STUDY OF CONDUCTING POLYPYRROLE FILMS IN THE MICROWAVE REGION

Dielectric properties of the electrochemically synthesised polymer polypyrrole with a wide range of doping levels are presented. Methods for determining the complex dielectric constant in the microwave regime are discussed. The variation of the complex dielectric constant as a function of polymer dopant concentration at room temperature using cylindrical and rectangular cavity perturbation methods at frequencies of 2.45 GHz and 10 GHz is presented. Measurements indicate that the real and imaginary parts of the dielectric constant increase in magnitude with increasing polymer doping level. Complex dielectric constant measurements were continued on semiconducting polypyrrole films with a dc conductivity range of 1x10(-3)-5x10(-2) S/cm for the temperature range 90K-300K. The real part epsilon' of the complex dielectric constant increased slightly with increase of temperature whereas the imaginary part epsilon'' increased significantly with temperature. The rate of change of the dielectric loss increased with temperature and the magnitude of the loss at a given temperature increased with increasing polymer doping levels. Reflection, transmission and absorption behaviour of polypyrrole films with dc conductivities ranging from 0.001 S/cm to 50 S/cm are also presented. Results indicate that conductivity of the doped polypyrrole films have a significant effect on transmission, reflection and absorption of microwaves. Samples with low conductivity (low dopant concentration) exhibited high transmission whereas highly conducting films were reflective. Significant absorption of microwave radiation was only observed for samples of intermediate conductivity. Solutions by theoretical methods were in good agreement with the experimentally measured results from the polypyrrole films and hence confirm the dependability of the dielectric measurement method used.