The Effect of Viscosity and Ion Size on the Transduction of Ionic Polymer Metal Composite Actuators

Ionic polymer membranes plated with platinum and gold serve as actuators when a small potential is applied. However, the water used to hydrate the membrane evaporates during use, decreasing actuator performance. Ionic liquids are being considered as a replacement for water because of their low vapor pressure. Prior studies show that the large ion size and high viscosity of ionic liquids slow the response time of the polymer membrane when a voltage is applied. This study examines the relationships of ion size and viscosity to transduction by modeling ionic liquids with inexpensive salts of varying ion size and glycerol/water solutions. Based on these results several ionic liquids were selected and tested for use as membrane sol­ vents. This study includes frequency response, step response, and impedance tests of samples impregnated with Li+, K+, Cs+, TMA+, TEA+, and TBA+. Actuators solvated in solutions with a viscosity similar to 70–80 wt. % glycerol solutions (18–46 cP) and cation size similar to that of TMA+ (0.347 nm) appear to yield the best results. When used as the membrane solvent, the ionic liquid 1-ethyl-3-methyl imidazolium trifluoromethanesulfonate (IL #3) resulted in the greatest strain per charge per area of the three ionic liquids tested in this study.