Critical Exponent of Conductivity and Percolation Phenomena of Carbon Black-Polyethylene Composites

Abstract

It seems that there is a confusion of the critical exponent of conductivity of composites which is caused by the way of determining the percolation threshold. In this paper, the percolation behavior, the critical exponent of conductivity and the electrical conduction mechanism of carbon black-polyethylene composites are discussed based on studying the whole change of resistivity and dielectric constant for carbon loading. There are two transitions of resistivity for carbon loading. Below the first transition, resistivity shows an ohmic behavior and the value of it is almost the same as that of polyethylene. Between the first and second transitions, the change in resistivity is very sharp, leading to a large critical exponent of conductivity, and a non-ohmic electric field dependence of current has been observed. This electric field dependence has been discussed with a tunneling conduction. Beyond the second transition, the electric field dependence of current shows an ohmic behavior and a gentle change in resistivity has been observed for carbon loading. The critical exponent of conductivity estimated by using the second transition is satisfied with the universal law of conductivity. Dielectric constant has been observed beyond the first transition and diverges around the second transition. It is concluded that the percolation threshold should be the second transition of resistivity for the carbon black-resin composites.