AN INVESTIGATION OF THE CONDUCTIVITY STABILITY OF ACID-DOPED POLYANILINES

Solution-cast, free-standing polyaniline films were doped with hydrochloric acid (HCl), sulfuric acid (H2SO4), methanesulfonic acid (CH3SO3H) and p-toluenesulfonic acid (p-CH3C6H4SO3H), and their conductivity stability was examined at different elevated temperatures under different environments. As indicated by a kinetic analysis of these data, most of the doped films were found to exhibit better room temperature stability in air than in dry nitrogen. An exception to this trend was the H2SO4-doped film which displayed a significantly better room temperature conductivity stability in nitrogen. When compared to other conducting polymers, it was found that the protonic acid-doped polyaniline films in general exhibit better stability than the doped poly(3-alkylthiophenes) (P3ATs), but are less stable than the aryl sulfonate-doped polypyrroles. Spectroscopic studies revealed that the doping process of an HCl-doped film could be thermally reversed at 180-degrees-C under nitrogen without any indication of major changes in the structure of the polymer backbone.