Preparation And Properties Of Graphene/poly(Ether Sulfone) Conductive Composites

As driven by the growing demands of modern manufacturing, the traditional metalconductive material are replacing by polymer conductive composites(CPC) in manyapplication areas, which ascribe to its numbers of advantages, such as low density, goodanti-corrosion properties, high strength, good processing performance, adjustable resistance,nonlinear conduction behavior and so on. The conductivity of CPC depends on the particlesize, aspect ratio and orientation of fllers along with processing route. So, graphene isthought as the ideal reinforcing fillers in preparing the polymer conductive composites,attributed to the2-D structure and excellent physical properties. Poly (ether sulfone) knownas high performance polymer with understanding properties, is chosen as the polymermatrix in this study. However, effcient reinforcement will be largely limited becausegraphene tends to agglomerate within a polymer matrix. Therefore, introducing suitablechemical groups to the surface of graphene by covalent functionalization process caninhabit their aggregation and result in even dispersion in PES and better interfacialinteractions.Chemical functionalized graphene (f-G) was obtained by the reaction of the residualepoxide and carboxyl functional groups on the hydrazine-reduced graphene sheets withhydroquinone. The efficacy of the functionalization reaction of graphene was confirmed byXPS and TGA analysis. AFM and TEM images showed that the functionalized graphenecould be easily exfoliated in N-methyl-2-pyrrolidone (NMP) and functionalized graphenenanosheets were composed of single or bilayers of graphene sheets. The conductivef-G/PES composites were fabricated by solution casting method in NMP and the alternatingcurrent (AC) and direct current (DC) properties of f-G/PES composites were investigated.It had been observed that good dispersion of f-G nanosheets in PES matrix resulted in alow percolation threshold of0.335vol%, which could be comparable to the best valuesreported. Hopping type of charge transport occurred during the insulator–semiconductortransition of f-G/PES composites. The dielectric constant of the composites increased withincrease of f-G content and the dielectric constant of f-G/PES composites with5wt%f-Gincreased to238at1000Hz. This result indicated that these composites could perhaps beused as high dielectric constant materials. Impedance measurement was carried out toevaluate interfacial capacitance of the composites, and the interfacial capacitance of thecomposites increased to1041.9pF of f-G/PES with5wt%f-G from30.48pF of f-G/PESwith0.5wt%f-G. Inspired by the previous work reported on the other references, the performance off-G/PES composites could be greatly further enhanced by the introduction of carbonnanotubes. Therefore, the ternary blends were detailedly investigated. Firstly, enhancementon the mechanical properties and DC conductivity of composites by five kinds of fillers:pristine multi-walled carbon nanotubes(p-CNTs)﹑functional multi-walled carbonnanotubes (f-CNTs)﹑functional graphene sheets(f-G)﹑functional graphene sheets-pristine multi-walled carbon nanotubes(f-G-p-CNTs) and functional graphene sheets-functional multi-walled carbon nanotubes(f-G-f-CNTs), were compared and manyinteresting results were found as follows: Much higher tensile strength could be obtainedby incorporation of f-CNTs, while better tensile modulus would be achieved byintroduction of f-G in composites. Moreover, composites demonstrated a higherconductivity in case of hybrid filler. Thus the hybrid filler surpasses the performance ofindividual f-G, f-CNTs or p-CNTs. This was ascribed to the synergistic effect among thegraphene nanosheets and carbon nanotubes, which caused the co-dispersion of thegraphene nanosheets and carbon nanotubes in polymer matrix, and provided the moreeffective percolating network for electrical transport. Then, in order to study the synergeticeffect of hybrid fillers further, electrical conductivity and tensile properties as a function ofthe f-CNTs in the hybrid filler at hybrid filler loading of5wt%, was investigated. Thetensile strength of the composites increased monotonically as the fraction of the f-CNTsincreased, while the tensile modulus and electrical conductivity showed the pronouncedmaximum value at a f-G:f-CNTs filler ration of1and1/3respectively. Consequentlysynergetic effect on different properties of compsites revealed corresponding optimal ratioof f-G:f-CNTs. When the weight ration of f-G and f-CNTs was fixed as1, f-G-f-CNTs/PEScomposites showed a percolation threshold of0.250vol%, much lower than that of f-G/PEScomposites and better tensile properties than that of pristine PES.