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Effects of electrode degradation and solvent evaporation on the performance of ionic-polymer–metal composite sensors

An ionic-polymer–metal composite (IPMC) consists of an ionic polymer membrane and metallic electrodes plated on both surfaces. When it bends, a voltage is generated between the two electrodes across the membrane. Since it works not only in aqueous solution similar to in vivo but also in air, it can be used for embedded biomedical as well as surface-mounted sensors. The present study investigates the effect of solvent evaporation and mechanisms of electrode degradation of an IPMC when it is operated as a sensor. The output voltages and electrode resistances were measured with several cyclic bending motions applied on the sensor in both aqueous solution and air. There was a good correlation between the sensor voltage and the bending angle when the sensor was tested in aqueous solution. The sensor worked for a long time without attenuation in the output voltage in an aqueous solution. The output voltage, however, decreased rapidly when the sensor was operated in air. The results of resistance measurement showed that the electrode on the compressive side deformed more and generated more cracks than on the tensile side. Optical microscopic images taken on the electrode surfaces validated the results. The results provided very useful information needed to understand electrode degradation and solvent evaporation and to improve the performance of IPMC sensors.