Chromatic reaction of polyaniline film and its characterization

Abstract

Chemical oxidation in acidic aqueous solution leads to multiple colour changes from yellow, green, blue, purple to red at a polyaniline film-coated platinum surface, which has been compared with an electrochromic reaction reported previously and characterized by absorption spectroscopy on a transparent SnO₂ glass surface, ESCA spectroscopy, cyclic voltammetry, ring–disk voltammetry and potentiometry on a platinum electrode. The multiple colour changes can be applied to analysis as a sensitive colour indicator. The polymerization mechanism of aniline and the redox mechanism of polyaniline film, which are concerned with chromatic reaction, were discussed with a stereochemical approach. It is observed that the colour change is dependent on the hydrogen atom number linked to the nitrogen atoms in polyaniline backbone, which unified the acid–base and the redox colour change mechanisms of polyaniline.