HIGH-PRESSURE ELECTRICAL-CONDUCTIVITY STUDIES OF ACID DOPED POLYBENZIMIDAZOLE

Electrical conductivity studies of acid doped poplybenzimidazole (PBI) and 85% phosphoric acid have been carried out. The PBI contained abou t 600 mol% of 85% phosphoric acid and the electrical conductivity was deduced from complex impedance studies which were made at frequencies from 10 to 10(7) Hz. Measurements were made at pressures up to 0.25 GP a and temperatures of about 25, 50 and 75 degrees C. Similar measureme nts were also carried out on 85% phosphoric acid. At room temperature the electrical conductivity decreases with increasing pressure for bot h acid doped PBI and 85% phosphoric acid. This behavior is expected fo r normal liquids and for ions in polymers where the viscosity increase s with pressure. The resultant positive activation volume for the acid doped PBI has a magnitude similar to that for polymer electrolytes ba sed on perfluorosulfonic acid containing relatively small amounts of w ater. Further, as temperature increases, the activation volume becomes smaller. Consequently, the acid doped PBI behaves like a polymer elec trolyte where ion transport is mediated by segmental motions of the po lymer. Consequently, the acid doped PBI behaves like a polymer electro lyte where ion transport is mediated by segmental motions of the polym er. On the other hand, the activation volume at room temperature for 8 5% phosphoric acid is much smaller than for acid doped PBI. In additio n, at 75 degrees C the electrical conductivity increases with increasi ng pressure which gives rise to a negative activation volume. Conseque ntly, there is very little similarity between the electrical behavior of the 85% phosphoric acid and of the acid doped PBI which were studie d in the present work. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.