percolation threshold polymer composite
November 13th, 2020

Thus, graphene is one of the most efficient fillers available due to its large aspect ratio. There are also further challenges classifying these production methods, so broad categories of GRMs are outlined below. The obtained fibrous SRG/PVDF mixture was vacuum filtrated and dried and finally hot-pressed into thin sheets of approximately 1 mm thick. (b) Graphene enables a significantly lower percolation threshold in PET than graphite (adapted from [56], copyright 2010, with permission from Elsevier). Polymer 1998, 39: 99–107. For example, models have shown that agglomeration of the filler will lead to lower percolation thresholds [68]. The covalent functionalisation of GO, however, is reversible to a certain extent, and some electrical conductivity can be recovered. For PC they measured a lower percolation threshold at a loading of 2.5 wt.% and yielding a conductivity of 7.7\times 10^{-6} S m−1. One concept for increasing the electrical conductivity is doping graphene with heteroatoms such as nitrogen [141]. When material is uniformly distributed, it cannot form a conductive network; if, however, the same amount of material is localised in a smaller volume, a network is more likely formed. Functionalised graphene materials are emerging as attractive alternatives to TRGO and CRGO as reinforcements for polymers. In this study, we fabricated graphene/polymer composites using solvothermal reduction of GO in the polymer solution. The incorporation of functional groups during dry grinding has been recently reported [105]. The building block of such materials are single GO sheets which, due to their excellent processability in solution, can assemble in uniform and continuous thin (~10 nm) films on large scale (tens of cm2). Because of the presence of carbonyl and carboxyl functional groups on its surface, the thickness of the sheets was approximately 1 nm, slightly thicker than graphene [31]. The electrical conductivities were found to increase dramatically from 7\times 10^{-7} S m−1 to 0.02 S m−1 as the number of bilayers was increased from one to two (i.e. However, for practical applications such as polymer nanocomposites, there is a balance of quality against the ability to produce the material on the required scale. 10.3144/expresspolymlett.2012.31, Moazzami GM, Sharif F: Enhancement of dispersion and bonding of graphene-polymer through wet transfer of functionalized graphene oxide. A composite is a material that consists of two or more materials or phases, whose final properties differ from those of the original materials. The use of TRGO to enhance the electrical performance of polymers has been successfully demonstrated for thermoplastics. At more advanced levels of reduction, the patches become more connected and transport proceeds via percolation [30]. For example, Du et al [57] prepared high density polyethylene nanocomposites with graphene nanosheets (GNSs) and carbon nanotubes. Tjong SC: Polymer nanocomposite bipolar plates reinforced with carbon nanotubes and graphite nanosheets. Unfortunately you do not have access to this content, please use the. Gong XY, Liu J, Baskaran S, Voise RD, Young JS: Surfactant-assisted processing of carbon nanotube/polymer composites. N-doped TRGO produced via thermolysis has been reported to improve the electrical conductivity of both graphene and the corresponding polymer composites [109]. You will only need to do this once. 10.1021/cm0630800. In addition to thermoplastics, elastomers have also recently been combined with GO materials. 10.1002/adma.200600703, Jiang MJ, Dang ZM, Yao SH, Bai JB: Effects of surface modification of carbon nanotubes on the microstructure and electrical properties of carbon nanotubes/rubber nanocomposites. ABS, Acrylonitrile butadiene styrene; BA, Butyl acrylate; CB, Carbon black; CNT, Carbon nanotube; CRGO, Chemically reduced graphene oxide; CVD, Chemical vapour deposition; DMG, Dry-milled graphene; DOS, Density of states; EG, Expanded graphite; EMI, Electromagnetic interference; EP, Epoxy; f-GNP, Functionalised-graphite nanoplatelets; GA, Graphene aerogels; GNP, Graphite nanoplatelets; GNS, Graphene nanosheets; GO, Graphene oxide; GRM, Graphene related materials; HDPE, High-density polyethylene; HI, Hydroiodic acid; iPP, Isotactic polypropylene; LbL, Layer-by-layer; LLDPE, Linear low-density polyethylene; MLG, Multilayer graphene; N-TRGO, Nitrogen-thermally reduced graphene oxide; NR, Natural rubber; PA11, Polyamide 11; PA12, Polyamide 12; PA6, Polyamide 6; PC, Polycarbonate; PCL, Polycaprolactone; PE, Polyethylene; PEI, Polyethyleneimine; PI, Polyimide; PLA, Polylactic acid; PMMA, Poly(methyl methacrylate); POSS, Polyhedral oligomeric silsesquioxane; PP, Polypropylene; PS, Polystyrene; PU, Polyurethane; PVC, Polyvinyl chloride; rGO, Reduced-graphene oxide; SAN, Styrene-acrylonitrile; SBR, Styrene-butadiene; sPS, Syndiotactic polystyrene; TPU, Thermoplastic polyurethane; TRGO, Thermally reduced graphene oxide; UHMWPE, Ultra-high-molecular-weight polyethylene; VRH, Variable range hopping; XNBR, Carboxylated nitrile butadiene rubber. Express Polym Lett 2012, 6: 283–292. This model is called Efros and Shklovskii (ES-VRH) and is described by a charge transport equation similar to the Mott model, where the exponent γ does not depend on system dimensions and is equal to 1/2. This sensitivity allowed them to monitor breathing and pulse, as well as the movement of a spider (as shown in figure 7(d)). Better performance over greater strains is possible by embedding graphene in a flexible nanocomposite. (b) The conductivity of SBR composites as a function of electrical frequency (adapted from [103], John Wiley & Sons, copyright 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim). Nanoscale Research Letters Chem Mater 2002, 14: 44–51. * Views captured on Cambridge Core between . However, the promotion of one electron to the unfilled state creates a hole in the occupied site. This value is relatively high compared to other solution-processable techniques, as shown in figure 1(g), and also avoids the use of harsh chemicals and high temperatures. (g) Modelling the voltage drop across a composite's filler network as it is strained (adapted from [162], copyright 2012 American Chemical Society). Traditional carbon-based fillers (such as carbon nanotubes (CNTs) [6] and carbon black (CB) [7]) make excellent candidates for conductive composites because of their high electrical conductivity combined with good mechanical properties. Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China, Shenzhen Research Institute, City University of Hong Kong, Shenzhen, China, You can also search for this author in The mechanism of resistance change is a combination of two processes, both of which depend upon the microstructure of the conducting network. There is still a need to create networks that are more reproducible, and stable for longer. The platelets overlapped in regions and they formed a conductive network, whose resistance changed under strain. Electrically conductive composites comprising polymers and graphene are extremely versatile and have a wide range of potential applications. In general, such systems are continuous thin films corresponding to a non-percolative regime, which can be described as a dense mesh. Of all the carbon nanofillers, GRMs remain the most promising candidates for electrically conductive polymer composites because of their large surface areas, large aspect ratios, and high electrical conductivities. The large aspect ratios of the SRG sheets make the percolation threshold even smaller. This makes TRGO a very promising nanomaterial to blend with polar polymers [54, 82, 102–112]. The covalent functionalisation of GO has a detrimental impact on its conductivity with reported values generally in the range of 2 \times 10^{-2} S m−1 [29], significantly lower than those of graphene, and this renders GO unsuitable for most conductive applications. The extremely high conductivity of monolayer graphene is one of its most attractive properties. Therefore, alternative fillers are being sought. Frequency dependency of (a) dielectric constant and (b) electrical conductivity of SRG/PVDF composite with various filler contents. These graphene composites had ultimate conductivity values of 2–4 orders of magnitude higher than those with CNTs produced in the same way. and 0.9 vol.%), and to a value of 0.05 S m−1 with three bilayers (1.3 vol.%). As shown in the inset of Figure 5, the Zener tunneling predicts the nonlinear current density (JNL) very well on the basis of the tunneling equation, i.e., J = AEnexp(−B/E) where A, B, and n are constants [51].

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