Non-linear current-voltage characteristics in anisotropic epoxy resin graphite flake composites

The conductivity of an isotropic composite materials constituted of single-crystal graphite flakes in an epoxy resin and subjected to a variable d.c. electric field has been studied. Non-linearities in the current-voltage characteristics have been found and are discussed with in the framework of two theoretical models, the non-linear random resistor network and the dynamic random resistor network. We show that our materials can be modelled by the non-linear random resistor network, which, to our knowledge, is the first time that the predictions of this model seem so well supported in a real, three-dimensional composite.