volcanic conduit, i.e. in the diatreme (White, 1991; Lorenz et al., 2003). Alginite is greyish-green, greenish-grey, sometimes pitted, similar to Aleurite. It can be crumbled by hand easily. Its solidity is 0,5-1,5 kg/cm2 and its consistency is 2,1-2,4 gr/cm3. Its water content is 17-35% which decreases to 4-5% under laborator circumstances and its volume reduced to 1,122 kg/l. These data refer to a relatively large amount of clay minerals (montmorrilonite, illite, cornish stone). Particle content studies state that Alginite contains 20-60% clay fraction. Aleurite is the other important component. Its calcite content varies between 15-26%, and its dolomite content is between 3-18% (Solti, 2008, Vass 1998).


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Scan microscope confirmed that alginite is composed of clay minerals, calcium carbonate and phosphate crystals, diatom frustules, Botryococcus colonies, pollen grains, plant detritus, charcoal fragments, etc. (Solti, 1987; Vass, 2000; Pápay, 2001). The general characteristics of the chemical composition of Pula alginit soil (Hungary) states Solti (2008). Alginit contains humus 10 - 33%, constraint Ak 60 - 150, higroscope 2.30 - 11.04, pH 6.6 - 7.7. Lime 4-60%, dry matter 50-95%, water pH 8,1-8,2, potassium chloride pH 7,42-7,47, CaCO3 content: 15-25%, natural water capacity 56,7 cm3/100 cm3 alginite. Nutrient content - phosphorous 60-1200 ppm, potassium 400-3200 ppm, magnesium 320-2700 ppm, calcium 25000-90000 and nitrogen 2-60 ppm. Mineral content: montmorrolite, illite, kaolinite, calcite, aragonite, dolomite, feldspar, quartz. Organic - geochemic characteristics of alginite from Pinciná: parameter of Rock-Eval pyrolysis, TOC, TIC and humus content (average from 74 samples of VPA-7 well): 9.02 TOC weight %, 15,6 humus weight %, S1 - 2,87 mg HC.grock-1, S2 – 43,55 mg HC.grock-1, HI - 459,95 mg HC. grock-1, GP – 46,02 kg HC. grock-1, Tmax 433,41° C. The main clay minerals are illite, kaolinite and smectite. The alginite is a good sorbent, especially it is able to sorb Pb2+ from poluted water (Vass 1998). Kulich et al. (2001) determined in samples from alginit Pinciná: humus 6.5 – 33.1 %, Water pH: 7.2-8.3, Potassium chloride pH: 7.42-7.47, Nutrient content phosphorous 24.2 – 280 mg.kg-1, potassium 158 - 2010 mg.kg-1, magnesium 921- 3200 mg.kg-1, calcium 1584 - 8540 mg.kg-1 and nitrogen (NO3) 8.9 - 4020 mg.kg-1, Na 175 – 396, Mn 75-713, Cu 15.1 – 28.7 , B 20 – 116.1, Mo 0.7 – 1.4 and Zn 27 – 115.The siliceous microfossils—diatom and chrysophycean stomatocystae—of the diatomite and alginite from two maars (Jelsovec and Pincina) of the Late Miocene Podrecany Basalt Formation in Southern Slovakia have been studied. The ecological analysis of the microfossils studied points to a shallow lake environment with ph = 7–8, salinity of 0.3–0.5 %, temperate climate. The nutrient spectrum from the Jelsovec maar where diatomite was deposited suggest an oscillation of oligotrophic and eutrophic conditions. In Pincina maar where alginite was deposited the eutrophic conditions prevailed. The exellent state of Botryococus braunii soft bodies preservation points to a stratified water column in the lake with anaerobic conditions at the bottom. In the Jelsovec maar organic matter is practically missing. The water column was not stratified, even the bottom water was oxygenated and oligotrophic conditions prevailed (Ognjanova-Rumenova, Vass, 1998). To characterize the changes in soil water content and soil microbial activity in association with the amendment of alginite we established a pot experiment.



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Five variants of soil-alginite mixtures were tested in three replicates with two forest soils (Areni-Dystric Cambisol and Eutric Cambisol) with different texture: a loose sandy soil and a sandy loam. Soil samples for soil analysis were taken approximately two months, six months and one year after establishment of the experiment. Gravimetric soil water content closely correlated with the dose of alginite in both soils. Basal respiration and catalase activity increased with the dose of alginite in the sandy soil, but not in the sandy loam, where the highest response was observed at intermediate doses of alginite. The correlations of microbial activity parameters with moisture were also much closer in the sandy soil than in the sandy loam. The amendment with alginite was thus effective in improving some of the selected microbial activity indicators, but the optimum dose of alginite strongly depends on soil texture (Gomoryova et al. 2009). Pula maar was among the first locations in Europe where maar lake deposits (alginite) were mined commercially for agricultural purposes, having been active since the 1980s (Jámbor and Solti, 1976; Solti, 1986, 1987). The alginite having any phytotoxic effect can be used in agriculture as a fertiliser, for melioration of the sandy structurless soils, for the cultivation of the plants in arid regions. It is good starter in planting trees. Its ability to trapp ammonia has a positive effect upon the soil nutrient regimen and improves the hygiene in the livestock feedlots. Alginite reduces transfer of nutrients from soil into ground and surface waters (Solti, 2008, Vass 1998). However, the microstructure of the surface, features of physico-chemical properties of the individual fractions of this natural organic-mineral material is not well understood. So the purpose of this work was to obtain new fundamental knowledge of Pincina alginites chemical composition, analytical properties and sample surface microsculpture. Research is original and made by using modern scientific equipment.

EXPERIMENTAL PART The objects of the study were representative fraction Pincina alginite, airdried, insoluble in water (Figure 1). The objectives of the study were to: -

study of the chemical composition Pincina alginite; study of the isolated fractions surface microstructure; determination of antioxidant activity, spectral characteristics, and chromatographic profiles of Pincina alginite extracts.


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Figure 1. The test fraction Pincina alginate.

The chemical composition of the alginite – basic petrogenic elements (Si, Al, Ti, Fe, Mg, Ca, K, P, S) were determined by local energetic dispersion spectrometry (EDS). Relative errors of the chemical analysis were the following: with the element content from 1 up to 5% - not more than 10%; with the content from 5 up to 10% - not more than 5%; with the content over 10% - not more than 2%. 500 particles of alginite were investigated.



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The locality of the analysis was 3 mkm, the sections not less than 12 mkm were scanned. The morphology of the particles surface was studied by scanning electron microscopy (SEM) by Zeiss EVO-15SL microscope. Antioxidant activity was measured by inhibition of DPPH methanol and water extracts. We used a spectrophotometer Thermo (Blois, 1958). Spectrophotometric characteristics and chromatographic profiles obtained by analyzing Pincina alginate extracts. Extraction was carried out with distilled water, saline solution, 50% ethanol and phosphate buffer pH 7.4 for 12 hours at room temperature with continuous shaking. Alginate samples previously dispersed to 2-5mm.

DISCUSSING OF THE RESULTS Chemical composition Pincina alginite. Petrogenic elements in the studied Lucenec alginite fractions distributed relatively evenly and form a row: Si> Al> Fe> Mg> K> Ca ≈ Ti> P ≈ Na (Table 1). The silicon content in the samples is high. The presence of sodium in the samples of fractions 1, 2 and 3c is an indicator of monmorillonit, which is found in these samples by electron-microscopic study (Table 2). Table 1. Chemical composition of Pincina alginate, percent from mass mass % Elements

Fraction 1

O 47,35 Na 0,64 Mg 0,84 Al 13,48 Si 27,57 P 0,37 S 0,44 Ca 0,75 K 2,39 Ti 1,32 Fe 5,95 Note: "-" element not found.

Fraction 2 46,18 0,54 2,21 4,87 29,15 0,42 0,79 1,17 2,54 0,92 4,12

а 44,58 1,37 16,94 21,82 10,01 0,18 4,56

Fraction 3 b 49,16 22,06 25,72 1,78 1,92 -


с 47,32 0,28 1,35 13,13 26,34 0,34 0,46 0,62 2,45 1,05 5,89

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A higher content of oxide K and Ca in the samples indicates the presence of calcite and kaolinite. A detailed study of alginite fractions yielded results that significantly complement the previously obtained (Table 2). Micromorphology particle surface Pincina alginite. Detailed study of the alginite particles with 1500-20000 magnification revealed a variety of minerals and many silicified floral and microorganism remnants. Table 3 shows the characteristic features of each fraction surface structure. In explored samples were found montmorrilonite group minerals, mica, kaolinite, clinoptilolite. Table 2. Comparative сhemical composition of Pincina alginate

Element

our results mass %

O Na Mg Al Si P S Ca K Ti Fe

44.58 – 49.16 0.28 – 0.64 0,84 – 2.21 4.87 – 22.06 21.82 - 27,57 0.34 – 0.42 0.44 – 0.79 0.62 – 1.17 1.78 – 10.01 0.18 - 1,92 4.12 – 5.95

Pincina (Slovakia) Vass (1998) Kulich et al., ppm (2001) mg.kg-1 179 1083 - 1432 921 - 32000 11.0 – 22,5* 78 – 222 24 - 280 6278 - 12794 1584 - 8540 280 – 321 158 - 2010 1.10 – 1.34* 38775 0,90 – 5.70*

Pula (Hungary) Solti (1998) ppm 12,5* 429-1200 320-2700

60-1200 25000-90000 400-3200 3024 1,6-3,16*

Table 3. The results of the studied alginite fractionselectron microscopic analysis




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Svetlana Motyleva, Jan Brindza, Radovan Ostrovsky et al. Table 3. (Continued)



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Our results correspond to the literature data on the mineral composition of alginite (Vass, 1998; Kulich et al., 2001). In most of the samples were found slightly decomposed organic matter, silicified algae and microorganisms. They retained the structure of the vegetation elements and look like detritus. Our studies confirm the theory of the bacteria role in the formation of clay minerals (Solti, 1987; Konhauser et al., 1993; Vass, 2000; Pápay, 2001,


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Rozanov, 2007, 2009). Local EDS analysis also points to organic origin of the inclusions. The content of K in the biomorphic structure (Figure 2 - 1) is 2.9 times greater than the background of the content of the element (Figure 2 - 2). The discovered form (Figure 2 - 3) contains S about 50 times grate then background concentrations of the element. Perhaps this form belongs to the cyanobacteria.

Figure 2. Microfotographi, EDS data shows filament end quantitative results of a content of elements.



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Figure 3. Spectrometry characteristic alginit extracts.

Аantioxidant activity Pincina alginite. Percentage radical inhibition of 2,2 –dipheny l-picrylhydrazyl by dispersed Pincina alginite samples (total antioxidant activity) is from 4.7 to 11.9% (Table 4). Spectra of extracts mainly take the form of smooth flowing curves, with no express absorption minimum and maximum. This is evidence of the absence or minimum content of phenolic compounds and carcinogenic polycycloaromatic hydrocarbons in the extracts (Figure 3). Absence of absorption maximums in the visible region is consistent with weak extracts pigmentation. The results of chromatographic studies support the conclusion - phenolic compounds in these extracts were not found (Figure 4). Alginite extracts, obtained with phosphate buffer pH 7, were stained intensely and have a difference in spectral characteristics. In the UV region is pronounced minimum, and in the visible region pronounced maximum. Chromatographic profile indicates the extraction of phenolic compounds from alginita samples by phosphate buffer (Figure 4).


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Table 4. The total antioxidant activity (AOA) of Pincina alginate extracts № fraction 1 (brown) 2 3

extractant CH3OH 96% H2 O 0,617±0,004 0,664±0,001 0,656±0,001 0,669±0,002 0,637±0,002 0,635±0,002

% АОА CH3OH 96% H2 O 10,9 11,1 4,7 6,2 10,7 11,9

Figure 4. Alginit extracts profil of chromatographic.

CONCLUSION 1

2

3 4

The chemical composition of representative Pincina alginate fractions was studyed. Results significantly complements the existing information on the alginite chemical composition. The structural and morphological features of Pincina alginite was discovered. Many poorly decomposed organic remnants - silicified algae and microorganisms was found. By local EDS analysis showed the chemical structure of the inclusions. Aqueous extracts of the Pincina alginite samples have antioxidant activity. The availability of a comprehensive analytical study of the alginite composition and properties was displayed. The use of original approaches (determination of antioxidant activity, the study of the



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spectral characteristics and chromatography) in a study of alginite extracts will advance the frontiers of its application.

REFERENCES Blois, M. S. Antioxidant determinations by the use of a stable free radical / Nature. – 1958; 181: 1199-2000 Gomoryova, E., Vass, D., Pichler, V., Gregor, J., Gomory, D., Effect of alginite amendment on microbial activity and soil water content in forest soils. Journal Biologia (Bratislava) 2009 Vol. 64 No. 3 pp. 585-588.ISSN 0006-3088. DOI 10.2478/s11756-009-0081-z Hajós, M., 1976. A Pulai PUT-3 Sz. fúrás felsõpannóniai képzõdményeinek diatóma flórája [Diatom flora in Upper Pannonian sediments of borehole PUT-3 at Pula village, Transdanubia] [in Hungarian with English abstract]. MAFI Évi. Jel.1974-évről,(263–285). Hartyáni, Z., Pécsi, I., Merényi, L., Szabó, S., Szauer, J., Szilágyi, V., 2000. Mineralogical and chemical investigation of soil formed on basaltic bentonite at Egyházaskesző, Transdanubia, Hungary. Acta Geol. Hung. 43, 431–445. Jámbor, A., Solti, G., 1976. Geological conditions of the Upper Pannonian oilshale deposit recovered in the Balaton Highland and at Kemeneshat [in Hungarian with English abstract]. MÁFI Évi. Jel. 1974-ről, 193–219. Konhauser, K. O., Fyle, W. S., Ferris, F. G., Beveridge, T. J. Metal sorption and mineral precipitation by bacteria in two Amasonian river: Rio Solimoes and Rio Negro //Geology. 1993. V. 21. P. 1103–1106 Kulich, J., Valko, J., Obernauer, D., 2001. Perspective of exploitation of alginit in plant nutrition. In: Journal of Central European Agriculture, Volume 2 (2001) No. 3-4 Lorenz, V., Goth, K., Suhr, P., 2003. Maar-Diatrem-Vulkanismus - Ursachen und Folgen Die Guttauer Vulkangruppe in Ostsachsen als Beispiel für die komplexen Zusammenhänge. Z. geol. Wiss., Berlin 31, 267–312. Ognjanova-Rumenova, N., Vass, D., 1998. Paleoecology of the late miocene maar lakes, Podrecany basalt formation, Southern Slovakia, on the basis of siliceous microfossils In: Geologica carpathica, Volume 49, number 5/1998, pages 351-368. Pápay, L., 2001. Comparative analysis of Hungarian maar-type oil shales (alginites) on the basis of sulfur content. Oil Shale 18, 139–148.


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Rozanov, A.Yu. Some problems of bacterial mineralization and sedimentation // Proc. SPIE. 2002. V. 4939. Р. 83–87. Rozanov, A. Yu., Astafieva, M. M.. The Evolution of the Early Precambrian Geobiological Systems // Paleontological Journal. 2009. V. 43. №. 8. Р. 61–72 Solti, G., 1986. Az egyházaskeszői tufakráterben települő bentonit és alginit telep. [Bentonite and alginite in the Egyházaskeszö tuff crater]. MAFI Evi. Jel. 1986-ról, 379–397. Solti, G., 1987. Az alginit [The oil-shale]. MAFI Alkalmi Kiadványa, Budapest, 1–41. Solti, G., Lobitzer, H., Ravasz, C., 1988. Az osztrák maar bazalttufa kráterek alginit célu vizsgálata. [Monitoring of potential oil shale deposits of basaltic tuff maars in Austria]. MAFI Evi. Jel. 1988(1)-ról, 439–450. Solti, G., 2008. Alginit ... the mineral which stores water and nutrients. ALGINIT information sheets. 18ps. www.alginit-austria.com Vass, D., 1998. Economic and ecologic importance of the non - metalic deposits in basalt maars of Southern Slovakia. Acta Montanistica Slovaca Ročník 3 (1998), 1, 59-70. Vass, D., 2000. Alginite: a sedimentary rock rich in organic matter: raw material of nature protection. Geol. Soc. Greece, Spec. Publ. 9, 235–239. White, J. D. L., 1991. Maar-diatreme phreatomagmatism at Hopi Buttes, Navajo Nation (Arizona), US. Bull. Volcanol. 53, 239–258.



Chapter 5

RELAXATION AND DYNAMICS OF SPIN CHARGE CARRIERS IN POLYANILINE V. I. Krinichnyi* Institute of Problems of Chemical Physics, Russian Academy of Sciences, Moscow Region, Russian Federation

The main results of the study of charge transfer in polyaniline modified with sulfuric, hydrochloric, camphorsulfonic, 2-acrylamido-2methyl-1-propanesulfonic and para-toluenesulfonic acids at various (9.7 – 140 GHz) wavebands EPR obtained in the Institute of Problems of Chemical Physics RAS are summarized. The methods of determining the composition of polarons with different mobility and their main magnetic, relaxation and dynamics parameters from effective EPR spectra are described. The dependences of the nature, electronic relaxation, dynamics of paramagnetic centers, and the charge transfer mechanism on the method of synthesis, the structure of the acid molecule, and the polyaniline oxidation level are shown.

Keywords: Polyaniline, conducting polymers, EPR, spin, polaron, conducting mechanism, relaxation

* Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7(496) 515 3588. E-mail: [email protected].


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V. I. Krinichnyi

Within the class of conducting polymers, polyaniline (PANI), see Fig.1, is of special interest because of its excellent stability under ambient conditions and well perspective of utilization in molecular electronics [1,2]. The PANI family is known for its remarkable insulator-to-conductor transition as a function of protonation or oxidation level [3]. Depending on the protonation or oxidation level it can be in leucoemeraldine (LE), pernigraniline (PN), emeraldine base (EB), or emeraldine salt (ES) forms (Fig.1). PANI-LE is fully reduced state. PANI-PN is fully oxidized state with imine links instead of amine links. These two forms are poor conductors, even when doped with an acid. PANI-EB is neutral form, whereas PANI-ES is a p-type semiconductor with hole charge carriers [4]. It is semicrystalline, heterogeneous system with a crystalline (ordered) region embedded into an amorphous (disordered) matrix [5]. When PANI is doped with an acid, intermediate bipolaron and more stable polaron structures form as shown in Fig. 1. Such charge carriers transfer elemental charges during their intrachain and interchain diffusion as well as hopping inside and between well-ordered crystallites [6]. In polaron structure, a cation radical of one nitrogen acts as a hole and such holes acts as positive charge carriers. The electron from the adjacent nitrogen (neutral) jumps to this hole and it becomes electrically neutral initiating motion of the holes (Fig. 1). However, in bipolaron structure, this type of movement is not possible since two holes are adjacently located (Fig. 1). This polymer differs from polyacetylene (PA), poly(paraphenylene) (PPP), other PPP-like organic conjugated polymers in several important aspects. In contrast with these polymer systems it has no charge conjugation symmetry. Besides, both carbon rings and nitrogen atoms are involved in the conjugation. The phenyl rings of PANI can rotate or flip, significantly altering the nature of electron-phonon interaction. So, an additional mobility of macromolecular units can modulate sufficient electronphonon interactions and, therefore, lead to more complex mechanism of electron transfer in PANI [7]. This results in somewhat of a difference in magnetic and charge-transport properties of PANI compared with other conducting polymers. Theoretically and experimentally was shown [8] that charges in PANI, as in case of other conducting polymers, are transferred by polarons moving along individual polymer chains. At low doping level a hopping charge transfer between polarons and bipolarons predominates in PANI. In modified polymer a number of such charge carriers increases and their energy levels merge and form metal-like band structure, so called polaron lattice [6,9]. Stronger spin-orbit and spin-lattice interactions of the polarons diffusing along the chains is also characteristic of PANI. Upon protonation of PANI-EB or oxidation of PANI-LE insulating forms of PANI their


Relaxation and Dynamics of Spin Charge Carriers in Polyaniline

111

conductivity increases by more than 10 orders of magnitude whereas a number of electrons on the polymer chains remains constant in the ES form of PANI [10]. Such a doping is accompanied by appearance of the Pauli susceptibility [11,12], characteristic for classic metals, due to formation of high-conductive completely protonated or oxidated clusters with the characteristic size about 5 nm in amorphous polymer. While doping of PANI-EB films with the sulfonated dendrimers gives direct current macroconductivity (dc) up to ca. 10 S/cm, the hydrogensulfated fullerenol-doped materials show metallic characteristics with room temperature (RT) dc as high as 100 S/cm [13] that is about 6 orders of magnitude higher than the typical value for fullerene-doped conducting polymers. In some cases diamagnetic bipolarons [6] and/or antiferromagnetic interacting polaron pairs [14] each possessing two elemental charges can also be formed in heavily doped polymer. The effective crystallinity of polymer increases up to ~ 50 – 60 %. The lattice constants of the PANI-EB and PANI-ES forms [5,9,15-17] are presented in Table 1. H N

N

H N

N

(a) N H

N H

N H H N

N

+ N H

H N N H

H N

.+ N H

A

A

-

A

H N

(b)

+ N H

-

A

.+

n H N

(c)

N H

n H N

.+ N H

n

A

H N

.+ N H

A H N

H N

.+ A

H

H N

N

N

.+ N H

-

A

(d) n

Figure 1. Chemical structures of emeraldine base (a) and its full (50%) protonation with formation of single bipolarons (b), polaron pairs (c) followed by their separation in more stable form (d).


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V. I. Krinichnyi

Crystallinity and, therefore, conducting properties of PANI essentially depend on structure of a dopant introduced. The mechanism of charge transfer in heavily doped PANI is also dependent sufficiently on the nature of a dopant as well as on the method of the polymer synthesis. For instance, the Fermi level in PANI doped with sulphuric (PANI-SA) or hydrochloric (PANI-HCA) acid lies in the region of localized states, therefore is considered as a Fermi glass with localized electronic states [15], whereas the Fermi level energy F of PANI highly doped with camphorsulphonic acid (PANI-CSA) lies in the region of extended states governing metal behavior of the latter near the metalinsulator boundary [18,19]. On the other hand, optical (0.06 – 6 eV) reflectance measurements of e.g. in PANI-CSA [15,20-22] suggest that this polymer is a disordered Drude-like metal near the metal-insulator boundary due to improved homogeneity and reduced degree of structural disorder. From optical measurements it was determined that the effective charge carrier mass m*  2me, the mean free path l*  0.7 nm and the density of states at the Fermi level n(F)  1 state per eV per two ring repeat units [15,20]. Studies of the effect of doping level on both the electronic transport and film morphology of PANI-CSA shown a direct correlation between the degree of crystallinity (induced by hydrogen bonding with the CSA counter ion) and the metallic electronic properties [23-25]. This leads to the improvement of crystallinity and metallic conductivity of the polymer in the series PANI-HCA  PANI-SA  PANI-CSA at comparable modification levels. However this deduction is not always conformed to results obtained at PANI study by other methods and other authors [26]. Table 1. Lattice constants (in nm) determined for polyaniline (PANI) Polymer a B c Reference PANI (e.b.) 0.765 0.575 1.020 [5] PANI-HCA (e.s.) 0.705 0.860 0.950 [5] PANI-SA (e.s., p.o.r.) 0.430 0.590 0.960 [9] PANI-CSA 0.590 0.100 0.720 [15] PANI-DBSA (o.r) 1.178 1.791 0.716 [16] PANI-pTSA 0.440 0.600 1.100 [17] Abbreviations: e.b. – emeraldine base, e.s. – emeraldine salt, p.o.r. - pseudo-orthogonal cell, o.r. – orthrombic cell, HCA - hydrochloric acid, SA - sulphuric acid, CSA camphorsulphonic acid, DBSA - dodecylbenzenesulphonic acid, pTSA - ptoluenesulfonic acid.



113

Typical dc conductivity is frequently a result of various electronic transport processes and is ca. 10 – 102 S/cm for disoriented and oriented PANI-ES [3,10,18,27-34]. For example, this value has been determined for PANI-CSA to be in the range dc  1.0102 – 3.5102 S/cm at room temperature [33,35]. The variety of conducting properties makes difficult to investigate completely and correctly by usual experimental methods true charge dynamics along a polymer chain, which can be masked by interchain, interglobular and other charge transfer processes. The inhomogeneity of distribution of the counterion molecules results in an additional complexity of experimental data interpretation. The electronic structure of PANI-ES has been described theoretically by the metallic polaron lattice model [6,36] with a finite n(F) value [37]. An analysis of experimental data on the temperature dependencies of dc conductivity, thermoelectric power, and Pauli-like susceptibility allowed MacDiarmid, Epstein et al. [27,30,38-41] to declare that PANI-EB is completely amorphous insulator in which 3D granular metal-like domains of characteristic size of 5 nm are formed during its doping and transformation into PANI-ES. A more detailed study of the complex MW dielectric constant, EPR line width, and electric field dependence of conductivity of PANI-ES [5,9,27,28,30,42] allowed them to conclude that both chaotic and oriented PANI-ES consist of some parallel chains strongly coupled into "metallic bundles" between which ID VRH charge transfer occurs and in which 3D electron delocalization takes place. The intrinsic 3D conductivity of the domains was evaluated using Drude model [43] at alternating current as ac  107 S/cm at 6.5 GHz [44], which was very close to the value expected by Kivelson and Heeger for the metal-like clusters in highly doped Naarmann trans-PA [45]. However, ac conductivity of the sample does not exceeds ac  7102 S/cm [44]. It means that other processes, which make difficult its determination, mask the true process of electron transfer by usual experimental methods. The polaronic charge carriers in PANI and other conducting polymers are characterizing by electron spin S = ½, so then the Electron Paramagnetic Resonance (EPR) method is widely used for the study of relaxation and dynamics properties of such paramagnetic centers (PC) in these systems [4649]. The oxidation or protonation of PANI-EB leads to the monotonically increase in PC concentration accompanied with the 3-cm waveband EPR line narrowing from 2 G down to 0.5 G [50,51]. Lapkowski et al. [51] and MacDiarmid and Epstein [52] showed the initial creation of Curie spins in EB, indicating a polaron formation, followed by a conversion into Pauli spins, which shows the formation of the polaron lattice in high conductive PANI-ES


114

V. I. Krinichnyi

[53,54]. The method enables to determine both the spin-lattice and spin-spin relaxation occurring with the times T1 and T2, respectively, as well as the diffusion of spin charge carriers along and between chains with appropriate coefficients D1D and D3D, respectively, even in PANI with chaotically oriented chains in scale from several macromolecular unites [46,47]. These parameters are important to understand how relaxation and transport properties of spin charge carriers depend on the structure and dynamics of their microenvironment (lattice, anion etc.). It should be noted that diffusion of electron spin effects nuclear relaxation of protons in PANI, so in principle the Nuclear Magnetic Resonance (NMR) spectroscopy can additionally be used for the study of electron spin dynamics in PANI [55]. Such investigations were mainly carried out for highly doped PANI-HCA [56-60]. It was noted, however, [47], that the data on PANI proton relaxation experimentally obtained by NMR method [56-58], reflect an electron spin dynamics indirectly and consequently cannot give a correct enough conception of charge transfer in polymer. On the other hand, EPR method registers just electron relaxation of spin charge carriers, that allows more precisely to determine relaxation and dynamic parameters of polarons in PANI and in others conducting polymers. Spin-spin relaxation of polarons governs their peak-to-peak EPR line width Bpp at electron spin precession frequency ωe. The dependencies T1 

1/2 p (here ωp is the angular frequency of nuclear spin precession) and Bpp  obtained respectively for nuclear and electron spins by comparatively 1/2 e low-frequency EPR and NMR methods for highly protonated PANI-ES were interpreted in terms of 1D diffusion and 3D hopping of a polaron. D1D value was obtained to be respectively near to 1014 and 1012 rad/s and weekly depend on the doping level, while D3D value strongly depends on y and correlated with both dc and ac conductivities of PANI-HCA [56]. The anisotropy of this motion A = D1D/D3D varies at room temperature from 104 in PANI-EB down to 10 in PANI-ES. This fact was interpreted in favor of existence even in highly protonated PANI of single high-conductive chains, between which Q1D charge transfer is realized [61]. Such an interpretation differs from the alternate model of formation of Q3D metal-like clusters in amorphous phase of the polymer [38,39]. Besides, the diffusion constants were determined from EPR line width which may reflect different processes carrying out in PANI. Indeed, at registration frequencies less than 10 GHz the lines of multicomponent spectra or spectra of different radicals with close magnetic resonance parameters overlap due mainly to low spectral resolution. So, line



115

width of PANI at these frequencies generally represents a superposition of various contributions of localized and delocalized PC. The presence in the PANI of oxygen molecules can also affect its magnetic resonance parameters. In this case the change in line width of organic systems is normally explained by dipole-dipole interaction of polarons with spin S = ½ with the oxygen molecules possessing sum spin S = 1. It was found [62-66] that oxygen can reversibly broad EPR spectrum of PANI without remarkable change of its conductivity. Previous vacuumization of the sample leads to more promising effect that is characterized by relaxation time of spin-spin interaction [66-69]. However, Kang et al. have shown [70] that the contact of PANI-HCA with air leads to reversible decrease in the intensity and increase in the width of the EPR spectrum of PANI at simultaneous decrease in its conductivity. Such change in the polymer properties was explained by the decrease of the polaron mobility at its interaction with air. The opposite effect, however, was registered in the study of polypyrrole [71] and PANI-HCA [72]. In the latter case the diffusion of the oxygen into the polymer was proposed to lead to reversible increase in the polymer line width and conductivity due to acceleration of a polaron motion along the polymer chain. As in case of other conducting polymers, some highly doped PANI samples demonstrate EPR spectra with Dyson contribution [73] as result of interaction of MW field with spin or/and spineless charge carriers [74,75]. This additionally results in ambiguous interpretation of the data obtained on electron relaxation and dynamics, and also on mechanism of charge transport in conducting polymers. In the present Chapter are considered the results of multifrequency EPR study of magnetic and charge transport properties of PANI-EB and PANI-ES doped with different acids up to y  0.60 [48,76-91]. Powder-like PANI-SA was synthesized by polymerization via a modification of the general oxidation route with (NH4)2S2O8 in 1.0 M hyrochloric acid which was doped into aqueous solution of sulfuric acid with an appropriate pH value [92]. PANIHCA was synthesized by the chemical oxidative polymerization of 1 M aqueous solution of polyaniline sulfate in the presence of 1.2 M ammonium persulfate at 278 K [93]. Film-like high-molecular-weight polyaniline synthesized in Durham at 248 K [94,95] was used as an initial material for PANI-ES doped with CSA and 2-acrylamido-2-methyl-1-propanesulphonic (AMPSA) as films of ~50 m thick which were cast from m-cresol or dichloroacetic acid solutions onto Si wafers and allowed to dry in air at 313 K [94,96]. It was studied also powder-like


116

V. I. Krinichnyi

para-toluenesulfonic-acid-doped PANI-ES (PANI-pTSA) with y = 0.5 doping level and 30% crystalline volume fraction [17]. Figure 2 shows 3-cm (νe = ωe/2π = 9.7 GHz) and 2-mm (νe = 140 GHz) waveband EPR spectra of an initial, PANI-EB sample, and PANI slightly doped with different numbers of sulfuric acid molecules. At the 3-cm waveband PANIEB demonstrates a Lorentzian three-component EPR signal consisting of asymmetric (R1) and symmetric (R2) spectra of paramagnetic centers which should be attributed respectively to localized and delocalized PC (Fig.2,a). R2 PC keep line symmetry at higher doping levels. At the 2-mm waveband the PANI EPR spectra became Gaussian and broader compared with 3-cm waveband ones (Fig.2,b), as is typical of PC in other conducting polymers [49,79]. At this waveband delocalized PC demonstrate an asymmetric EPR spectrum at all doping levels. The analysis of EPR spectra obtained at both wavebands EPR showed that the line asymmetry of R2 PC in undoped and slightly doped PANI samples can be attributed to anisotropy of the g-factor which becomes more evident at the 140 GHz waveband EPR. The line width of these PC weakly depends on the temperature.

R1

gzz Azz

PANI-EB

gzz

gyy

R1

PANI-EB gxx Azz

PANI-SA0.01 30 G

R2 50 G

PANI-SA0.01

PANI-SA0.03 PANI-SA0.03

(a)

(b)

Figure 2. Typical room temperature 3-cm (a) and 2-mm (b) waveband EPR absorption spectra of PANI-EB and this sample slightly doped by sulphuric acid. The absorption spectra calculated with g xx= 2.0060 32, g yy 2.003815, g zz = 2.002390, Axx = A yy = 4.5 Gauss, Azz = 0.2 Gauss (R1), and with g = 2.004394 and g|| = 2.003763 (R2) are shown by dashed lines.

Therefore, the R1 with strongly asymmetric EPR spectrum can be 



attributed to a — (Ph- NH -Ph)— radical with g xx = 2.006032, gyy = 2.003815, gzz = 2.002390, Axx=Ayy = 4.5 G, and Azz = 30.2 G, localized on a short polymer chain. The magnetic parameters of this radical differ weakly from



117



those of the Ph- NH -Ph radical [97], probably because of a smaller delocalization of an unpaired electron on the nitrogen atom (  πN = 0.39) and of the more planar conformation of the latter. Assuming a McConnell proportionality constant for the hyperfine interaction of the spin with nitrogen nucleus Q = 23.7 G [97], a spin density on the heteroatom nucleus of N(0) = (Axx+Ayy+Azz)/(3Q) = 0.55 is estimated. At the same time another radical R2 is formed in the system with g = 2.004394 and g|| = 2.003763 which can be attributed to PC R1 delocalized on more polymer units of a longer chain. Indeed, the model spectra presented in Fig.2 well fit both the PC with different mobility. The lowest excited states of the localized PC were determined from equation [97,98]   (0)   2 1   En* 

g xx 

g yy g zz

(1)

  (0)   2 1   E*  2

where  is the spin-orbit coupling constant, ρ(0) is the spin density, En* and E* are the energies of the unpaired electron n* and * transitions, 

respectively, to be En* = 2.9 eV and E* = 7.1 eV at  N = 0.56 [99]. In PANI-HCA the R1 also demonstrates the strongly anisotropic spectrum with the canonic components gxx= 2.00522, gyy= 2.00401, and gzz= 2.00228 of g tensor, and hyperfine coupling constant Azz = 22.7 G. Radicals R2 are registered at g =2.00463 and g|| = 2.00223. It was shown earlier [100,101] that gxx and Azz values of nitroxide radicals localized in a polymer are sensitive to changes in the radical microenvironmental properties, for example polarity and dynamics. The shift of the PC R2 spectral X component to higher fields with у and/or a temperature increase may be interpreted not only by the growth of the polarity of the radical microenvironment, but also by the acceleration of the radical dynamics near its main molecular X axis. The effective g-factors of both PC are near to one another, i.e. = 1/3(g xx + gyy + gzz)  = 1/3(g||+2g). This indicates that the mobility of a fraction of radicals R1 along the polymer chain increases with the polymer doping. Such a depinning of the mobility results in an exchange between the spectral components of the PC and, hence, to a


118

V. I. Krinichnyi

decrease in the anisotropy of its EPR spectrum. In other words, radical R1 transforms into radical R2, which can be considered as a polaron diffusing along a polymer chain with a minimum diffusion rate [102]

D10D 

( g   g e ) B B0 , 

(2)

giving D1D = 6.5108 rad/s. 0

As in case of other conducting polymers, at the 2-mm waveband in both in-phase and /2-out-of-phase components of the dispersion EPR signal of neutral and slightly doped PANI, the bell-like contribution with Gaussian spin packet distributions due to the adiabatically fast passage of the saturated spin packets by a modulating magnetic field is registered (insert of Fig.3,b). This effect was not observed earlier in studies of PANI at lower registration frequencies [103]. It can be used for determining of relaxation and dynamics parameters of these PC.

T1 T1T2 T2

T1 T1T2 T2 PANI-EB PANI-EB PANI-SA PANI-SA 0.01 0.01

-2 -2

1010

-2 -2

PANI-HCA PANI-HCA 0.01 0.01

1010

PANI-HCA PANI-HCA 0.03 0.03 in-phase in-phase

PANI-SA PANI-SA 0.03 0.03 PANI-SA PANI-SA 0.21 0.21

-3 -3

-4 -4

-5 -5

/2-out-of-phase /2-out-of-phase

-4 -4

1010

1010

1010

50 G 50 G

1010

T1,2 (sec) T1,2 (sec)

T1,2 (sec) T1,2 (sec)

1010

-3 -3

-5 -5

1010

(a)(a)

(b) (b)

-6 -6

1010

-6 -6

1010

-7 -7

1010

-7 -7

100 100 150 150 200 200 250 250 300 300

Temperature Temperature(K) (K)

1010

100 100 150 150 200 200 250 250 300 300

Temperature Temperature(K) (K)

Figure 3. Temperature dependences of the effective spin-lattice and spin-spin relaxation times of polarons in undoped, PANI-EB, (a) as well as in PANI-SA and PANI-HCA (a,b) samples with different doping levels. In the insert (b) are shown typical 2-mm waveband EPR in-phase and /2-out-of-phase dispersion spectra of PANI-EB registered at room temperature (solid line) and 200 K (dotted line).



119

The relaxation times of adiabatically saturated PC in -conducting polymers can be determined separately from the analysis of the u1-u3 components of its dispersion spectrum as [104,105]

T1 

3m (1  6) ,  e2 B120 (1  )

(3)

T2 

 m

(4)

(here ωm is the ac modulation frequency,  = u3/u2, B10 is the MW polarizing field at which the condition u1 = –u2 is valid) at mT1 > 1 and

T1 

u 3 , 2m u1

(5)

T2 

u3 2m (u1  11u 2 )

(6)

at mT1 < 1. The amplitudes of ui components are measured in the central point of the spectra, when  = e. Relaxation times of an initial, PANI-EB, and slightly doped PANI-SA and PANI-HCA samples calculated from Eqs.(3) to (6) are shown in Fig.3 as functions of temperature. The Figure demonstrates that the increase in the doping level of the polymer leads to shortening of the effective relaxation times of PC, which can be due to an intensification of the spin exchange with the lattice and with other spins stabilized on neighboring polymer chains of highly conducting domains. It should be noted that spin relaxation in the polymer at high temperatures are mainly determined by the Raman interaction of the charge carries with lattice optical phonons. The probability and rate of such a process are dependent on the concentration n of the PC localized, 1

e.g., in ionic crystals (WR  T1 1

(WR  T1

 п2 T7) and in -conjugated polymers 1

 nT2) [106]. The available data suggest that the T1

values of PC

in slightly (up to у  0.03) doped PANI are described by a dependence of the


120

V. I. Krinichnyi 1

type T1  nT-k, where k = 3 – 4. The k exponent decreases with the y increase. This indicates the appearance of an additional channel of the energy transfer from the spin ensemble to the lattice at the polymer doping, as is the case in classical metals. At a medium degree of oxidation у  0.21, the electronic relaxation times become comparable and only slightly temperature dependent because of an intense spin-spin exchange in metal-like domains of higher effective dimensionalities. Providing that T1 = T2 for the PANI sample with у = 0.21, an effective rate of Q1D and Q2D spin motions in this polymer can be evaluated as well. It seems that both the rates calculated in the frameworks of such spin diffusions should be near to one another. The shape of /2-out-of-phase dispersion signal of PC localized in PANIEB changes with the temperature (insert of Fig.3,b) indicating the defrosting of anisotropic macromolecular librations in this polymer. The correlation of such motions was determined as [46,49]



x,y τ cx,y  τ c0 u3x,y / u3y,x





,

(7)

x (here  is a constant determining by an anisotropy of g-factor) with τ c0 =

5.410-8 sec and  = 4.8 to be τ cx =3.510-5exp(0.015 eV/kBT). Similar dependencies were also obtained for slightly doped samples. The activation energy of the polymer chains librations lies near to that determined for PANIHCA [80]. Upper limit for correlation time was determined R1 to be equal to 1.310-4 sec and corresponds to u 3x / u 3y = 0.22 in Eq.(7) at 125 K. The relaxation times of electron and proton spins in PANI should vary [56]. This is a depending on the spin precession frequency as T1,2  n-1 1/2 e case for PANI-SA and PANI-HCA, therefore, the experimental data obtained for these polymers can be explained by a modulation of electronic relaxation by Q1D diffusion of R2 radicals along the polymer chain, and by Q3D hopping of these centers between chains with the diffusion coefficients D1D and D3D, respectively. Both the diffusion coefficients D1D and D3D can be calculated from relations [98,107]

T11   2  2 J (e )  8J (2e ) ,


(8)


T21   2  3J (0)  5J (e )  2 J (2e ), where     10  e  S ( S  1)n 1

2

4 2

(9)

1  3cos  r 2

121

2 6

is the averaged

constant of the spin dipole interaction in a powder-like sample, e is the hyromagnetic ratio for electron,  = h/2 is the Planck constant, n = n1 + n2/

2 , n1 and n2 are the concentration of mobile and localized spins, respectively,  is the angle between the external magnetic field B0 and spin precession direction, r is a minimal distance between spins, J(ωe) = (2ωeD1D)1/2 at D3D≤ωe≤D1D and J(ωe) = (2ωeD1D)-1/2 at ωe≤D3D [108]. Assuming spin situation near the units of the cubic lattice with concentration of the monomer units Nc and constant r0 = (8/3Nc)-1/3, the above sum can be simplified as

1  3cos   r 2

2 6

6

= 6.8 r0

[109].

The temperature dependences of the effective dynamic parameters D1D and D3D calculated for both types of PC in several PANI samples from the data presented in Fig.3 using Eqs.(8) and (9) are presented in Fig.4. It seems to be justified that the anisotropy of the spin dynamics is maximum in the initial PANI sample, and decreases as у increases. 10

16

16

D1D D3D

D1D D3D

10

14

10

12

10

10

PANI-HCA0.01

PANI-EB PANI-SA0.01

10

14

10

12

10

10

PANI-HCA0.03

PANI-SA0.03

D1,3D (rad/sec)

D1,3D (rad/sec)

10

D1D D2D

10

8

10

6

10

4

10

2

PANI-SA0.24

(a) 100

150

200

250

Temperature (K)

300

10

8

10

6

(b) 100

150

200

250

300

Temperature (K)

Figure 4. Temperature dependences of effective coefficients of the intrachain and interchain polaron diffusion in undoped, PANI-EB as well as in PANI-SA (a) and PANI-HCA (b) samples with different doping levels.


122

V. I. Krinichnyi

At e/2  10 GHz was found [56], that the high anisotropy of the spin dynamics is retained in PANI-HCA with у = 0.6 even at room temperature. However, our experimental data indicate that the anisotropy of the motion of the charge carriers is high only in PANI-HCA and PANI-SA with у < 0.21. Such a discrepancy is likely due to the limitations appearing at the study of spin dynamics at low frequencies. At y  0.21 the system dimensionality seems to grow in PANIES, and at high temperatures the spin motion tends to become almost isotropic. The increase in the dimensionality at the polymer doping is accompanied by a decrease in the number of electron traps, which reduces the probability of electron scattering by the lattice phonons and results in the virtually isotropic spin motion and relatively slight temperature dependences of both the electronic relaxation and diffusion rates of PC, as is the case for amorphous inorganic semiconductors [110,111]. The conductivity of a conducting polymer due to dynamics of N spin charge carriers can be calculated from the modified Einstein relation 1,3D(T) = Ne2 =

Ne2 D1,3D d12,3D , k BT

(10)

where e is elemental charge,  is the charge carrier mobility, d1,3D are the intrachain, c, and interchain, b, lattice constants summarized in Table 1, and kB is the Boltzmann constant. By assuming that the diffusion coefficients D of spin and diamagnetic charge carriers have the same values, one can obtain from Eq.(10) 1D = 0.1 S/cm and 3D = 110-5 – 510-3 S/cm at room temperature for the PANI-HCA sample with 0 < y < 0.03. At D1D = D3D, these values were determined to be 1D = 50 – 180 and 3D = 30 – 100 S/cm. Thus, the conclusion can be drawn, that 3D grows more strongly with y that is the evidence for the growth of a number and a size of 3D quasi-metal domains in PANI-ES. Let us consider the charge transfer mechanisms in the initial and slightly doped PANI samples. The fact that the spin-lattice relaxation time of РАNI is strongly dependent on the temperature (see Fig.3) means that, in accord with the energy conservation law, electron hops should be accompanied by the absorption or emission of a minimum number of lattice phonons. Multiphonon processes become predominant in neutral PANI because of a strong spin-lattice interaction. For this reason, an electronic dynamics process occurring in the polymer should be considered in the framework of Kivelson‘s formalism [112-114] of isoenergetic electron transfer between the polymer chains involving optical



123

phonons, because spin and spineless charge carriers probably exist even in an undoped polymer (see Fig.2). In the frames of this model charged spin charge carriers are coulombically bound to charged impurity sites. The excess charge on the carrier site makes a phonon-assisted transition to a neutral carrier moving along another chain. The temperature dependency of the conductivity is then defined by the probability of that the neutral charge carrier is located near the charged impurity and its initial and the final energies are within kBT, hence ac conductivity can be determined as [114]

N i2 e 2  y ||3  2 e  2e L     ac (T )  ln  0 e   384k BT T   y (T )  4

 k 3 e  ln T n 1  , (11)   4

where k1 = 0.45, k2 = 1.39 and k3 are constants, (T) = 0(T/300 K)n+1 is the transition rate of a charge between neutral and charged carrier states, = ynych(yn+ych)-2, yn, and ych are respectively the concentrations of neutral and charged carriers per monomer unit, R0 = (4Ni/3)-1/3 is the typical separation between impurities which concentration is Ni;  = (||  )1/3, ||, and  are 2

dimensionally averaged, parallel and perpendicular decay lengths for a charge carrier, respectively; L is a number of monomer units per a polymer chain. In this case a weak coupling of the charge with the polymer lattice is realized when hops between the states of a large radius take place. Figure 5 shows that the experimental data for 1D of the initial РАNI sample is fitted well by Eq.(11) with 0 = 2.710-10 S K s cm-1, k3 = 3.11012 s K9.5, and n = 8.5. In contrast to undoped trans-PA, some quantity of charged carriers exist even in the initial, PANI-EB sample, so the above Kivelson mechanism can determine its conductivity. Such an approach is not evident for РАNI doped up to 0.01  y  0.03 with less strong temperature dependence. The model of charge carrier scattering on optical phonons of the lattice of metal-like domains described above seems to be more convenient for the explanation of the behavior of their conductivity. The concentration of mobile spins in PANI-HCA0.01 sample is yp = 6.110-5 per one benzoid ring. Taking into account that each bipolaron possesses dual charge, ybp = 1.210-3 and = 2.310-2 can be obtained. The concentration of impurity is Ni = 2.0∙1019 cm-3, so then the separation between them R0 = (4Ni/3)-1/3 = 2.28 nm is obtained for this polymer. The prefactor 0 in Eq.(11) was determined to be 3.51019 Hz. Assuming spin delocalization over five polaron sites [115] along the polymer chain, || = 1.19 nm is obtained as well. The


124

V. I. Krinichnyi

decay length of a carrier wave function perpendicular to the chain can be determined from the relation [112,113]

 

b , ln  0 / t  

(12)

where 20 is the band gap, b is the lattice constant, and t is the hopping matrix element estimated as [116]

 ph D3D exp 2 E p 3

4

2 

t =

 2E p       , ph  

(13)

where ωph = 2πνph is the phonon frequency and Ep is the polaron formation energy. Using 20 = 3.8 eV [117] typical for -conjugated polymers Ep  0.1 eV [116], D3D = 3.6108 rad/s determined for PANI-HCA0.01, t = 7.110-3 eV,  = 0.079 nm and  = 0.20 nm are obtained for this sample. The similar procedure gives = 7.910-2, 0 = 2.11017 sec-1,  = 0.087 nm. and  = 0.21 nm for PANI-HCA0.03 sample with yp = 1.110-3 and ybp = 1.210-2. Temperature dependences of the PANI-SA0.01 and PANI-SA0.03 samples can be explained in terms of the Kivelson and Heeger model [45] of the charge carrier scattering on the lattice optical phonons in metal-like clusters embedded into polymer matrix. In the framework of this model the total conductivity of the polymers can be expressed in the form [45,118]

 ac (T ) 

Ne2d12D Mt02kBT 83 2

  Eph     1   0T sinh   kBT  

  Eph     1 , (14) sinh   kBT  

where M is the mass of the polymer unit, t0 is the transfer integral, for the electron equal approximately to 2.5 – 3 eV, Eph is the energy of the optical phonons, and  is the constant of electron-phonon interaction. As can be seen in Fig.5, the lD(T) dependence obtained for these samples is fairly well fitted using Eq.(14) with Eph = 0.12 and 0.11 eV, respectively. These values are near to energy (0.19 eV) of the polaron pinning in heavily doped PANI-ES [119]. A comparatively strong temperature dependency obtained for 3D of the initial sample can probably be described in the frames of the Elliot model of a



125

thermal activation of charge carriers over energetic barrier Ea from widely separated localized states in the gap to close localized states in the valence and conducting bands tails [120]. In this case ac term of a total conductivity is defined mainly by a number of charge carriers excited to the band tails, therefore

 E  ac (T )  0Te exp   a  ,  k BT 

(15)

where 0    1 is a constant reflecting the dimensionality of a system under study and Ea is the energy for activation of charge carrier to extended states. As the doping level increases the dimensionality of the polymer system rises and activation energy of charge transfer decreases. An approximately linear dependency of  on Ea was registered [121] for some conjugated polymers. At the same time Parneix et a.l. [122] showed  = 1 – kBT/Ea ( = 6, Ea = 1.1 eV) dependency for, e.g., lightly doped poly(3-methylthiophene). Therefore,  value can be varied in 0.3 – 0.8 range and it reflects the dimensionality of a system under study. As it is seen from Fig.5, Eq.(15) well fits 3D(T) dependence with Ea equal to 0.033 and 0.41 eV for low- and high-temperature regions, respectively. The activation energy of interchain charge transfer in slightly doped samples is Ea = 0.102 eV for PANI-SA0.01 and Ea = 0.103 eV for PANI-SA0.03 (Fig.5). Note that the spin diffusion coefficients and consequently the conductivities, calculated from the spin relaxation of PANI-ES with у = 0.21, in frameworks of one- and two-dimensional spin diffusion, are near to one another (see Fig. 4 and Fig. 5). This fact can possibly be interpreted as the result of the increase of system dimensionality above the percolation threshold lying near у  0.1. However, this can be also due to the decrease in accuracy of the saturation method at high doping levels. In this case the dynamics parameters of both spin and spineless charge carriers can be evaluated from the Dyson-like EPR spectrum of PANI with у  0.21 using the method described below. Figure 6 shows the dependency of line width of the PANI-SA on the temperature and doping level. The predominance of extremal Bpp(T) curves evidences for the dipole-dipole exchange interaction of mobile PC with other spins in Q1D polymer system resulting in its effective EPR spectrum broadening. The collision of these PC should to broad EPR spectrum as [72,123]


126

V. I. Krinichnyi

4

10

1D 2D

PANI-SA0.21

2

10

0

1,3D (S/cm)

10

1D

3D

PANI-EB PANI-SA0.01

-2

10

PANI-SA0.03 -4

10

-6

10

-8

10

-10

10

100

150

200

250

300

Temperature (K) Figure 5. Temperature dependency of the ac conductivity due to polaron motion along (1D, filled symbols) and between (3D, open symbols) polymer chains in the PANI-EB and slightly doped PANI-SA samples as well as an effective rate of spin diffusion in PANI-SA0.21 calculated, respectively, in the framework of Q1D (closed symbols) and Q2D (semi-filled symbols) spin transport. The lines show the dependence calculated from Eq.(11) with 0 = 2.710-10 S K-1s cm-1, k3 = 3.11012 s K-9.5, and n = 8.5 (upper dashed line), those calculated from Eq.(14) with 0 = 3.9510-6 S cm-1 K-1 and Eph = 0.12 eV (upper dash-dotted line), 0 = 1.7510-6 S cm-1 K-1 and Eph = 0.11 eV (upper dotted line), and those calculated from Eq.(15) with 0 = 8.210-21 S K-1s0.8cm-1 and Ea = 0.033 eV (low temperature region) and 0 = 3.910-12 S K-1s0.8cm-1 and Ea = 0.41 eV (high temperature region) (lower dashed line), 0 = 4.510-14 S K-1s0.8cm-1 and Ea = 0.102 eV (lower dash-dotted line), 0 = 3.110-13 S K-1s0.8cm-1 and Ea = 0.103 eV (lower dotted line).

 2  , ( Bpp )  phopCg  khopCg  2  1  

(16)

where p is the flip-flip probability during a collision of both spins, hop is the frequency of the polaron hopping along a polymer chain, Cg is the number of guest PC per each aniline ring, k = 0.5 for S = 1/2,  = (3/2)2Jex/  ωhop, and


127


Jex is a constant of spin exchange interaction. If the ratio J ex /  exceeds the frequency of collision of both types of spins, the condition of strong interaction is realized in the system leading to a direct relation of spin-spin interaction and polaron diffusion frequencies, so then lim(p) = 1/2. In the

 / 2 ( J ex / hop)2 .

opposite case lim(p) = 9/2

According to the spin

exchange fundamental concepts [123] the extremal character of the (Δ)(T) dependency should evidence the realization of both types of spin-spin interaction respectively at Т  Тс and Т  Тс. An additional reason of the line broadening can be spin localization with the temperature decrease at ТТс. The reason of such exchange can be an interaction of PC localized on neighboring polymer chains modulated by macromolecular librations. Assuming activation character of spin-spin interaction with activation energy Ea, when hop =  hop 0

exp(-Ea/kBT), one can write for effective line width

Bpp (T )  B  0 pp

kCg 0hop exp(  Ea / k BT )   0 exp(  E / k T )  2  a B    e 1   hop   3J ex     

.

(17)

Table 2. The B pp (in G),  hop (in 1016 rad/s), Ea (in eV), Jex(in eV) 0

0

parameters calculated from Eq.(17), and the P (in emu/mol one ring), n(F) (in states/eV one ring), C (in emu K/mol one ring), k1 (in emu K/mol one ring), and Jaf (in eV) values determined from Eq.(18) for different PANI samples Polymer

0 0hop Bpp

PANI-SA0.21 a PANI-SA0.21 b PANI-SA0.42 a PANI-SA0.42 b PANI-SA0.53 a PANI-SA0.53 b PANI-HCA0.50 PANI-AMPSA 0. 4 a,c PANI-AMPSA 0. 4 a,d PANI-AMPSA 0. 6 a,c

4.5 4.6 3.1 2.7 2.5 2.4

0.75 0.96 17 5.1 17 93

Ea 0.021 0.018 0.051 0.021 0.052 0.024

Jex 0.72 0.19 0.64 0.59 0.49 0.66

P

3.110-5

n(F)

C

0.65 1.210-2

k1

Jaf

4.2

0.051

48.6

0.057

0.90 1.410-3

1.4 1.9

1.610-2

9.810-7 1.110-4 2.210-5

4.510-4 0.42 7.210-3 1.710-2


1.510-2 0.001 1.110-2 0.005 1.710-2 0.004

128

V. I. Krinichnyi Table 2. (Continued) 0 0hop Bpp

Polymer PANI-AMPSA 0. 6 a,d PANI-CSA 0. 5 a,c PANI-CSA 0. 5 a,d PANI-CSA 0. 6 a,c PANI-CSA 0. 6 a,d PANI-pTSA0.5 a,e PANI-pTSA0.5 b,e PANI-pTSA0.5 a,f PANI-pTSA0.5 b,f a

Ea

Jex

P 5.310-3 5.210-7 2.710-4 8.510-7 7.110-5 7.910-6 3.310-6

12.2 1.31019 0.102 0.36 1.7 9.61017 0.058 0.28

5.610-4

n(F)

C

6.510-1 2.310-4 1.2 2.710-2 4.210-4 1.8 2.210-2 0.6 1.310-3 0.12 1.110-3 9.1 27 3.910-2 3.5

k1

Jaf

1.210-2 9.110-3 1.58 6.610-3 2.13 1.44 0.29

0.006 0.005 0.004 0.014 0.004 0.099 0.041

b

Notes: determined at 3-cm waveband EPR, determined at 2-mm waveband EPR, c determined for PC R1, d determined for PC R2, e in nitrogen atmosphere, f in air atmosphere.

Figure 6 indicates good applicability of this approach to the interpretation of the PANI-SA line width. The appropriate parameters calculated from Eq.(17) are summarized in Table 2. The activation energy of spin-spin interaction Ea decreases at the increase of polarizing magnetic field and lies near activation energy of the macromolecular librations (0.015 eV) determined above. This is an evidence of the dependency of the spin-spin interaction on an external magnetic field and its correlation with macromolecular dynamics in the system. The Bpp(T) dependences presented evidence also of different charge transport mechanisms in this polymer with different doping levels. The mechanism affecting the line width, however, depends also on the electron precession frequency, so then the line width does not directly reflects the relaxation and dynamics parameters of PC in this polymer. The g-factor of PC R2 in PANI-SA with у  0.21 becomes isotropic and decreases from gR2 = 2.00418 down to giso = 2.00314. This is accompanied by a narrowing of the R2 line (Fig.6). Such effects can be explained by a further depinning of Q1D spin diffusion along the polymer chain, and therefore spin delocalization, and by the formation of areas with high spin density in which a strong exchange of spins on neighboring chains occurs. This is in agreement with the supposition [27,30,38-41] of formation in amorphous PANI-EB of high-conductive massive domains with 3D delocalized electrons.



129

8 y = 0.53

1 y = 0.42

6

Bpp (G)

y = 0.21

20 G

4

PANI-SA0.21 2 PANI-SA0.42

giso

PANI-SA0.53 3

2

4 5 6

0 100

150

200

250

300

Temperature (K) Figure 6. Temperature dependence of line width of PC in PANI-SA with different doping levels registered at 3-cm (open points) and 2-mm (filled points) wavebands. The dependences calculated from Eq.(17) with = 0.59 eV (1), 1

0hop = 5.11016 s-1, Ea = 0.021 eV, Jex

0hop = 9.51015 s-1, Ea = 0.018 eV, Jex= 0.19 eV (2), 0hop = 7.51015 s-

, Ea = 0.021 eV, Jex= 0.72 eV (3),

0hop = 9.31017 s-1, Ea = 0.024 eV, Jex= 0.66 eV (4),

0hop = 1.71017 s-1, Ea = 0.051 eV, Jex= 0.64 eV (5), and 0hop = 1.91017 s-1, Ea = 0.052 eV, Jex= 0.49 eV (6) are shown by dashed lines. Insert – RT 2-mm waveband absorption spectra of PC in PANI-SA with different doping levels. Top-down dotted lines present the spectra calculated from Eq.(19), Eq.(22), and (23) with respective D/A = 0.895, Bpp = 1.48 G, D/A = 0.16, Bpp = 7.10 G, and D/A =0.53, Bpp = 5.86 G.

The doping of the PANI with sulphuric acid leads to an inverted -like temperature dependence of an effective paramagnetic susceptibility (see Fig.7), as occurs in the case of polyaniline perchlorate [75]. However, this does not lead to a strong narrowing of the PC line (Fig.6). As in the case of e.g. PANI treated with ammonia, this should indicate a strong antiferromagnetic spin interaction due to a singlet-triplet equilibrium in the PANI-SA between N spins with S = ½. This should lead to appearance in the total paramagnetic susceptibility  except the Pauli susceptibility of the Fermi gas P also of a temperature-dependent contributions of localized Curie PC C


130

V. I. Krinichnyi

and the term ST coming due to a possible singlet-triplet spin equilibrium in the system [124,125],  = P + C + ST = NA 2 Neff k  exp  J af / k BT    n(  F )   1 3k BT T 1  3exp  J af / k BT 

2

2 eff

(18)

where NA is the Avogadro‘s number, eff = Bg S ( S  1) is the effective 2 /3kB = C is the Curie constant per magneton, μB is the Bohr magneton, N  eff

mole-C/mol-monomer, k1 is a constant, and Jaf is the antiferromagnetic exchange coupling constant. The contributions of the c and p terms to the total paramagnetic susceptibility depend on various factors, for example, on the nature and mobility of charge carriers can vary at the system modification.

PANI-SA0.21

4

10

PANI-SA0.53 10

0

PANI-SA0.21



-1

(mol/emu)

T (emu T/mol)

PANI-SA0.53

3

10

10

-1

10

-2

100

150

200

250

300

Temperature (K)

100

150

200

250

300

Temperature (K)

Figure 7. Temperature dependence of inversed paramagnetic susceptibility and T product (insert) of PANI-SA samples with different doping levels. Above and lower dashed lines show the dependences calculated from Eq.(18) with respective P = 3.110-5 emu/mol, C = 1.210-2 emu K/mol, k1 = 4.2 emu K/mol, Jaf = 0.051 eV, and P = 1.410-3 emu/mol, C = 1.610-2 emu K/mol, k1 = 48.6 emu K/mol, Jaf = 0.057 eV.



131

Indeed, Fig.7 shows that the paramagnetic susceptibility experimentally determined for the PANI-SA samples is well reproduced by Eq.(18) with the parameters also presented in Table 2. The Jaf value is close to that (0.078 eV) obtained for the ammonia treated PANI [75]. Note that n(F) determined for PANI-SA, consistent with those determined earlier for PANI heavily doped with other counterions [11,21,126]. With the assumption of a metallic behavior one can estimate that the energy of NP Pauli spins in e.g. PANI-ES, with 0.21  y  0.53, F = 3Np/2n(F) [110] is to be 0.1 – 0.51 eV [86]. This value is near to that (0.4 eV) obtained, e.g., for PANI-CSA [20]. From this value the number of charge carriers with mass mc = me in heavily doped PANI-SA [110], Nc = (2mcF/  2 )3/2/32  1.71021 cm-3 is evaluated. 37.5 GHz

9.7 GHz T, K

PANI-CSA0.5

30

PANI-CSA0.6

190

PANI-AMPSA0.4

210

PANI-AMPSA0.6

150 G 230

140 GHz

PANI-AMPSA0.6

290

20 kHz

200 G

30 G

(a)

(b)

Figure 8. (a) 3-cm waveband EPR (left) and 400 MHz 1H NMR (right) spectra of PANI-CSA0.5 sample registered at different temperatures. Top-down dashed lines show sum of two spectra each calculated from Eq.(19), Eq.(20), and (21) with respective D1/A1 = 0.041, Bpp1 = 19.9 G, D2/A2 = 0.034, Bpp2 = 492 G; D1/A1 = 0.12, Bpp1 = 18.1 G, D2/A2 = 0.042, Bpp2 = 173 G; D1/A1 = 0.31, Bpp1 = 21.7 G, D2/A2 = 0.04, Bpp2 = 172 G; D1/A1 = 0.34, Bpp1 = 24.1 G, D2/A2 = 0.03, Bpp2 = 152 G; D1/A1 = 0.26, Bpp1 = 28.4 G, D2/A2 = 0.02, Bpp2 = 111 G. (b) RT 8-mm and 2-mm waveband EPR spectra of PANI-CSA and PANI-AMPSA with different doping levels. The spectrum calculated with D/A = 1.30 and Bpp = 5.33 G is shown as well.


132

V. I. Krinichnyi

The Nc value is close to a total spin concentration in PANI-SA. This fact leads to the conclusion that all PC take part in the polymer conductivity. For heavily doped PANI-SA samples, the concentration of spin charge carriers is less than that of spineless ones, due to the possible collapse of pairs of polarons into diamagnetic bipolarons. The velocity of the charge carrier near the Fermi level can be calculated [110], as vF = 2d1D/  n(F) = (3.3 – 7.2)107 cm/s typical for other conducting polymers [49,79]. The shape of EPR spectrum of PANI-ES depends on the nature of counterion. Figure 8 presents EPR spectra of highly doped film-like PANICSA and PANI-AMPSA samples registered at different polarizing frequencies. For the comparison, NMR spectra of PANI-CSA0.5 registered at different temperatures are presented as well. These spectra were analyzed to contain Dysonian contribution [73] due to interaction of the exciting MW field with charge carriers in the material bulk. This leads to the appearance of the skin-layer on the sample surface. When the thickness of skin-layers  becomes comparable or thinner than a characteristic size of a sample, e.g. due to the increase of intrinsic conductivity ac, the time of charge carrier diffusion through the skin-layer becomes essentially less than a spin relaxation time and the Dysonian line with characteristic asymmetry factor A/B (the ratio of intensities of the spectral positive peak to negative one) is registered as it is shown in the insert of the Fig.6. Such line shape distortion is registered in EPR spectra of highly-doped PANI and other conjugated polymers [4749,103,127]. Generally, first derivative of the Dysonian line consists of absorption and dispersion terms,

2x 1 x2 d A  D dB (1  x 2 ) 2 (1  x 2 ) 2

(19)

where x = 2(B-B0) / 3Bpp . If a skin-layer is formed on a surface of polymer L

plate with a thickness of 2d the coefficients A and D can be determined from relations [128]

A

1  cosh p cos p sinh p  sin p ,  2 p (cosh p  cos p) (cosh p  cos p) 2


(20)


D

sinh p sin p sinh p  sin p ,  2 p (cosh p  cos p) (cosh p  cos p) 2

where p = 2d/,  

133

(21)

2 / 0e ac , and 0 is the magnetic permeability for

vacuum. From the analysis it was determined that the line asymmetry parameter A/B is correlated with the coefficients A and D of Eq.(19) simply as A/B = 1 + 1.5 D/A independently on the EPR signal line width. Thus, it appears to be possible to determine correctly line width, magnetic susceptibility, g-factor of PC with Dysonian EPR spectra shown above. Konkin et al. shown [85] that in case of PANI-CSA and PANI-AMPSA the Dysonian line asymmetry factor A/B and therefore the ratio D/A depend more complicated on the 2d/ ratio in Eq.(20) and Eq.(21). The D/A(2d/) dependences calculated for these polymer presented in Fig.9. It was shown the applicability of these functions for the analysis of Dysonian EPR spectra of PC in an initial and also in two, three and four times incrassate PANI films (Fig.9). Such procedure allows determining intrinsic conductivity σac of both the highly doped film-like PANI-CSA and PANI-AMPSA samples directly from their Dysonian spectrum.

PANI-CSA0.5

2.0 3d

PANI-CSA0.6 PANI-AMPSA0.6

2d

D/A

1.5 4d 3d 2d 4d

1.0

Plate 2d

1d

Sphere 1d

0.5

3d

0.0 0

1

2

3

4

5

6

7

2d/ Figure 9. The theoretical D/A(2d/) dependencies calculated [85] and experimentally determined for the PAN-CSA and PAN-AMPSA films with different plate thickness (nd) at 3-cm waveband EPR and 300 K.


134

V. I. Krinichnyi

EPR spectra of PANI-CSA and PANI-AMPSA were then analyzed as sum of two different spin ensembles coexisting in these polymers with different Dysonian shapes, namely narrow EPR spectrum of PC R1 with g = 2.0028 localized in amorphous polymer matrix and broader EPR spectrum of PC R2 with g = 2.0020 and higher mobility in crystalline phase of the polymers. The cooling of the samples leads to the decrease in the relative concentration of PC R2 and to the monotonous increase in its line width, as it is seen in Fig.8 and Fig.10. In the same time, the line width of PC R1 decreases monotonously and the sum spin concentration increases at the temperature decrease. Besides, NMR line width decreases at such a sample cooling (Fig.8) due possible to the decrease of interaction of electron and proton spins. The RT Bpp value of PC R2 in e.g. PANI-AMPSA0.6 decreases from 54 down to 20 and then down to 5.3 G at the increase of registration frequency e/2 from 9.7 up to 36.7 and then up to 140 GHz (Fig.8), so one can express this value as Bpp(e) = 1.5 + 2.2109 -0.84 G. Such extrapolation reveals the dependence of spin-spin e relaxation time on the registration frequency and allows estimating correct line width at e  0 limit to be 1.5 G.

R1

R2 PANI-CSA0.5

Bpp (G)

PANI-CSA0.6

100 R1

R2 PANI-AMPSA0.4 PANI-AMPSA0.6

10 0

50

100

150

200

250

300

Temperature (K) Figure 10. Temperature dependence of line width of PC R1 and R2 in PANI-CSA and PANI-AMPSA samples with different doping levels determined from their 3-cm waveband EPR spectra taking into consideration the Dyson contribution.


10

5

10

3

10

10

135

0

1

R1

R2 PANI-AMPSA0.4 PANI-AMPSA0.6 PANI-CSA0.5

T (emu K/mol)



-1

(mol/emu)


PANI-CSA0.6

10

-1

10

-2

10

-3

0

50

100

150

200

250

300

Temperature (K)

0

50

100

150

200

250

300

Temperature (K) Figure 11. Temperature dependence of inversed effective paramagnetic susceptibility  and T product (insert) of PANI-AMPSA and PANI-CSA samples with different doping levels. Top-down dashed lines show the dependences calculated from Eq.(18) with respective P = 9.810-7 emu/mol, C = 4.510-4 emu K/mol, k1 = 1.510-2 emu K/mol, Jaf = 0.001 eV, P = 8.510-7 emu/mol, C = 4.210-4 emu K/mol, k1 = 6.610-3 emu K/mol, Jaf = 0.014 eV, P = 5.210-7 emu/mol, C = 2.310-4 emu K/mol, k1 = 9.110-3 emu K/mol, Jaf = 0.005 eV, P = 2.210-5 emu/mol, C = 1.710-2 emu K/mol, k1 = 1.710-2 emu K/mol, Jaf = 0.004 eV, P = 1.110-4 emu/mol, C = 7.210-3 emu K/mol, k1 = 1.110-2 emu K/mol, Jaf = 0.005 eV, P = 7.110-5 emu/mol, C = 2.210-3 emu K/mol, k1 = 2.13 emu K/mol, Jaf = 0.004 eV, P = 2.710-4 emu/mol, C = 2.710-2 emu K/mol, k1 = 1.58 emu K/mol, Jaf = 0.004 eV, P = 5.310-3 emu/mol, C = 6.510-1 emu K/mol, k1 = 1.210-2 emu K/mol, Jaf = 0.006 eV.

The narrowing of the line on raising the PANI temperature can be explained by averaging of the local magnetic field caused by HFI between the localized spins whose energy levels lie near the Fermi level. The EPR line of PANICSA and PANI-AMPSA may also be broadened to some extent by


136

V. I. Krinichnyi

relaxation due to the spin-orbital interaction responsible for linear dependence of T11 on temperature [53]; however, this interaction seems to be rather weak in our case. It is significant that for both types of PC the line widths are appreciably larger than those obtained previously for the fully oxidized powder-like and film-like PANICSA (0.35 and 0.8 G, respectively) [53], which indicates a higher conductivity of the samples under study. Comparison of the Bpp values obtained for different PANICSA samples [85] suggested that a crystalline phase is formed in the amorphous phase of the polymer, beginning with the oxidation level у = 0.3, and that the paramagnetic centers of this newly formed phase exhibit a broader EPR spectrum. In the amorphous phase of the polymer, the paramagnetic centers of radicals of the R1 type are characterized by less temperature-dependent line width and are likely not involved in the charge transfer being, however, as probes for whole conductivity of the sample. At the same time, the magnetic resonance parameters of radicals of the R2 type should reflect the charge transport in the crystalline domains of PANICSA and PANI-AMPSA. The line width of PANI appreciably decreases on replacement of the CSA anion by the AMPSA anion (see Fig.10), which is likely due to the shortening of spin-spin relaxation time of both PC. Figure 11 depicts the effective paramagnetic susceptibility of both the R1 and R2 PC as function of temperature. The Jaf values obtained are much lower of the corresponding energy (0.078 eV) obtained for ammonia-doped PANI [75]. It is seen that at low temperatures when T  Tc  100 K the Pauli and Curie terms prevail in the total paramagnetic susceptibility  of both type PC in all PANI samples. At T  Tc, when the energy of phonons becomes comparable with the value kBTc  0.01 eV, the spins start to interact that causes the appearance of the last term of Eq.(18) in sum susceptibility as result of the equilibrium between the spins with triplet and singlet states in the system. It is evident that the R1 signal susceptibility obeys mainly the Curie law typical for localized isolated PC, whereas the R2 susceptibility consists of the Curie-like and Pauli-like contributions. The n(F) values obtained for the charge carriers in PANI-CSA and PANIAMPSA are also summarized in Table 2. This value increases in series PANIAMPSA0.4  PANI-CSA0.5  PANI-CSA0.6  PANI-AMPSA0.6. This density of stated of polarons in PANI-CSA is in agreement with that obtained previously in the optical (0.06—6 eV) [15] and EPR [53] studies of this polymer. The Fermi energy of the Pauli-spins was calculated to be F  0.2 eV. This value is lower than the Fermi energy obtained for highly CSA- (0.4 eV)



137

[20] and sulfur- (0.5 eV) [48,86] doped PANI. Assuming again that the charge carrier mass in heavily doped polymer is equal to the mass of free electron (mc = me), the number of charge carriers in such a quasi-metal [110], Nc  4.11020 cm-3 was determined. This is close to the spin concentration in this polymer; therefore, one can conclude that all delocalized PC are involved in the charge transfer in PANI-CSA0.6. The velocity of charge carriers near the Fermi vF level was calculated to be 3.8107 cm/s for PANI-CSA that is close to those evaluated for this polymer from the EPR magnetic susceptibility data, (2.8 – 4.0)107 cm/s [129,130], and 6.2107 cm/s for PANI-AMPSA. 30 e, GHz

25 9.7

Bpp (G)

20 140

15 20 G

N2

10

O2 9.7 GHz 140 GHz

5

0 100

150

200

250

300

350

Temperature (K) Figure 12. Insert – 3-cm and 2-mm wavebands EPR spectra of the PANI-pTSA0.50 sample in nitrogen (solid lines) and air (dashed lines) atmosphere. Temperature dependence of line width of PC in the PANI-pTSA sample with the presence of nitrogen and oxygen molecules registered at 3-cm and 2-mm wavebands EPR. The lines show the dependences calculated from Eq.(17) with 0.058 eV, Jex= 0.28 eV (dash-dotted line),

0hop = 9.61017 s-1, Ea =

0hop = 1.31019 s-1, Ea = 0.102 eV, Jex=

0.36 eV (dotted line).


138

V. I. Krinichnyi

Thus, main PC in the highly doped PANICSA and PANI-AMPSA samples are localized at T  Tc. This is the reason for the Curie type of susceptibility of the sample and should lead to the VRH charge transfer between the polymer chains. The spin-spin exchange is stimulated at Т  Тc due likely to the activation librations of the polymer chains. The activation energies of these librations lie within the energy range characteristic of PANICSA [131] and PANI-HCA [80,82]. The Ea value depends on the effective rigidity and planarity of the polymer chains that are eventually responsible for the electrodynamic properties of the polymer. PANI-pTSA0.50 in nitrogen atmosphere at 3-cm waveband EPR demonstrates Lorentzian exchange-narrowed line which an asymmetry factor A/B is 1.03 (Fig.12). The exposure of the samples to air was observed to lead to reversible line broadening and an increase in the asymmetry factor up to 1.27. The asymmetry of the EPR line may be due to either unresolved anisotropy of the g-factor or the presence in the spectrum of the Dyson term [73] as in case of other highly doped conducting polymers. To verify these assumptions, the 2-mm waveband EPR spectra of the sample were recorded. It is seen from Fig.12 that this polymer in this waveband EPR also exhibits a single asymmetric line, whose asymmetry factor varies at the exposition to air from 1.68 up to 1.95. This fact indicates substantial interaction of PC even in high fields, the line asymmetry of these PC indeed results from the interaction of a MW field with charge carriers in the skin layer. Dysonian EPR spectra of the samples were calculated from Eq.(19) with the following coefficients A and D for skin-layer on the surface of a spherical powder particle with radius R [128]: 8 sinh p sin p (sinh p  sin p) (sinh 2 p  sin 2 p) 4 A 8 8 (sinh p  sin p)  4 3  2    1, 2 9 p p (cosh p  cos p) p (cosh p  cos p) p (cosh p  cos p) (cosh p  cos p) 2

(22)

4 D 8 (sinh p  sin p) 4 (sinh 2 p  sin 2 p) (sinh p  sin p) 2 sinh p sin p (23)  ,    9 p 3 (cosh p  cos p) p 2 (cosh p  cos p) 2 p (cosh p  cos p) (cosh p  cos p) 2

(here p = 2R/) and the main magnetic parameters were obtained. As the operating frequency increases from 9.7 up to 140 GHz, the Bpp value of PC in the PANI sample increases not more than by a factor of 2 (Fig.12). Such insignificant line broadening with the operating frequency increase was not observed in studies on other conducting polymers, including PANI. This may be evidence for stronger exchange interaction between PC in the polymers, which is not completely relieved in strong magnetic field. The



139

temperature dependences of the effective absorption line width of this sample determined at both the 3-cm and 2-mm wavebands EPR are presented in Fig.12. It is seen that Bpp of PC in the sample containing nitrogen slightly depends on temperature. Air diffusion into the sample leads to the reversible extremal broadening of their EPR line (Fig.12). At the increase of polarizing frequency from 9.7 GHz up to 140 GHz the characteristic temperature Tc of the Bpp(T) dependences presented shifts from 160 K to 130 K (Fig.12). Such effect was interpreted as result of activation dipole-dipole interaction of polarons with oxygen molecules possessing sum spin S = 1. The Bpp(T) dependences were fitted by Eq.(17) with appropriate parameters listed in Table 2 (Fig.12). It is seen that the experimental data obtained can be rationalized well in terms of this theory. The obtained value of Jex sufficiently exceeds the corresponding spin-exchange constant for nitroxide radicals with paramagnetic ions, Jex 0.01 eV [123].

10

5



-1

(mol/emu)

N2

10

4

O2 9.7 GHz 140 GHz

T (emu K/mol)

10

0

10

-1

10

-2

10

-3

100

10

3

10

2

100

150

150 200 250 Temperature (K)

200

250

300

300

Temperature (K)

Figure 13. Temperature dependence of inversed effective paramagnetic susceptibility and T product (insert) of PC in PANI-pTSA0.5 exposed to nitrogen (open symbols) and oxygen (filled symbols). By the ―‖ symbol is shown the appropriate data obtained for this system in [132] by using a ―force‖ magnetometer in a dc external magnetic field of 5103 G. Dashed and dotted lines show the dependences calculated from Eq.(18) with respective P = 3.310-6 emu/mol, C = 1.110-3 emu K/mol, k1 = 0.29 emu K/mol, Jaf = 0.041 eV and P = 7.910-6 emu/mol, C = 1.310-3 emu K/mol, k1 = 1.44 emu K/mol, Jaf = 0.099 eV.


140

V. I. Krinichnyi

Figure 13 shows the temperature dependence for the paramagnetic susceptibility of PANI-pTSA0.50 sample in the absence and in the presence of oxygen in the polymer matrix. An analysis of the paramagnetic susceptibility of the nitrogen containing sample determined at 3-cm and 2-mm wavebands EPR showed that it can be described by Eq.(18) with the parameters summarized in Table 2. These data show that the transition of registration frequency from 9.7 GHz to 140 GHz leads to decrease in Jaf of nitrogen containing PANI-pTSA0.5 from 0.099 eV down to 0.041 eV due possible to the field effect. The Figure reveals that the effective susceptibility of the PANIpTSA0.50 without oxygen, as determined from 3-cm waveband EPR spectra, slightly varies with temperature. However, this quantity determined from the 2-mm waveband EPR spectra noticeably decreases with a decrease in temperature. The exposure of the polymer to air increases proportionally all components of its magnetic susceptibility. This value of the sample exposed to air increases and exhibits non-monotonic temperature dependence in the 3-cm and 2-mm wavebands EPR with a characteristic temperature maximum at 160 and 150 К. This effect is discussed above and attributed to the spin exchange interaction. The Pauli susceptibility of the sample is close to that determined in [17] at n(F) = 22.8 eV-1. Note, that the  measured for this polymer by more direct method [132] exhibits smaller temperature dependency. The velocity of charge carriers and the Fermi energy were calculated as vF = 2d1D/  n(F) and F = 3Ne/2n(F) to be 3.1106 cm/s and 0.16 eV, respectively. The latter value is less of Fermi energy obtained earlier for PANI-SA, PANI-CSA and PANI-AMPSA. Intrinsic conductivity and mechanism of charge transfer in PANI with doping level lying above the percolation threshold depend on the structure and number of counterion introduced into a polymer. At high doping level the saturation of spin-packets decreases significantly due to the increase in direct and cross spin-spin and spin-lattice interactions. Besides, Dysonian term appears in EPR spectra of such polymers due to the formation of skin-layer on their surface. In contrast with the saturated dispersion EPR signal, the Dysonian line ―feels‖ both types of charge carriers, spin polarons, and spineless bipolarons, as effective charge ensemble, diffusing through a skin layer. The number and dynamics of each type of charge carriers can differ; thus the electronic dynamics properties of the sample should depend on its doping level. In order to determine this correctly the analysis of both the dc and ac conductivities is required.


dc,ac (S/cm)


10

2

10

1

10

0

ac

-1

10

141

dc

PANI-HCA0.50 PANI-SA0.53 PANI-SA0.42

-2

10

PANI-SA0.21

100

150

200

250

300

Temperature (K) Figure 14. Temperature dependency of ac (filled symbols) and dc (open symbols) conductivity calculated from Dyson-like EPR line of the PANI-HCA and PANI-SA samples with different doping levels. Top-down dotted lines present the dependences calculated from Eq.(26) with respective with k1 = 9.2103 S K0.5/cm, T0 = 2.8103 K, k2 = 0.53 S/K cm, Eph = 0.042 eV, k1 = 3.5104 S K0.5/cm, T0 = 1.1104 K, k2 = 1.310-2 S/K cm, Eph = 0.062 eV, k1 = 7.3105 S K0.5/cm, T0 = 1.9104 K, k2 = 9.210-3 S/K cm, Eph = 0.063 eV, and d = 1. Dash-dotted line shows the dependence calculated from the same equation with k1 = 8.4102 S K0.5/cm, T0 = 3.6103 K, k2 = 0.51 S/K cm, Eph = 0.048 eV and d = 1. Top-down dashed lines show the dependences calculated from Eq.(28) with respective

 01

= 1.47 S cm-1 K-1,

= 0.86 S cm-1 K-1, K-1,

|  02 = 2.110-2 S cm-1 K-1, and Eph = 0.12 eV,  01

|  02 = 4.310-2 S cm-1 K-1, and Eph = 0.087 eV,  01 = 0.48 S cm-1

|  02 = 8.510-3 S cm-1 K-1, and Eph = 0.049 eV and  01 = 0.41 S cm-1 K-1,  02 =

5.710-3 S cm-1 K-1,

| Eph = 0.052 eV, and  = -1.

The analysis shown that the dc conductivity in PANI-HCA and PANI-SA samples presented in Fig.14 vs. temperature can be described in the framework of the models of Q1D Variable Range Hopping (VRH) of charge carriers


142

V. I. Krinichnyi

between crystalline high-conducting regions through amorphous bridges [111] and their scattering on the lattice optical phonons in metal-like clusters. VRH mechanism of charge motion results in the following dependence of the dc and ac conductivity of a d-dimensional system on temperature [111,133] 1   d T   1  dc (T )   0 exp   0   ,  T    

(24)

4

   1  ac (T )  e 2 k BTn 2  F  L 5 e ln 0    0T , 3  e 

(25)

where 0 = 0.390e2[n(F)L/(kBT)]1/2 and T0 = 16/kBn(F)z at d = 1, 0 = 0e2[9/8kBTn3/2(F)/L]1/2 and T0 = 18.1/kBn(F)3 at d = 3 in equation for dc conductivity, 0 is a hopping attempt frequency, z is the number of nearestneighbor chains, is the averaged length of charge wave localization function, and T0 is the percolation constant or effective energy separation between localized states depending on disorder degree in amorphous regions. The conductivity is essentially determined by the phonon bath and by the distributional disorder of electron states in space and energy respectively above and below T0. The distance R and average energy W of the charge carriers hopping are R-4 = 8kBTn(F)/9 and W-1 = 4R3n(F)/3, respectively. DC conductivity of the samples is a combination of Eqs.(14) and (24):

 (T )  k T -1 dc

1 1

 0.5

1 1   d 1   E   T   ph  1  1   1 exp  0    k 2 T sinh  T    k BT     

(26)

The parameters of Eq.(26) determined from the fitting of experimental data are summarized in Table 3. It is seen from the Table that both the percolation constant and lattice phonon energy of PANI-ES decrease at the increase of polymer doping level. A transition from localization to delocalization of charge carriers occurs when 2t/321/2T0 is equal to a unit [28]. This value was calculated for PANI-SA0.21, PANI-SA0.42, PANI-SA0.53, and PANI-HCA0.50 using t = 0.29 eV [86] and T0 determined to be 0.31, 0.53, 2.1, and 3.1 eV,


143


respectively. An increase in this value with у means increasing the charge-carrier delocalization as a result of an increase in the interchain coherence. This value is higher than unity for heavily doped PANI-HCl [134], and decreases down to 0.1 – 0.4 for heavily doped derivatives of polyaniline, namely, poly(otoluidine) and poly(o-ethylaniline) [135]. One can conclude that the insulator-tometal transition in PANI-SA is of localization-to-delocalization type, driven by the increased structural order between the chains and through an increased interchain coherence. PANI-SA0.53 and PANI-HCA0.50, possess a more metallic behavior, and the properties of PANI-SA у  0.42 demonstrate it to be near an insulator/metal boundary. The inherent disorder present in slightly doped PANI keeps the electron states localized on individual chains. At low у the structural disorder in polyaniline localizes the charge to single chains (Curie-like carriers), and the higher doping leads to the appearance of delocalized electron states (Pauli-like carriers). This holds typically for the formation in PANI-ES with у  0.21 metal-like domains, according to the island model proposed by Wang and co-workers [27,30]. This is consistent with that drawn earlier on the basis of data obtained with ТЕМ and X-ray-diffraction methods [77]. Table 3. The k1 (in S K0.5/cm), T0 (in K), k2 (in S/K cm),  ph (in eV) values determined from the fitting of dc by Eq.(26), and  01 (in S/K cm),

 02 (in S/K cm), and |ph (in eV) ones determined from the fitting of ac by Eq.(28) for different PANI samples Polymer

k1

T0

k2

Eph

 01

02

PANI-SA0.21 PANI-SA0.42 PANI-SA0.53 PANI-HCA0.50 PANI-AMPSA 0.4 PANI-AMPSA 0.6 PANI-CSA 0.5 PANI-CSA 0.6 PANI-pTSA0.5 a PANI-pTSA0.5 b

7.3105 3.5104 9.2103 8.4102 1.2103 1.1103 5.6103 5.5103

1.9104 1.1104 2.8103 3.6103 209 277 521 753

9.210-3 1.310-2 0.53 0.51 0.31 0.18 1.7 0.29

0.063 0.062 0.042 0.048 0.022 0.020 0.028 0.024

26

4.6104 0.19

0.41 0.48 0.86 1.5 1.68 1.62 1.99 2.27 13.3 24.9

5.710-3 8.510-3 4.310-2 2.110-2 1.57 0.76 0.68 0.64 0.25 10.8

0.027

a

| Eph

0.052 0.049 0.087 0.12 0.037 0.039 0.039 0.036 0.027 0.022

Notes: determined at 3-cm waveband EPR, b determined at 2-mm waveband EPR.


144

V. I. Krinichnyi

Activation energy of dipole-dipole interaction of a polaron with neighboring spins determined from Eq.(26) is near to that of superslow anisotropic librations obtained by the Saturation Transfer EPR (ST-EPR) method [48,49,136]. This means that macromolecular dynamics plays an important role in interacting processes taking place in spin reservoir. The lattice librations modulate the interacting spin exchange and consequently the charge transfer integral. Assuming that polaron is covered by both electron and excited phonon clouds, we can propose that both spin relaxation and charge transfer should be accompanied with the phonon dispersion. Such cooperating charge-phonon processes seem to be more important for the doped polymers the high-coupled chains of which constitute 3D metal-like clusters. Aasmundtveit et al. [67] have shown that 3-cm waveband EPR line width and consequently the spin-spin relaxation rate of PC in PANI depend directly on its dc conductivity. The comparison of Bpp(T) and ас(T) functions presented in Fig.6 and Fig.14 demonstrate the additivity of these values at least for the higher doped polymers. Besides, Khazanovich [137] have found that spin-spin relaxation depends on the number of spins on each polymer chain Ns and on the number of neighboring chains Nc with which these spins interact as follows: 1 2

T

 0 4 2     18 ln N c  . 21ln 50 N s  e 

(27)

Using T2 = 1.710-7 sec, ij = 1.21045 cm-6, and 0 = 6.11013 rad/s determined from experiment, a simple relation Nc  55exp(Ns) of these values is obtained from Eq.(27). This means that at least seven interacting spins exist on each chain as spin-packet and interact with Nc = 20 chains, i e. spin and charge 3D hopping does not exceeds distance more than 3c3D. Figure 14 exhibits the temperature dependence of the ac conductivity of highly doped PANI-SA and PANI-HCA samples determined from their Dysonian 2-mm EPR spectra using Eq.(19), Eq.(22), and Eq.(23) as well. The shape of the temperature dependences presented demonstrates non-monotonous temperature dependence with a characteristic point Tc  200 K. Such a temperature dependency can be attributed to the above-mentioned interacting charge carriers with lattice phonons at high temperatures (the metallic regime) and by their Mott VRH at low temperatures (the semiconducting regime). In this case the charge transfer should consist of two successive processes, so



145

then the ac conductivity should be expressed as a combination of Eq.(14) and Eq.(25)

 ac (T )   0 T  1



|    Eph      1    02 T sinh .    k T  B       

(28)

Figure 14 shows that the experimental  ac values obtained for PANI-SA and PANI-HCA are fitted well by Eq.(28) with the appropriate parameters listed in Table 3. The energy determined for phonons in PANI sample lies near to that (0.066 eV) evaluated from the data obtained by Wang et al. [27,30]. RT ac of heavily doped PANI-SA and PANI-HCA, estimated from the contribution of spin charge carriers, does not exceed 140 S/cm. This value is much smaller than ac(e)  107 S/cm calculated theoretically [138]; however, it lies near that obtained for metal-like domains in PANI at 6.5 GHz [44]. The ac/dc ratio for these domains can be evaluated to be 80 for PANI-HSA 0.50 and 18, 7, and 4 for PANI-SA with y = 0.21, 0.42, and 0.53, respectively. Taking into account that the ac = dc condition should be fulfilled for classic metals [110], one can conclude a better structural ordering of these domains in PANI-SA. Charge carriers diffuse along these polymer chains with the constant D 1D can be determined from relation ac = 2

e 2 n( F)D 1D c1D to vary within 510 13 – 1.110 14 rad/s at room temperature that exceeds at least by an order of magnitude D 1D determined above for slightly doped samples. The RT mean free path [110] li = acmcvF/(Ne2) calculated for the highly doped PANI-SA and PANI-HCA is near to 0.5 and 6.0 nm, respectively. These values are smaller than that estimated for oriented trans-PA [45], but also holds for extended electron states in these polymers as well. The energy of lattice phonons obtained from ac data lies near the energy Jaf of the interaction between spins (see Table 2), that shows the modulation of spin-spin interaction by macromolecular dynamics in the system. DC and ac conductivity of the highly doped PANI-CSA and PANIAMPSA determined respectively by the dc conductometry method [85] and from the Dysonian spectra of the R2 PC are given in Fig.15 as function of temperature. Charge carrier hops through amorphous part of the sample and then diffuses through its crystalline domain, so then the dc term of the total


146

V. I. Krinichnyi

conductivity of the samples should be determined by 1D VDH between metallike domains accompanied by the charge carriers scattering on the lattice phonons in these domains described by Eq.(14) and Eq.(24). These processes occur parallel, so the effective conductivity can be expressed by Eq.(26). Temperature (K) 0

50

100

150

200

250

300

0

50

100

150

200

250

300

800 700

R1

R1

R2

R2

450 400

600 500

350

400 300 300

dc

100

250

dc

PANI-CSA0.6

PANI-CSA0.5

200

140

 (S/cm)

 (S/cm)

200

140 120 120 100

dc

dc

80

PANI-AMPSA0.4 0

50

100

150

200

250

PANI-AMPSA0.6 300

0

50

100

150

200

100

80 250

300

Temperature (K)

Figure 15. Temperature dependence of dc (open symbols) conductivity measured conductometrically and ac (filled symbols) conductivity determined from 3-cm, 8-mm, and 2-mm wavebands EPR Dysonian spectra of the R2 paramagnetic centers stabilized in the PANI-AMPSAy and PANI-CSAy samples. Top-down dashed lines present the dependences calculated from Eq.(28) with  = -1 and respective  0 = 2.27 S/K cm, 1

| =  02 = 0.64 S/K cm, E = 0.036 eV,  01 = 1.99 S/K cm,  02 = 0.68 S/K cm, Eph | ph

0.039 eV, cm,

| = 0.037 eV,  0 = 1.62 S/K  01 = 1.68 S/K cm,  02 = 1.57 S/K cm, Eph 1

| = 0.039 eV as well as from Eq.(26) with d = 1 and  02 = 0.76 S/K cm, Eph

respective k1 = 5.5103 S K0.5/cm, T0 = 753 K, k2 = 0.29 S/K cm, Eph = 0.024 eV, k1 = 5.6103 S K0.5/cm, T0 = 521 K, k2 = 1.7 S/K cm, Eph = 0.028 eV, k1 = 1.1103 S K0.5/cm, T0 = 277 K, k2 = 0.18 S/K cm, Eph = 0.020 eV, k1 = 1.2103 S K0.5/cm, T0 = 209 K, k2 = 0.31 S/K cm, Eph = 0.022 eV.



147

Figure 15 shows that dc conductivity of the polymers experimentally obtained is fitted well by Eq.(26) whose fitting parameters are summarized in Table 3. The vF value was calculated for the PANI-CSA and PANI-AMPSA systems, to be 2.4107 and 6.0107 cm/s, respectively [85]. In contrast with other conducting polymers, lower T0 parameter is characteristic for these samples. This is evidence of the longer averaged length of charge wave localization function in the samples. Indeed, value was determined for PANI-CSA0.6, PANI-CSA0.5, PANI-AMPSA0.6, and PANI-AMPSA0.4, to be 17, 37, 264, and 239 nm, respectively. The n(F) increases in series PANIAMPSA0.4  PANI-CSA0.5  PANI-CSA0.6  PANI-AMPSA0.6. AC conductivity of the polymers is also reflects the above mentioned successive mechanisms, so the experimental data can be circumscribed by Eq,(28). Indeed, it is seen from Fig.15 that the ac(T) dependences obtained experimentally for mobile R2 PC are fitted well by Eq.(28) with the parameters summarized in Table 3. The energy determined for phonons in these PANI samples lies near to that obtained for other polymers [48,49] and evaluated (0.066 eV) from the data determined by Wang et al. for HCl-doped PANI |

[27,30]. It is evident that E ph and Ea obtained above for the PANI-CSA0.5 sample lie near. This means that protons situated in crystalline domains indeed sense electron spin dynamics. The data obtained can be evidence of the contribution of the R1 and R2 PC in the charge transfer through respectively amorphous and crystalline parts of the polymers. RT ac values determined from Dysonian spectra of R2 PC lies near respective dc values that is characteristic for classic metals. The and Eph values determined above for mediatory doped samples correlate. This means that the higher the value, the stronger interaction of PC with phonons in metal-like crystallites. There is some tendency in the increase of RT dc and ac conductivities in the series PANI-AMPSA0.6  PANI-AMPSA0.4  PANI-CSA0.5  PANI-CSA0.6 ―feeling‖ by the R2 PC. The data obtained can be evidence of indirect contribution of the R1 PC and direct contribution of the R2 PC in the charge transfer through respectively amorphous and crystalline parts of the polymers. RT ac values determined from Dysonian spectra of R2 PC lies near respective dc values that is characteristic for classic metals. Thus, main PC are localized in the highly doped PANI-CSA and PANI-AMPSA samples at low temperatures. This originates the Curie type of susceptibility of the samples and the VRH charge transfer between their polymer chains. The spin-spin exchange is stimulated at high temperature region due likely to the activation librations of the polymer chains [139,140]. Both pinned and delocalized PC


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are formed simultaneously in the regions with different crystallinity. An antiferromagnetic interaction in crystalline domains is stronger then that in amorphous regions of PANI-CSA and PANI-AMPSA. Charge transport between crystalline metal-like domains occurs through the disordered amorphous regions where the charge/spin carriers are more localized. The assumption that higher purity PANI coupled with homogeneous doping would give rise to no EPR signal, characteristic of a purely bipolaronic matrix, is in contradiction with the increase of ac conductivity with spin concentration in polymer systems. Both PANI-CSA and PANI-AMPSA reveal better electronic properties over PANI-SA and PANI-HCA, as shown by their electrical conductivity which is both greater in magnitude and follows metallic temperature dependence. The change of conductivity with temperature is consistent with a disordered metal close to the critical regime of the metalinsulator transition with the Fermi energy close to the mobility edge [53,54].

3

 (S/cm)

10

ac

2

10

(N2)

ac (O2)

9.7 GHz 140 GHz 1

10

da

100

150

200

250

300

Temperature (K)

Figure 16. Temperature dependence of dc and ac conductivity determined from 3-cm and 2-mm waveband EPR Dysonian spectra of the PANI-pTSA0.5 sample obtained in nitrogen (open symbols) and air (filled symbols) atmosphere. Dash-dotted line shows the dependence calculated from Eq.(26) with k1 = 26 S K-0.5/cm, T0 = 4.6104 K, d = 3, k2 = 0.19 S/K cm,  ph = 0.027 eV. Above and below dashed lines present the dependences calculated from Eq.(28) with  0 = 13.3 S/K cm,  0 = 0.25 S/K cm, 1



| ph

= 0.027 eV and

2

 01 = 24.9 S/K cm,  02 = 10.8 S/K cm, |ph = 0.022 eV,

respectively, and  = 1.



149

Figure 16 shows the temperature dependence of dc determined by the dc conductometry method for the PANI-pTSA0.50. An analysis of these dependences leads to the conclusion that these polymers exhibit respectively 1D and 3D VRH at low temperature region, typical of a granular metal. As in case of other PANI, the dc value is determined by strong spin-spin interaction at high temperatures. Experimental data is shown from Fig.16 to be well described by Eq.(26) with the parameters presented in Table 3. The averaged length of charge wave localization lies in PANIpTSA0.50 near 11 nm and exceeds the effective radius of a quasi-metallic domain equal to 4 nm [141]. It can be due to closely electronic properties of the metal-like domains embedded into the polymer matrix. It allows to evaluate charge transfer integral t in such domains from relation connecting T0 values at 1D and 3D VRH [134], T0(3D) = 256 T0(1D) ln(2 T0(1D) /t), to be 0.10 eV. The most probable carrier hopping range R = (T0/T)1/2/4 is 34 nm in PANI-pTSA0.50 at room temperature. The hopping energy W of a charge carrier in these polymers determined respectively in terms of the 3D VRH, W = kB(T0T3)1/4/2, and 1D VRH, W = kB(T0T)1/2/2, models is 0.045 eV that is of the order of kBT. The data make it possible to calculate the velocity of charge carriers vF = 4.0106 cm/s moving near the Fermi energy with an energy of F = 0.34 eV. The latter value lies near to that determined for PANI-CSA (0.4 eV) [20] and PANI-SA (0.5 eV) [83,86]. This is in agreement with the supposition earlier made by Pelster et al. [141] that the charge transport in PANI-pTSA takes place via two contributions: metallic conduction through a crystalline core of 8 nm, and thermally activated tunneling (hopping) through an amorphous barrier of 1-2 nm diameter. Spin-lattice and spin-spin relaxation times measured by the saturation method [142] at 3-cm waveband EPR for the PANI-pTSA0.50 are respectively 1.210-7 and 3.110-8 sec (in the nitrogen atmosphere) and 1.110-7 and 1.610-8 sec (in the air) [88,89]. If one supposes that the polarons in this polymer possess mobility and diffuse along and between polymer chains with the diffusion coefficients D1D and D3D, respectively, D1D = 3.5108 and D3D = 1.1109 rad/s (in the nitrogen atmosphere) and D1D = 8.11011 and D3D = 2.3108 rad/s (in the air) are evaluated from Eq.(8) and Eq.(9). A corresponding conductivities due to so possible polaron mobility calculated from Eq.(10) are respectively 1D = 2.510-4 S/cm, 3D = 2.310-4 S/cm and 1D = 29 S/cm, 3D = 2.410-3 S/cm. This means that D1D < D3D in the sample without oxygen; however, the conductivity appears to be practically isotropic in character. The D1D/D3D ratio for the sample exposed to air increases to ~104,


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V. I. Krinichnyi

which substantially exceeds the value D1D/D3D ~ 50 obtained for highly doped PANI-HCA [56]. The conductivity of this sample also becomes anisotropic, 1D/3D ~104, and is also determined mainly by the diffusion of paramagnetic center along the polymer chain. The data obtained can be compared with those evaluated from the Dysonian EPR spectra. The ac values determined for the PANI-pTSA0.50 sample from its Dysonian 3-cm and 2-mm waveband EPR spectra by using Eq.(19), Eq.(22), and Eq.(23) are also shown in Fig.16 vs. temperature. An intrinsic conductivity of both the samples visibly increases at their exposition on air (Fig.16). RT conductivity obtained for e.g. the former sample at 3-cm waveband EPR is a two orders of magnitude higher than 1D and 3D calculated above in terms of Q1D polaron diffusion along the ―single conducting chain‖ [56]. Hence, it may be concluded that the conductivity in these polymers, as in other polyanilines, is mainly determined by the mobility of 3D-delocalized electrons in metal-like domains in which paramagnetic polarons are localized on parallel chains because of their strong exchange interaction. The temperature dependence of intrinsic conductivity can be interpreted in terms of the VRH mechanism of charge carriers and their scattering on the polymer lattice phonons respectively in amorphous and crystalline phases of the samples. Analogous to other PANI, the charge carrier crosses these phases one after another, so the resulting conductivity should be described by Eq.(28). As Fig.16 shows, Eq.(28) approximates well the ac(T) conductivity evaluated for all the PANI samples exposed on air with the parameters listed in Table 3. The | Eph value obtained for both the samples correlate with Eph determined from

the fitting of their dc(T) dependences in terms of the same charge transport mechanism (Table 3). This fact confirms additionally supposition above made on the existing of strong spin dipole-dipole interaction in crystalline domains. A decrease in ac with an increase in the registration frequency may as result of e.g. of the influence of external magnetic field on the spin-exchange process in the polymer or deeper penetration of MW field into the polymer bulk at 2-mm waveband EPR. Indeed, the intrinsic conductivity should be higher if the skin-layer is formed on metal-like domains with a smaller radius in PANI particles. Therefore two types of PC are formed in PANI, as in case of main conducting polymers, polarons localized on chains in amorphous polymer regions and polarons moving along and between polymer chains. During the polymer doping the number of the mobile polarons increases and the conducting chains become crystallization centers for the formation of the



151

massive metal-like domains of strongly coupled chains with 3D delocalized charge carriers. This process is accompanied by the increase of the electronphonon interaction, crystalline order, and interchain coupling. The latter factor plays an important role in the stabilizing of the metallic state, when both 1D electron localization and ―Peierls instability‖ are avoided. Above the percolation threshold the interaction between spin charge carriers becomes stronger and their mobility increases, so part of the mobile polarons collapses into diamagnetic bipolarons. Besides, the doping changes the interaction of the charge carriers with the lattice phonons, and therefore the mechanism of charge transfer. It also results in an increase of the number and size of highly conducting domains containing charge carriers of different nature and mobility, which lead to an increase in the conductivity and Pauli susceptibility. This process is modulated by macromolecular dynamics, and is accompanied by an increase in the crystalline order (or dimensionality) and planarity of the system. In the initial PANI the charges are transferred isoenergetically between solitary chains in the framework of the Kivelson formalism. The growth of the system dimensionality leads to the scattering of charge carriers on the lattice phonons. The charge 3D and 1D hops between these domains in the medium and heavily doped PANI, respectively. In heavily doped PANI the charge carriers are transferred according to the Mott VRH mechanism which is accompanied by their scattering on the lattice phonons. This is in agreement with the concept of the presence of 3D metal-like domains in PANI-ES rather than the supposition that 1D solitary conducting chains exist even in heavily doped PANI. In contrast with PANI-SA and PANI-HCA characterized as a Fermi glass with electronic states localizes at the Fermi energy due to disorder, PANICSA, PANI-AMPSA, and PANI-pTSA are disordered metals on the metalinsulator boundary. The metallic quality of ES form of PANI grows in the series PANI-HCA  PANI-SA  PANI-pTSA  PANI-AMPSA  PANICSA. The data presented show the variety of electronic processes, realized in PANI, which are stipulated by the structure, conformation, packing and the degree of ordering of polymer chains, and also by a number and the origin of dopants, introduced into the polymer. Among the general relationships, peculiar to these compounds are the following ones. Spin and spineless non-linear excitations may exist as charge carriers in organic conducting polymers. The ratio of these carriers depends on various properties of the polymer and dopant introduced into it. The increase of doping


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level leads to the change of charge transfer mechanism. Conductivity in neutral or weakly doped samples is defined mainly by interchain charge tunneling in the frames of the Kivelson formalisms, which is characterized by a high enough interaction of spins with several phonons of a lattice and leads to the correlation of Q1D spin motion and interchain charge transfer. These mechanisms ceases to dominate with the increase of doping level and the charge can be transferred by its thermal activation from widely separated localized states in the gap to close localized states in the tails of the valence and conducting bands. Therefore, complex quasi-particles, namely the molecular-lattice polarons are formed in some polymers because of libronphonon interactions analogously to that it is realized in organic conjugated macromolecules. It should be noted that as conducting polymers have a priori a lower dimensionality as compared with molecular crystals, their dynamics of charge carriers is more anisotropic. In heavily doped samples the dominating is the interchain Mott charge transport, characterized by strong interaction of charge carriers with lattice phonons. A higher spectral resolution at 2-mm waveband EPR provides a high accuracy of the measurement of magnetic resonance parameters and makes gfactor of organic free radicals an important informative characteristic. This allows the establishment of the correlation between the structure of organic radicals and their g tensor canonic values, providing the ability of PC identification in conducting polymers. The multifrequency EPR study allows obtaining qualitatively new information on spin carrier and molecular dynamics as well as on the magnetic and relaxation properties of polymer systems.

ACKNOWLEDGMENTS The author expresses his gratitude to Prof. Dr. G. Hinrichsen, Prof. A.P. Monkman and Dr. B. Wessling for the gift of polyaniline samples, to Dr. E.I. Yudanova and Dr. N.N. Denisov for the assistance in EPR experiments, as well as to Prof. Dr. H.-K. Roth for fruitful discussions. The support by the Russian Foundation of Basic Researches, grant 12-03-00148 is gratefully acknowledged.



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[85] Kon'kin, AL; Shtyrlin, VG; Garipov, RR; Aganov, AV; Zakharov, AV; Krinichnyi, VI; Adams, PN; Monkman, AP; Phys. Rev. B 2002, 66, 075203/1-075203/11. [86] Krinichnyi, VI; Roth, HK; Hinrichsen, G; Lux, F; Lüders, K; Phys. Rev. B 2002, 65, 155205/1-155205/14. [87] Krinichnyi, VI; Roth, HK; Hinrichsen, G; Synth. Met. 2003, 135, 431432. [88] Krinichnyi, VI; Tokarev, SV; Polym. Sci. A 2005, 47, 261-269. [89] Krinichnyi, VI; Tokarev, SV; Roth, HK; Schrödner, M; Wessling, B; Synth. Met. 2005, 152, 165-168. [90] Krinichnyi, VI; Konkin, AL; Monkman, A; Synthetic Metalls 2012, 162, 1147–1155. [91] Krinichnyi, VI; Yudanova, EI; Wessling, B; Synth. Met. 2013, 179, 67– 73. [92] Lux, F, PhD Thesys, Technical University of Berlin, 1993. [93] Timofeeva, ON; Lubentsov, BZ; Sudakova, YZ; Chernyshov, DN; Khidekel, ML; Synth. Met. 1991, 40, 111-116. [94] Adams, PN; Laughlin, PJ; Monkman, AP; Kenwright, AM; Polymer 1996, 37, 3411-3417. [95] Adams, PN; Monkman, AP, United Kingdom Patent No. 2287030 (1997). [96] Adams, PN; Devasagayam, P; Pomfret, SJ; Abell, L; Monkman, AP; J. Phys. 1998, 10, 8293-8303. [97] Buchachenko, AL; Vasserman, AM, Stable Radicals (Russ); Khimija: Moscow, 1973, 408 p. [98] Carrington, A; McLachlan, AD, Introduction to Magnetic Resonance with Application to Chemistry and Chemical Physics; Harrer & Row, Publishers: New York, Evanston, London, 1967, 295 p. [99] Long, SM; Cromack, KR; Epstein, AJ; Sun, Y; MacDiarmid, AG; Synth. Met. 1994, 62, 287-289. [100] Krinichnyi, VI; Appl. Magn. Reson. 1991, 2, 29-60. [101] Krinichnyi, VI; J. Biochem. Bioph. Methods 1991, 23, 1-30. [102] Poole ChP; Electron Spin Resonance. A Comprehensive Treatise on Experimental Techniques, Int. Sci. Publ., London, 1967, 922 p. [103] Bernier, P in Handbook of Conducting Polymers; T. E. Scotheim; Ed.;Marcel Deccer, Inc.: New York, 1986; Vol. 2, pp. 1099-1125. [104] Pelekh, AE; Krinichnyi, VI; Brezgunov, AY; Tkachenko, LI; Kozub, GI; Vysokomolekul. Soedin., Seriya A 1991, 33, 1731-1738.


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[125] Salavagione, H; Morales, GM; Miras, MC; Barbero, C; Acta Polym. 1999, 50, 40-44. [126] Kahol, PK; Pinto, NJ; McCormick, BJ; Solid State Commun. 1994, 91, 21-24. [127] Kahol, PK; Clark, GC; Hehring, M in Conjugated Conducting Polymers; H. Kiess; Ed.;Springer-Verlag: Berlin, Heidelberg, New York, 1992; Vol. 102, pp. 217-304. [128] Chapman, AC; Rhodes, P; Seymour, EFW; Proc. Phys. Soc. 1957, B 70, 345-360. [129] Beau, B; Travers, JP; Banka, E; Synth. Met. 1999, 101, 772. [130] Beau, B; Travers, JP; Genoud, F; Rannou, P; Synth. Met. 1999, 101, 778. [131] Pratt, FL; Blundell, SJ; Hayes, W; Nagamine, K; Ishida, K; Monkman, AP; Phys. Rev. Lett. 1997, 79, 2855-2858. [132] Raghunathan, A; Kahol, PK; Ho, JC; Chen, YY; Yao, YD; Lin, YS; Wessling, B; Phys. Rev. B 1998, 58, R15955-R15958. [133] Austin, IG; Mott, NF; Adv. Phys. 1969, 18, 41-102. [134] Kahol, PK; Pinto, NJ; Berndtsson, EJ; McCormick, BJ; J. Phys. 1994, 6, 5631-5638. [135] Pinto, NJ; Kahol, PK; McCormick, BJ; Dalal, NS; Wan, H; Phys. Rev. B 1994, 49, 13983-13986. [136] Krinichnyi, VI in Advanced ESR Methods in Polymer Research; S. Schlick; Ed.;Wiley: Hoboken, NJ, 2006, pp. 307-338. [137] [Khazanovich, TN; Vysokomolekul. Soedin. 1963, 5, 112. [138] Lim, HY; Jeong, SK; Suh, JS; Oh, EJ; Park, YW; Ryu, KS; Yo, CH; Synth. Met. 1995, 70, 1463-1464. [139] Krinichnyi, VI; J. Phys. Chem. B 2008, 112, 9746-9752. [140] Krinichnyi, VI; J. Chem. Phys. 2008, 129, 134510-134518. [141] Pestler, R; Nimtz, G; Wessling, B; Phys. Rev. B 1994, 49, 12718-12723. [142] Poole, CP, Electron Spin Resonance, A Comprehensive Treatise on Experimental Techniques; John Wiley & Sons: New York, 1983, 780 p.




Chapter 6

NEW POLYALKENYL-POLY (MALEIC-ANHYDRIDE-STYRENE) BASED COUPLING AGENTS FOR ENHANCING THE FIBRE/MATRIX INTERACTION Csilla Varga University of Pannonia, MOL, Department of Hydrocarbon and Coal Processing, Hungary

ABSTRACT Although several types of fibres and matrices have appeared in the last four decades in military and aircraft applications in the weekdays glass fibre reinforced polyester composites are the most widely used among thermoset matrices since proper, satisfactory properties can be coupled with low cost by their application. Therefore, development of glass fibre reinforced polyester composites is always timely. For treating the surface of the glass fibres such polyalkenyl-poly (maleic-anhydride-styrene) based coupling agents have been synthesized at our Department which are able to improve the different mechanical properties of the polyester and vinyl ester composites by enhancing the fibre/matrix interactions. The preliminary aspect of choosing the adequate structure of the additives was to establish possibly strong interactions between the fibre and the additive and between the additive and the matrix. Furthermore, economical aspects of the production and application of the additives


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Csilla Varga were also to keep in mind as the advantageous price/value ratio is also needed for possible substitution of the expensive silane based sizings applied by the glass fibre producers. So therefore, the effects of the additive treating of different forms of E-glass fibres (chopped fibre mat and woven [0/90°] fabric) both silane sized and unsized types will be dealt with. Analytical information about the additives has been collected by FT-IR and GPC measurements for determining the most possible structures of them. The minimally needed concentration and optimal impregnation times will also be shared. Moreover, the effects of the molar rate of the additional chemicals (alcohols and amines) used for creating the proper structure of the additives have also been investigated both with chopped fibre mat and woven [0/90°] fabric reinforcements. Weathering behaviour will also be detailed, exactly the effects of the additive treating on the water-uptake of the composites and on the mechanical properties either. Tensile, flexure and impact properties of the polyester and vinyl ester composites will be discussed. SEM micrographs taken of the broken surface of the composites have been used to study the fibre/matrix interactions. FT-IR technique and FT-Raman Microscopy measurements have been carried out in order to arrive at a comprehensive understanding how the structures of our newly developed coupling additives influence the fibre/matrix interface.

INTRODUCTION In recent years polymer composites have been applied in increasing quantities in a lot of fields of activities and have received widespread attention because of their high specific strength and modulus. They are used in everyday utensils and devices, in structural materials and in vehicles too. Generally, composites consist of several phases and interfaces exist between them playing an important role in the characteristics of the end-product besides the properties of the raw materials. For satisfying the new requirements arising almost every day developments of new materials and technologies are needed in many cases for which the importance of the knowledge and the use of interfacial interactions are getting higher and higher. Interfaces and the phases between them are playing a similarly important role in each composite and the surface modification should be chosen based on the purpose and on the properties of the systems. There are no generally applicable materials and additives which are efficient either in fibre reinforced composites, in polymer blends or in nanocomposites. The composite elements also determine the modification technique of the interface.


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Silane type coupling agents and maleic-anhydride grafted polymers are often applied but in most cases they are used in different composites upon previous successful results and the chemical composition of the parts are not taken into account. However, the common features of the interfacial interactions in heterogeneous systems are worth consideration. New expectations for the structural materials could be satisfied not only by the development of new composites but also by further development of existing ones. For that rethinking of the previous results and experiences and revealing of the possible new ways or methods previously considered unworkable are needed. Conventional fibre reinforced thermosets is one of them. Glass fibres are the most widely used to reinforce plastics due to their low cost and fairly good mechanical properties [1]. But in the last few years the interest in glass fibre reinforced thermosets decreased probably due to the detailed study of the effects of coupling agents and the mechanisms of coupling carried out so far and sizings containing silanes function also properly in glass fibre containing systems. Research has been continued, however, less vigorously as further development of the existing methods and technologies could also be successful. If more efficient additives can be used for improving the mechanical properties, similar technical requirements can be met by application of lower amounts of raw materials.

OBJECTIVES Although several types of fibres and matrices have appeared in the last four decades in military and aircraft applications, glass fibre reinforced polyester composites are the most widely used thermosets since proper, satisfactory properties can be coupled with low cost. Therefore, development of glass fibre reinforced polyester composites is always timely [1]. In areas where higher stiffness and better chemical resistance is needed, vinyl esters are mostly used because they are between polyesters and epoxies regarding the prices and properties, but the differences in their properties could compensate for the higher price than that of the polyesters because there will be no need for application of epoxies with much higher prices [2, 3]. By modification of the polymer chains of additives successfully used for treatment of carbon fibres [4] with application of styrene comonomer, new composition of terpolymer (polyalkenyl-poly(maleic-anhydride-styrene)) based additives have been produced for glass fibre reinforced thermoset


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composites. The effects of the matrix type and of the orientation of the reinforcements have been studied on the mechanical properties in additive treated glass fibre containing polyester and vinyl ester composites. The effects of the modification with the additives have been investigated by studying the mechanical properties of the composites and the properties of the fibre/matrix interface. Besides the economical aspects of the additive production and application had to also be kept in mind because advantageous priceperformance ratio is also needed for possible substitution of the silane containing sizings mostly applied by glass fibre producers [5, 6]. The main aims of the experimental work presented in this chapter have been the improvement of the mechanical properties of different glass fibre reinforced composites by application of new types of additive package. The application possibilities of those additives, the advantageous concentrations, the relationships between the composition of the additives and the mechanical properties of the composites containing the abovementioned additives, and the mechanisms of the improving effects have been studied.

EXPERIMENTAL Materials AROPOL M105 TB polyester (Ashland Inc. USA) and DERAKANE 41145 vinyl ester (Ashland Inc. USA) were applied for the matrices in the composites. Polyester resin had the density of 1100kg/m3 at 25°C, dynamic viscosity of 1200mPas at 23°C and styrene content of 41%. The resin was cured with 1% cobalt-naphthenate and 1% M50. Vinyl ester resin had the density of 1090kg/m3 at 20°C, dynamic viscosity of 650-900mPas at 23°C and styrene content of 45%. That resin was cured with 2% BUTANOX. Other properties of the matrices were summarized in Table 1. Both chopped glass fibre mats (fabric weight: 490g/m2) and glass woven [0/90°] fabric (fabric weight: 450g/m2) were applied as reinforcement and no significant differences were found in their chemical compositions (Table 2). The chopped fibre mat is a sheet of reinforcement material comprised of randomly oriented chopped fibres held together with a resinous binder. Therefore, the effects of the fabrication type and the fibre orientation can also be investigated. All the experimental polyalkenyl-poly(maleic-anhydride-styrene) based additives were synthesized at the MOL Department of Hydrocarbon and Coal



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Processing (Institute of Chemical and Process Engineering, University of Pannonia). Main physical and chemical properties of the used coupling agents were listed in Table 4 in the subsection 4.1. Table 1. Properties of thermoset resins properties

crosslinked resin

liquid resin

commercial name monomer acid number, mgKOH/g sample tensile strength, MPa tensile modulus, MPa strain at break, % flexure strength, MPa flexure modulus, MPa

polyester AROPOL M105TA orthophthalic acid 19 55 3600 2.0 90 4100

vinyl ester VIAPAL UP4834 BT/66 bisphenol-A ≤8 78 3377 3.2 126 2882

Table 2. Elementary composition of differentially oriented glass fibre reinforcements according to EDAX element, % chopped fibre mat woven [0/90°] fabric

O 42.84 39.48

Na 0.76 0.39

Mg 0.79 0.67

Al 9.09 9.27

Si 28.57 29.69

K 0.21 0.55

Ca 17.27 19.39

Ti 0.19 0.25

Fe 0.29 0.30

Preparation of Glass Fibre Reinforced Thermoset Composites Glass fibres were treated in the hydrocarbon solution of the coupling agents and heat treatment was applied at 110°C for half an hour after drying. Glass fibre reinforced polyester and vinyl ester composites were produced by hand lay-up laminating at Balatonplast Ltd. Mechanical properties of standardized, dog-bone samples were investigated which were cut from the five layer-laminates with a CNC machine. Specimens had the dimensions of 5mm x 5mm x 150mm in case of chopped fibre mat reinforced samples and 5mm x 3mm x 150mm for woven fabric reinforced ones.


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Methods Tensile Test Tensile properties (MSZ EN ISO 527-1-4:1999) were determined by an INSTRON 3345 universal tensile testing machine. The temperature in the laboratory was 20°C and the relative humidity was 50% during the mechanical tests. Tensile tests were carried out at 90mm/min crosshead speed and results were averaged over 5 specimens. Charpy Impact Test A CEAST Resil Impactor was applied to measure the Charpy impact strength of the produced composites according to MSZ EN ISO 179-2:2000 standard test method. Analytical Measurements A TENSOR 27 type FT-IR spectrometer and an Opus5.5 software was used for evaluation of the FT-IR analysis. Dispersive Raman Microscope was used to map the transition layer between the fibres and the matrix. Spectral resolution was 9cm-1 and the spectral range was 80-4400cm-1 with 1μm resolution of the interphase. The average molecular weight was estimated by using gel permeation chromatography (Cecil GPC, PL Gel column, autosampler, CE 4200 refractive index detector), calibrated by polystyrene standards [7]. Elutions were performed using de-gassed THF as the eluent at a flow rate of 1.0 ml/min. Scanning Electron Microscopy (SEM) was used to study the structure of fractured faces of specimens and to follow the possible interaction between the reinforcements and the matrices. The applied apparatus was a Phillips XL30 ESEM instrument. Weathering Test The commercial device from Q-Lab (Xe-1000S) was used for laboratory simulation of damaging effects of weathering on materials. A Xe UV-lamp was used as light source at 340nm which can reproduce the natural UVradiation. The materials were daily exposed to UV radiation for 11.0 hours, then to condensation of water without UV radiation for 2.5 hours and finally 10.5 hours without radiation and water spraying for three weeks. Value of the irradiation was 0.41W/m2 at 55°C. Temperature during water cycle was 50°C.



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COUPLING AGENTS During investigation of the coupling agents the effects of the length of the carbon chains of the reagents for the additives and the molar ratio of the reagents will be discussed for which the detailed analytical study of the additives is also needed. The relationship among mechanical properties and reproducibility of additives and composites will be shown and also the effects of the additives on the mechanical properties of the abovementioned composite systems after weathering.

Analytical Study of the Additives Styrene containing additives produced by different alcohol and amine reagents in different molar ratios (derivatives of polyalkenyl-poly(maleicanhydride-styrene) terpolymers) were applied in glass fibre reinforced composites. Composition of the additives is given in Table 3. Table 3. Raw materials of polyalkenyl-poly(maleic-anhydride-styrene) based additives additive

terpolymer olefin sign component A1 TP1 C16-18 A2 TP2 C20-24 A3 TP2 C20-24 A4 TP2 C20-24 A5 TP2 C20-24 A6 TP3* C20-24 A7 TP3* C20-24 * produced in industrial scale.

alcohol component dodecanol dodecanol dodecanol dodecanol n-butanol dodecanol dodecanol

amine component n-butyl-amine n-butyl-amine n-butyl-amine dodecyl-amine n-butyl-amine n-butyl-amine dodecyl-amine

molar ratio MR-1 MR-1 MR-2 MR-1 MR-1 MR-1 MR-1

Additives were produced in two-step reactions. The acid numbers of the terpolymers (TP1, TP2 & TP3) synthesized in the first step were 160.7mg KOH/g sample, 157.4mg KOH/g sample and 148.5mg KOH/g sample respectively, Mw molecular weights were 3490g/mol, 4050g/mol and 3790g/mol. Polydispersities were 1.150, 1.175 and 1.260. FT-IR spectroscopy was used to qualitatively characterize the terpolymers (Fig. 1). The characteristic peaks of the methyl- and methylene-groups were easily identified in the 3000cm-l–2800cm-l wave number ranges. The


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stretching vibrations of the methyl- and methylene-groups were determined at 2956cm-l (asCH3), at 2922cm-l (asCH2) and at 2853cm-l. The latter absorption band was characteristic for the symmetric stretching vibration of both the methylene-groups (sCH2) and the methyl-groups (sCH3) because the absorption wave numbers are close. 2010.11.20. 18:01:01

0.00

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D:\!Munka\Kutatás\analitikai vizsgálatok\FT-IR\!spektrum fájlok\köztitermékek\PÉK\2009\PÉK_1_09.0

3500

3000

2500 2000 Wavenumber cm-1 Page 1 of 1

1500

1000

Figure 1. Typical FT-IR spectrum of a polyalkenyl-poly(maleic-anhydride-styrene) terpolymer.

Over 3000cm-1 the aromatic CH stretching vibration occurred either. Below the 1000cm-1 wave numbers lots of vibrations could be found. Deformation vibrations of the aromatic CH-groups appeared at 767cm-1 and 691cm-1. Deformation vibration of the methylene-groups was found at 721cm-1 with very high absorbance indicating long carbon chains in the chemical. The absorption peak of the stretching vibration of the C=C double bond appeared at 1610cm-1, and the bands of the vinyl-groups were found at 1000cm-l and at 908cm-l: absorption band of the -CH= group at 1000cm-l and band of the =CH2 part at 908cm-l. The Y-shaped band characteristic for the two carbonyl-groups of the anhydride rings (asC=O and sC=O) appeared at 1857cm-1 and at 1778cm-l. The asymmetric -(O=C)O- vibration was seen at 1220cm-1, and stretching vibration of the -C-O-C- bands were at 1065cm-1. The ether band (γ-C-O-C-)



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was characterized at 925cm-l. According to FT-IR spectra the TP3 terpolymer was stated to contain less styrene in the polymer chain. The structures of the additives were also determined by FT-IR spectroscopy. A typical FT-IR spectrum was shown in Fig. 2. Comparing the spectra of the additives and the terpolymer the following differences could be stated. 2011.02.06. 19:58:49

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3500

3000


1500

1000

Figure 2. Typical FT-IR spectrum of a polyalkenyl-poly(maleic-anhydride-styrene) based coupling agent.

In the 1300-950cm-1 wave number ranges the vibration of the -(O=C)Ogroups (1218cm-1) could be determined with very low intensities, but new bands occurred at 1195cm-1, 1170cm-1 and 1136cm-1 wave numbers. The latter peaks appeared due to the new functional groups in the additives compared to the terpolymer. The band at 1170cm-1 was attributed to the ester groups, the others were considered to be characteristic of the amide- and imide groups. The stretching vibration of the -C-O-C- relation can be seen only with low intensities as in the case of the -(O=C)O- groups. From those characteristics the product was deduced to contain unreacted anhydride rings too, since the characteristic vibration bands were found in the spectra of the additives but further components have also been evolved. Reduced intensity of the peak (γC-O-C-) at 925cm-1 was also due to the reactions.


CH3

CH3

R1

CH2

CH2

CH

CH

CH2

CH

NH CH2 CH3

O

O a

CH2 CH3

R2 b

k

CH2

CH2

O

O

O

O

OH

CH3 m

CH

CH2

CH

CH2 O

O CH2

l

CH2

CH

O

O

CH3

R2 b

n

N CH2

o

CH3

CH2

d

CH

CH2

O CH3 a p

(R1: alkyl-chain with carbon numbers of the olefin monomer; R2: alkyl-chain with R1-2 carbon numbers; a, b: 3-11; d: alkyl-chain with R1-2 carbon numbers; k: 0,3-1, l: 2-4; m: 1-2; n: 0,1-1; o: 2-4; p:1-3). Figure 3. Possible structure of polyalkenyl-poly(maleic-anhydride-styrene) based additives.


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Based on the FT-IR spectra the structures of the different additives were established to be very similar because the absorption bands were found at the same wave numbers leading us to the observation that vibrations were caused by functional groups in similar chemical environments. Wave number shifting caused by the differences in the molecular weights did not occur or even was not perceptible as the additives have high, many thousands g/mol molecular weights. According to the FT-IR analysis the structure in Fig. 3 was presumed for the additives. The chemical structure of additive A4 differed from the others as no vibration was found at 1733cm-1 characteristic of ester groups, therefore, the additive contained only unreacted anhydride-rings, imide and ester-amide parts. Analytical properties (acid and saponification numbers) of the additives and their possible structures used to be determined only by titration (Table 4). But those two values did not give any information about the ratios of the different N-containing (ester-amide and imide) derivatives in the additive. Only the concentration of the anhydride rings and the free carboxylic groups (in the half-ester derivative) could be determined. Owing to the different reactivity of the derivatives for neutralisation, the measured values are sometimes very far from the theoretical values calculated from the amounts of reagents fed in. Table 4. Analytical properties of polyalkenyl-poly(maleic-anhydridestyrene) based coupling agents

additive A1 A2 A3 A4 A5 A6 A7

acid number mg KOH/g sample 66.2 45.4 18.9 34.8 39.0 60.0 56.5

saponification number mg KOH/g sample

molecular weight polydispersity (Mn) g/mol

111.7 68.3 116.9 57.6 68.6 101.8 95.5

3652 4212 4207 4287 4094 3988 3920

1.224 1.206 1.210 1.325 1.260 1.235 1.258

Therefore, a new method was developed in order to determine the acid and saponification numbers and the most possible structures of the additives based on FT-IR analysis. As carbonyl-groups of the different derivatives give bands


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in the FT-IR spectrum with high absorbance they were used in the new method [8]. During FT-IR analysis the integrated area under the different carbonylpeaks were used in order to quantitatively determine the concentration of the different derivatives in the additives (Table 5). The different carbonyl-peaks were associated with the various derivatives in the additives. So band at 1778cm-1 was attributed to the anhydride rings, the peak at 1733cm-1 was associated with the ester-groups of the half-ester and of the ester-amide and the peak at 1699cm-1 was established to be characteristic for the free carboxylic, amide and imide groups. Concentration of the derivatives was calculated from the ratio of the integrated areas of the proper peaks. Unreacted anhydride was considered to remain in the additive based on the applied molar ratio of the reagents in the additive production process. Table 5. Estimated ratio of polyalkenyl-poly(maleic-anhydride-styrene) based coupling agents additive A1 A2 A3 A4 A5 A6 A7

unreacted anhydride 0.2098 0.1623 0.1900 0.1937 0.3105 0.1804 0.1788

half-ester 0.4191 0.2945 0.1904 0.2674 0.0459 0.4324 0.4108

ester-amide 0.1855 0.2716 0.3098 0.2694 0.3218 0.1936 0.2052

imide 0.1855 0.2716 0.3098 0.2694 0.3218 0.1936 0.2052

Results of the FT-IR method (Table 5) show that the ratio of derivatives is dependent on the type and molar ratio of the reagents fed in. Additives could be reproduced successfully since according to results of the FT-IR analysis the concentration of the different carbonyl-groups was almost identical. By increasing the molar ratio of the reagents (additive A3 with MR-2) the concentration of the ester-amide derivative can be increased so the polarity of the additives can be changed.

Conditions of Additive Treatment The additive adsorption characteristics of glass fibre surfaces have been determined (Fig. 4). For woven [0/90°] fabric type reinforcements the covering of the surface by the additive took 10 minutes, but for chopped fibre



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mats 15 minutes were needed. The mass of the adsorbed additive on different structures of fibres was related to the mass of the reinforcement before impregnation. For woven fabric type reinforcements less additive was needed in the composites. chopped fibre mat

woven [0/90°] fabric

30

adsorbed additive, %

25 20 15 10 5 0 0

5

10 15 20 impregnation time, min

25

30

Figure 4. Adsorption curves of additive A2 on reinforcements of different orientations.

Characteristics of the adsorption of additive on the fibre surface showed that the surface of the woven fabric type reinforcement could be covered in shorter time than the surface of the chopped fibre mat, probably because the additive solution could not reach the inside of the glass fibre bundles due to the close weaving, therefore, it stayed on their surface.

MECHANICAL PROPERTIES In this chapter the effects of the carbon chain lengths of the reagents of the additive (i.e. alcohol and amine) on the mechanical properties of the composites will be discussed. Generally, tensile modulus reflects the capability of both the fibre and the matrix to transfer the elastic deformation in case of small strains without


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interface fracture. Therefore, it is not surprising that tensile modulus is less sensitive to the variation of interfacial interactions than tensile strength and the latter is strongly associated with failure behaviour. That is why only different strengths of composites were presented in detail. Typical stress-strain curves were shown in Fig. 5.

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0.5

1.0

1.5

2.0

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Elongation, mm without additive A4

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Figure 5. Typical stress–strain curves of chopped glass fibre mat reinforced polyester composites.

As the mechanical properties of the composites are basically affected by their glass fibre content, it was determined according to MSZ EN ISO 34511:1999 standard test method at 800°C. Glass fibre contents were 35.0±0.2% in polyester and 33.4±1.0% in vinyl ester composites. It means that differences in mechanical properties were caused by the additives and their compatibilizing effects and not by differences in their glass fibre contents.

Effect of the Polymer Chain Length of the Additive The effect of the chain length of the olefin component of the additive on the mechanical properties of polyester composites was also investigated



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(Figure 6). Decreasing the carbon number of the olefin component of the additive impaired the mechanical characteristics of the composite compared to the reference. It is well known that the impact resistance is highly influenced by the strength of the interfacial bonds and by the properties of the matrix and the fibre. Impact energy is dissipated by debonding, fibre and/or matrix fracture and fibre pull-out. Fibre fracture dissipates less energy compared to fibre pullout. The former is common in composites with strong interfacial bonds while the occurrence of the latter is a sign of weak bonds. In composites containing additive A1 (Figure 18) fibre pull-out will occur so there are weak interactions in that system [10, 15]. tensile reference : 40 tensile strength: 95MPa flexure strength: 173MPa 30 2 impact strength: 94kJ/m 20

change in strength, %

50

flexure

impact

10 0 -10 -20 -30 -40 A1

A2 additive

Figure 6. Mechanical properties of glass fibre reinforced polyester composites with changing the chain length of the olefin reagent of the additive (A1: C16-18; A2: C20-24).

Therefore, the effects of the additives were influenced not only by the structural properties and the relative ratio of the functional groups derived from maleic-anhydride rings but also by the length of the polymer chain of the additive.


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The Effect of the Molar Ratio of the Reagents Since additives with different functional groups are advantageous for fibre/matrix interactions, molar ratios of the alcohol and amine reagents were chosen accordingly. As ratios of the functional groups derived from the anhydride-rings and therefore, also those of the derivatives (half-ester, esteramide and imide) can be influenced by the molar ratios of the aforementioned reagents, the proper setting of these ratios will be of paramount importance regarding the effectiveness of the additive. For studying these effects two additives were produced with different molar ratios (A2 & A3) and chopped glass fibre mat reinforced polyester composites were made with them. The ratio of the derivatives in the additives was given in Table 5 and changes in the mechanical properties of the composites in Fig. 7. tensile

impact

50


40 30 20 10 0 -10 A2

A3 additive

Figure 7. Mechanical properties of treated glass fibre reinforced polyester composites with different reagent molar ratios of the additive.

By application of additive A2 both properties were significantly improved indicating strong fibre/matrix interaction. Tensile and impact strength changed in the ±10% range of error of the production technology by increasing molar ratios of the reagents (additive A3), which proves that the additive had but a slight influence on the interfacial interaction compared to that of the reference sample. However, it means also that the increased ratio of the ester-amide derivatives is not beneficial for improving the fibre/matrix interaction. Therefore, the molar ratio of additive A2 was applied in subsequent



experiments for studying the effects of the types of reagents and the orientation of reinforcements.

The Effect of Commercial Silane Sizing

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Figure 8. FT-IR spectra of glass fibres (a. silane sized; b. silane sized and treated with additive A2).


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The effects of additive A2 were investigated in glass fibre reinforced polyester composites containing glass fibres previously sized by the producer with silane coupling agent. The FT-IR spectrum of the glass fibre surface gave some information on the structure of the silane (Fig. 8. /a). The exact chemical structure could not be determined but the peaks of the hydrocarbon groups (methyl and methylene) at around 3000cm-1, the bands of the carbonyl-groups at 1776cm-1 and the ether functional groups (1130cm-1) indicated that there were not only Si-OH groups on the surface of the glass fibre but other groups as well. Silane sized chopped glass fibre mats were treated with our synthesized additive A2 (Fig. 8 /b) then were applied in composites laminated with polyester resin. Changes in mechanical properties related to the reference were represented in Fig. 9. tensile

impact

50


40 30 20 10 0 -10 -20 -30 sized

unsized

Figure 9. Mechanical properties of polyester composites reinforced with sized and unsized glass fibres and treated also with additive A2.

Comparing changes in mechanical properties of composites containing sized and unsized, but A2 additive treated glass fibre showed huge differences. However, in the latter case when glass fibres treated only with the experimental additive were used for reinforcing the polyester the resistance against both tensile and impact stresses were improved compared to the composite containing no additive. The changes of those mechanical properties



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in the same direction led us to the conclusion that strong interaction was established between the fibres and the matrix. Outstanding increase in the impact strength was experienced beside the significant decrease in the tensile strength in the sized and A2 additive treated glass fibre reinforced composites. In that case only weak interaction could be emerged between the glass fibre and the polyester, efficient load transfer could not be maintained because the matrix took up the load during impact stresses but in case of the tensile testing it could not transfer it to the incorporated fibres. So the experimental additive will be efficient if unsized glass fibres are used; in case of silane sized glass fibres the interaction will be reduced.

The Effect of the Additive Type in Polyester Composites The effect of the carbon chain length of the alcohol reagent on the mechanical properties is shown in Fig. 10. The effectiveness of the additive (A2) was unambiguously increased with the alcohol of higher chain length. By application of the short alcohol of C4 carbon number for the additive (A5) only the properties of the untreated chopped glass fibre mat reinforced polyester could be reached. tensile

50

flexure


40 30

impact reference: tensile strength: 95MPa flexure strength: 173MPa impact strength: 94kJ/m 2

20 10 0 -10 -20 A2

A5 additive

Figure 10. Mechanical properties of glass fibre reinforced polyester composites with changing the chain length of the alcohol reagent of the additive (A2: C12; A5: C4).


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By using additive A2 (dodecanol and n-butyl-amine reagents) tensile strength increased by 6%, the flexure strength by 10%, and impact strength by 44% compared to the properties of the untreated glass fibre reinforced polyester. The importance of the trends of the changes was not only in the great extent of increase but also in the simultaneous improvement of various mechanical properties (tensile, flexure and impact strength) [9-15]. The load acting on the matrix was not transferred to the reinforcement in an efficient way with additive A5 because a weak interface results in low stiffness and strength but high resistance to fracture. tensile

50

flexure


40 30

impact reference: tensile strength: 95MPa flexure strength: 173MPa 2 impact strength: 94kJ/m

20 10 0 -10 -20 A2

A4 additive

Figure 11. Mechanical properties of glass fibre reinforced polyester composites with changing the chain length of the amine reagent of the additive (A2: C4; A4: C12).

Increasing the carbon number of the amine reagent in the additive (A4) impact resistance of the composite could be improved related to the composite containing untreated glass fibres while tensile and flexure strengths decreased (Fig. 11). The impact strength increased by 22% compared to the composite with the additive containing amine of lower carbon chain length (A4), and the tensile strength increased by 11.5%. In the latter case the tensile strength of the reference polyester composite containing untreated glass fibre could be achieved. The phenomena mentioned quite often in the literature, namely that poor interfacial interaction between fibres and matrix results in opposite changes in



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resistance against different stresses [8, 11] could also be observed with additives A4 and A5. But by applying additive A2 all the properties were improved compared to the reference indicating stronger interfacial interactions (Chapter 0).

Effects of the Reinforcement Type Since additive A2 seemed to be the most efficient among the experimental additives for improving the mechanical properties of polyester composites, the effects of the orientation of the reinforcement on the mechanical properties were also investigated by using that additive for glass woven [0/90°] fabric reinforced composite beside the chopped fibre mat reinforced one. Tensile and impact strengths were higher for woven [0/90°] fabric reinforced composites than for chopped fibre mat reinforced ones because one part of the fibres in the woven fabric type reinforcement can be found in the direction of the stress. Since the woven fabric is two-dimensional and the stress is applied perpendicularly flexure strength was lower than in chopped fibre mat reinforced composites. 100

tensile

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impact


80

60

40

20

0 chopped fibre mat

woven [0/90°] fabric

(reference data for the woven fabric reinforced composite: tensile strength: 197 MPa, flexure strength: 63.3 MPa, impact strength: 190 kJ/m2). Figure 12. Mechanical properties of glass fibre reinforced polyester composites with different fibre orientation with application of A2.


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Tensile strength of the woven [0/90°] fabric reinforced polyester increased by 34% compared to the reference due to the application of the additive (Fig. 12), and improvements were 93.5% for flexure strength and 59.5% for impact strength. So additive A2 was also effective in that composite system but the level of improvements was even higher than in the chopped fibre mat reinforced composite. As the fibre contents of the composites were 63.5±1.2% and the elementary composition of the glass fibres did not differ significantly only the type of the fabrication so the reason for the improvement could only be the smoother additive sizing on the more even fibre structure.

The Effect of the Additive Type in Vinyl Ester Composites The 33.62.1% fibre contents of the investigated vinyl ester composites meant that the changes in the mechanical properties had been mostly due to the applied additives and not to the effect of the different fibre contents. The effectiveness of the additives in those composites were far from that found in polyester ones which can obviously be related to the differences in the matrices because the same additive treated chopped glass fibre mats were used for both composites. The effectiveness of additive A2 containing long enough hydrocarbon chain connecting to the ester group which was more advantageous for polyester composites significantly fell behind in almost all of the properties of the vinyl ester composite containing untreated glass fibre. Decreasing the carbon number of the alcohol reagent of the additive (A4) resulted in further significant deterioration of the properties (Fig. 13). Tensile strength was lowered by 30% compared to the untreated fibre reinforced composite while the impact strength deteriorated by 23% and the flexure strength was reduced by 34%. Therefore, decreasing the carbon chain length of the alcohol will not be beneficial for improving the mechanical properties. Increasing the carbon chain length of the amine reagent (additive A5) had a positive effect on the mechanical properties of the composites (Fig. 14). By application of additive A5 the mechanical properties, especially the impact strength could be improved by 25% related to the additive containing amine with a shorter chain length (A2) but the mechanical properties of the reference could not be surpassed. Increasing the carbon number of the amine influenced neither the tensile nor the flexure strength compared to additive A2.


New Polyalkenyl-Poly (Maleic-Anhydride-Styrene) … tensile


0

flexure

183

impact

-10

-20

-30

-40

reference: tensile strength: 107MPa; flexure strength: 174MPa; impact strength:148kJ/m 2 A2

A4 additive

Figure 13. Mechanical properties of glass fibre reinforced vinyl ester composites in function of the chain length of the amine reagent of the additive (A2: C4; A4: C12). tensile


0

flexure

impact

-10 reference: tensile strength: 107MPa flexure strength: 174MPa impact strength: 148kJ/m 2

-20

-30 A2

A5 additive

Figure 14. Mechanical properties of glass fibre reinforced vinyl ester composites in function of the chain length of the alcohol reagent of the additive (A2: C12; A5: C4).


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The Effect of the UV-Light and Water Additives (A6 & A7) from the terpolymer of industrial scale production (TP3) had other effects on the mechanical properties of the composites than the additives from laboratory scale terpolymers as the incorporation of styrene had difficulties during the industrial scale process (Figs 15-16.). The background of the production and the differences in effectiveness will not be detailed as it was studied in our previous report [6] with other composition of coupling agents. In this chapter only the effect of UV-light and water will be discussed on mechanical properties of glass fibre reinforced composites. Additives resulted in weaker interfacial interactions both in polyester and in vinyl ester composites as shown in Figs 15-16. because mechanical strength decreased related to the reference samples. Both additives gave positive effects on the mechanical properties of polyester composites due to the weathering. Lower decrease of the mechanical properties could be realized. tensile

impact


20 0 -20 -40 -60 -80 before weathering

after weathering

before weathering

A6

after weathering A7

additive Figure 15. Mechanical properties of glass fibre reinforced polyester composites before and after weathering.



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Opposite effects could be experienced with vinyl ester composites (Fig. 16) during weathering. Both tensile and impact strength decreased after weathering by at least 10% related to the properties before weathering. tensile

impact


80 60 40 20 0 -20 -40 before weathering

after weathering

before weathering

A6

after weathering A7

additive

Figure 16. Mechanical properties of glass fibre reinforced vinyl ester composites before and after weathering.

Application of additives produced from industrial scale terpolymer deteriorated the fibre/matrix interaction so the styrene content of the coupling agents is a crucial factor but weathering can have positive effect on the mechanical properties.

FIBRE/MATRIX INTERACTIONS Surface morphology of the broken surface of composites after tensile testing and fibre/matrix interactions were studied on SEM graphs. According to SEM photos fibres were fully separated from the polymer in composites containing untreated fibres (Fig.17). In case of the composite having good mechanical strength (A2) (Fig.19) the compatibility of glass fibres and the polymer was improved since less fibres were pulled out of the matrix and they were broken at the surface; furthermore, the surface of the fibres was covered with polymer at many places after breaking. The SEM graph of the sample with moderate mechanical strength was shown in Fig. 20 (additive A4). The surface of the glass fibres became clean because fibres were easily separated


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from the matrix. Glass fibre bundles were easily pulled out of the crosslinked polymer, therefore, they could not carry out their reinforcing task. Stronger adhesion was established in composites containing treated glass fibre because the sizes of the holes between the fibres and the matrix were significantly reduced or even eliminated [1, 13-15]. The strength of the interaction is comparable to the strength of the cohesion bonds inside the matrix as there were polymer layers connected to the surface of the fibres pulled out of the matrix.

a.) magnification: 100x

b.) magnification: 1000x Figure 17. Broken surface of untreated glass fibre reinforced polyester composite.



a) magnification: 100x

b) magnification: 1000x Figure 18. Broken surface of A1 additive treated glass fibre reinforced polyester composite.


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b) magnification: 1000x Figure 19. Broken surface of the A2 additive treated glass fibre reinforced polyester composite.



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b) magnification: 1000x Figure 20. Broken surface of the A4 additive treated glass fibre reinforced polyester composite.

Strength of the interactions can also be estimated from the energy at break [16]. With additive A2 energy at break was higher than that of the reference indicating that fibre breakage occurred more often in that composite than in the reference, while fibre pull-out dominated with application of additive A4. SEM graphs also supported those phenomena. SEM graphs of glass fibre reinforced vinyl ester composites were shown in Figs 21-23. Significant fibre pull-out could be observed in additive treated glass fibre reinforced composites so additives seemed not to be efficient enough because only small surfaces of


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the fibres had been covered with the matrix after break. Fibre pull-out occurred also in untreated glass fibre reinforced vinyl ester but at a lower degree, however, the polymer did not connect well to the fibres after break. Considering the energies at break application of additives (A2, A4) enhanced fibres pull-out from the matrix compared to that of the reference.


b) magnification: 1000x Figure 21. Broken surface of untreated glass fibre reinforced vinyl ester composite.



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b) magnification: 1000x Figure 22. Broken surface of the A2 additive treated glass fibre reinforced vinyl ester composite.


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b) magnification: 1000x Figure 23. Broken surface of the A4 additive treated glass fibre reinforced vinyl ester composite.

Possible interactions in glass fibre reinforced composites were investigated also by FT-IR spectroscopy. Glass fibres did not contain any commercial sizings because only the vibrations of the free OH-groups of the glass fibre surface occurred in the FT-IR spectrum (Fig. 24 ~885cm-1).


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According to the expectations the intensities of the absorption peaks in the spectrum of the additive treated glass fibres (Fig. 24/d) were much lower than those of the additive but the wave numbers of the maximum values of the peaks did not differ from each other. Therefore, additives A1, A4, A5 were determined not to be connected chemically to the glass fibre surface since other vibrations characteristic of new groups did not appear in the spectrum of the additive treated glass fibres compared to the spectrum of the additive. Deformation vibration of the -C-O-C- (~910cm-1) bond in those four additives and the vibration for the silanol groups of the fibre surface appeared together in the spectrum of the additive treated glass fibre.

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c.c

(a: glass fibre, b: additive, c: additive treated glass fibre) Figure 25. Investigation of the interfacial interactions with FT-IR spectra in case of A2 additive.


650

60


197

Comparing the spectra of the glass fibre and the A2 additive treated glass fibre (Fig. 25) the low intensity of the vibration at ~885cm-1 characteristic of the silanol groups at the fibre surface was conspicuous in the spectrum of the treated glass fibre as the intensive absorption peaks of the additive suppressed them meaning that not only Si-OH bonds can be found on the surface of the treated glass fibre. The ratio of the intensities of the carbonyl-groups in different chemical environments also changed in the range of the carbonylvibrations (1810cm-1-1680cm-1). The intensity of the absorption peak characteristic of the ester-group of the dicarboxylic-acid-half-ester derivative (1733cm-1) decreased to lower values than for the peak of the unreacted anhydride (1778cm-1), therefore, the relative concentration of the half-ester reduced. Structure of the composites was investigated also by FT-Raman Microscopy (Fig. 26). Polymer matrix (position 0)

Position 2

Position 3

Position 4

Position 5

Glass fibre (position 9)

Figure 26. Glass fibre/polyester interface on FT-Raman spectra with A2 additive.

Due to the broad and intensive absorption peak characteristic of the glass fibre the glass fibre/additive/matrix interface can be studied in a difficult way because the absorption peak of the glass fibre suppressed vibrations derived from other components. The transition layer between the fibre and the matrix could be easily determined in the Raman spectra of the interphones with 1μm


198

Csilla Varga

resolution. Positions 2 and 3 were the two edges of the interphones, at position 3 the vibrations of the glass fibres dominated but the vibrations of the matrix occurred too although superimposed on the absorption peak of the glass fibre only with very low intensities. At position 2 absorption peaks of the matrix occurred but the peak for the glass fibre at about 1400cm-1 can also be seen. The absorption peaks of the additive could not be exactly determined on none of the spectra because of the applied low concentration of the additive.

POSSIBLE FIBRE/MATRIX INTERACTIONS According to the mechanical properties the strongest fibre/polyester interface was likely to be with additive A2 (Fig. 27). Hydroxyl-groups on the surface established H-bonds with the ester-amide, imide and anhydride groups of the additive and according to FT-IR spectra the free carboxylic-groups of the half ester derivative could make covalent bonds with the OH-groups of the surface. As the additive contained unsaturated bonds in addition to the benzene rings, the additive - after connecting to the fibre surface - could take part in the crosslinking reactions during the composite processing. In case of additive A4 containing ester-amide, imide and anhydride rings much weaker mechanical properties were measured related to the reference. Comparing the FT-IR spectra (untreated fibre/additive treated fibre/additive) (Fig. 24.) no significant differences were observed compared to the other additives so vibrations characteristic of new groups did not appear in the spectrum of the additive treated fibre with respect to the spectrum of the additive. But it is important from the point of view of interfacial interactions that no dicarboxylic-acid-half-ester groups could be substantially detected which might have established more H-bonds and chemical bonds with the OHgroups at the glass fibre surface (Fig. 28). So the deterioration of the mechanical properties could only indirectly be attributed to the shortening of the carbon chain length of the alcohol reagent. In case of additive A5 the free carboxylic-groups were likely to establish H-bonds with the glass fibre surface too, which can be responsible enough for achieving better mechanical properties than with additive A4 (Fig. 29). In additive A4 no dicarboxylic-acid-half-ester derivatives were observed, however, with additive A5 the effectiveness of additive A2 could not be achieved because no chemical bonds were established with the glass fibre surface.


O

O

O

HO

O

O

O O

O O

O

O

H2C

O

O O

H2C

CH2

CH2

CH

CH

CH2

CH

CH3

NH CH2 CH3

O

O a

CH2

O

l

m

CH

CH2

CH

CH2 O

O

CH3

CH2

k

CH2

CH

O

O

O

R2 b

CH3

CH2

CH2

O

O

O

CH3

R2 b

n

Si

OH

HO

Si

HO

OH

Si

d

CH2

CH2

CH3 a p

CH3

OH

OH HO

s CH2

O

N CH2

o

OH

HO

O H2C

H2C

CH3

R1

H

O

OH

HO

Si

OH

HO

Si

OH

glass fibre H-bonds

(R1: alkyl-chain with carbon numbers of the olefin monomer; R2: alkyl-chain with R1-2 carbon numbers; a, b: 3-11; d: alkyl-chain with R1-2 carbon numbers; k: 0, 3-1, l: 2-4; m: 1-2; n: 0, 1-1; o: 2-4; p: 1-3) Figure 27. Possible interface in A2 additive treated glass fibre reinforced polyester composite.


O

O

O

HO

O

O

O O

O O

O

O

H2C

O

O O

H2C

CH2

CH2

CH

CH

CH2

CH

CH3

NH CH2 CH3

O

O a

CH2

O

k

O

O CH3

R2 b

CH3

CH2

CH2

O

O

CH2

CH

CH

CH2

CH O

R2

HO

Si

OH

Si

HO

OH

Si

N CH2

o

CH2

d

CH2

CH2

O CH3 a p

CH3

OH OH

OH HO

s

CH2

O

n

OH

HO

O

m

l

O H2C

H2C

CH3

R1

H

O

OH

HO

Si

OH

HO

Si

OH

glass fibre H-boncds

(R1: alkyl-chain with carbon numbers of the olefin monomer; R2: alkyl-chain with R1-2 carbon numbers; a, b: 3-11; d: alkyl-chain with R1-2 carbon numbers; k: 0,3-1, l: 2-4; m: 1-2; n: 0,1-1; o: 2-4; p:1-3) Figure 28. Possible interface in A4 additive treated glass fibre reinforced polyester composite.


O

O

O

O

O

O O

O

HO

O

O

O

H2C

O

O O

H2C

H

O H2C

H2C

CH3

O

CH3

s R1

CH2

CH2

CH

CH

CH2

CH

O

O NH CH2 CH3

O

O a

CH2

O

k

O mH

OH

HO

HO

Si

OH

HO

Si

HO

OH

Si

CH2

OH

HO

CH2

CH

CH2

H

R2 b

Si

n

CH3

OH

HO

Si

CH2

d

CH2

CH2

O

N CH2

o

OH

O

OH

CH

O

O

CH3

l

CH2

CH

O

O

O

R2 b

CH3

CH2

CH2

CH3 a p

CH3

OH OH

HO

Si

OH

glass fibre H-bonds

(R1: alkyl-chain with carbon numbers of the olefin monomer; R2: alkyl-chain with R1-2 carbon numbers; a, b: 3-11; d: alkyl-chain with R1-2 carbon numbers; k: 0,3-1, l: 2-4; m: 1-2; n: 0,1-1; o: 2-4; p:1-3) Figure 29. Possible interface in A5 additive treated glass fibre reinforced polyester composite.


O

O

O

O

O

O O O

HO

CH3

OH

O

CH3

OH

O

O

O

CH3

OH

O

O

O

O O OH

CH3

O

O CH3

O

O

O

OH

H2C

CH3

CH3

R1

CH2

CH2

CH

CH

CH2

CH

NH CH2 CH3

O

O a

CH2

O

CH3

l

m

CH

CH2

CH

CH2 O

O CH2

k

CH2

CH

O

O

O

R2 b

CH3

CH2

CH2

O

O

O

CH3

R2 b

n

Si

OH

HO

Si

HO

OH

Si

d

CH2

CH2

CH3 a p

CH3

OH

OH HO

CH2

O

N CH2

o

OH

HO

p

OH

CH3

H2C

H

O

O

OH

HO

Si

OH

HO

Si

OH

glass fibre H-bonds

(R1: alkyl-chain with carbon numbers of the olefin monomer; R2: alkyl-chain with R1-2 carbon numbers; a, b: 3-11; d: alkyl-chain with R1-2 carbon numbers; k: 0,3-1, l: 2-4; m: 1-2; n: 0,1-1; o: 2-4; p:1-3) Figure 30. Possible interface in A2 additive treated glass fibre reinforced vinyl ester composite.



203

The differences among the effectiveness of the additives could be caused by the different characteristics and strengths of the additive/fibre interactions in the composites laminated with the same polyester matrix. Therefore, the ratio of different functional groups in the structure of the additives plays a significant role and the ratio of the apolar/polar groups of the derivatives also influences the mechanical properties of the final product in function of the strength of the established interface. Additive/matrix interactions have also a significant effect on the properties of the interfaces and not only the connection of the additive to the fibres plays an important role. As the same additive treated glass fibres were applied in the two, polyester and vinyl ester resins, the fibre/additive interaction should be the same or similar in composites containing the same additive treated fibre. The differences in the solubility of the additive in the resin and the connection of the additive to the fibre surface became key points for improving the mechanical properties. The additive could establish chemical bonds with the polyester resin due to the unsaturated double bonds in the additive, because it could partake in the polymerisation creating a cross-linked structure. In case of vinyl ester (Fig. 28) the double bond in the additive may be built in the crosslinked structure but the monomer was also polar enough for the good connection to the glass fibres and the additive treatment reduced the polarity of the surface pushing the monomer off from the glass fibre surface, thus deteriorating the mechanical properties of the composites.

CONCLUSION Usually, the quality of a fibre reinforced composite depends considerably on the fibre/matrix interface because only a well formed interface allows stress transfer from the matrix to the fibres. Therefore, the good interfacial interactions between the matrix and the fibres are essential to improve the mechanical strength of a composite. The forming, investigation and characterisation of the fibre/matrix interaction are complicated questions. The type of the interaction influences lots of properties, mechanical characteristics but the mechanical properties of the components, but they are affected also by the fibre length and the fibre content. The behaviour of the composite will be also affected by the type of stresses during its use through the fibre/matrix interaction. According to the experimental results of this chapter the followings could be stated:


204

Csilla Varga 











The experimental additive will be effective if unsized glass fibres are used; in case of silane sized glass fibres the interaction will be deteriorated. The ratio of the different functional groups in the structure of the additives plays a significant role and the apolar/polar groups of the derivatives also influence the mechanical properties of the final product depending on the strength of the interphase formed. Not only the structural properties and the relative ratio of the functional groups derived from the maleic-anhydride rings influenced the effects of the additives but also the length of the polymer chain of the additive. As the fibre contents of the composites were 63.5±1.2% and the elementary composition of the glass fibres (chopped fibre mat and woven [0/90°] fabric) did not differ significantly only the type of fabrication the improvement in the mechanical strengths could be attributed to the smoother additive sizing on the more even fibre structure in the woven [0/90°] fabric reinforcement. In case of vinyl ester composites the monomer of the resin was also polar enough for the good connection to the glass fibres and the additive treatment reduced the polarity of the surface pushing the monomer off from the glass fibre surface, thus deteriorating the mechanical properties of the composites. Application of additives produced from the industrial scale terpolymer deteriorated the fibre/matrix interaction so the styrene content of the coupling agents is a crucial factor but weathering can have positive effect on the mechanical properties of the composites.

ACKNOWLEDGMENTS The research was funded by the Baross Gábor Program (OMFB694/2007), TÁMOP-4.2.1/B-09/1/KONV-2010-0003 and TÁMOP-4.2.2.A11/1/KONV/2012-0071 projects (financial support by the Hungarian State and the European Union) whose support the author gratefully acknowledges. The author is grateful to the Institute of Chemical Engineering Cooperative Research Centre of the University of Pannonia for the financial support received for this work. The author is also grateful for her supervisor Prof. L. Bartha and for Prof. Gy. Deák for their professional help and advice.



205

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Wambua, P.; Ivens, J.; Verpoest I. Compos Sci Technol 2003, 63, 12591264. Varelidis, P.C.; Kominos, N.P.; Papaspyrides, C.D. Compos Part A 1998, 29, 1489-1499. Aziz, S.H.; Ansell, M.P.; Clarke, S.J.; Panteny, S.R. Compos Sci Technol 2005, 65, 525–535. Varga, Cs.; Miskolczi, N.; Bartha, L.; Lipóczi, G.; Falussy, L. Hungarian Journal of Industrial Chemistry 2008, 36, 137-142. Varga, Cs.; Miskolczi, N.; Bartha, L.; Lipóczi, G. Mater Design 2010, 31, 185-193. Varga, Cs.; Miskolczi, N.; Szakács, H.; Lipóczi, G. Mater Design 2011, 32, 12-20. Czél, Gy.; Kollár M. Anyagvizsgálati Praktikum, Sunplant Kiadó, Miskolc, 2008. Varga, Cs. PhD Theses, University of Pannonia, Veszprém, 2010. Elias, H-G. An introduction to Plastics; 2nd edition; Wiley-VCH; Weinheim, 2003. Pritchard, G. Plastics Additives An A-Z Reference; 2nd edition; Chapman & Hall, London, 2006. Soutis, C. Mater Sci Eng A 2005, 412, 171–176. Abdelmouleh, M.; Boufi, S.; Belgacem, M.N.; Dufresne, A. Compos Sci Technol 2007, 67, 1627-1639. Herrera-Franco, P.J.; Valadez-González, A. Compos Part A 2004, 35, 339-345. Ganster, J.; Fink, H-P.; Pinnow, M. Compos Part A 2006, 37, 17961804. Dányádi, L. PhD Theses, Budapest University of Technology and Economics, Budapest, 2009. Shah, V. Handbook of plastics testing and failure analysis; 3rd edition; Wiley & Sons, Hoboken, 2007.



INDEX # 21st century, 42

A ABA, 38 absorption spectra, 116, 129 acetone, 21, 22 acid, x, 5, 14, 16, 17, 35, 42, 44, 53, 63, 67, 68, 69, 71, 75, 78, 79, 80, 81, 109, 110, 112, 115, 116, 129, 165, 167, 171, 197, 198 acidic, 11 acidity, 74 acrylate, 82 acrylic acid, 17, 43, 45 activation energy, 120, 125, 127, 128 additives, x, xi, 161, 162, 163, 164, 167, 169, 170, 171, 172, 174, 175, 176, 181, 182, 184, 185, 189, 195, 198, 203, 204 adhesion, 19, 186 adsorption, 19, 29, 34, 60, 65, 172, 173 aerospace, 84 age, viii, 55, 95 agglomerate, viii, 56 aggregation, 24, 25, 27 agriculture, 97 alanine, 68 alcohols, xi, 81, 162

algae, ix, 93, 94, 95, 103, 106 Alginite, ix, 93, 94, 95, 97, 105, 108 alkylation, 64 alternative treatments, 35 alters, 35 amine(s), xi, 8, 64, 110, 162, 167, 173, 176, 180, 182, 183 amino, 11, 17, 43, 68, 77, 79 amino acid(s), 11, 17, 43, 68, 77, 79 ammonia, 64, 97, 129, 131, 136 ammonium, 63, 67, 76, 77, 78, 79, 115 amplitude, 26 anhydride ring, 168, 169, 171, 172, 175, 198, 204 aniline, 126 anisotropy, 114, 116, 118, 120, 121, 122, 138 antibody, 28, 31, 32, 51 anticancer drug, 14, 18, 41 antigen, 43 antigen-presenting cell, 43 antioxidant, 97, 105, 106 antitumor, 12, 29 apoptosis, 42 aqueous humor, 9 aqueous solutions, 79 aqueous suspension, 48 Argentina, 1, 55, 74 aspartate, 40 aspiration, 18 assets, 24


208

Index

asymmetry, 116, 132, 133, 138 atmosphere, viii, 66, 83, 84, 128, 137, 138, 148, 149 atomic force, 47 atoms, 110 attachment, 27, 29, 34 Austria, 108

B bacteria, ix, 94, 103, 107 band gap, 124 base, 110, 111, 112 behaviors, 16 bending, 88, 90, 92 benzene, 198 bi-dimensional, viii, 55 bioavailability, 5, 9, 11, 29, 47 biocompatibility, 11, 16, 17, 19, 57, 68, 69 biodegradability, 16, 17, 57, 68, 69 biodegradation, 9, 35, 53 biodistribution, viii, 2, 3, 5, 18, 29, 40, 49, 51 biological behavior, 47 biological fluids, 8 biological media, 19 biological systems, 17 biomedical applications, 10, 13, 14, 35, 39, 43 biomolecules, 17, 68 biopolymers, 69 bisphenol, 165 blends, 22 blood, 11, 15, 17, 24, 27, 28, 29, 30, 32, 47, 51 blood circulation, 11, 15, 28, 29 blood vessels, 30, 32, 51 blood-brain barrier, 17 bloodstream, 12, 27, 29 Boltzmann constant, 122 bonding, 70, 88, 112 bonds, 72, 175, 186, 197, 198 bone, 11, 40, 165 brain, 7, 9, 38, 44, 47 brain cancer, 7, 38

brain tumor, 7 breast cancer, 14, 31 brittleness, 56 Brownian motion, 26 butadiene, 73

C calcitonin, 9 calcium, 56, 96 calcium carbonate, 56, 96 caldera of the volcano, ix, 94 camphorsulfonic, x, 109 cancer, 12, 13, 31, 32, 35, 36, 40, 41, 42, 44, 50, 51 cancer cells, 32, 42 candidates, 6, 84 capillary, 32 carbamazepine, 23 carbon, 15, 25, 53, 56, 110, 163, 167, 168, 170, 173, 175, 179, 180, 182, 198, 199, 200, 201, 202 carbon dioxide, 53 carbon nanotubes, 15 carboxyl, 8, 67 carboxylic groups, 171 case studies, 42 catalysis, 75 catalyst, 81 catalytic activity, 80 catalytic properties, 63, 74 cation, 60, 64, 65, 66, 67, 71, 76, 80, 110 cationic surfactants, 64, 76, 78, 81 CEC, 63, 64, 66, 78, 82 cell culture, 25 cell surface, 28, 32 Central Europe, 107 central nervous system, 42 central octahedral layer, viii, 55 ceramic, vii, viii, 83, 84, 85, 86, 88, 89, 90, 91 ceramic lubricating materials, vii, ix, 84, 85, 86 ceramic materials, ix, 84, 85, 89 chain transfer, 74, 77, 81


209

Index challenges, viii, 43, 83, 84 charge density, 66 chemical, viii, x, xi, 2, 8, 15, 56, 59, 63, 67, 68, 70, 74, 75, 82, 94, 96, 97, 98, 106, 107, 115, 162, 163, 164, 165, 168, 171, 178, 197, 198, 203 chemical bonds, 67, 70, 198, 203 chemical characteristics, 94 chemical properties, 74, 97, 165 chemical reactions, 8 chemotherapy, 14, 50, 51 China, 59, 83, 91 chitosan, 8, 11, 18, 29, 37, 38, 42, 44, 45, 48, 50 cholesterol, 8 chromatography, 107 circulation, 18, 26, 29, 50 clay minerals, 41, 57, 58, 61, 62, 63, 65, 70, 76, 81, 95, 96, 103 cleavage, 35 climate, 96 clinical application, 32, 36 clinical trials, 12 clusters, 111, 113, 114, 124, 142, 144 coatings, 50, 74, 76 cobalt, 164 coenzyme, 47 coherence, 143 colon, 18, 44 colorectal cancer, 31 commercial, 9, 16, 26, 165, 166, 192 compatibility, viii, 56, 62, 66, 70, 185 complement, 49, 100 complex interactions, 36 complexity, 113 compliance, 5 composites, vii, x, xi, 14, 36, 41, 57, 60, 79, 82, 84, 85, 86, 88, 89, 90, 91, 161, 162, 163, 164, 165, 166, 167, 173, 174, 175, 176, 178, 179, 180, 181, 182, 183, 184, 185, 189, 192, 197, 203, 204 composition, vii, x, 19, 24, 51, 63, 73, 79, 88, 94, 95, 96, 97, 98, 99, 100, 103, 106, 109, 163, 164, 165, 182, 184, 204 compounds, 17, 43, 63, 78, 81, 151

conception, 114 condensation, 70, 72, 73, 166 conduction, 149 conductivity, 57, 111, 112, 113, 115, 122, 123, 124, 125, 126, 131, 132, 133, 136, 140, 141, 142, 144, 145, 146, 147, 148, 149, 150, 151 conductor, 110 conjugation, 34, 110 construction, 4 containers, 28 contamination, 22 contradiction, 148 convergence, 40 cooling, 134 copolymer(s), 5, 12, 15, 16, 17, 19, 36, 38, 40, 41, 43 copper, 76 correlation(s), 47, 97, 112, 120, 128, 152 corrosion, viii, 83, 85 corrosion resistance, viii, 83, 85 cosmetics, 2, 9 cost, x, 15, 56, 59, 161, 163 covalent bond, 63, 70, 198 covering, 172 crystalline, viii, 34, 51, 53, 55, 58, 110, 116, 134, 136, 142, 145, 147, 149, 150, 151 crystallinity, 34, 35, 111, 112, 148 crystallites, 110, 147 crystallization, 150 crystals, 96, 119, 152 CSA, 112, 113, 115, 131, 132, 133, 134, 135, 136, 138, 140, 145, 147, 149, 151 cultivation, 97 curcumin, 42, 44, 47 cure, 66 cyclooxygenase, 42 cytokines, 8 cytoplasm, 30 cytotoxicity, 7, 11, 16, 38

D decay, 123, 124 decomposition, 68


210

Index

deduction, 112 defects, 25 degradation, 4, 9, 15, 17, 22, 32, 33, 34, 35, 36, 52, 53, 66 degradation mechanism, 35, 67 degradation process, 34 degradation rate, 34 degree of crystallinity, 112 dehydration, 80 deposition, 21, 25, 46, 89 deposits, 59, 95, 97, 108 derivatives, 45, 143, 167, 171, 172, 176, 198, 203, 204 dermatology, 9, 43 desorption, 34, 35, 48 diatom frustule, 96 dielectric constant, 113 diffraction, 143 diffusion, 8, 17, 22, 34, 35, 44, 45, 46, 47, 110, 114, 115, 118, 120, 121, 122, 125, 126, 127, 128, 132, 139, 149, 150 diffusion process, 46 diffusion rates, 122 digestion, 6, 38 dimensionality, 122, 125, 151, 152 diseases, 3, 35 disorder, 112, 142, 143, 151 dispersion, viii, 6, 34, 55, 57, 61, 62, 64, 69, 76, 94, 98, 118, 119, 120, 132, 140, 144 displacement, 21, 46 disposition, 42 distilled water, 99 distribution, 18, 22, 23, 26, 31, 32, 60, 62, 88, 90, 113 diversity, 57 DNA, 9, 39 docetaxel, 7, 38 DOI, 107 dopants, 151 doping, 110, 112, 113, 114, 116, 118, 119, 121, 122, 125, 128, 129, 130, 131, 134, 135, 140, 141, 142, 148, 150, 151 dosage, 15 double bonds, 203 drug carriers, vii, 2, 30, 37, 38, 40, 42, 45

drug delivery, vii, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 19, 23, 26, 27, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 46, 48, 50, 51, 53 drug efflux, 32 drug interaction, 40 drug release, viii, 2, 3, 5, 6, 8, 11, 13, 14, 15, 33, 34, 35, 41, 43, 53, 74 drugs, vii, 1, 2, 3, 4, 8, 9, 11, 12, 13, 15, 17, 18, 20, 22, 26, 27, 29, 35, 40, 41, 50, 51 dry matter, 96 drying, 20, 21, 22, 23, 47, 48, 165 DSC, 24 dynamic viscosity, 164

E ecological raw material, ix, 94 elaboration, 77 elastic deformation, 173 election, 3 electric field, 113 electrical conductivity, 148 electrolyte, 21 electron, 24, 25, 69, 72, 99, 110, 113, 114, 115, 117, 120, 121, 122, 124, 128, 134, 137, 142, 143, 144, 145, 147, 151 electron microscopy, 25 Electron Paramagnetic Resonance (EPR), vii, x, 13, 29, 30, 31, 50, 51, 109, 113, 114, 115, 116, 118, 125, 128, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 143, 144, 146, 148, 149, 150, 152, 155, 158 electron state, 142, 143, 145 electronic structure, 113 electrons, 25, 111, 128, 150 emission, 122 emulsions, 9, 21 encapsulation, 3, 5, 6, 34, 38, 44 energy, viii, x, 24, 62, 74, 83, 84, 90, 94, 110, 112, 120, 122, 124, 125, 128, 131, 135, 136, 138, 140, 142, 144, 145, 147, 149, 151, 175, 189 energy conservation, 122


211

Index energy transfer, 120 engineering, 69 entrapment, 6, 10, 17, 46 environment(s), 4, 26, 35, 84, 96, 171, 197 enzymes, 68 epithelia, 52 EPR spectra, vii, x, 109, 115, 116, 131, 132, 133, 134, 137, 138, 140, 144, 150 equilibrium, 129, 136 equipment, 22, 23, 84, 97 erosion, 34, 35 ESR, 159 ester, x, xi, 8, 16, 161, 162, 164, 165, 169, 171, 172, 174, 176, 182, 183, 184, 185, 189, 190, 191, 192, 197, 198, 202, 203, 204 ester bonds, 8 ethanol, 22, 71, 99 ethyl acetate, 20 ethylene, 5, 8, 12, 15, 19, 40, 45, 66 ethylene glycol, 5, 8, 12, 15, 19, 40, 45 ethylene oxide, 8, 19, 40, 45 Europe, 59, 97 European Union, 204 evaporation, 20, 21, 22 evidence, 33, 34, 105, 122, 127, 128, 138, 147 experimental condition, 89, 90 exploitation, 107 exposure, 138, 140 expulsion, 8 extraction, 105 extracts, x, 94, 97, 99, 105, 106, 107

F fabrication, 37, 40, 41, 47, 52, 81, 85, 88, 91, 164, 182, 204 fat, 6, 8 fatty acids, 69, 81 feedstock, 22 Fermi level, 112, 132, 135 ferromagnetic, 111, 148 fibers, 56

field emission scanning electron microscopy, 25 filament, 104 filler surface, 70 fillers, 56, 69, 81 films, 52, 72, 111, 115, 133 filtration, 20, 21 financial, 74, 91, 204 financial support, 74, 91, 204 flammability, 57 flexibility, 15, 25 flora, 107 fluctuations, 26 fluid, 6 foams, 53, 75 folate, 41 folic acid, 32 Food and Drug Administration (FDA), 2, 11, 15, 16, 32 force, 64, 139 formation, 46, 64, 72, 81, 87, 95, 103, 107, 111, 113, 114, 124, 128, 140, 143, 150 fracture toughness, 85, 86, 88, 90 fragments, 31, 32, 96 free radicals, 152 friction, 84, 86, 87, 89, 90 FTIR, 24, 82 fullerene, 111 functionalization, 28, 61

G gastrointestinal tract, 7 gel, 166 gel permeation chromatography (GPC), xi, 162, 166 gene therapy, 9 genes, 18 genomics, 4 geological periods, ix, 93 Germany, 72 glass fibre, vii, x, 161, 162, 163, 164, 165, 167, 172, 173, 174, 175, 176, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187,


212

Index

188, 189, 190, 191, 192, 195, 197, 198, 199, 200, 201, 202, 203, 204 glass fibre reinforced polyester, vii, x, 161, 163, 175, 176, 178, 179, 180, 181, 184, 186, 187, 188, 189, 199, 200, 201 glass transition, 34 glass transition temperature, 34 glioblastoma, 51 glioma, 30 glucocorticoids, 40 glycol, 7 good behavior, 12 grain boundaries, 85 grain size, 86 graph, 185 graphite, 86, 91 Greece, 108 green alga, ix, 94, 95 growth, 29, 31, 117, 122, 151 growth factor, 31 guidance, ix, 84, 85

H hair, 43 hair follicle, 43 half-life, 8, 29 hardness, 84 harmful effects, 28 hemoglobin, 29, 50 heptane, 73 heterogeneous systems, 163 hexane, 22 HHS, 153, 155, 158 high strength, 88 homogeneity, 34, 60, 112 host, 70 human, viii, 2, 4, 11, 27, 31, 32, 36, 51, 69 human body, 4, 11 human existence, 4 human health, 69 humidity, 166 humus, 96 Hungary, 95, 96, 100, 107 Hunter, 37, 49, 76, 82

hybrid, 8, 14, 61, 72, 81 hydrocarbons, 105 hydrogels, 39, 41 hydrogen, 72, 112 hydrolysis, 16, 70 hydrophilic, viii, 8, 11, 12, 17, 18, 28, 35, 50, 56, 62, 64 hydrophilicity, 21, 24, 34 hydrophobicity, 21, 34, 35, 73 hydroxyl, 8, 70 hydroxyl groups, 70 hygiene, 97 hyperfine interaction, 117 hyperthermia, 11

I ideal, 4, 15 identification, 152 image, 25 immobilization, 70 immune response, 27 impact strength, 166, 176, 179, 180, 181, 182, 185 impregnation, xi, 162, 173 improvements, viii, 55, 56, 57, 61, 182 impurities, 63, 123 in vitro, 6, 7, 29, 38, 39, 45, 46, 47, 52 in vivo, 11, 17, 18, 28, 29, 39, 43, 48, 51, 52 industry, 13, 22 inflammation, 49 ingredients, vii, 2, 3, 5, 30 inhibition, 42, 99, 105 inhomogeneity, 113 inorganic clays, vii, viii, 56 insulin, 9 integration, 85, 88, 89, 90 integrity, 6, 38 interface, xi, 35, 64, 162, 164, 174, 180, 197, 198, 199, 200, 201, 202, 203 internalization, 29, 33, 36 interphase, 166, 204 ions, viii, 55, 56, 58, 139 IR spectra, 169, 171, 177, 194, 196, 198 IR spectroscopy, 167, 169, 192


213

Index iron, 11, 63 irradiation, 166 isoleucine, 68 issues, ix, 3, 8, 26, 30, 31, 93

J Japan, 72

K kinetics, 15 KOH, 167, 171 Krebs cycle, 16

L lactic acid, 5, 12, 16, 52 lakes, 95, 107 layered architecture, 10 layered double hydroxides, 41 leaching, 70 lead, vii, 1, 5, 28, 31, 32, 110, 115, 129, 138, 151 leakage, 6 leucine, 68 ligand, 12, 31, 32 light, 15, 25, 49, 166, 184 light scattering, 15, 25, 49 linear dependence, 136 lipids, 6, 9, 15 liposomes, 2, 4, 6, 7, 9, 36, 38, 39 liquid chromatography, 94 liquid phase, 46, 75 liver, 27, 29, 50 livestock, 97 localization, 127, 142, 147, 149, 151 low density, viii, 83, 85 low temperatures, 136, 144, 147 lubricants, 85, 88 lubricating technology, ix, 83 lung cancer, 31 lung disease, 45 lying, 67, 125, 140

lymph, 18 lysine, 45, 80

M machinery, 84 macro components, ix, 94, 95 macromolecular systems, 10 macromolecules, 30, 45, 49, 52, 152 macrophages, 27, 33, 50 magnesium, 21, 96 magnetic field, 11, 118, 121, 128, 135, 139, 150 magnetic properties, 11 magnetic resonance, 11, 114, 115, 136, 152 magnetic resonance imaging (MRI), 11, 40 magnitude, 111, 145, 148, 150 manufacturing, 19 masking, 28 mass, x, 30, 64, 66, 69, 71, 88, 94, 99, 100, 112, 124, 131, 137, 173 materials, vii, viii, ix, 2, 11, 14, 15, 25, 26, 27, 36, 43, 56, 57, 61, 63, 69, 74, 77, 78, 83, 84, 85, 88, 89, 90, 94, 95, 111, 162, 163, 166, 167 materials science, 69 matrix, viii, x, xi, 5, 8, 14, 34, 35, 55, 62, 64, 67, 70, 72, 76, 83, 85, 110, 124, 148, 161, 162, 164, 166, 173, 175, 176, 179, 180, 185, 190, 197, 203, 204 matter, 24 measurement(s), xi, 26, 112, 152, 162 mechanical properties, x, xi, 52, 61, 72, 85, 88, 90, 161, 162, 163, 164, 167, 173, 174, 176, 178, 179, 180, 181, 182, 184, 185, 198, 203, 204 media, viii, 6, 12, 25, 34, 83, 84 medical, 2, 53 medicine, vii, 2, 3, 11, 36, 40 melt, 34, 62, 66, 76, 82 metabolized, 16 metal oxides, 25 metals, vii, 25, 111, 120, 145, 147, 151 metastatic cancer, 47 meter, 2


214

Index

methacrylic acid, 43 methanol, 99 methyl methacrylate, 43 methylene chloride, 22 mice, 18, 43 microelectronics, viii, 83, 84 microemulsion, 9 micrometer, 56 microorganism(s), 16, 103, 100, 106 microparticles, 16, 18, 32, 52, 53 microscope, 2, 96, 99 microscopy, x, 25, 47, 48, 69 microspheres, 45, 46, 48, 52, 53 microstructure, 25, 72, 85, 88, 97 military, x, 161, 163 mineralization, x, 94, 108 Miocene, 95, 96 misunderstanding, 2 models, 48, 82, 142, 149 modifications, 57, 67, 74, 79 modulus, 62, 162, 165, 173 moisture, 22, 97 molar ratios, 167, 176 mole, 130 molecular dynamics, 152 molecular weight, 19, 34, 35, 45, 66, 166, 167, 171 molecular weight distribution, 34 molecules, 2, 4, 5, 8, 11, 19, 28, 31, 32, 34, 44, 49, 57, 59, 63, 64, 66, 70, 72, 113, 115, 116, 137, 139 molybdenum, 86 monolayer, 72, 73 monomers, 16, 19, 70 morphology, 23, 25, 63, 77, 80, 99, 112, 185 Moscow, 109, 155, 157, 158 Moses, 153, 154 mucus, 17, 43, 45

N nanocomposites, 14, 56, 57, 58, 60, 61, 62, 66, 67, 69, 70, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 85, 86, 88, 89, 91, 92, 162

nanocrystals, 25 nanodevices, vii, 1, 5, 7, 8, 11, 31 nanomaterials, 2, 25, 61 nanomedicine, 3, 12, 27, 36, 42 nanometer(s), 2, 4, 12, 56 nanometer scale, 4 nanometric scale particles, viii, 55 nanoparticles, vii, viii, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 27, 28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 55, 61, 82 nanosystems, 11, 42 nanotechnology, viii, 2, 3, 5, 51, 55 National Academy of Sciences, 51 National Research Council, 74 natural polymers, 5, 8 natural resources, ix, 93 Navajo Nation, 108 neutral, 18, 24, 29, 110, 118, 122, 123, 152 nitrogen, 96, 110, 117, 128, 137, 138, 139, 140, 148, 149 nitroxide, 117, 139 nitroxide radicals, 117, 139 nonequilibrium, 78 non-Hodgkin‘s lymphoma, 31 non-ore potential, ix, 93 North Africa, 59 Nuclear Magnetic Resonance (NMR), 82, 114, 131, 132, 134 nucleus, 117 nutrient(s), ix, 30, 94, 95, 96, 97, 108 nutrition, 8, 107

O obstacles, 6, 30 OH-groups, 192, 198 oil, 6, 8, 20, 107, 108 oleic acid, 48 oligomers, 73 oligotrophic conditions, 96 one dimension, 56 opacity, 56 optimization, 42, 74, 91, 92


Index orbit, 110, 117 organ(s), 11, 28, 66, 67, 76, 79 organic compounds, 62 organic matter, ix, x, 63, 93, 94, 96, 103, 108 organic solvents, 21, 73 organism, vii, 1, 4, 27, 31, 36 organize, 58 organophilic, viii, 56 oscillation, 96 overlap, 114 oxidation, x, 84, 109, 110, 113, 115, 120, 136 oxygen, viii, ix, 30, 50, 55, 56, 57, 58, 94, 115, 137, 139, 140, 149

P PAA, 17 paclitaxel, 29, 37, 51 PAN, 133 parallel, 72, 88, 113, 123, 146, 150 paramagnetic centers, x, 109, 113, 116, 136, 146 partition, vii, 1 pathophysiological, 30 peptide(s), 18, 28, 31, 39, 68 perchlorate, 129 percolation, 125, 140, 142, 151 permeability, 13, 29, 30, 31, 38, 50, 51, 57, 133 permeation, 17 PET, 77 phagocytic cells, 27, 33 phagocytosis, 27, 34, 45, 49 pharmaceutical(s), vii, 2, 13, 22, 24, 30, 47, 48, 50, 69 pharmaceutics, 3 pharmacokinetics, 49 pharmacological treatment, 9 phase transformation, 88 PHB, 16 phenol, 62 phenolic compounds, 105 phenylalanine, 68

215

phonons, 119, 122, 123, 124, 136, 142, 144, 145, 146, 147, 150, 151, 152 phosphate, 96, 99, 105 phospholipids, 38 phosphorous, 67, 96 photoelectron spectroscopy, 24 physical interaction, 8 physical properties, vii, 1 physicochemical properties, 3, 38, 73, 80 phytotoxicity, ix, 94 pigmentation, 105 pigs, 52 Planck constant, 121 plants, 97 plastics, 163, 205 platelets, 61, 64, 68, 70, 73, 77, 78 platform, 11, 17 playing, 162 PMMA, 16, 17, 43, 79 polar, 203, 204 polar groups, 203, 204 polarity, 6, 39, 73, 117, 172, 203, 204 polarons with different mobility, vii, x, 109 pollen, 96 poly(3-hydroxybutyrate), 16 polyalkenyl-poly, x, 161, 163, 164, 167, 168, 169, 170, 171, 172 polyamides, 66 polyaniline, x, 109, 110, 112, 115, 129, 143, 152 polybutadiene, 73 polycarbonate, 66 polydispersity, 171 polyesters, 163 polyhydroxyalkanoates, 42, 43 polymer blends, 35, 162 polymer composites, 14, 56, 162 polymer industry, 56 polymer matrix, 34, 59, 60, 61, 62, 64, 124, 134, 140, 149 polymer nanocomposites, 14, 61, 81 polymer properties, 115 polymer synthesis, 112 polymer systems, 110, 148, 152 polymeric composites, 52


216

Index

polymeric materials, viii, 55, 56 polymeric matrices, vii, viii, 55, 56, 59, 70 polymeric micro, vii, viii, 2, 3, 20, 21, 22, 23 polymerization, 19, 62, 64, 69, 76, 78, 81, 115 polymers, vii, viii, 1, 3, 5, 10, 11, 12, 13, 14, 15, 16, 17, 19, 21, 28, 35, 42, 56, 62, 66, 70, 109, 110, 113, 115, 116, 118, 119, 120, 124, 125, 132, 134, 138, 140, 144, 145, 147, 149, 150, 151, 152, 163 polypeptide, 25 polypropylene, 82 polysaccharide, 18 polystyrene, 75, 81, 82, 166 polyurethane(s), 53, 62, 69 polyurethane foam, 69 porosity, 73, 80 Portugal, 79 potassium, 96 precipitation, 21, 107 preparation, ix, 3, 17, 18, 21, 25, 38, 45, 46, 52, 58, 59, 62, 66, 69, 74, 75, 76, 81, 84, 91 preservation, 96 prevention, 28 price/value ratio, x, 162 probability, 32, 119, 122, 123, 126 producers, x, 162, 164 production costs, 74 production technology, 176 proliferation, ix, 94, 95 proportionality, 117 protection, 9, 16, 108 proteins, 8, 18, 27, 28, 31, 32, 39, 44, 68 proteolytic enzyme, 17 proteomics, 4 protons, 57, 64, 114, 147 pulmonary diseases, 43 purification, 63 purity, 66, 148 PVA, 18, 20, 21, 44 pyrolysis, 96

Q quality of life, 26 quartz, 63, 96 quaternary ammonium, 63, 78

R radiation, 166 radical polymerization, 77 radicals, 114, 118, 120, 136, 152 radius, 26, 123, 138, 149, 150 Raman spectra, 197 raw material supplies, ix, 93 raw materials, 88, 162, 163 reaction temperature, 72 reactions, 62, 67, 70, 71, 167, 169, 198 reactive sites, 71 reactivity, 70, 171 reagents, 167, 171, 172, 173, 176, 180 receptors, 18 recognition, 18, 28 refractive index, 166 reinforcement, 164, 173, 180, 181, 204 relaxation, vii, x, 109, 113, 114, 115, 118, 119, 120, 122, 125, 128, 132, 134, 136, 144, 149, 152 relaxation properties, 152 relaxation rate, 144 relaxation times, 118, 119, 120, 149 reliability, ix, 84, 85 remediation, 79 requirements, 4, 12, 22, 84, 162, 163 RES, 28 researchers, vii, 1, 2, 4, 7, 8, 11, 31, 33, 35, 84 resins, 62, 165, 203 resistance, viii, 35, 44, 83, 84, 85, 163, 175, 178, 180, 181 resolution, 25, 114, 152, 166, 198 resources, 16, 68 respiration, 97 response, 4, 6, 97 rheumatoid arthritis, 31


Index ribonucleotide reductase, 51 rings, 110, 171, 176, 198 risks, 5 room temperature, 21, 70, 71, 86, 99, 111, 113, 114, 116, 118, 122, 145, 149 routes, 9, 16, 62 Russia, 59, 93

S safety, x, 30, 51, 94 salinity, 96 salts, 57, 64, 66, 67, 69, 74, 77, 78, 81 saturation, 78, 125, 140, 149 SAXS, 61 scanning electron microscopy, x, 25, 94, 99 scattering, 26, 122, 123, 124, 142, 146, 150, 151 scattering intensity, 26 science, vii, 3, 4, 32, 36 sedimentary process, ix, 94 sedimentation, 63, 108 sediments, 107 selectivity, 24, 26, 31 self-assembly, 36 SEM micrographs, xi, 162 semiconductor, 110, 122 sensitivity, 24 sensors, 74 serum, 27, 48 serum albumin, 48 shape, 3, 22, 24, 25, 33, 51, 52, 60, 120, 132, 144 shear, 66, 84 shock, 85 showing, 36 side effects, vii, 1, 3, 6, 8, 9, 14, 26 silane, x, 70, 71, 72, 73, 77, 80, 162, 164, 177, 178, 179, 204 silanol groups, 195, 197 silica, viii, 17, 19, 45, 52, 55, 56, 58, 82 silicon, 99 simulation, 166 single chain, 143 sintering, 86, 90

217

siRNA, 51 skeleton, viii, 10, 83, 85 skin, 9, 39, 43, 49, 132, 138, 140, 150 Slovakia, 93, 95, 96, 100, 107, 108 sodium, 68, 69, 71, 72, 73, 77, 99 software, 166 solid matrix, 19 solid phase, 76 solid surfaces, 19 solid tumors, 29, 30 solubility, vii, 1, 3, 5, 8, 15, 18, 19, 21, 39, 203 solution, 20, 21, 22, 47, 62, 64, 68, 69, 75, 77, 99, 115, 165, 173 solvents, 21, 22, 73 sorption, 107 South America, 59 species, 63 spectral component, 118 spectrophotometric method, 76 spectroscopy, 24, 47, 114 spin, 109, 110, 113, 114, 115, 117, 118, 119, 120, 121, 122, 123, 125, 126, 127, 128, 129, 131, 132, 134, 136, 137, 138, 139, 140, 144, 145, 147, 149, 150, 151, 152 spin dynamics, 114, 121, 122, 147 spleen, 27, 29, 32 stability, 3, 6, 8, 9, 12, 15, 24, 48, 66, 68, 76, 78, 84, 110 stabilization, 28, 45 starch, 16 state, 2, 14, 25, 34, 41, 57, 95, 96, 110, 112, 151 states, 52, 96, 112, 117, 123, 125, 127, 136, 142, 143, 151, 152 sterile, 15 stress, 88, 90, 174, 181, 203 stress-strain curves, 174 stretching, 168, 169 strong interaction, x, 127, 152, 161, 179 structural defects, 70 structure, ix, x, xi, 6, 8, 10, 12, 19, 25, 51, 57, 58, 60, 63, 67, 68, 72, 75, 78, 85, 88, 89, 90, 94, 103, 104, 106, 109, 110, 112,


218

Index

114, 140, 151, 152, 161, 162, 166, 170, 171, 178, 182, 203, 204 styrene, x, 78, 161, 163, 164, 167, 168, 169, 170, 171, 172, 184, 185, 204 substitution, x, 59, 162, 164 substrate, 47 sulfate, 8, 46, 115 sulfur, 107, 137 sulfuric acid, 115, 116 Sun, 45, 52, 157 superparamagnetic, 11, 40 supervisor, 204 surface area, 2, 32, 33, 60, 63, 80 surface chemistry, 11 surface energy, 57, 80 surface modification, 24, 67, 162 surface properties, 24, 63 surface reactions, 24 surface structure, 100 surface treatment, 28, 62 surfactant, 19, 21, 22, 47, 61, 64, 66, 67, 69, 71, 77 susceptibility, 111, 113, 129, 130, 131, 133, 135, 136, 137, 138, 139, 140, 147, 151 swelling, 8, 14, 60, 70, 77, 81 symmetry, 110, 116 synergistic effect, 86 synthesis, x, 5, 38, 39, 40, 56, 62, 75, 109 synthetic polymers, 8

T talc, 58 tamoxifen, 14 target, 3, 4, 8, 11, 15, 16, 25, 28, 31, 49, 61 target organs, 15 taxa, 95 techniques, 20, 24, 25, 37, 60, 76, 78 technologies, 2, 162, 163 technology, viii, ix, 2, 26, 40, 83, 84, 85, 90, 94 TEM, 25, 69, 72 temperature, viii, 12, 19, 20, 22, 26, 64, 66, 72, 83, 84, 85, 86, 87, 90, 91, 113, 116, 117, 119, 120, 121, 122, 123, 124, 125,

126, 127, 129, 134, 135, 136, 139, 140, 142, 144, 145, 147, 149, 150, 166 temperature dependence, 121, 122, 123, 129, 139, 140, 144, 148, 149, 150 tensile strength, 165, 174, 179, 180, 181 testing, 166, 179, 185, 205 tetrahedral layers, viii, 55 texture, 97 therapeutic agents, 4, 8 therapeutic effects, 47 therapeutic goal, 3, 4, 19, 33 therapeutics, 44, 50, 51 therapy, 13, 29, 39, 41, 48, 51 thermal activation, 125, 152 thermal degradation, 67 thermal properties, 44, 67, 79 thermal stability, 57, 61, 63, 66, 69, 80 thermal treatment, 51 thermograms, 68 thermogravimetric analysis (TGA), 24, 66, 68, 82 thermosets, 163 tissue, 9, 13, 16, 38 tissue engineering, 16, 38 toxic side effect, 5 toxicity, 5, 11, 15, 20, 28, 40, 68 Toyota, viii, 55 transferrin, 32, 47 transformation(s), 52, 75, 113 transition rate, 123 transmission, 25, 69 Transmission Electron Microscopy (TEM), 25, 49, 60 transparency, 72 transport, 16, 17, 33, 35, 43, 110, 112, 113, 114, 115, 126, 128, 136, 148, 149, 150, 152 transport processes, 113 treatment, viii, 5, 7, 11, 28, 30, 31, 32, 35, 52, 56, 63, 64, 71, 79, 163, 165, 203, 204 tribology, 84, 85, 86 tuff, 108 tumor(s), 12, 29, 30, 31, 32, 41, 50, 51 tumor cells, 30 tunneling, 149, 152


219

Index

W

U ultrasound, 26, 49 uniform, 22, 89 united, 157 United Kingdom (UK), 72, 157 USA, 37, 42, 59, 68, 71, 164 UV light, 71, 73 UV radiation, 166

V vaccine, 43 vacuum, 133 valence, 125, 152 valine, 68 vancomycin, 38 variables, 19, 66 vasculature, 30, 50 vegetation, 103 vehicles, 5, 31, 34, 41, 84, 162 velocity, 26, 34, 132, 137, 140, 149 versatility, 2, 36 vibration, 168, 169, 171, 195, 197 viral vectors, 9 viscosity, 17, 21, 164 vitamin A, 9 vitamin E, 7, 14

Washington, 45 water, ix, x, xi, 5, 6, 8, 14, 19, 20, 21, 22, 25, 29, 35, 40, 46, 50, 67, 71, 77, 94, 95, 96, 97, 99, 107, 108, 162, 166, 184 water absorption, 14 wave number, 167, 168, 169, 171, 195 WAXS, 61 weak interaction, 175, 179 wear, ix, 84, 85, 86 welfare, 35 workers, 143

X XPS, 24 x-ray diffraction, 82 XRD, 24, 60, 68, 78

Y yield, 19

Z zeolites, ix, 74, 94 zirconia, 91
