THERMAL-TREATMENT AND OXYGEN EXPOSURE DEPENDENCE OF THE ELECTRONIC-STRUCTURE OF POLYANILINE - AN X-RAY PHOTOELECTRON-SPECTROSCOPY APPROACH

Polyaniline films were deposited on conducting glass working electrodes. Electropolymerization occurred at room temperature in a 1.0 M HBF4 aqueous solution of aniline (0.1 M) by using the potentiostatic technique (800 mV vs SCE). The thermal treatment of protonated polyemeraldine removes the dopant. This phenomenom is accompanied by a drastic modification of the chemical structure of the polymer. The X.P.S. of Nls and Cls levels reveals cross-linking reactions and modifications in atomic charge distribution. The exposure time to atmosphere (0 to 180 days) of the polyleucoemeraldine acidic (0 % imine nitrogen) does not modify the stoechiometry of the polymer, checked by the evolution of C/N atomic ratio. Nevertheless, the oxidation state of the polyaniline is stronghly enhanced at 50 % imine nitrogen is found from a careful X.P.S. analysis. In addition to the two well-known redox couples, a third one is identified as corresponding to the quinone/hydroquinone system.