Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity

Abstract

Field-grading materials (FGMs) are used to reduce the probability for electrical breakdowns in critical regions of electrical components and are therefore of great importance. Usually, FGMs are heavily filled (40 vol.%) with semi-conducting or conducting particles. Here, polymer-grafted reduced graphene oxide (rGO) is used as a filler to accomplish percolated networks at very low filling ratios (<2 vol.%) in a semi-crystalline polymer matrix: poly(ethylene-co-butyl acrylate) (EBA). Various simulation models are used to predict the percolation threshold and the flake-to-flake distances, to complement the experimental results. A substantial increase in thermal stability of rGO is observed after surface modification, either by silanization or subsequent polymerizations. The non-linear DC resistivity of neat and silanized rGO and its trapping of charge-carriers in semi-crystalline EBA are demonstrated for the first time. It is shown that the polymer-grafted rGO improve the dispersibility in the EBA-matrix and that the graft length controls the inter-flake distances (i.e. charge-carrier hopping distances). By the appropriate selection of graft lengths, both highly resistive materials at 10 kV mm and FGMs with a large and distinct drop in resistivity (six decades) are obtained, followed by saturation. The nonlinear drop in resistivity is attributed to narrow inter-flake distance distributions of grafted rGO.

Byproduct-free curing of a highly insulating polyethylene copolymer blend: an alternative to peroxide crosslinking

“…3,4 The insulation of the most advanced type of HVDC cable consists of low-density polyethylene (LDPE), which (in contrast to other grades of polyethylene) can be produced with a high degree of both physical and chemical cleanliness, resulting in the required low conductivity. Several strategies such as blending with high-density polyethylene (HDPE) 3 and the addition of metal oxide nanoparticles [4][5][6][7][8] or reduced graphene oxide 9 have been proposed as means to further reduce the conductivity.…”

Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications

“…The extremely large specific surface area of all nanofillers can be exploited to improve many material properties. Traditional composites are typically designed for improving the mechanical properties of the material, but nanocomposites are more versatile; for instance, the thermal and electrical properties are also influenced by the addition of nanofillers such as graphene, ZnO, or Al 2 O 3 [1,2].…”

“…Moreover, if hydrophilic inorganic nanoparticles, such as SiO 2 , Al 2 O 3 , or ZnO, are introduced directly into a hydrophobic polymer matrix, the particle miscibility and the adhesion between the particles and the matrix can easily become unsatisfying. Even though a proper surface modification of the nanofillers can significantly improve the dispersion [2,3], it is still a major challenge for scientists and material producers to obtain completely controlled dispersions.…”

“…Graphene, graphene oxide (GO), and (partially) reduced graphene oxide (rGO) have interesting electrical properties [2,7,8,9,10,11] and have therefore attracted attention as promising fillers for the next generation of non-linear resistive FGMs [2,7,8,9,10,11]. For instance, the addition of 2.5 vol.% partially reduced GO into a silicone rubber matrix and resulted in a material with non-linear resistivity [12].…”

Effect of Filler Orientation on the Electrical Conductivity of Carbon Fiber/PMMA Composites

“…A decreased particle size, when AR and all other variables are kept constant, generally result in a decreased percolation threshold due to shorter average inter-particle distances [12] An increased applied voltage (or temperature) can potentially result in a decreased percolation threshold, because the maximum hopping/tunneling distances for the electrons will increase if they have higher energy [13]. If the fillers are surface modified with dense insulating grafts, the shortest possible interparticle distance will be limited, resulting in a higher and narrower percolation threshold [14]. The dispersion of the fillers also effect the percolation threshold [1,15].…”