On the percolative behaviour of polymeric insulator-conductor composites: polyethylene oxide-polypyrrole

Abstract

The authors report measurements of both the AC and the DC electrical conductivity of polymeric insulator-conductor composites in a broad range of compositions for frequencies between 1 kHz and 1 MHz. The dependence of the DC conductivity with the additive concentration exhibits a crossover, from a traditional percolative behaviour sigma varies as ( phi - phi _c)^t for t2 depending on the particle size of the additive. The AC conductivity behaves as sigma varies as omega ^s for frequencies higher than a particular critical frequency, which is temperature and concentration dependent and with an exponent of about 0.5. The explanation of these results in terms of the random resistor network of Miller and Abrahams (1960) can account for the DC conductivity measurements considering the real concentration of sites which depends on the particle radius. The same model has been used to explain the AC conductivity results, taking into account the dependence of the correlation length on the additive concentration.