ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE STUDIES OF POLY(ORTHO-TOLUIDINE) FILMS EXPOSED TO AQUEOUS PERCHLORIC-ACID SOLUTIONS

We describe electrochemical quartz crystal microbalance measurements o n poly(o-toluidine) (PoT) films exposed to aqueous perchloric acid sol utions (pH 0 to 2). Crystal impedance measurements show the films to b ehave rigidly. PoT redox snitching occurs in two stages and is accompa nied by nonmonotonic mass changes that are the result of perchlorate c ounterion, proton co-ion, and solvent transfers. The extent and rate o f each of these transfers are dependent upon electrolyte concentration , experimental time scale, and the switching potential, so that observ ations in a single electrolyte on a fixed time scale cannot be unambig uously interpreted. In the first and second oxidation stages, respecti vely, electroneutrality is satisfied predominantly by anion entry and proton exit. Throughout, there is solvent expulsion, to the extent of up to three water molecules per redox site converted. Transient experi ments allow partial separation of the total mass change into individua l species contributions. As the electrolyte concentration is decreased , there is progressive failure to establish first solvation, then co-i on transfer, then redox (electron/counterion transfer) equilibria.