Effect of protonation media on chemically and electrochemically synthesized polyaniline

Abstract

Polyaniline films have been prepared both chemically and electrochemically using formic ('Pani-Formic'), boric ('Pani-Boric') or acetic acid ('Pani-Acetic') as protonation media. Among the three, formic acid seems to be a better protonating medium because it selectively yields the conducting phase of polyaniline. The variation of potential with the amount of oxidizing agent suggests one dimensional growth of polymer chain, which proceeds through a PG/EM mechanism as indicated by spectral data. The Pani-Boric and Pani-Acetic acid demonstrate three- and four-step decomposition patterns, respectively, with complete decomposition at about 760°C. Pani-Formic acid, in contrast, reveals a three-step decomposition pattern with 90% weight loss at about 900°C and shows a tendency to react with the Pt sample holder. The films of polyaniline generated electrochemically also suggest formic acid to be a better protonating medium for achieving a relatively greater fraction of conducting emeraldine salt. However, boric acid produces excellent quality adherent films with very high deposition rate. Morphological features give strong support to this observation. The films of Pani-Formic and Pani-Acetic acids show a spongy network and globular morphology, respectively, while Pani-Boric acid yields an extremely uniform surface coating. Furthermore, cyclic voltammetry reveals different patterns depending upon the formation of different oxidation states and the results are in accordance with optical absorption studies.