Bipolaron saturation in polypyrrole

Abstract

Saturation of bipolaron, the species responsible for conduction in polypyrrole (PPy), has been studied using positron annihilation lifetime (PAL) spectroscopy, conductivity, and electron spin resonance (ESR) measurement. It is observed that when strong oxidizing agents are used, the defects are predominantly bipolarons as is evident from the PAL spectroscopic studies coupled with ESR measurements and its saturation occurs right at the onset of oxidation. However, in the case of a mild oxidizing agent, the dominant defects are bipolarons only at higher oxidizing strengths $[g~1.0(N)]$ and no saturation is attained even at the highest strength studied. Conductivity data corroborate the findings.