Dendrimers: Structure, Synthesis, Properties, and Potential Applications in Oil and Gas industry
Written By Miad Alawad, Mohammed Bataweel, and Aymen Almohsin EXPEC ARC-‐PTT, Saudi Aramco (2015)
Abstract This report summarizes several literatures and patents for Dendrimers. Dendrimers have been used in the medical field such as, releasing the drug delivery, targeting drug delivery, and solubility enhancement drugs. They also could be used potentially for oil field applications such as, sand consolidation, synthetic sweet spot in tight formation, wettability alteration for tight gas, high temperature fracture fluids using sea water, and scale inhibitor.
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Introduction Nanotechnology is very important study now a days, and Nanotechnology uses structures size in ranging in size from 1 nm to 100 nm. One of the Nano agens named Nano Dendrimers, and they can be defined as a family of Nano sized 3D polymer with highly branched architecture that could be monodisersity or macromolecular (Willems et al, 2005). The word Dendrimers derived from Greek word Dendron meaning tree and mores meaning part (Margaret Rouse, 2005) (fig-‐1).
Fig-‐1: shows the definition of Dendrimers in Greek word (Christensen, etal.2006)
Dendrimers have numerous characteristics; for example, both of the architectures and monodisperses are the important .Having the molecular architecture leads to enhance the physiochemical properties for Dendrimer.Also, the generation of Dendrimers can lead to create the shape of Dendrimers moreover, the generation can be a high or low generation, so when the generation is high, the shape of Dendrimers will be spherical.In contrast, when the generation is low, the shape of Dendrimers will be elliptical (Malik et al, 2012).Dendrimers could be found in nature, and they are like monodisperse (Malik et al, 2012). Both size and shape of Dendrimers can be controlled or manipulate(Malik et al ,2012).There are so many patents and publications for Dendrimers in 2005 (fig-‐2).This report will highlight the structure, brief of synthesis, properties, and some of the potential applications of the Dendrimers in petroleum field.
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Fig-‐2: shows the number of publications and patents according to the chemical abstracts citation index (2005).
Terms and Nomenclature in Dendrimer Chemistry Dendrimers can be classified as the following based on their structures. Hyper-‐branched polymers describe the main class of polymers. Dendrigrafts, Dendron, and Dendrimers are monodisperse, and they can be referred as hyper-‐branched polymers (Christensen et al, 2006) (fig-‐3). Dendron is a Dendritic edge without having a core, and Dendrimers can be prepared by consisting of two or more Dendron (Christensen et al, 2006). Frechet –type Dendrons play an important role for both covalent and non-‐covalent assembly of Dendrimers, and Frechet –type Dendrons are the most commercially available (Christensen et al, 2006)(fig-‐3). Generation has so many hyper branching, and the hyper branching will grow from the center until reach the end of the surface point (Christensen et al, 2006).Shell is located between the generation space or focal point, and shell could be outer or inner shells. Outer shells consist of both pincer and functional groups, but inner shells consist of branching inside the Dendrimers (Christensen et al, 2006) (fig-‐3a). Pincer is located on the outer shells; moreover, focal points or generation space can be generated the pincer (Christensen et al, 2006) (fig-‐3a). End groups have so many alternative names; for instance, terminal group, and surface group (Christensen et al, 2006) (fig-‐ 3b).
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Fig -‐3: shows the evolution of polymers towards Dendritic structure (Christensen et al, 2006)
Fig-‐3b: shows the end group or terminal group (Christensen et al ,2006)
Fig-‐3a: shows the pincer and the outer shell (Christensen et al, 2006
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Molecular Structure The molecular structure of Dendrimers consists of either one atom or a group of atoms classified as the core (Choi, 2013) Dendrimers are around shaped, core, interior, and surface the three main parts of Dendrimers (Cheng et al, 2006-‐2007)(Fig 4a &4b.).The Core is located in the center. Many branching can be holed by core; also, molecular and reactive terminal groups must be in the core for many interactions (Cheng et al, 2006-‐2007). The Interior of Dendrimers consists of internal cavitities, generation, shells, and branches. Internal cavities are empty spaces inside Dendrimers and empty spaces can be used for molecular encapsulation or drugs. Genration is a branching point. Shells could be inner or outer shells. Inner shells have many of branches, but outer shells have many of pincer and end group. Branches are very important due to the fact that they can prepare the generation and internal cavities (Cheng et al, 2006-‐ 2007). Surface consists of functional groups and pincers. Physical properties can be determined by functional groups either in solid or in aqueous solutions (Cheng et al, 2006-‐2007). The Generation of Dendrimers can determine the number of functional groups (Cheng et al, 2006-‐ 2007).
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Fig-‐4a & 4b: shows the 3 main parts of Dendrimers (Willems et al,2005).
Synthesis of Dendrimers The way for Synthesis Dendrimers is very important because many sides of the molecular can be controlled (Choi, 2013). Size, shape, surface, flexibility, and topology can be controlled or adjusted (Choi, 2013). Divergent, convergent, and mixed methods are three main parts of the synthesis processes ( Cheng et al,2006-‐2007)( Malik et al,2012).The divergent synthesis of poly (amidoamine) was published in 1984 by Tomalia et al (Cheng et al,2006-‐2007).Divergent method will begin from the core until reaching the surface point ( Cheng et al,2006-‐ 2007).Divergent method is very important when large amounts of Dendrimers are created ( Choi,2013). High generation can be constructed by divergent method ( Cheng et al,2006-‐2007) (fig-‐5).Convergent method is totally different than divergent method due to the fact that synthesis will start from the branching until reach the core ( Choi,2013). Easy purification and characterization and the ability of combing or linking with a branching without a core are the features of the convergent process (Cheng et al,2006-‐2007). Dendrimers can be synthesized widely by using divergent method; in contrast, convergent method is very difficult to use (Cheng et al,2006-‐2007) (fig-‐6).Mixed method can be done by mixing the convergent and divergent methods together ,and mixed method has been used so far (Malik et al,2012).
Fig-‐6 :shows the convergent method (Shogo Hashizume(M2),11.12.6.Tue)
Fig -‐5: shows the divergent method (Shogo Hashizume(M2),11.12.6.Tue)
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Types of Dendrimers
Types of Dendrimers depend on three main components; for example, the composition and structure of the core, the number of functional groups, and the branches. These can show the differences between types of Dendrimers (Institute of Organic Chemistry and Biochemistries, 2005). PAMAM Dendrimer, PPI Dendrimer, Hybrid Dendrimer, Amphiphilic Dendrimer, Frechet-‐ Type Dendrimer, Peptide Dendrimer, and PAMAMOS Dendrimer are some of the important types of Dendrimers. PAMAM Dendrimers (Poly (Amido Amine)) are widely used in so many fields .The other name for PAMAM is starburst(Institute of Organic Chemistry and Biochemistries ,2005).PAMAM Dendrimers can be synthesized by divergent method(Malik et al,2012). Both solubility and reactivity are very high due to the fact they have so many functional groups and internal cavities (Malik et al,2012).Functional groups of PAMAM Dendrimers consist of high amido density (Malik et al,2012).PPI Dendrimers consist of diamino butane with amines in the functional groups, and PPI Dendrimers consist in the interior tertiary propylene amine (Malik et al,2012). Both material science and biology used PPI Dendrimers (Malik et al,2012) .Hypride Dendrimers are a unique type of Dendrimers since these Dendrimers combine characteristic of Dendritic and linear polymer 7. Amphiphilic Dendrimers have two different halves of electrons ,and the different half could be electron donating or electron withdrawing 8.Peptide Dendrimers have amino acid in the interior ,so these Dendrimers can be used for vaccine delivery 9. Frechet –type Dendrimers have carboxylic acid group on the surface 9. PAMAMOS Dendrimers are hydrophilic in the interior and hydrophobic in the exterior 9.
Properties Dendrimers have very unique properties due to having special structures and compositions. Dendrimers properties may lead to find new potential applications in oil and gas fields .Monodispersity,nanoscale Dimensions, solubility ,reactivity ,viscosity, loading capacity (molecular container property ), biocompatibility, effective of PH , effective of ionic strength, covalent conjugation ,polyvalency,self assembling ,electrostatic interaction are very significant properties for Dendrimers . Dendrimers are totally different than liner polymers since Dendrimers have very unique properties that can be called Monodispersity. Monodispersity is one molecular or the same molecular combining with each other to make Dendrimers .Nanoscle Dimension and shapes are one of the Dendrimers properties. Both well organized synthesis and controllable properties can lead to have a nanoscale dimension and shape (Chenget al,2006-‐2007).Solubility and reactivity can be controlled by the functional groups. Dendrimers will be soluble in very high in organic solvent (Yiyun (Barbara Klajnert et al ,2001).Viscosity is low in Dendrimers, but viscosity is high in liner polymers. The relationship between the molecular weight and the intrinsic viscosity is an inverse relationship (fig-‐7), but in
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some cases will act like liner polymers. When the weight increases, the viscosity will increase until reaching very maximum point or maximum generation, so intrinsic viscosity will decline again due to the fact that prohibiting the interaction between outer branches and the molecular.
Fig -‐ 7: shows the relationship between the intrinsic viscosity and weight
Loading capacity (molecular container property) is a very good property for drug delivery (willems et al, 2005). Internal cavities are one of the most important structures in Dendrimers because internal cavities can be used to encapsulate the drug and other molecular inside the empty spaces (willems et al, 2005). Biocompatibility is another property. Dendrimers could be low in toxicity if the end groups are anionic, but Dendrimers could be high in toxicity if the end groups are cationic (willems et al,2005). Dendrimes and the effect of PH are very important properties due to leading to new potential applications. Both PAMAM and PPI were affected by PH. First using PAMAM Dendrimer at a low PH, The charges of both functional groups and interior will be positive, so charges will lead to extend conformation and increase the hollows due to repulsion forces (fig-‐8-‐c)(Christense et al,2006). At a neutral PH, the charges of functional groups will be positive ,but the interior will not see any charges ,so a neutral PH will lead to have back folding ,and decrease the number of hollows ( fig-‐8-‐b)(Christense et al,2006 ). At a high PH, the repulsion forces will reach the minimum( fig-‐a)(Christense,et al.2006) .In contrast, using PPI at a low PH will not see any charges on the functional group ,but positive charges will be in the interior ,so they will lead to repulsion forces inside Dendrimers( Christense et al,2006). At a medium PH,back folding occurs due to the attractive forces ( Christense et al,2006). At a high PH,negative charges of functional groups occur on the surface, but no charges occur in the interior, so the repulsion forces will extend conformation again( Christense et al,2006) ( fig-‐9). PPI Dendrimers and the effect of Ionic strength is totally smeller to PAMAM inPH (fig-‐10). Covalent conjugation is a strategy that it can be used to couple small molecular with Dendrimer’s scaffolds (Elham Abbasi et al, 2014).Polyvalence is very important and useful due to having many sides of functionalization ,and polyvalence can produce many interactions between the guest and functional groups (Elham Abbasi et al ,2014). Self
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assembling is a very interesting part for chemistry, and there are three ways for self assembling. Creating Dendron with core is one way to self assemble, and this way is important due to leading to spontaneous formation (Elham Abbasi et al, 2014). Electrostatic interaction is a property, which depends on the charges on the surface. Not only does a surface have many functional groups, but also a surface may have polyelectrolytes, so attractive or repulsion forces occur (Elham Abbasi et al, 2014).
Fig -‐8: It shows the effect of PH for PAMAM Dendrimers (Christense et al,2006).
(Fig-‐9): It shows the effect of PH for PPI Dendrimers (Christense et al,2006).
(Fig-‐10) shows the effect of ionic strength for PPI (Christense et al, 2006).
Topological Examination of The Functionalization of Dendrimers Hyper branches hold many functional groups. Functional groups can be distributed on the surface, and the location of functional groups plays an important role in Dendrimers (F vogtle et al,2000). Monofunctionalization, Functionalization of Dendritic polyamines, Global Bifunctionalization of Dendrimers,and Bifunctionalization of individual end groups are examples of functional groups, location, and the role (F vogtle et al,2000). Monofunctionalization can be
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referred to as a core, branching, and surface (fig -‐11). When Dendron coats the porphyry core, the core will receive a micro-‐environment (F vogtle et al,2000). Not only does a surface act as a sensor for poisonous sulphur dioxide gases, but also a surface can be used for catalytically active substances (F vogtle et al, 2000).
( Fig -‐11)Location of the functional groups in monofunctionalized Dendrimers (F vogtle,et al.2000).
The Functionalization of Dendritic polyamines is another example for topological examination of the functionalization of dendrimers. When a reaction happens between the functional groups and the reactive groups, the functionalization of dendrimers in the periphery occurs (F vogtle et al, 2000). Periphery has many functional groups that can be converted, so the conver in of functional groups will lead to selecting a reactive segment and ignoring other segments in Dendrimers (F vogtle et al, 2000). Global Bifunctionalization of Dendrimers contain two different types of functional groups (fig-‐12). Functional groups can affect the properties of Dendrimers (F vogtle et al,2000). Some applications need to work with two functional groups since two functional groups will help for developing new applications (F vogtle et al,2000).
Fig-‐12: It shows the Global Bifunctionalization of Dendrimers (F vogtle,et al.2000).
Bifunctionalization of individual end groups is important due to the fact that two functional groups are very close to each other which leads to interacting very easily, and two different functional groups can affect the solution behavior( fig-‐13)(F vogtle et al,2000). Kim et al mentioned the method for Bifunctionalization of individual end groups 12.
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Fig-‐12: It shows the Bifunctionalization of individual end groups (F vogtle et al,2000).
Applications This paragraph will introduce applications for dendrimers. Dendrimers have many different families, and each family has very special properties. Different properties will lead to discover new applications that can help in future. Both current applications and potential applications can be used for Dendrimers in different fields. Current applications for Dendrimers are widely used in medical fields; for instance, vitro diagnostic, contrast agent, delivery of drug, boron neutron capture therapy, drug carriers, and cardiac testing arethe most common applications. Also, current applications can be used in different major .For example, engineering, consumer goods, power, environmental are also current applications (willems et al, 2005). In contrast, potential applications may use in oil ,gas ,and industrial fields.Scale inhibitor,Wettability alteration for tight gas to mitigate condensate banking,Create deep sweet-‐ spot, Sand consolidation, Water remediation,HTHP stability enhancement,Equipment coating,Removal of H2S and CO2,Acid neutralization, and Formation strengthens while drilling are some of potential applications in oil field. Scale inhibitor is one of the most important potential applications since Dendrimers may be used as scale inhibitor. Oil fields use many fluid sources; for instance, seas and ponds are main sources for water. These sources contain ca ion and ions, so cat ion and ions are very easy to combine with each other. When cations and ions combine with each other, they will cause damage in equipments. Dendrimers could be one of the solutions for reducing the damages due to having an excellent performances of disparity and having very high of calcium (pub. No: US 2014-‐0319064 A1. 2014). Synthetic Sweet Spots in Tight Formations by Injection of Nano Encapsulated Reactants is another potential application. Sweet spot is an area within reservoir .A Sweet spot needs for enhancing well productivity by using the Stimulation (massive hydraulic fracturing) method (fig-‐13). Stimulation can be done by injecting the viscous fluid with Dendrimers in certain conditions; for example, High flow rate and High pressure to create a fracture are the conditions. The requirement for this method is producing the low permeability of commercial gas due to near well bore fracture (US20130126175 A1.2013).
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( Fig -‐13 )shows the fracture by Stimulation method
Wettability alteration for tight gases to mitigate condensate banking is very important for studying due to many problems in the oil field.One of the major problems that reduces the productivity of gas is condensate banking. The production of gas is driven by pressure differences between the reservoir and the wellbore. As a result, the gas flows from the high pressured reservoir to the low pressure wellbore. While that gas flows in these conditions, some gas condensated could be dropped in the near-‐wellbore area due to many reasons. Those condensated drops plug the rock borethorats and prevent the gas flow because of its high capillary pressure. That is called condensate banking. Injecting dendrimers in the near wellbore formation can alter the wettability of the rock to break down the surface tension between the condensated droplets and the rock surface in order to reduce the capillary pressure and enhance the productivity of the gas.
Conclusion Dendrimers are a very interesting topic due to the fact that they have very attractive shapes and properties. This report went through definition, terms and Nomenclatures, structure, synthesis, properties, andapplications. Dendrimers could be like a gate to solve many problems in the oil field in the future .Both application and generation can determine the cost for Dendrimers. Nanotechnology plays an important role, so we need to study very deeply in this area.
Acknowledgements I would like thank the two doctors, Mohammed Bataweeland Aymen Almohsin for being cooperative with me in this report To Mohammed Bataweel especially, I would like to thank
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Mohammed Bataweel because he gave me this important topic, and he trusted me to present this topic. I really appreciate all your help during my co-‐op time in Aramco .You have generously shared your expertise and experience with me, and I truly appreciate the support and net working contacts you have given me during the time of my presentation and writing report. I truly appreciate the time you spent to help me. Thank you again Mohammed Bataweel and Aymen Almohsin.
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