Potential-step response of absorption at conducting-to-insulating conversion of polyaniline films for demonstrating the slow relaxation

Absorption of polyaniline films responding to a potential step from a conducting state to an insulating state showed linear variations with logarithmic electrolysis time when the stepped potential E was less than the percolation threshold potential E-c. Then the slope of the linear relation varied with E. The observation demonstrates more directly the slow relaxation than the time-dependence of the voltammetric peak potentials or the charge reported previously. The relaxation of the absorption is also more essential in the faradaic process than measurements of currents or potentials because it includes no capacitive contribution. Comparison of the current-time curve with the time-derivative of the absorption showed that most of the current before 0.5 s was capacitive due to the charging of the double layer. The capacitance vs E curve was linear for E > E-c whereas it deviated from the proportionality for E < E-c. This behavior reflected on whether the anodic voltammetric peak appeared or not when the initial potential was less or more than E-c. (C) 1997 Elsevier Science Ltd.