Evidence for Two Separate Doping Mechanisms in the Polyaniline System

Abstract

In situ Fourier-transform infrared spectra of polyaniline give clear evidence for an insulator-to-metal transition in the first oxidation step and a metal-to-insulator transition in the second oxidation step. The former originates from a pure protonic mechanism without intercalation of counter ions whereas in the latter counter-ion insertion without protonic activity occurs. In the metallic form of the polymer a free-carrier absorption peak is explicitly observed and found to be in agreement with an effective-medium-type dielectric function for a granular metallic system.