Nonlinear DC conduction behavior in epoxy resin/graphite nanosheets composites

Epoxy resin (ER)/graphite nanosheet (GN) composites with a low percolation threshold (owing to particular geometry of GN with the high aspect ratio) were fabricated. The nonlinear conduction behavior of ER/GN composites above the percolation threshold by the action of variable DC electrical field was investigated. For specimens, the current density or current reduces with decreasing graphite nanosheets concentrations, and the J–E curves are well fitted by a cubic, J=σ1E+σ3E3. Moreover, the crossover current density Jc, at which nonlinearity takes place, scales with the linear conductivity σ1 as Jc∼σ1x, with x≈1.390 and the third-order conductivity, σ3, also scales with Jc as Jc∼σ3y, with y≈1.175. Through the discussion of the nonlinearity within the framework of two theoretical models, the nonlinear random resistor network (NLRRN) and the dynamic random resistor network (DRRN), it is indicated that neither of these two models can fully explain our experimental results. Taking into account the microscopic structures and conduction processes of the composites, it is likely that a combination of these two models explain the nonlinear characteristics better.