Polyaniline, a novel conducting polymer. Morphology and chemistry of its oxidation and reduction in aqueous electrolytes

TLDR

The study proposes that the emeraldine salt form of polyaniline possesses a symmetrical conjugated structure with extensive charge delocalization arising from a novel polymer–salt doping mechanism rather than conventional oxidation. Electrochemical synthesis yields a fibrillar emeraldine salt film, and cyclic voltammetry of its oxidation and reduction in aqueous HCl across –0.2 to 1.0 V vs. SCE and pH –2.12 to 4.0 reveals the chemical changes and compounds formed.

Abstract

The emeraldine salt form of polyaniline, conducting in the metallic regime, can be synthesized electrochemically as a film exhibiting a well defined fibrillar morphology closely resembling that of polyacetylene. Cyclic voltammograms of chemically synthesized and electrochemically synthesized polyaniline are essentially identical. Probable chemical changes which occur and the compounds which are formed when chemically synthesized poly-aniline is electrochemically oxidized and reduced between –0.2 and 1.0 V vs. SCE in aqueous HCl solutions at pH values ranging from –2.12 (6.0 mol dm–3) to 4.0 have been deduced from cyclic voltametric studies. These are shown to be consistent with previous chemical and conductivity studies of emeraldine base and emeraldine salt forms of polyaniline. It is proposed that the emeraldine salt form of polyaniline has a symmetrical conjugated structure having extensive charge delocalization resulting from a new type of doping of an organic polymer–salt formation rather than oxidation which occurs in the p-doping of all other conducting polymer systems.