X-ray photoelectron spectroscopic investigations of the chain structure anddoping mechanisms in polyaniline

Abstract

X-ray photoelectron spectroscopy has been used to investigate the atomic species, and their bonding, within the conductive polymer polyaniline (PANi). PANi was grown electrochemically using HCl as the electrolyte ion and all three of PANi's oxidation states were investigated. Measurements of the C 1s, N 1s, O 1s and Cl 2p core levels and the valence band have been made on each of these oxidation states. Bond potential model calculations have been used to aid the analysis of the observed spectra. The main findings of this work show that semi-quinone radical cations are the dominant species in the conductive form, and that these are localized. Furthermore, evidence is given to verify that hydrolysis accounts for the principal polymer electrochemical degradation process, and that ring substitution of the halogen counter ion also occurs. Valence band measurements indicate a 30-40 degrees torsion angle between adjacent rings along the polymer backbone. The results are discussed in terms of previously reported oxidation mechanisms.