Decrease in electrical conductivity upon oxygen exposure in polyanilines doped with HCl

Abstract

The electrical conductivity of polyanilines doped with HCl was decreased upon exposure to oxygen and was increased reversibly upon evacuation. The line intensity and the line width of the EPR signals were decreased and increased, respectively, upon exposure to oxygen. The former represents the reduction in the concentration of polarons due to the spin–spin interaction of oxygen with paramagnetic polarons, generated by HCl doping process, and the latter the reduction in the mobility of polarons due to the partial localization of delocalized polarons. Therefore, it was concluded that the decrease in conductivity arose from the reduction in both the concentration and the mobility of polarons, the charge carriers for electrical conductivity. However, the decrease in the electrical conductivity was very small whereas the decrease in the polaron concentration was substantial. It was also found that the time scale for the diffusion of oxygen molecules was much longer than that for the spin–spin reaction of oxygen with polarons. Therefore, the small decrease in electrical conductivity may be associated mostly with the reduced mobility of polarons by localizing reaction instead of the reduced polaron concentration.