OPTICAL AND ELECTRICAL AC RESPONSE OF POLYANILINE FILMS

The small-amplitude periodic optical transmittance response of redox polymer films is derived and related to the corresponding electrical behaviour. The combination of optical and electrical measurements allows Faradaic and non-Faradaic charging processes to be distinguished. The analysis of the modulated transmission data obtained for polyaniline films on indium-doped tin oxide coated transparent electrodes in 1.0 mol dm-3 H2SO4 indicates that the capacitance measured in a.c. experiments is associated with redox transformations in the PANI film. The a.c. capacitance was found to be lower than the pseudo-capacitance derived from cyclic voltammograms and possible reasons for this discrepancy are discussed. The absorption coefficient of the polaron has been derived from the relationship between the modulated transmittance and the film capacitance which also shows that bipolaron states are formed at potentials more positive than 0.15 V vs. SCE.