Reversible nonlinear conduction behavior for high-density polyethylene/graphite powder composites near the percolation threshold

The reversible nonlinear conduction (RNC) behavior of high-density polyethylene/graphite powder composites with various graphite powder volume concentrations slightly above the threshold has been studied. The relationships between the current density (J) and electric field (E) of the composites, as shown in J(E) curves, can be well described by the scaling functions of J/J_c ∼ (E/E_c)^α1 when E < E_c and J/J_c ∼ (E/E_c)^α2 when E > E_c, where J_c is the crossover current density and E_c is the crossover electric field. The results indicate that J_c scales with the linear conductivity σ_o as J_c ∼ σ_o^x. It is believed that the macroscopic RNC is a combined result of the microscopic conduction processes, involving electronic transporting along carbon chains and tunneling or hopping across thin polymer bridges.