Ionic liquids as stable solvents for ionic polymer transducers

Nation(TM) membranes are known to operate as electromechanical actuators and sensors. The transduction in the material is caused by redistribution of the mobile cations in the material, which is made possible because the material is saturated with a solvent. Typically, the solvent used is water, although its use limits the performance of these materials. This is due to the chemical breakdown of the water at relatively low operating voltages and the loss of the water to evaporation when these devices are operated in air, causing a corresponding loss of performance. In the current work, the use of highly stable ionic liquids to replace water is explored. Ionic liquids have the advantage of greater electrochemical stability than water, thus offering the possibility of higher actuation voltages for these materials. Also, ionic liquids are known to be non-volatile and therefore will not evaporate out of the polymer as water will. In this work, the use of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid is demonstrated as a viable solvent for Nation(TM) polymer actuators and sensors. This ionic liquid melts at -9degreesC and has an electrochemical stability Window of 4.1 V [Inorg. Chem. 35 (1996) 1168], making it a promising candidate to replace water in ionic polymer transducers. Experimental results indicate that Nafion(TM) transducers solvated with this ionic liquid have improved staility when operated in air as compared to the same materials solvated with water, although the magnitude of the response is decreased as compared to the water samples at high frequencies. The main drawback associated with the use of ionic liquids is a reduction in the speed of the response as compared to water, although the initial results are promising and demonstrate the potential for this approach. (C) 2004 Elsevier B.V. All rights reserved.