EFFECT OF AGING INDUCED DISORDER ON TRANSPORT-PROPERTIES OF PANI-CSA

Thermal variations of both the conductivity (sigma) and the thermopowe r (S) have been measured on polyaniline (PANI) films protonated by cam phor sulfonic acid (CSA) in m-cresol, after aging at 130 degrees C in air for times up to 30 days. We show that, with increasing disorder: i )the temperature dependence of sigma changes continuously from a very flat one to another which is of the type sigma(T) proportional to exp( -(T-0/T)(1/2)), as observed in HCl doped PANI and ii) a U-shaped contr ibution, similar to that one observed in PANI-HCl, is progressively ad ded to the linear temperature dependence of the thermopower in pristin e PANI-CSA. We show that all the data can be accounted for in a single heterogeneous picture of metallic regions separated by insulating bar riers, the major effect of aging being a broadening of the barriers at the expense of the grains.