ELECTROCHEMICAL INSITU CONDUCTIVITY AND POLARON CONCENTRATION MEASUREMENTS AT SELECTED CONDUCTING POLYMERS

Electrochemical in-situ conductivity and esr measurements of Polyaniline (PANI), Polypyrrole (PPy) and Polythiophene (PTh) films are performed in aqueous solutions of various pH-values and in non-aqueous solution. No esr signal is found in PTh, the spin density in PANI and PPy shows a potential dependence correlated with the cyclic voltammograms. At electrode potentials of maximum spin density, PANI and PPy are not yet fully conducting. Maximum conductivity, on the other hand, is accompanied by a small spin density. On the basis of the polaron-bipolaron model the single line esr spectrum is attributed to the presence of polarons. From our results we conclude that these polarons merely initiate electrical conductivity. Moreover, the spinless bipolarons, which are the result of polaron recombination, seem to prevail in the highly conducting polymer films and are thus responsible for intrinsic conductivity in these polymers.