The effects of counter ions on characterization and performance of a solidpolymer electrolyte actuator

A perfluorocarboxylic acid membrane was chemically plated with gold bends u nder electric stimuli in water. When exchanged with alkali metal ions as co unter ions, the displacement is rapid, though charge-specific displacement, or 'pumping' efficiency, is small. The fast response is thought to be link ed with the small radius of the hydrated ion relative to the hydrophilic ch annel size in the membrane. In contrast, the charge-specific displacement w ith alkyl ammonium ions increases, while the rate decreases, systematically with molecular size. The effects are interpreted in terms of an 'ion-pumpi ng' model, in which the size of the hydrated ion relative to that of the hy drophilic channel is of paramount importance. A good 'pumping' ion inevitab ly effects only a slow displacement. (C) 2001 Elsevier Science Ltd. All rig hts reserved.