Dynamic percolation in an insulator-conductor composite: Polyethyleneoxide-polypyrrole, as studied by a.c. conductivity measurements

Abstract

We report measurements of a.c. conductivity in the Insulator-Conductor polymeric system Polyethyleneoxide-Polypyrrole for frequencies between d.c. and 9.4 GHz. The a.c. conductivity is shown to follow the general law σ(ω) ⋍ ω x for frequencies higher than a critical frequency. For every concentration of polypyrrole a frequency region has been found where the predictions for anomalous diffusion in three-dimensional fractal percolating clusters (x = 0.6) can be considered as fulfilled. The calculated critical frequencies exhibit a dependence on the concentration of the sonducting polypyrrole additive as expected by the theory through the expression for the correlation length of the Random Resistor Network of Miller and Abrahams. This model was previously employed to describe the d.c. behaviour of these composite systems.