Effect of aging induced disorder on transport properties of PANI-CSA

Thermal variations of both the conductivity (σ) and the thermopower (S) have been measured on polyaniline (PANI) films protonated by camphor sulfonic acid (CSA) in m-cresol, after aging at 130°C in air for times up to 30 days. We show that, with increasing disorder: i)the temperature dependence of σ changes continuously from a very flat one to another which is of the type σ(T) ∞ exp(-(T0/T)1/2), as observed in HCI doped PANI and ii) a U-shaped contribution, similar to that one observed in PANI-HCI, is progressively added to the linear temperature dependence of the thermopower in pristine PANI-CSA. We show that all the data can be accounted for in a single heterogeneous picture of metallic regions separated by insulating barriers, the major effect of aging being a broadening of the barriers at the expense of the grains.