Polymer

Copyright © 2014 by American Scientific Publishers All rights reserved. Printed in the United States of America

Reviews in Advanced Sciences and Engineering Vol. 3, pp. 48–65, 2014 (www.aspbs.com/rase)

Electrical Conductivity of Graphene/Polymer Nanocomposites Jizhen Zhang, Jianguo Qiu, and Jingquan Liu∗ School of Chemistry, Chemical and Environmental Engineering; Laboratory of Fiber Materials and Modern Textile, The Growing Base for State Key Laboratory, Qingdao University, Qingdao 266071, China

ABSTRACT Graphene is a promising material for the preparation of graphene/polymer composites with enhanced electrical, mechanical, thermal, and gas barrier properties at extremely low loading ratio due to its unique structure. Not only do the properties of graphene and polymer complement each other, the new properties may also emerge due to the synergistic effect. The conductivity of the graphene/polymer composites can be tuned from 10−17 to 102 S m−1 , which not only depends on the quality of graphene and but also the polymers utilized. This review describes the recent developments that are related to conductive graphene/polymer nanocomposites. Different strategies for the preparation of such nanocomposites are described, including physical processing, covalent bonding and specific affinity. Advantages and disadvantages of each method are also addressed. Moreover, potential applications in the fields of electronic and photonic devices, clean energy, and sensors are also presented. KEYWORDS: Graphene, Graphene Oxide, Conductivity, Graphene/Polymer Composite, Surface Modifications.

CONTENTS 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Preparation of Conductive Graphene/Polymer Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Physical Mixing . . . . . . . . . . . . . . . . . . . . . . 2.2. Covalent Bonding . . . . . . . . . . . . . . . . . . . . . 2.3. Specific Affinity . . . . . . . . . . . . . . . . . . . . . . 3. The Electrical Properties of Graphene/Polymer Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Electrical Percolation Threshold and Conductivity of Graphene/Polymer Composites . . . . . . . . . . . 3.2. Conductivity Influencing Factors . . . . . . . . . . . . 4. Application of Conductive Nanocomposites . . . . . . . . 5. Summary and Outlook . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . References and Notes . . . . . . . . . . . . . . . . . . . . . .

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1. INTRODUCTION Graphene, a one-atom-thick 2-dimensional carbon nanostructure, has evoked enormous interest since its debut in 2004.1–4 Graphene’s unique structure endows it with remarkable characteristics such as the electric field effect,4 5 superlative mechanical strength,6 large specific surface area,7 8 high transparency,9–11 and excellent thermal conductivity.12–14 Based on these extraordinary properties, graphene already has been utilized for a great ∗

Author to whom correspondence should be addressed. Email: [email protected] Received: 31 August 2013 Accepted: 27 October 2013

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number of applications such as sensors,15 catalysis fields,16 energy-storage devices,17 environmental fields,18 capacitors,19 transparent conductive films,10 and highfrequency transistors.20 Graphene possesses high current carrying capacity (up to 109 A cm−2 and high thermal conductivity (up to 5000 W m−1 K−1 .21 Graphene’s highly conjugated 2D structure contributes to its excellent electrical properties.22–24 In addition to its superb charge carrier behavior, graphene also possesses excellent mechanical strength, the breaking strength is 42 N m−1 and the Young’s modulus is 1.0 TPa, indicating graphene is one of the strongest material ever found.6 25 Most of these record properties refer to a pristine material under somewhat idealized conditions. However, in its applications various factors might affect the conductivity, such as interaction with the underlying substrate during the measurement, structure defect, surface charge traps,26 interfacial phonons27 and substrate ripples.28 In reality, graphene needs to adapt to the complex conditions that are dictated by specific applications.29 The exploration of polymer nanocomposites has greatly broadened the areas of materials science research.30–32 Owing to their unique properties and low cost, polymer nanocomposites have become the candidate for numerous potential applications in the automotive, aerospace, construction and electronic industries. Nowadays, polymer composite materials play an important role in high-tech fields. In traditional composites, a high concentration of 2157-9121/2014/3/048/018

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conventional filling modifiers is essential for an ideal performance. In the last decades, new members of carbon family showed impressive properties and provided new fillers for polymer composites.33–35 Among carbon nanostructures, graphene oxide (GO) and graphene have attracted the greatest attention of sciences and industries. Until now, bottom-up and top-down approaches are two popular methods of producing graphene. Chemical vapor deposition (CVD),36 37 arc discharge,38 epitaxial growth on SiC,39 40 chemical conversion,41 reduction of CO,42 and unzipping carbon nanotubes43–45 are included in bottom-up processes. The graphene sheets produced by bottom-up process are much pure and more attractive for fundamental studies and electronic applications. However, bottom-up process can not meet the need, as preparation of graphene-based nanocomposites requires a large amount of graphene sheets preferably with modifiable surface structure. In general, the top-down approaches including mechanical exfoliation,4 thermal deposition, oxidation of graphite46 and liquid-phase exfoliation of graphite25 47–51 are frequently used to synthesize graphene. The Hummers

method is one of the most developed methods in literature and much suitable for large scale production. However, this method consumes large quantity of detrimental strong acids (e.g., H2 SO4 , HNO3 , oxidants (e.g., KMnO4 , K2 S2 O8 , H2 O2 and the carcinogenic reductant (hydrazine). Furthermore, graphene sheets produced via oxidation–reduction approach are usually small in size and retain many defects due to the harsh oxidation conditions used. In addition, the reduction process gives relatively hydrophobic graphene sheets, which tends to aggregate irreversibly, which greatly hinder their production, storage and processing. Theoretical and experimental studies have indicated that the single-layered graphene has extremely high surface area, good conductivity and outstanding mechanical strength indicating that graphene has great potential for improving the mechanical, electrical, thermal, and gas barrier properties of polymers. Moreover, graphene and polymer complement each other to improve the performance of composites. It is well-known that the conductivity of polymer matrix can be dramatically improved when conductive

Jizhen Zhang received his bachelor in applied chemistry at Qingdao University, China, in 2012. He is currently a Master candidate under the supervision of Professor Jingquan Liu. His current research interests include the preparation of graphene oxide and graphene and their composite with other materials for the applications in energy storage and electronic applications.

Jianguo Qiu received his Bachelor’s degree from Shandong Normal University in 2001. After graduation, he obtained a lecture position at Qingdao University. He earned Master degree from Shandong University in 2007. He has published more than 20 papers and participated in a number of research and management projects. His current research interest focuses on the preparation of nanomaterials.

Jingquan Liu received his bachelor from Shandong University in 1989. His master and Ph.D. were obtained from the University of New South Wales (UNSW) in 1999 and 2004 respectively, where his Ph.D. was undertaken under the guidance of Professor Justin Gooding. In 2004 he worked as a CSIRO-UTS post-doctoral fellow prior to returning to UNSW with Professor Tom Davis as a Vice-Chancellor’s Research Fellow in 2006. In 2010 he took up a professorship at Qingdao University. He has co-authored over 75 peer-reviewed research papers with more 3000 citations. His research interests focus on the synthesis of various bio- and nano-hybrids of versatile polymeric architectures.

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nanoparticles are introduced into system. In order to enhance the conductivity of polymer, graphite,52 53 carbon nanotube.54 55 and graphene have been introduced into polymer matrix. Previous studies indicated an association between the conductivity of composites and the spatial distribution of fillers in the polymer. If the dispersion of graphene is too poor to form networks, the composites can not exhibit a good conductivity. However, owing to the irreversible aggregation of graphene, an overdispersion of the fillers may be unfavorable to achieve a high conductivity neither.56 57 Three main methods used to prepare graphene/polymer composites are solution blending,34 58 59 in-situ polymerization,60 61 and melt compounding.62 63 Most composites are prepared via relatively weak non-specific interaction forces between graphene and polymers. On the other hand, covalent linkages and specific affinities between graphene-based filler and the supporting polymer gradually draw people’s attention. In this review we focus particularly on the electrical conductive graphene/polymer composites. The methods for preparing graphene/polymer composites, their electrical properties and the relevant applications are also discussed.

2. PREPARATION OF CONDUCTIVE GRAPHENE/POLYMER NANOCOMPOSITES 2.1. Physical Mixing 2.1.1. Non-Covalent In Situ Polymerization Non-covalent in situ polymerization technique provides a very straightforward way to prepare graphene/polymer nanocomposites. This method generally involves mixing of graphene in monomer or a solution of monomer, followed by in situ polymerization. This is a good strategy to fabricate graphene/polymer composites with strong interaction between graphene and polymer matrix. For example, graphene/polyaniline (PANI) can be prepared in two steps: (i) homogenous composites of GO and polyaniline nanofibers were prepared by in situ polymerization of aniline in a suspension of GO in acidic solution; (ii) the GO/polyaniline composites were reduced by hydrazine.64 (Fig. 1) However, the PANI in the composites can also be reduced from the highly conductive halfly oxidized emeraldine base (EB) state to the reduced neutral leucoemeraldine (LB) state during the reduction process, so reoxidation and reprotonation are necessary to recover the conductive PANI structure after the reduction of GO. A very high capacitance of 480 F g−1 at a current density of 0.1 A g−1 was achieved. The research revealed that high specific capacitance and good cycling stability can be achieved either by doping chemically modified graphene sheets with PANI or by doping the bulky PANIs with graphene/GO. This approach has been used to produce a variety of other composites, such as graphene/PS,61 graphene/PANI,64–66 graphene/polyurethane (PU),67 68 50

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Fig. 1. Illustration of the process for preparation of graphene/PANI composites. Reprinted with permission from [64], K. Zhang, et al., Chem. Mater. 22, 1392 (2010). © 2010, American Chemistry Society.

graphene/poly(ethylene) (PE),69 graphene/Poly(methyl methacrylate) (PMMA),70 71 graphene/PS,72 graphene/ nylon-6,73 graphene/poly(pyrrole) (PP)74 and CRGO/poly (3,4-ethylenedioxythiophene) (PEDOT).75 In situ polymerization can also be an efficient way to produce composites with covalent bonding between the matrix and filler, the relevant examples will be given in the following grafting-from sections. 2.1.2. Solution Blending Solution blending is a simple way to fabricate homogeneous graphene/polymer composites.76 77 According to the Hummers method,78 GO is a layer material generally produced by the oxidation of graphite. Different from pristine graphite and graphene, GO sheets are heavily oxygenated, bearing hydroxyl and epoxide functional groups on their surface, and carbonyl and carboxyl groups located at the sheet edges.79 80 The presence of these functional groups endows GO with strongly hydrophilia, which allows graphite oxide to readily swell and disperse in water and highly polar organic solvents.81–83 As a result, it is convenient for GO to mix with different kinds of polymers in solution.84–86 The dispersion of hydrophobic graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge.87 An efficient method to improve the dispersion of graphene is blending polymer with GO and subsequently in situ reduce GO to graphene. For example, Stankovich and co-workers first prepared graphene/PS nanocomposites by dispersing phenyl isocyanate modified GO into PS solution.7 A plot of the electrical conductivity of graphene/PS composites versus a function of filler volume fraction was shown in Figure 2. The Rev. Adv. Sci. Eng., 3, 48–65, 2014

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Fig. 2. Electrical conductivity of the graphene/PS composites versus filler volume fraction. Main figure, composite conductivity, c , plotted against filler volume fraction, . Right inset, logc plotted against log(– c , where c is the percolation threshold. Solid lines in both graphs are calculated conductivities based on the fitting (inset, log–log plot) of the experimental data to the effective conductivity equation described in the text. Fitted parameters were: t = 274 ± 020, f = 10492±052 S m−1 and c = 01 vol.%. Left inset: top and middle diagrams illustrated the four-probe setup for in-plane and transverse measurements, respectively; bottom diagram, one of the computed distributions of the current density (contour lines) with local directions and magnitude (shown by arrows) in a specimen for the following conditions-the sample thickness was twice the electrode width and the gap between them, and the in-plane resistivity was 10 times lower than the transverse resistivity. Reprinted with permission from [7], S. Stankovich, et al., Nature 442, 282 (2006). © 2006, Nature Publishing Group.

composites exhibited a typical percolation behavior after GO/PS composites being treated by chemical reduction, and the introduction of graphene to PS increased the conductivity to higher than 10 orders of magnitude. Percolation in the composites occurs when the filler concentration is near 0.1 vol.%. At only 1 vol.% loading of chemical reduced graphene (CRGO), the composite has a conductivity of ∼ 0.1 S m−1 , indicating that highly conductive graphene/polymer composites can be constructed using a low loading of graphene. This method was compared with directly mixed graphene with polymer. It was found that this twostep process can effectively prevent the aggregation of graphene during reduction and composites exhibit high electrical conductivity at a very low percolation threshold (0.028 vol.%).88 Graphene/PVC composite was also fabricated into thin film via solution blending, where PVC was dissolved in DMF and graphene prepared through cationic surfactant mediated exfoliation.89 Such a strategy has an advantage in improving the dispersion of graphene sheets due to the presence of surfactant. When graphene was added into PVC as a filler the resulting composite exhibited improved thermal stability, mechanical strength and electrical conductivity. Consequently, the maximum conductivity observed was 0.058 S/cm at 6.47 vol.% of the Rev. Adv. Sci. Eng., 3, 48–65, 2014


filler content which is 10 times higher than that of the single walled CNT/PVC composites.90 However, it is difficult to remove the trace of residual solvents for solution blending91 and the loss of hydrophilicity can lead to irreversible agglomeration process when the GO was reduced into graphene. Moreover, reduction-extractive dispersion technology can effectively promote the dispersion of graphene nanosheets and consequently an excellent conductive network is formed in the matrix.92 The percolation threshold of the composite is about 0.15 vol.%. When the graphene nanosheet content is lower than 1.5 vol.%, the conductivity of the composites is 3–5 orders of magnitude higher than that of composites filled with graphite nanosheets. Since solution blending is efficient, requires no expensive instruments, and allows for a well dispersion of graphene sheets in polymer solution. GO, functionalized graphene oxide (FGO), graphene and functionalized graphene (FG) have been filled in different kinds of polymer solution via solution blending, respectively. For example, Kim et al.76 combined thermoplastic polyurethane (TPU) with graphene and GO via three methods and revealed that the solvent-based process were more effective for obtaining well-distributed graphene throughout the matrix than melting processing. Various polymer composites such as graphene/PVA,93 graphene/Poly(vinylidene fluoride) (PVDF),94 Graphene/ polyethylene (PE),95 graphene/PVDF/PMMA,96 graphene/ Polycarbonate (PC),97 graphene/PMMA,98 FG/Acrylonitrile-butadiene-styrene (ABS)99 thermally reduced graphene sheets (TRG)/poly[(-methylstyrene)-co-(acrylonitrile)]/PMMA,100 graphene/poly(styrene-co-butadieneco-styrene) (SBS)101 have been prepared using this technique. 2.1.3. Melt Compounding Melt compounding is another important processing for high-yield production of polymer composites, which involves the mixing of filler materials and polymer matrices under high-shear forces at elevated temperatures. Comparing with solution blending and in situ polymerization, melt compounding is often considered as more eco-friendly and allows for large-scale production. However, studies suggest that the drawbacks of this method are low degree dispersion of graphene sheets in polymer matrix, which leads to phase separation and compromised mechanical and transport properties.76 102 103 Recently, polylactide (PLA)-exfoliated graphite composites have been successfully prepared by mixing PLA and exfoliated graphite in a mechanical mixer at 175– 200 C.104 Similar route was introduced to production of graphene/polymer composites. Graphene/polyethylene terephthalate (PET) composite was fabricated via feeding thermal reduced GO into PET at 285 C and the incorporation of graphene improved the electrical conductivity of PET with a sharp transition from electrical 51


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2.2. Covalent Bonding In a short period, there are numbers of literatures that focused on preparing graphene/polymer nanocomposites via covalent bonding emerged. As a matter of fact, because graphene has a similar structure with fullerenes and carbon nanotubes, the fabrication strategies of graphene/polymer nanocomposites benefits a lot from their developments. Though graphene sheets are chemical inert compared with fullerenes and carbon nanotubes,108 it is noteworthy that the GO and reduced graphene oxide (RGO) have sufficient oxygen-containing functional groups so that the surface of the GO sheets can be modified in a variety of ways, such as covalent modification via the amidation of the carboxylic groups,109–115 nucleophilic substitution of epoxy groups, diazonium salt coupling116 117 and other methods. Covalent functionalization of pristine graphene typically requires reactive species that can form covalent adducts with the sp2 carbon structures in graphene. These reactive species (such as reactive intermediates of radicals, nitrenes, carbenes, and arynes) covalently modify graphene through free radical addition, CH insertion, or cycloaddition reactions.108 (Fig. 3). GO is heavily oxygenated and is regarded as insulation. Moreover, the surface modification sometimes damages the plane structure and lead to a further decline of conductivity. As a result, the insulating GO must be reduced to graphene through chemical reduction or thermal reduction118 to render the material electrically conductive.24 In contrast, He and Gao119 reported that covalent functionalization may keep the conjugation network of graphene because only a small fraction of sp2

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insulator to semiconductor at a low percolation threshold of 0.47 vol.%, and a high electrical conductivity of 2.11 S m−1 was achieved with only 3.0 vol.% of graphene.105 In another research,106 polyethyleneoctene rubber grafted with maleic anhydride (POE-g-MA) was added by melt compounding to improve the electrical conductivity of graphene/polyamide 12 (PA12) nanocomposites with a low percolation threshold of 0.3 vol.%. A rapid increase in electrical conductivity from 2.8 × 10−14 S m−1 of PA12 to 6.7 × 10−2 S m−1 was achieved when ∼ 1.38 vol.% graphene was introduced. Graphene sheets were found to be homogeneously dispersed in PA12 matrix. It is noteworthy that the electrical conductivity of this composite is higher than those of many other graphene-filled binary systems by melt compounding,76 and even comparable to some composites prepared by in situ polymerization and solution blending. However, owing to thermal instability of most chemically modified graphene, melt blending for graphene has so far been limited to a few studies with the thermally stable graphene oxide or exfoliated graphite. Additionally, the use of high shear forces can sometimes damage the structure of filler materials, such as carbon nanotubes and graphene sheets.107

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bonds undergo the change into sp3 ones, and thus would not impact the electrical properties of graphene considerably. The conductive functionalized graphene is promising in fabrication of novel electrical and electronic materials and devices. 2.2.1. Grafting to Methodology Covalent bonding for the preparation of graphene/polymer composites involves the reaction between functional molecules and groups on graphene sheets. To date, the modification of graphene with polymers has been accomplished by two main methodologies: “grafting-from” and “grafting-to.” The grafting-to approach provides a convenient strategy to modify the surface of materials utilizing a terminal-functionalized polymer chain reacting with an appropriately treated substrate. There are two possible routes to realize grafting-to modifications: one method is to make functionalized GO (FGO) or graphene react with specific polymer, another one is to functionalize polymer first, followed by reacting with specific groups on GO edge.113 120 In the first case, the properties of composites not only depend on the molecular weight also rely on the polydispersity of the polymer. Moreover, the efficiency of coupling is related to the number of active groups on GO or graphene surface. Esterification or amidation reactions between carboxylic groups on GO surface and hydroxyl or amine groups on the polymer chain have been reported: A kind of bio-based polyester (PE) was synthesized by polycondensation between plant-derived diols and diacids. It was then grafted onto GO surface via the easterification between hydroxyls of PE and carboxyls of GO. Subsequently, the grafted GO was reduced by vitamin C (Fig. 4). The prepared composite exhibits high electrical and thermal conductivities. The uniform dispersion Rev. Adv. Sci. Eng., 3, 48–65, 2014

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Fig. 4. Schematic of synthesis of GO/PE and graphene/PE composite. Reprinted with permission from [121], Z. Tang, et al., Macromolecules 45, 3444 (2012). © 2012, American Chemical Society.

of graphene, strong interfacial covalent bonding between graphene and PE and the network of graphene sheets were responsible for concurrently improved electrical and thermal conductivities.121 Another example of grafting-to was via esterification between the carboxy groups in GO and the hydroxyl groups in PVA.115 In addition, Mullen et al.122 found that the hydrazine alone was not sufficient to achieve maximum reduction, and the remaining carbonyls allowed RGO to react with hydroxyl groups on polymer via the esterification. Similarly, graphene sheets were successfully modified with poly(vinyl alcohol) (PVA) via the carbodiimide-activated esterification reaction between the carboxylic acid moieties on the graphene sheets and hydroxyl groups on PVA123 and alkoxyaminefunctionalized PMMA was grafted onto CRGO via radical reaction.124 In addition,125 the surface functionalization of GO can be achieved by grafting polymer chains to its surface via direct use GO as the initiator for polymerization of N -vinylpyrrolidone (NVP). This indicated that surface properties of GO could be tailored by grafting different polymer chains to meet the needs of various applications. Composites prepared via grafting polymer to FGO were also reported. FGO was synthesized and subsequently incorporated into polyurethane acrylate (PUA) by UV curing technology.126 The results showed that FGO sheets were uniformly dispersed into the PUA matrix and formed strong interfacial adhesion with PUA owing to the formation of the cross-linking networks between FGO and PUA after UV curing. By contrast, untreated GO/PUA nanocomposites exhibited relatively low thermal stability and poor mechanical properties than its modifiedGO counterpart. Likewise, poly(arylene ethernitrile) (PEN) was grafted to 4-aminophenoxyphthalonitrile functionalized GO127 and treelike hyperbranched poly(3-ethyl-3hydroxymethyloxetane) was efficiently synthesized and grafted onto hydroxy-functional graphene nanosheets.128 In addition to the modification methods aforementioned, other approaches were also developed. Pristine carbon nanostructures display a natural tendency to undergo Diels–Alder (DA) reactions with a range of functional dienes and dienophiles without the need of a catalyst. This has sparked significant scientific interest in exploiting the DA reaction as a powerful Rev. Adv. Sci. Eng., 3, 48–65, 2014

strategyfor functionalization of graphene surface.129 130 More precisely, in a recent work of Yuan et al.131 GO was functionalized with cyclopentadienyl-capped poly(ethylene glycol) monomethyl ether (mPEG-Cp) through a one-step DA “click” reaction without any catalyst. Subsequently chemical reduction at 80 C generated graphene/mPEG-Cp nanocomposites. Similarly, cyclopentadienes (CPs) with Raman and electrochemically active tags were patterned covalently onto graphene surfaces using force-accelerated DA reactions that were induced by an array of elastomeric tips mounted onto the piezoelectric actuators of an atomic force microscope.129 This force-accelerated cycloadditions was a feasible route to locally alter the chemical composition of graphene defects and edge sites under ambient atmosphere and temperature. After functionalization of the graphene basal plane its conductivity was well maintained. This method could find utility in sensors, electronics, and optical devices. The grafting efficiency via grafting-to is usually low due to the difficulty in matching the unique surface chemistry of GO with the specific functionality on polymer chains. More importantly, there are many active sites on preprepared polymer and GO sheet, and the selectivity of chemical reaction between these active sites is hardly controlled; thus, the final structure of grafts is ill-defined. For example, the multifunctionalized groups of the preprepared polymer chains inevitably act as covalent crosslinker between graphene sheets to form the interconnection of graphene. In addition, the steric effect of polymer would reduce the graft efficiency. Although the concept that the well-defined structure and perfect dispersion of graphene in host matrix is essential for the electrical and thermal performances of the matrix is prevalent, it is believed that the formation of graphene network in polymer host is the origin for significantly improving the electrical property and mechanical strength. 2.2.2. Grafting-from Methodology In most cases, grafting-from process is necessary for surface modification of graphene or GO. It appears that the agglomeration can be mitigated and the dispersibility can be ameliorated by functionalized graphene. In addition, graphene functionalization is available to improve the 53


affinity of graphene in various solvents and reinforce the interaction between compounds in nanocomposites. For instance, graphene/polyimide (PI) nanocomposites prepared via a two-stage process consisting of (a) surface modification of graphene and (b) in situ polymerization.132 In the grafting-from approach, polymer chain grows from the graphene surface. As a result, this method not only minimizes the steric effect also offers template for growing of desired polymers.133 Living/control radical polymerization is an efficient way to precisely control the molecular weight and molecular weight distributions, as well as gain functionality terminated polymers. For example, Goncalves and cooperators134 grafted poly(methyl methacrylate) (PMMA) chains from the GO surface via atom transfer radical polymerization (ATRP), yielding a nanocomposite which was soluble in chloroform. In addition, by selective modification of graphene surface, graftingfrom method can be used to prepare special patterned composites.135 Reversible addition-fragmentation chain transfer (RAFT) polymerization136 137 is also widely applied. For example, Jiang et al.138 used alkoxysilanefunctionalized RAFT agents modified GO, and subsequently prepared GO/polymer nanocomposites with exactly controlled molecular weight, relatively low polydispersity and variable grafting density of grafted chains. In this one-pot approach, simultaneous coupling reaction and RAFT process using Z-group functionalized RAFT agent seemed to afford grafted chains with shorter chain length, narrower molecular weight distribution and lower grafting density than R-group functionalized RAFT agent mediated reaction, which could be attributed to different grafting process and noticeable shielding effect. The resultant composites were of exfoliated morphology and enhanced solubility and dispersibility in a wide range of

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solvents including hexane and water. The surface modification offers an opportunity to alter GO morphologies and makes it possible to prepare varied composites. As shown in Figure 5, graphene oxide/polypropylene (GO/PP) nanocomposites can also be prepared via in situ Ziegler-Natta polymerization.139 A Mg/Ti catalyst species was incorporated on GO via surface functional groups including –OH and –COOH, giving a supported catalyst system primarily structured by nanoscale, predominantly single GO sheet. Subsequent propylene polymerization led to the in situ formation of PP matrix, which was accompanied by the nanoscale exfoliation of GO, as well as its gradual dispersion. High electrical conductivity was discovered with thus prepared GO/PP nanocomposites; for example, at a GO loading of 4.9 wt%, c was measured at 0.3 S m−1 . Besides changing the polymerization methods and polymer types, scientists also attempted to change the initiation methods. Recently, -ray irradiation-induced graft polymerization was successfully used to decorate GO sheets with poly(vinyl acetate) (PVAc).140 Otherwise, water-dispersible graphene with temperature-responsive surfaces was synthesized by grafting poly(N -isopropylacrylamide) (PNIPAM) from graphene via surface-initiated ATRP.141 Comparing both methods through the examples described above, it seems that grafting-to allows the covalent attachment of a wider variety of polymers to graphene. The polymers grafted from graphene are those produced principally by some type of radical polymerization. The drawback with grafting-from methodology is the decrease of the polymerization rate at the later stage of polymerization.142 143 In these cases, the immobilization of the initiator on the graphene sheets is relatively easy. In addition, the grafting-to and grafting-from methods create new linkages between graphene and the attached

Fig. 5. Fabrication of GO/PP nanocomposites by in situ Ziegler-Natta polymerization. Reprinted with permission from [140], B. Zhang, et al., Nanoscale. 4, 1742 (2012). © 2012, American Chemical Society.

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polymer, which might cause additional defects on the graphene sheet and weaken the intrinsic properties of graphene correspondingly. However, it has also proved that the polymerization took place at the graphene defects and its conjugated structure has not been damaged. Therefore, the electrical properties of graphene is maximally protected.144 2.3. Specific Affinity It is difficult to efficiently modify pure graphene through covalent bonding because the ideal graphene lacks active groups on its surface. In order to address this problem, non-covalent interaction such as hydrogen bonding, electrostatic interaction and – interaction are introduced into modification of GO and graphene.53 135 145–148 2.3.1. Hydrogen Bonding In contrast to the block graphene/polymer composites that the graphene fillers are randomly distributed in the polymer matrices, the layered graphene derivatives in polymer matrix can be fabricated for specific applications, such as the directional load-bearing membranes, and thin films for photovoltaic applications.149 Recent increasing interests focus on the construction of nanoscale layer-by-layer (LBL) assembled materials. Hydrogen bonding opened a new opportunity for the LBL technique. For example


ultrathin multilayer (GO/PVA)n films were fabricated by bottom-up layer-by-layer assembly of poly(vinyl alcohol) and exfoliated GO via hydrogen bond, in which exfoliated GO nanosheets were used as the building blocks.150 (Fig. 6) Also, PVA can form hydrogen bonds with sulfonated RGO in water. A well dispersion of sulfonated graphene was achieved and showed a percolation threshold at a sulfonated RGO concentration of 0.37 wt.%.151 2.3.2. Electrostatic Interaction It is well-known that the GO and RGO sheets are highly negatively charged when dispersed in an aqueous solution, especially in an alkaline solution, due to the ionization of the phenolic hydroxyl and carboxylic acid groups.87 According to this property, the self-assembly of negatively charged RGO with positively charged polymer has been performed to fabricate graphene/polymer composites.152 153 Pham and coworkers153 carried out an approach for the preparation of highly conductive CRGO/PMMA composites by self-assembly of positivecharged PMMA latex particles with negative-charged GO sheets through electrostatic interactions, followed by hydrazine reduction. The PMMA latex was prepared by surfactant-free emulsion polymerization, where cationic free radical initiators provided the positive charges on the surface of the PMMA particle. (Fig. 7) The obtained RGO/PMMA exhibited excellent electrical properties with

Fig. 6. (a) Schematic of the composite film deposition process using glass substrate. The basic buildup sequence for the simplest film architecture A/Bn includes four steps: (1) and (3) represent the adsorption of PVA and GO nanosheets, respectively, and (2) and (4) refer to wash steps. The cycle could be repeated as necessary to obtain the desired number of bilayers (GO/PVA)n . (b) Simply schematic representation of the assembling process (left) with an interaction of GO surface and PVA macromolecular chains and the internal architecture of the GO/PVA ultrathin film (right). Reprinted with permission from [152], S. A. Ju et al., ACS Appl. Mater. Interfaces 3, 2904 (2011). © 2011, American Chemical Society. Rev. Adv. Sci. Eng., 3, 48–65, 2014

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Fig. 7. (a) Schematic illustration of self-assembly of PMMA latex and GO, followed by hydrazine reduction of GO and (b) photographs of PMMA latex, GO dispersion, GO/PMMA, and RGO/PMMA suspensions. Reprinted with permission from [153], V. H. Pham, et al., ACS Appl. Mater. Interfaces 4, 2630 (2012). © 2012, American Chemical Society.

a percolation threshold as low as 0.16 vol.% and an electrical conductivity of 64 S m−1 at only 2.7 vol.%. Moreover, the mechanical properties of RGO/PMMA were also significantly improved. The storage modulus of RGO/PMMA increased by about 30% at 4.0 wt.% RGO at room temperature while the glass transition temperature of RGO/PMMA increased 15 C at only 0.5 wt.% RGO. Similarly, LBL assembly via the Langmuir–Blodgett (LB) technique has been used to deposit GO sheets onto films of polyelectrolyte poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene sulfonate) (PSS).154 The resulting composite membrane showed enhanced directional elastic modulus by an order of magnitude, i.e., from 1.5 to 20 GPa with 8 vol% loading of the GO. Electrostatic interaction can be conveniently used to prepare graphene suspension. Graphite can be directly exfoliated into FG nanosheets with the assistance of an ionic liquid.155 These graphene nanosheets are individuated and homogeneously distributed into polar aprotic solvents. Different types of ionic liquids and different ratios of the ionic liquid to water can influence the properties of the graphene nanosheets. Graphene/PS composites synthesized by a solution blend route exhibited a percolation threshold of 0.1 vol.% and a conductivity of 13.84 S m−1 at only 4.19 vol.%. Electrostatic interactions were also used for synthesis of other graphene/polymer composites such as CRGO/PMMA,156 FGN/water-borne polyurethane (WPU)157 and graphene/PS.158 2.3.3. – Interactions As a non-covalent approach to modify graphene, – stacking interactions can be comparable to covalent attachment 56

in strength and hence provide more stable alternatives to the relatively weaker hydrogen bonding, electrostatic bonding and coordination bonding strategies as discussed above. Furthermore, – stacking modification does not disrupt the conjugation of the graphene sheets, and hence preserves the electronic properties of graphene. Therefore, – stacking interactions have been used to enhance the interaction between polymer and graphene.159 Pyrene is a -orbital rich group that can easily form strong – stacking interactions with other polyaromatic materials such as fullerene, carbon nanotubes and graphene. Pyrenetethered precursors have been successfully prepared160–162 and attached onto GO109 and graphene.163 A number of small -orbital rich aromatic molecules have also been attached previously onto graphene surface using the – stacking approach.164–170 For instance, positively charged imidazolium groups of imidazolium ionic liquids (Imi-ILs) underwent ion-exchange with negatively charged GO sheets and Imi-ILs were non-covalently attached onto the large surfaces of graphene through – and/or cation-stacking interactions,171 followed by in situ copolymerization of the vinyl-benzyl reactive sites with methyl methacrylate to fabricate graphene/PMMA composites. More importantly, vinyl-benzyl groups in imidazolium ionic liquids acted as cross-linking reactive sites to copolymerize with MMA to fabricate graphene/polymer composites. As expected, graphene sheets were uniformly dispersed in PMMA, and the resultant graphene/PMMA composites exhibited excellent electrical properties with a low percolation threshold. In addition, the combination between the PMMA matrix and graphene contributed greatly to mechanical and thermal properties of the final composites. Rev. Adv. Sci. Eng., 3, 48–65, 2014

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Fig. 8. A schematic of the direct exfoliation of graphene from graphite using amphiphilic block copolymers with multi-pyrene pendent groups, which were synthesized using the RAFT mechanism. Reprinted with permission from [51], Z. Liu, et al., Carbon 51, 148 (2013). © 2013 Elsevier.

As pyrene-tethered polymers are steadily absorbed onto graphene or GO via – stacking interactions, they can effectively stabilize single- and few-layer graphene flakes in aqueous dispersions.148 172 – stacking interaction is a convenient strategy to graft polymer onto graphene surface. Liu et al.51 prepared graphene/polymer composites by direct exfoliation of graphene from micro-sized graphite using a pyrene-functionalised amphiphilic block copolymer, poly(pyrenemethyl acrylate)-b-poly[(polyethylene glycol) acrylate] (polyPA-b-polyPEG-A) prepared via RAFT polymerization (Fig. 8). The one-step prepared graphene/polymer composites can not only be employed to prepare composite films with increased tensile strength and tunable conductivity, but can also be good precursors for the generation of pure graphene sheets.

3. THE ELECTRICAL PROPERTIES OF GRAPHENE/POLYMER NANOCOMPOSITES 3.1. Electrical Percolation Threshold and Conductivity of Graphene/Polymer Composites Recent theoretical173 and experimental174 175 studies have demonstrated that graphene-filled composites exhibit lower percolation thresholds and higher conductivities than those filled by CNTs. A conductive network of graphene sheets is not available at a low loading until the loading reach the percolation threshold, a connected network created a route Rev. Adv. Sci. Eng., 3, 48–65, 2014

for electronic transport, and the insulator turned into a semiconductor. A classical percolation model is frequently used for carbon based polymer composites to describe the relationship between composite conductivity (c and filler volume fraction () above the percolation threshold (c .7 171 That is, c = f − c / 1 − c t

for > c

where f and t are the conductivity of filler and critical exponents, respectively. Although f is not a real conductivity, it is positively related to the intrinsic conductivity of the pristine filler. These parameters can be determined by the least squares fitting of the experimental data. For example, as applied to Figure 2 we can obtain fitted parameters are: t = 274 ± 020, f = 10492±052 S m−1 and c = 01 vol.%.7 In Table I, the highest electrical conductivity and c of graphene/polymer composites from the literatures are summarized. It can be observed that graphene/polymer composites can have an electrical conductivity ranging from 10−17 to 102 S m−1 and a c ranging from 0.02 vol.% for graphene/P(St-co-MMA) composites to 7.5 wt.% for TRGO/polyamide6 (PA6) composites. It can be seen that most of graphene/polymer composites with high electrical conductivity are prepared with TRGO or CRGO as fillers, because of the lower production cost of RGO than that of graphene prepared by other methods such as graphene prepared by CVD (CVDG). Wang 57


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Table I. Electrical percolation threshold (c and the max conductivity (c of varied graphene/polymer composites. Polymer

Adulterant

PA6 PA12 PMMA PMMA PMMA PMMA Epoxy WPU PS PS PS PS

TRGO Graphene FG CRGO Non-covalent FG TRGO CRGO CRGO Graphene CRGO Graphene FGO

PS PS PS PS

FG TRGO Graphene GO

PS/PMMA PS/PMMA

FG FGO

P(St-co-MMA)

GO

PC PVA

FG GO

PVA PVC PEI PP PU PU PU PVDF PE PET Vinyl chloride/vinyl acetate copolymer Poly(styrene-co-butadieneco-styrene) (SBS)

7.5 wt.% 0.3 vol.% 0.16 vol.% 0.05 wt.% 0.25 vol.% 0.6 vol.% 0.52 vol.%

FG CRGO TRGO FGO FG FG TRGO FG Graphene TRGO CRGO

Melt extrusion Melt copulating Solution blending Solution blending Solution blending Solution blending Solution blending Solution blending In situ polymerization Solute blending Solute blending Solute blending and chemical reduction Solute blending Solution mixing In situ emulsion polymerization Solution blending and two steps reduction Solution blending In situ polymerization and chemical reduction Solution blending and chemical reduction Solution blending Solution blending and chemical reduction Solution blending Solution blending Solution blending In situ polymerization Solution blending Solution blending Solution blending Solution blending Solution blending Melt extrusion Solution blending

CRGO

Solution blending

et al.176 reported the preparation and dielectric properties of CRGO/PP composites with an ultra low percolation threshold as low as 0.033 vol%. This value is the lowest among those that have been reported in graphene-filled composites. However, the electrical properties of both CRGO/polymer and TRGO/polymer composites are much lower than those of the CVDG/polymer composites. For example, Chen et al.177 directly synthesized three-dimensional graphene sheets via templatedirected CVD. Even with a graphene loading as low as 0.5 wt%, the graphene/poly(dimethyl siloxane) composite showed a very high electrical conductivity of ∼ 1000 S m−1 , which was much higher than CRGO and TRGO/polymer composites. In addition, neat CRGO fibers were reported to have much higher electrical conductivity (about 2.5 × 104 S m−1 178 than CVDG/polymer and the other RGO/polymer composites reported because 58

c

Method

0.1 vol.% 0.19 vol.% 0.8 wt.% 0.1 vol.% 2.7 wt.% 0.075–0.33 vol.%

c (S m−1 ) −2

0.71 × 10 at 12 wt.% 0.067 at 1.38 vol.% 64 at 2.7 vol.% 0.037 at 2.0 wt.% 13.37 at 2.08 vol.% 3.11 at 1.8 vol.%

Ref.

5.1 at 5 vol.% 13.84 at 4.19 vol.% 72.18 at 2.45 vol.% 15 at 1.2 wt.% 1 at 2.5 vol.%

[179] [106] [153] [98] [171] [180] [181] [157] [155] [182] [183] [7]

10−4 at 5 wt.% 3.49 at 1.1 vol.% 0.029 at 2.0 wt.% 22.68 at 4 wt.%

[184] [185] [61] [186]

0.5 wt.% 0.35 vol.%

[187] [188]

0.02 vol.%

[188]

0.38 vol.% 1 wt.%

22.6 at 2.2 vol.% 10 at 7.5 wt.%

[97] [189]

2 wt.% 2 wt.% 2 wt.% 0.5 wt.% 1 vol.% 0.47 vol.% 0.15 vol.%

5.8 at 6.47 vol.% 0.0022 at 1.38 vol.% 0.3 at 4.9 wt.% 0.0275 at 6 wt.% 0.0492 at 7 wt.% 0.191 at 4 wt.% 10.16 at 2 wt.% 0.01 at 3.8 vol.% 2.11 at 3 vol.% 1 at 3.5 vol.%

[151] [89] [190] [139] [191] [68] [192] [193] [175] [105] [92]

0.25 vol.%

13 at 4.5 vol.%

[101]

0.37 wt.% 0.6 vol.% 0.21 vol.%

of compact stacking and low contact resistance between CRGO sheets. 3.2. Conductivity Influencing Factors The conductivity of composites is related to the both properties of basis materials and adulterants. It is well known that polymer can be recognized as conductive polymer and insulated polymer, and the former showed an impressive high conductivity than that of the latter. For example, PS is one traditional industry material with conductivity approximately 1.0 × 10−10 S m−1 . The conductivity of PS rocketed to a high conductivity after mixing with graphene sheets7 (Table I). In addition, mixing different kinds of polymers together may lead to double percolated structure. Mao et al.187 fabricated PS/PMMA blends filled with octadecylamine-FG conductive composites, and found that the electrical conductivity of the composites can Rev. Adv. Sci. Eng., 3, 48–65, 2014

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Fig. 9. Left: SEM images of PS/PMMA blends filled with 1.0 wt.% GE-ODA: (a) 70 w/30 w, (b) 50 w/50 w, (c) 30 w/70 w. (a) and (b) PMMA phase was etched by formic acid. (c) PS phase was etched by cyclohexane. Right: Conductivity (at 1 Hz) versus PMMA content in PS/PMMA blends. The measurements were performed at room temperature. The total weight concentration of GE-ODA incorporated in the entire polymer blends is fixed at 1.0 wt.%. Reprinted with permission from [187], C. Mao, et al., ACS Appl. Mater. Interfaces 4, 5281 (2012). © 2012, American Chemical Society.

be optimal when PS and PMMA phases form a cocontinuous structure and octadecylamine-FG nanosheets were selectively located and percolated in the PS phase. When the PS/PMMA ratio was 50 w/50 w, the formation of a perfect double percolated structure contributed to an extremely low electrical percolation threshold 0.5 wt.% (Fig. 9). Further research found that graphene/polymer composites of different polymers with the same polymerization degree exhibited similar conductivity.194 However, when the polymer chain was designed as random copolymer the conductivity was significantly decreased. It was also observed that the longer the grafted polymer chains the lower the conductivity.194 Also, the manipulation of the conductivity of graphene papers was realized at the molecular level, via either covalent bonding or – stacking interactions using either monofunctional or bifunctional molecules. The graphene papers can be tailored with controllable conductivity from around 10−3 to below 102 S m−1 195 (Fig. 10). Graphene sheets can provide electron transfer percolated pathways to improve electrically conductivity. The morphology of adulterant plays an important role in determining the percolation threshold. It was found that planar-like graphene is much more readily for percolate at lower loading than fiber-like carbon nanotube.76 185 All these experimental results indicate that rapid transition from insulation polymer to high conductivity composite depends on the formation of an interconnected conductivity graphene network. This means the superior conductivity arises from the high reduction degree of GO and its high dispersion and the formation of a network structure in the polymer matrix. At the same time, the mechanical and electrical properties of paper materials prepared by filtration are related to the concentration of CRGO. Park196 proposed that the electrical conductivity of composite films Rev. Adv. Sci. Eng., 3, 48–65, 2014


increased with the increasing concentration of graphene. An interesting result showed that a concentrated suspension will lead to agglomeration of reduced GO sheets, and the composite paper sample produced by the agglomerated mixture showed a significantly higher modulus and electrical conductivity than those generated from homogeneous colloidal suspensions. This will be helpful in preparation of graphene/polymer composites with low percolation threshold.197 The concentration of graphene can be controlled by phase separation in order to achieve low percolation threshold190 (Fig. 11). With the phase separation continued, the nuclei grew up. After removing the solvent from the cells, graphene/polyetherimide (PEI) nanocomposite foams were obtained. It was observed that the concentration of graphene was increased when the nuclei grew up. This action decreased the c from 0.21 vol.% of graphene/PEI nanocomposite to 0.18 vol.% of graphene/PEI foam. Furthermore, the foaming process significantly increased the specific electromagnetic interference (EMI) shielding effectiveness from 17 to 44 dB cm3 g−1 . In fact, the conductivity of composite sample not only related to the concentration of graphene also related to the degree of reduction of graphene. GO with hydroxyl and epoxide functional groups on their basal planes was deemed as insulation, the conductivity of GO can be adjusted by alter the C/O ratio.118 Zhang et al.198 studied the influence of surface chemistry of graphene on rheological and electrical properties of graphene/PMMA nanocomposites. Owing to the favorable interfacial interactions arising from polarity matching, the graphene with a C/O ratio of 13.2 showed a better dispersion in PMMA than those with lower C/O ratios, and thus this composites showed a dramatic increase in electrical conductivity of over 12 orders of magnitude, from 3.33×10−14 S m−1 with 0.4 vol.% of graphene to 2.38×10−2 S m−1 with 0.8 vol.% of graphene. The conductivity reaches up to 10 S m−1 at 2.67 vol.% and 20 S m−1 at 4.23 vol.%. It was believed that the residual oxygen functional groups contribute to the interaction between RGO and PMMA matrix, resulting in enhancement on the thermal properties of PMMA.98 It can be concluded that many factors including intrinsic electrical conductivity, aspect ratio, dispersion state, and contact resistance between graphene might affect the electrical properties of graphene/polymer composites.32 54

4. APPLICATION OF CONDUCTIVE NANOCOMPOSITES With significantly enhanced conductivity and mechanical properties, graphene/polymer composites usually have potential applications as antistatic coatings, electromagnetic interferences (EMI) shielding materials,180 190 199 200 electrode materials.9 29 64 201–206 etc. The EMI shielding is defined as the logarithmic ratio of incoming (Pi ) to outgoing power (Po ) of radiation. In general, efficiency 59


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Fig. 10. Schematic illustrating the modification of graphene sheets with (a) monoaryl diazonium salt, (b) biaryl diazonium salt, and (c) bipyreneterminated molecular wire. (d) Model proposed to illustrate the in-sheet and inter-sheet charge transfer. (1) The in-sheet charge transfer, (2) the electron hopping from one sheet to another, and (3) the charge transfer through the inter-sheet molecular conduits. Reprinted with permission from [195], J. Liu, et al., J. Phys. Chem. C 116, 17939 (2012). © 2012 American Chemical Society.

Fig. 11. (a) Schematic of preparation of PEI/graphene nanocomposite foam. (b) Electrical conductivity for graphene/PEI nanocomposites and microcellular foams as the function of graphene content. Reprinted with permission from [190], J. Ling, et al., ACS Appl. Mater. Interfaces 5, 2677 (2013). © 2013, American Chemical Society.

60

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of any shielding material is expressed in decibels (dB). Higher the decibel level of EMI shielding, less energy is transmitted through shielding material. EMI may be induced as electromagnetic radiation emitted by electric circuits under current operation. The EMI signal is undesirable because it not only impedes the good functionality of electronic devices but is also harmful to humans. Compared with conventional metal-based EMI shielding materials, conductive polymer composites and polymer composites with discontinuous conducting fillers are attractive for the development of effective EMI shielding applications because of their own superiorities, including being lightweight, anti-corrosive, flexible, and having processing advantages. Graphene/PMMA180 nanocomposites were prepared by solution blending and melt compounding. This novel graphene-PMMA nanocomposite microcellular foams with a low graphene loading of 1.8 vol% exhibited not only a high conductivity of 3.11 S m−1 , but also a good EMI shielding efficiency of 13–19 dB at the frequencies from 8 to 12 GHz. According to their research, EMI shielding efficiency is mainly attributed to the absorption rather than the reflection in the investigated frequency range and the presence of microcellular cells greatly improves the ductility and tensile toughness of the brittle graphene-PMMA nanocomposites. PS/carbon nanofiller composite foams was also prepared using a chemical blowing agent.207 The specific shielding effectiveness of this lightweight composite was as high as 64.4 dB cm3 g−1 . In addition to PS and PMMA, other polymer systems such as epoxy,181 PVDF,193 WPU157 and PDMS199 have also been used for the fabrication of EMI shielding materials. However, the general properties of these polymers, such as low heat-resistance, poor flame retardancy, and high smoke generation, restrict their use as


the EMI shielding materials in aerospace and other special fields. Electrode material is another significant application for graphene/polymer composites owing to their specific electrical property. For example, Lee et al.208 developed a new method to simultaneously transfer and dope chemical vapor deposition grown graphene onto a target substrate using a fluoropolymer as both the supporting and doping layer. This method was used to fabricate a flexible and transparent graphene electrode on a plastic substrate. Furthermore, Song and coworkers209 developed nanocomposites combining graphene with two promising polymer cathode materials, poly(anthraquinonyl sulfide) and polyimide, to improve their high-rate performance. The graphene/polymer nanocomposites were synthesized through a simple grafting-from polymerization in the presence of graphene sheets. The highly dispersed graphene sheets in the nanocomposite drastically enhanced the electronic conductivity and allowed the electrochemical activity of the polymer cathode to be efficiently utilized. This allows for ultrafast charging and discharging; the composite can deliver more than 100 mA h g−1 within just a few seconds. Graphene/polymer composites can also be served as electrical devices. A GO/polyoxometalate composite film has been prepared as follows201 GO and a Keggin-type polyoxometalate cluster H3 PW12 O40 (PW) are alternatively deposited on a substrate via electrostatic adsorption (Fig. 12). The PW cluster acts as a photocatalyst and reduces GO (RGO), yielding a product with good conductivity. Furthermore, photomasks were used to produce conductive patterns of RGO domains on the films, which served as efficient microelectrodes for photodetector devices. Supercapacitor devices based on conductive

Fig. 12. Schematic illustration of the fabrication procedure of RGO/PW multilayer films, which involves the LBL assembly of GO nanosheets and PW clusters using cationic polyelectrolytes PEI and PAH as electrostatic linkers, and a subsequent in situ photoreduction to convert GO to RGO. Reprinted with permission from [201], H. Li, et al., J. Am. Chem. Soc. 133, 9423 (2011). © 2011, American Chemical Society. Rev. Adv. Sci. Eng., 3, 48–65, 2014

61


flexible CRGO/PANI composite film exhibited large electrochemical capacitance (210 F g−1 at a discharge rate of 0.3 A g−1 . The greatly improved electrochemical stability and rate performances were also observed.86

5. SUMMARY AND OUTLOOK Graphene is a promising material for the preparation of graphene/polymer composites with improved electrical, mechanical, thermal properties at extremely low loading. Different synthetic strategies for the preparation of such nanocomposites are described, including not only physical processing, but also covalent bonding and specific affinity. The advantages and disadvantages of each method are also addressed. Moreover, potential applications in the fields of electronic and photonic devices, clean energy, and sensors are also presented. Several challenges need to be addressed for these nanocomposites to reach their full potential, such as homogeneous dispersion of materials with minimal aggregation, effective modification of graphene surface and well-controlled interfacial structure in composites. One of the most promising aspects of graphene/polymer composite is their potential for use in device and other electronics applications, owing to their high electrical conductivity. Further property improvements in graphenebased composites will be influenced by improved morphological control. Defects and wrinkles in platelets are likely to influence their reinforcing capabilities, and so exfoliation and/or dispersion techniques that promote a more elongated morphology could conceivably further improve mechanical properties of these composites. In addition, increased control over alignment and spatial organization of graphene-based fillers could be beneficial to the properties of almost all types of composites. Acknowledgments: Jingquan Liu acknowledges the fund from NSFC (51173087), NSF of Shandong (ZR2011EMM001), NSF of Qingdao (12-1-4-2-2-jc) and the Taishan Scholar Program of Shandong Provence for financial support.

References and Notes 1. 2. 3. 4.

5.

6. 7.

8.

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A. K. Geim and K. S. Novoselov, Nat. Mater. 6, 183 (2007). A. K. Geim, Science 324, 1530 (2009). D. Li and R. Kaner, Science 320, 1170 (2008). K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, Science 306, 666 (2004). K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos, and A. A. Firsov, Nature 438, 197 (2005). C. Lee, X. Wei, J. W. Kysar, and J. Hone, Science 321, 385 (2008). S. Stankovich, D. A. Dikin, G. H. B. Dommett, K. M. Kohlhaas, E. J. Zimney, E. A. Stach, R. D. Piner, S. T. Nguyen, and R. S. Ruoff, Nature 442, 282 (2006). M. D. Stoller, S. Park, Y. Zhu, J. An, and R. S. Ruoff, Nano Lett. 8, 3498 (2008).

Zhang et al.

9. J. Wu, H. A. Becerril, Z. Bao, Z. Liu, Y. Chen, and P. Peumans, Appl. Phys. Lett. 92, 263302 (2008). 10. R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T. Stauber, N. M. R. Peres, and A. K. Geim, Science 320, 1308 (2008). 11. S. Bae, H. Kim, Y. Lee, X. Xu, J.-S. Park, Y. Zheng, J. Balakrishnan, T. Lei, H. Ri Kim, Y. I. Song, Y.-J. Kim, K. S. Kim, B. Ozyilmaz, J.-H. Ahn, B. H. Hong, and S. Iijima, Nat. Nanotechnol. 5, 574 (2010). 12. A. A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, and C. N. Lau, Nano Lett. 8, 902 (2008). 13. J. Hu, X. Ruan, and Y. P. Chen, Nano Lett. 9, 2730 (2009). 14. M. Trushin and J. Schliemann, Phys. Rev. Lett. 99, 216602 (2007). 15. F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson, and K. S. Novoselov, Nat. Mater. 6, 652 (2007). 16. Y. Li, H. Wang, L. Xie, Y. Liang, G. Hong, and H. Dai, J. Am. Chem. Soc. 133, 7296 (2011). 17. S. Yin, Y. Zhang, J. Kong, C. Zou, C. M. Li, X. Lu, J. Ma, F. Y. C. Boey, and X. Chen, ACS Nano 5, 3831 (2011). 18. V. Chandra, J. Park, Y. Chun, J. W. Lee, I.-C. Hwang, and K. S. Kim, ACS Nano 4, 3979 (2010). 19. C. Liu, Z. Yu, D. Neff, A. Zhamu, and B. Z. Jang, Nano Lett. 10, 4863 (2010). 20. Y. M. Lin, C. Dimitrakopoulos, K. A. Jenkins, D. B. Farmer, H. Y. Chiu, A. Grill, and P. Avouris, Science 327, 662 (2010). 21. A. A. Balandin, Nat. Mater. 10, 569 (2011). 22. K. I. Bolotin, K. J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, and H. L. Stormer, Solid State Commun. 146, 351 (2008). 23. F. Schwierz, Nat. Nanotechnol. 5, 487 (2010). 24. G. Eda, G. Fanchini, and M. Chhowalla, Nat. Nanotechnol. 3, 270 (2008). 25. H. Chen, M. B. Muller, K. J. Gilmore, G. G. Wallace, and D. Li, Adv. Mater. 20, 3557 (2008). 26. E. H. Hwang, S. Adam, and S. Das Sarma, Phys. Rev. Lett. 98, 186806 (2007). 27. J. H. Chen, C. Jang, S. Xiao, M. Ishigami, and M. S. Fuhrer, Nat. Nanotechnol. 3, 206 (2008). 28. J. C. Meyer, A. K. Geim, M. I. Katsnelson, K. S. Novoselov, T. J. Booth, and S. Roth, Nature 446, 60 (2007). 29. J. Yao, Y. Sun, M. Yang, and Y. Duan, J. Mater. Chem. 22, 14313 (2012). 30. Y. Kojima, A. Usuki, M. Kawasumi, A. Okada, T. Kurauchi, and O. Kamigaito, J. Polym. Sci., Part A: Polym. Chem. 31, 983 (1993). 31. Y. Kojima, A. Usuki, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi, and O. Kamigaito, J. Mater. Res. 8, 1185 (1993). 32. T. Kuilla, S. Bhadra, D. Yao, N. H. Kim, S. Bose, and J. H. Lee, Prog. Polym. Sci. 35, 1350 (2010). 33. E. Badamshina, Y. Estrin, and M. Gafurova, J. Mater. Chem. A 1, 6509 (2013). 34. S. N. Barman, M. C. LeMieux, J. Baek, R. Rivera, and Z. Bao, ACS Appl. Mater. Interfaces 2, 2672 (2010). 35. B. Liu, M. Yang, Z. Zhang, G. Zhang, Y. Han, N. Xia, M. Hu, P. Zheng, and W. Wang, Langmuir 26, 9403 (2010). 36. X. Wang, H. You, F. Liu, M. Li, L. Wan, S. Li, Q. Li, Y. Xu, R. Tian, Z. Yu, D. Xiang, and J. Cheng, Chem. Vap. Deposition 15, 53 (2009). 37. E. Dervishi, Z. Li, F. Watanabe, A. Biswas, Y. Xu, A. R. Biris, V. Saini, and A. S. Biris, Chem. Commun. 0, 4061 (2009). 38. N. Li, Z. Wang, K. Zhao, Z. Shi, Z. Gu, and S. Xu, Carbon 48, 255 (2010). 39. E. Rollings, G. H. Gweon, S. Y. Zhou, B. S. Mun, J. L. McChesney, B. S. Hussain, A. V. Fedorov, P. N. First, W. A. de Heer, and A. Lanzara, J. Phys. Chem. Solids 67, 2172 (2006). 40. W. A. de Heer, C. Berger, X. Wu, P. N. First, E. H. Conrad, X. Li, T. Li, M. Sprinkle, J. Hass, M. L. Sadowski, M. Potemski, and G. Martinez, Solid State Commun. 143, 92 (2007). Rev. Adv. Sci. Eng., 3, 48–65, 2014

Zhang et al.

41. Y. Carissan and W. Klopper, Chem. Phys. Chem. 7, 1770 (2006). 42. C. D. Kim, B. K. Min, and W. S. Jung, Carbon 47, 1610 (2009). 43. J. Wang, Z. Shi, Y. Ge, Y. Wang, J. Fan, and J. Yin, J. Mater. Chem. 22, 17663 (2012). 44. D. V. Kosynkin, A. L. Higginbotham, A. Sinitskii, J. R. Lomeda, A. Dimiev, B. K. Price, and J. M. Tour, Nature 458, 872 (2009). 45. L. Jiao, L. Zhang, X. Wang, G. Diankov, and H. Dai, Nature 458, 877 (2009). 46. D. A. Dikin, S. Stankovich, E. J. Zimney, R. D. Piner, G. H. B. Dommett, G. Evmenenko, S. T. Nguyen, and R. S. Ruoff, Nature 448, 457 (2007). 47. S. Vadukumpully, J. Paul, and S. Valiyaveettil, Carbon 47, 3288 (2009). 48. X. L. Li, X. R. Wang, L. Zhang, S. W. Lee, and H. J. Dai, Science 319, 1229 (2008). 49. X. Li, G. Zhang, X. Bai, X. Sun, X. Wang, E. Wang, and H. Dai, Nat. Nanotechnol. 3, 538 (2008). 50. M. Choucair, P. Thordarson, and J. A. Stride, Nat. Nanotechnol. 4, 30 (2009). 51. Z. Liu, J. Liu, L. Cui, R. Wang, X. Luo, C. J. Barrow, and W. Yang, Carbon 51, 148 (2013). 52. G. Zheng, J. Wu, W. Wang, and C. Pan, Carbon 42, 2839 (2004). 53. R. Sengupta, M. Bhattacharya, S. Bandyopadhyay, and A. K. Bhowmick, Prog. Polym. Sci. 36, 638 (2011). 54. Z. Spitalsky, D. Tasis, K. Papagelis, and C. Galiotis, Prog. Polym. Sci. 35, 357 (2010). 55. H. Peng, J. Am. Chem. Soc. 130, 42 (2007). 56. D. W. Schaefer, and R. S. Justice, Macromolecules 40, 8501 (2007). 57. W. Bauhofer, and J. Z. Kovacs, Compos. Sci. Technol. 69, 1486 (2009). 58. C. Celik, and S. B. Warner, J. Appl. Polym. Sci. 103, 645 (2007). 59. M. Fang, K. Wang, H. Lu, Y. Yang, and S. Nutt, J. Mater. Chem. 20, 1982 (2010). 60. N. K. Srivastava, and R. M. Mehra, J. Appl. Polym. Sci. 109, 3991 (2008). 61. H. Hu, X. Wang, J. Wang, L. Wan, F. Liu, H. Zheng, R. Chen, and C. Xu, Chem. Phys. Lett. 484, 247 (2010). 62. X. L. Xie, Y. W. Mai, and X. P. Zhou, Mat. Sci. Eng. R 49, 89 (2005). 63. M. Zhang, D.-J. Li, D.-F. Wu, C.-H. Yan, P. Lu, and G.-M. Qiu, J. Appl. Polym. Sci. 108, 1482 (2008). 64. K. Zhang, L. L. Zhang, X. S. Zhao, and J. Wu, Chem. Mater. 22, 1392 (2010). 65. D. W. Wang, F. Li, J. Zhao, W. Ren, Z. G. Chen, J. Tan, Z. S. Wu, I. Gentle, G. Lu, and H. M. Cheng, ACS Nano 3, 1745 (2009). 66. X. Yan, J. Chen, J. Yang, Q. Xue, and P. Miele, ACS Appl. Mater. Interfaces 2, 2521 (2010). 67. X. Wang, Y. Hu, L. Song, H. Yang, W. Xing, and H. Lu, J. Mater. Chem. 21, 4222 (2011). 68. D. A. Nguyen, Y. R. Lee, A. V. Raghu, H. M. Jeong, C. M. Shin, and B. K. Kim, Polym. Int. 58, 412 (2009). 69. F. d. C. Fim, J. M. Guterres, N. R. S. Basso, and G. B. Galland, J. Polym. Sci., Part A: Polym. Chem. 48, 692 (2010). 70. J. Y. Jang, M. S. Kim, H. M. Jeong, and C. M. Shin, Compos. Sci. Technol. 69, 186 (2009). 71. X. Wang, J. Li, W. Qu, and G. Chen, J. Chromatogr. A 1218, 5542 (2011). 72. A. S. Patole, S. P. Patole, H. Kang, J.-B. Yoo, T.-H. Kim, and J.-H. Ahn, J. Colloid Interface Sci. 350, 530 (2010). 73. Z. Xu and C. Gao, Macromolecules 43, 6716 (2010). 74. S. Bose, T. Kuila, M. E. Uddin, N. H. Kim, A. K. T. Lau, and J. H. Lee, Polymer 51, 5921 (2010). 75. H. Zhou, W. Yao, G. Li, J. Wang, and Y. Lu, Carbon 59, 495 (2013). 76. H. Kim, Y. Miura, and C. W. Macosko, Chem. Mater. 22, 3441 (2010). Rev. Adv. Sci. Eng., 3, 48–65, 2014


77. H. Kim, S. Kobayashi, M. A. Abdur Rahim, M. L. J. Zhang, A. Khusainova, M. A. Hillmyer, A. A. Abdala, and C. W. Macosko, Polymer 52, 1837 (2011). 78. W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc. 80, 1339 (1958). 79. D. R. Dreyer, S. Park, C. W. Bielawski, and R. S. Ruoff, Chem. Soc. Rev. 39, 228 (2010). 80. D. Chen, H. Feng, and J. Li, Chem. Rev. 112, 6027 (2012). 81. C. Nethravathi, J. T. Rajamathi, N. Ravishankar, C. Shivakumara, and M. Rajamathi, Langmuir 24, 8240 (2008). 82. T. Szabó, A. Szeri, and I. Dékány, Carbon 43, 87 (2005). 83. P. Blake, P. D. Brimicombe, R. R. Nair, T. J. Booth, D. Jiang, F. Schedin, L. A. Ponomarenko, S. V. Morozov, H. F. Gleeson, E. W. Hill, A. K. Geim, and K. S. Novoselov, Nano Lett. 8, 1704 (2008). 84. Q. Bao, H. Zhang, J.-X. Yang, S. Wang, D. Y. Tang, R. Jose, S. Ramakrishna, C. T. Lim, and K. P. Loh, Adv. Funct. Mater. 20, 782 (2010). 85. T. Ramanathan, S. Stankovich, D. A. Dikin, H. Liu, H. Shen, S. T. Nguyen, and L. C. Brinson, J. Polym. Sci., Part B: Polym. Phys. 45, 2097 (2007). 86. Q. Wu, Y. Xu, Z. Yao, A. Liu, and G. Shi, ACS Nano 4, 1963 (2010). 87. D. Li, M. B. Muller, S. Gilje, R. B. Kaner, and G. G. Wallace, Nat. Nanotechnol. 3, 101 (2008). 88. H. Hu, G. Zhang, L. Xiao, H. Wang, Q. Zhang, and Z. Zhao, Carbon 50, 4596 (2012). 89. S. Vadukumpully, J. Paul, N. Mahanta, and S. Valiyaveettil, Carbon 49, 198 (2011). 90. G. Broza, K. Piszczek, K. Schulte, and T. Sterzynski, Compos. Sci. Technol. 67, 890 (2007). 91. F. Barroso-Bujans, S. Cerveny, R. Verdejo, J. J. del Val, J. M. Alberdi, A. Alegra, and J. Colmenero, Carbon 48, 1079 (2009). 92. T. Wei, G. Luo, Z. Fan, C. Zheng, J. Yan, C. Yao, W. Li, and C. Zhang, Carbon 47, 2296 (2009). 93. L. Jiang, X. P. Shen, J. L. Wu, and K. C. Shen, J. Appl. Polym. Sci. 118, 275 (2010). 94. S. Ansari, and E. P. Giannelis, J. Polym. Sci., Part B: Polym. Phys. 47, 888 (2009). 95. H. Kim, S. Kobayashi, M. A. Abdur Rahim, M. J. Zhang, A. Khusainova, M. A. Hillmyer, A. A. Abdala, and C. W. Macosko, Polymer 52, 1837 (2011). 96. S. Mohamadi, and N. Sharifi-Sanjani, Polym. Compos. 32, 1451 (2011). 97. M. Yoonessi and J. R. Gaier, ACS Nano 4, 7211 (2010). 98. X. Zeng, J. Yang, and W. Yuan, Eur. Polym. J. 48, 1674 (2012). 99. C. Heo, H.-G. Moon, C. S. Yoon, and J.-H. Chang, J. Appl. Polym. Sci. 124, 4663 (2012). 100. G. Vleminckx, S. Bose, J. Leys, J. Vermant, M. Wübbenhorst, A. A. Abdala, C. Macosko, and P. Moldenaers, ACS Appl. Mater. Interfaces 3, 3172 (2011). 101. Y.-T. Liu, X.-M. Xie, and X.-Y. Ye, Carbon 49, 3529 (2011). 102. R. Verdejo, M. M. Bernal, L. J. Romasanta, and M. A. LopezManchado, J. Mater. Chem. 21, 3301 (2011). 103. H. Kim, A. A. Abdala, and C. W. Macosko, Macromolecules 43, 6515 (2010). 104. I. H. Kim, and Y. G. Jeong, J. Polym. Sci., Part B: Polym. Phys. 48, 850 (2010). 105. H.-B. Zhang, W.-G. Zheng, Q. Yan, Y. Yang, J.-W. Wang, Z.-H. Lu, G.-Y. Ji, and Z.-Z. Yu, Polymer 51, 1191 (2010). 106. D. Yan, H.-B. Zhang, Y. Jia, J. Hu, X.-Y. Qi, Z. Zhang, and Z.-Z. Yu, ACS Appl. Mater. Interfaces 4, 4740 (2012). 107. A. Dasari, Z. Z. Yu, and Y. W. Mai, Polymer 50, 4112 (2009). 108. J. Park and M. Yan, Acc. Chem. Res. 46, 181 (2013). 109. Z. Liu, J. T. Robinson, X. Sun, and H. Dai, J. Am. Chem. Soc. 130, 10876 (2008).

63


110. S. H. Lee, D. R. Dreyer, J. An, A. Velamakanni, R. D. Piner, S. Park, Y. Zhu, S. O. Kim, C. W. Bielawski, and R. S. Ruoff, Macromol. Rapid Commun. 31, 281 (2010). 111. T. Ramanathan, A. A. Abdala, S. Stankovich, D. A. Dikin, M. Herrera-Alonso, R. D. Piner, D. H. Adamson, H. C. Schniepp, X. Chen, R. S. Ruoff, S. T. Nguyen, I. A. Aksay, R. K. Prud’Homme and L. C. Brinson, Nat. Nanotechnol. 3, 327 (2008). 112. H. Yang, F. Li, C. Shan, D. Han, Q. Zhang, L. Niu, and A. Ivaska, J. Mater. Chem. 19, 4632 (2009). 113. Y. Dong Sheng, K. Tapas, K. N. Hoon, K. Partha, and L. J. Hee, Carbon 54, 310 (2013). 114. R. L. D. Whitby, A. Korobeinyk, and K. V. Glevatska, Carbon 49, 722 (2011). 115. H. J. Salavagione, M. n. A. Goìmez, and G. Martiìnez, Macromolecules 42, 6331 (2009). 116. S. Mahouche-Chergui, S. Gam-Derouich, C. Mangeney, and M. M. Chehimi, Chem. Soc. Rev. 40, 4143 (2011). 117. H. L. Ma, H. B. Zhang, Q. H. Hu, W. J. Li, Z. G. Jiang, Z. Z. Yu, and A. Dasari, ACS Appl. Mater. Interfaces 4, 1948 (2012). 118. C. Gómez-Navarro, R. T. Weitz, A. M. Bittner, M. Scolari, A. Mews, M. Burghard, and K. Kern, Nano Lett. 7, 3499 (2007). 119. H. He and C. Gao, Chem. Mater. 22, 5054 (2010). 120. J. Liu, G. Chen, and M. Jiang, Macromolecules 44, 7682 (2011). 121. Z. Tang, H. Kang, Z. Shen, B. Guo, L. Zhang, and D. Jia, Macromolecules 45, 3444 (2012). 122. X. Wang, L. Zhi, and K. Mullen, Nano Lett. 8, 323 (2007). 123. L. M. Veca, F. Lu, M. J. Meziani, L. Cao, P. Zhang, G. Qi, L. Qu, M. Shrestha, and Y.-P. Sun, Chem. Commun. 0, 2565 (2009). 124. D. Vuluga, J.-M. Thomassin, I. Molenberg, I. Huynen, B. Gilbert, C. Jerome, M. Alexandre, and C. Detrembleur, Chem. Commun. 47, 2544 (2011). 125. R. Feng, W. Zhou, G. Guan, C. Li, D. Zhang, Y. Xiao, L. Zheng, and W. Zhu, J. Mater. Chem. 22, 3982 (2012). 126. B. Yu, X. Wang, W. Xing, H. Yang, L. Song, and Y. Hu, Ind. Eng. Chem. Res. 51, 14629 (2012). 127. Y. Zhan, X. Yang, H. Guo, J. Yang, F. Meng, and X. Liu, J. Mater. Chem. 22, 5602 (2012). 128. B. Kerscher, A.-K. Appel, R. Thomann, and R. Mülhaupt, Macromolecules 46, 4395 (2013). 129. S. Bian, A. M. Scott, Y. Cao, Y. Liang, S. Osuna, K. N. Houk, and A. B. Braunschweig, J. Am. Chem. Soc. 135, 9240 (2013). 130. N. Zydziak, B. Yameen, and C. Barner-Kowollik, Polymer Chemistry 4, 4072 (2013). 131. J. Yuan, G. Chen, W. Weng, and Y. Xu, J. Mater. Chem. 22, 7929 (2012). 132. T. Huang, Y. Xin, T. Li, S. Nutt, C. Su, H. Chen, P. Liu, and Z. Lai, ACS Appl. Mater. Interfaces 5, 4878 (2013). 133. E. Co¸skun, E. A. Zaragoza-Contreras, and H. J. Salavagione, Carbon 50, 2235 (2012). 134. G. Goncalves, P. A. A. P. Marques, A. Barros-Timmons, I. Bdkin, M. K. Singh, N. Emami, and J. Gracio, J. Mater. Chem. 20, 9927 (2010). 135. T. Gao, X. Wang, B. Yu, Q. Wei, Y. Xia, and F. Zhou, Langmuir 29, 1054 (2013). 136. J. Chiefari, Y. Chong, F. Ercole, J. Krstina, J. Jeffery, T. P. T. Le, R. T. A. Mayadunne, G. F. Meijs, C. L. Moad, and G. Moad, Macromolecules 31, 5559 (1998). 137. G. Moad, E. Rizzardo, and S. H. Thang, Australian Journal of Chemistry. 58, 379 (2005). 138. K. Jiang, C. Ye, P. Zhang, X. Wang, and Y. Zhao, Macromolecules 45, 1346 (2012). 139. Y. Huang, Y. Qin, Y. Zhou, H. Niu, Z. Z. Yu, and J. Y. Dong, Chem. Mater. 22, 4096 (2010). 140. B. Zhang, Y. Zhang, C. Peng, M. Yu, L. Li, B. Deng, P. Hu, C. Fan, J. Li, and Q. Huang, Nanoscale 4, 1742 (2012). 141. L. Ren, S. Huang, C. Zhang, R. Wang, W. Tjiu, and T. Liu, J. Nanopart. Res. 14, 1 (2012).

64

Zhang et al.

142. R. Verdejo, F. J. Tapiador, L. Helfen, M. M. Bernal, N. Bitinis, and M. A. Lopez-Manchado, Phys. Chem. Chem. Phys. 11, 10860 (2009). 143. F. Beckert, A. M. Rostas, R. Thomann, S. Weber, E. Schleicher, C. Friedrich, and R. Mülhaupt, Macromolecules 46, 5488 (2013). 144. M. Steenackers, A. M. Gigler, N. Zhang, F. Deubel, M. Seifert, L. H. Hess, C. H. Y. X. Lim, K. P. Loh, J. A. Garrido, R. Jordan, M. Stutzmann, and I. D. Sharp, J. Am. Chem. Soc. 133, 10490 (2011). 145. K. E. Riley, M. Pitoˇnaík, J. i. Cˇcernyí, and P. Hobza, J. Chem. Theory Comput. 6, 66 (2009). 146. K. E. Riley, M. Pitoòák, P. Jureèka, and P. Hobza, Chem. Rev. 110, 5023 (2010). 147. J. Liu, L. Tao, W. Yang, D. Li, C. Boyer, R. Wuhrer, F. Braet, and T. P. Davis, Langmuir 26, 10068 (2010). 148. J. Liu, W. Yang, L. Tao, D. Li, C. Boyer, and T. P. Davis, J. Polym. Sci., Part A: Polym. Chem. 48, 425 (2010). 149. Y. Xu, and G. Shi, J. Mater. Chem. 21, 3311 (2011). 150. X. Zhao, Q. Zhang, Y. Hao, Y. Li, Y. Fang, and D. Chen, Macromolecules 43, 9411 (2010). 151. R. K. Layek, S. Samanta, and A. K. Nandi, Carbon 50, 815 (2012). 152. S. A. Ju, K. Kim, J.-H. Kim, and S.-S. Lee, ACS Appl. Mater. Interfaces 3, 2904 (2011). 153. V. H. Pham, T. T. Dang, S. H. Hur, E. J. Kim, and J. S. Chung, ACS Appl. Mater. Interfaces 4, 2630 (2012). 154. D. D. Kulkarni, I. Choi, S. S. Singamaneni, and V. V. Tsukruk, ACS Nano 4, 4667 (2010). 155. N. Liu, F. Luo, H. Wu, Y. Liu, C. Zhang, and J. Chen, Adv. Funct. Mater. 18, 1518 (2008). 156. L. Lei, J. Qiu, Y. Zhao, X. Wu, and E. Sakai, Sci. Adv. Mater. 4, 912 (2012). 157. S. T. Hsiao, C. C. M. Ma, H. W. Tien, W. H. Liao, Y. S. Wang, S. M. Li, and Y. C. Huang, Carbon 60, 57 (2013). 158. E. Y. Choi, T. H. Han, J. Hong, J. E. Kim, S. H. Lee, H. W. Kim, and S. O. Kim, J. Mater. Chem. 20, 1907 (2010). 159. B. Shen, W. Zhai, C. Chen, D. Lu, J. Wang, and W. Zheng, ACS Appl. Mater. Interfaces 3, 3103 (2011). 160. W. Yuan, J. Yuan, M. Zhou, and C. Pan, J. Polym. Sci., Part A: Polym. Chem. 46, 2788 (2008). 161. X. Pei, Y. Xia, W. Liu, B. Yu, and J. Hao, J. Polym. Sci., Part A: Polym. Chem. 46, 7225 (2008). 162. B. N. Gacal, B. Koz, B. Gacal, B. Kiskan, M. Erdogan, and Y. Yagci, J. Polym. Sci., Part A: Polym. Chem. 47, 1317 (2009). 163. Y. Xu, H. Bai, G. Lu, C. Li, and G. Shi, J. Am. Chem. Soc. 130, 5856 (2008). 164. J. Liu, J. Tang, and J. J. Gooding, J. Mater. Chem. 22, 12435 (2012). 165. D.-W. Lee, T. Kim, and M. Lee, Chem. Commun. 47, 8259 (2011). 166. I. Kaminska, M. R. Das, Y. Coffinier, J. Niedziolka-Jonsson, P. Woisel, M. Opallo, S. Szunerits, and R. Boukherroub, Chem. Commun. 48, 1221 (2012). 167. H. Peng, L. Meng, Q. Lu, S. Dong, Z. Fei, and P. J. Dyson, J. Mater. Chem. 22, 14868 (2012). 168. X. Xu, D. Ou, X. Luo, J. Chen, J. Lu, H. Zhan, Y. Dong, J. Qin, and Z. Li, J. Mater. Chem. 22, 22624 (2012). 169. R. Oprea, S. F. Peteu, P. Subramanian, W. Qi, E. Pichonat, H. Happy, M. Bayachou, R. Boukherroub, and S. Szunerits, Analyst 138, 4345 (2013). 170. J. Malig, N. Jux, D. Kiessling, J.-J. Cid, P. Vázquez, T. Torres, and D. M. Guldi, Angew. Chem. Int. Ed. 50, 3561 (2011). 171. Y. K. Yang, C. E. He, R. G. Peng, A. Baji, X. S. Du, Y. L. Huang, X. L. Xie, and Y. W. Mai, J. Mater. Chem. 22, 5666 (2012). 172. D. Parviz, S. Das, H. S. T. Ahmed, F. Irin, S. Bhattacharia, and M. J. Green, ACS Nano 6, 8857 (2012). 173. S. Xie, Y. Liu, and J. Li, Appl. Phys. Lett. 92, 243121 (2008). 174. S. Chatterjee, F. A. Nüesch, and B. T. T. Chu, Nanotechnology 22, 275714 (2011). Rev. Adv. Sci. Eng., 3, 48–65, 2014

Zhang et al.

175. J. Du, L. Zhao, Y. Zeng, L. Zhang, F. Li, P. Liu, and C. Liu, Carbon 49, 1094 (2011). 176. D. Wang, X. Zhang, J.-W. Zha, J. Zhao, Z.-M. Dang, and G.-H. Hu, Polymer 54, 1916 (2013). 177. Z. Chen, W. Ren, L. Gao, B. Liu, S. Pei, and H.-M. Cheng, Nat. Mater. 10, 424 (2011). 178. Z. Xu, and C. Gao, Nat. Commun. 2, 571 (2011). 179. P. Steurer, R. Wissert, R. Thomann, and R. Mülhaupt, Macromol. Rapid Commun. 30, 316 (2009). 180. H. B. Zhang, Q. Yan, W. G. Zheng, Z. He, and Z. Z. Yu, ACS Appl. Mater. Interfaces 3, 918 (2011). 181. J. Liang, Y. Wang, Y. Huang, Y. Ma, Z. Liu, J. Cai, C. Zhang, H. Gao, and Y. Chen, Carbon 47, 922 (2009). 182. V. H. Pham, T. V. Cuong, T. T. Dang, S. H. Hur, B.-S. Kong, E. J. Kim, E. W. Shin, and J. S. Chung, J. Mater. Chem. 21, 11312 (2011). 183. E. Tkalya, M. Ghislandi, A. Alekseev, C. Koning, and J. Loos, J. Mater. Chem. 20, 3035 (2010). 184. H. Wu, W. Zhao, H. Hu, and G. Chen, J. Mater. Chem. 21, 8626 (2011). 185. X. Y. Qi, D. Yan, Z. Jiang, Y. K. Cao, Z. Z. Yu, F. Yavari, and N. Koratkar, ACS Appl. Mater. Interfaces 3, 3130 (2011). 186. N. Wu, X. She, D. Yang, X. Wu, F. Su, and Y. Chen, J. Mater. Chem. 22, 17254 (2012). 187. C. Mao, Y. Zhu, and W. Jiang, ACS Appl. Mater. Interfaces 4, 5281 (2012). 188. Y. Tan, L. Fang, J. Xiao, Y. Song, and Q. Zheng, Polymer Chemistry 4, 2939 (2013). 189. H. J. Salavagione, G. Martinez, and M. A. Gomez, J. Mater. Chem. 19, 5027 (2009). 190. J. Ling, W. Zhai, W. Feng, B. Shen, J. Zhang, and W. G. Zheng, ACS Appl. Mater. Interfaces 5, 2677 (2013). 191. A. V. Raghu, Y. R. Lee, H. M. Jeong, and C. M. Shin, Macromol. Chem. Phys. 209, 2487 (2008). 192. Y. R. Lee, A. V. Raghu, H. M. Jeong, and B. K. Kim, Macromol. Chem. Phys. 210, 1247 (2009).

Rev. Adv. Sci. Eng., 3, 48–65, 2014


193. V. Eswaraiah, V. Sankaranarayanan, and S. Ramaprabhu, Macromol. Mater. Eng. 296, 894 (2011). 194. L. Cui, J. Liu, R. Wang, Z. Liu, and W. Yang, J. Polym. Sci., Part A: Polym. Chem. 50, 4423 (2012). 195. J. Liu, R. Wang, L. Cui, J. Tang, Z. Liu, Q. Kong, W. Yang, and J. Gooding, J. Phys. Chem. C 116, 17939 (2012). 196. S. Park, J. W. Suk, J. An, J. Oh, S. Lee, W. Lee, J. R. Potts, J.-H. Byun, and R. S. Ruoff, Carbon 50, 4573 (2012). 197. H. Pang, T. Chen, G. Zhang, B. Zeng, and Z.-M. Li, Mater. Lett. 64, 2226 (2010). 198. H. B. Zhang, W. G. Zheng, Q. Yan, Z. G. Jiang, and Z. Z. Yu, Carbon 50, 5117 (2012). 199. Z. Chen, C. Xu, C. Ma, W. Ren, and H.-M. Cheng, Adv. Mater. 25, 1296 (2013). 200. Y. Yang, M. C. Gupta, K. L. Dudley, and R. W. Lawrence, Adv. Mater. 17, 1999 (2005). 201. H. Li, S. Pang, S. Wu, X. Feng, K. Müllen, and C. Bubeck, J. Am. Chem. Soc. 133, 9423 (2011). 202. J. Xu, K. Wang, S.-Z. Zu, B.-H. Han, and Z. Wei, ACS Nano 4, 5019 (2010). 203. D. Zhang, X. Zhang, Y. Chen, P. Yu, C. Wang, and Y. Ma, J. Power Sources 196, 5990 (2011). 204. J. Li, H. Xie, Y. Li, J. Liu, and Z. Li, J. Power Sources 196, 10775 (2011). 205. X. Zhang, Z. Sui, B. Xu, S. Yue, Y. Luo, W. Zhan, and B. Liu, J. Mater. Chem. 21, 6494 (2011). 206. Z. Gao, W. Yang, J. Wang, B. Wang, Z. Li, Q. Liu, M. Zhang, and L. Liu, Energy Fuels 27, 568 (2012). 207. D. X. Yan, P. G. Ren, H. Pang, Q. Fu, M. B. Yang, and Z. M. Li, J. Mater. Chem. 22, 18772 (2012). 208. W. H. Lee, J. W. Suk, J. Lee, Y. Hao, J. Park, J. W. Yang, H.-W. Ha, S. Murali, H. Chou, D. Akinwande, K. S. Kim, and R. S. Ruoff, ACS Nano 6, 1284 (2012). 209. Z. Song, T. Xu, M. L. Gordin, Y.-B. Jiang, I.-T. Bae, Q. Xiao, H. Zhan, J. Liu, and D. Wang, Nano Lett. 12, 2205 (2012).

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