EFFECTS OF SOLVENT AND ELECTROLYTE ON THE ELECTROCHROMIC BEHAVIOR AND DEGRADATION OF CHEMICALLY PREPARED POLYANILINE-POLY(VINYL ALCOHOL) COMPOSITE FILMS

Effects of solvent and electrolyte on the electrochromic behavior and degradation of polyaniline in nonaqueous aprotic media, as well as its electrochemical redox and degradation mechanisms, were investigated with chemically prepared polyaniline-poly (vinyl alcohol) composite films and polyaniline homogeneous films. Visible and FT-IR absorption spectra of the polyaniline films, oxidized electrochemically at various polarization potentials, showed that the mechanisms in aprotic media involved two successive oxidation processes. In contrast to aqueous systems, the higher oxidation process involved further anion insertion without deprotonation, and the degradation was due to partial formation of the electrochemically inactive quinonediimine structure at excessive polarization potentials. From investigations of solvent and electrolyte effects, it is suggested that the electrochromic behavior and degradation of polyaniline are influenced by the electron-donating and accepting ability of solvents, acceptor strength of electrolyte cations, and the nucleophilic character of electrolyte anions. It was also suggested that some anions like PF6-, BF4- and ClO4-;, as well as protons, are constrained in the PVA matrix by specific electrostatic interactions and steric effects to improve the stability of polyaniline in the highly oxidized state. (C) 1994 John Wiley and Sons, Inc.