Redox heterogeneity in polyaniline films: from molecular to macroscopic scale

Heterogeneity relates to the principal features of polyaniline (PAn). For the most part the heterogeneity in PAn belongs to redox type. Our detailed investigation of the vacuum deposited PAn and the study of the luminescence of PAn base (by Shimano and MacDiarmid) reveal the existence of a block structure of PAn molecules formed of quinoid and amine units. There are also direct evidences of existence of the redox heterogeneity in PAn in nano scale (Kelvin scanning microscopy). We have observed by optical and Kelvin the microscopy the formation of various types of the redox heterogeneous structures in microscopic scale in the course of the chemical or electrochemical treatment of the vacuum thermally deposited or electrochemically produced PAn films. Macroscopic scale redox heterogeneity was observed also under chemical oxidation of the vacuum deposited PAn and in the course of PAn matrix synthesis. Hence, multilevel redox heterogeneity from molecular to macroscopic scale takes place in PAn. The fundamental reason for the redox heterogeneity formation is the autocatalytic, non-equilibrium character of the oxidation processes in PAn coupled with non-linear mass transfer processes. Evidently this type of heterogeneity influences markedly the whole range of PAn properties including conductivity.