Effects of counter-ions on the performance of IPMCs

Ionic Polymer-Metal Composites (IPMCs) are materials capable of exhibiting large motion sensing and actuation capabilities in an electric field produced by a small voltage. Laboratory observations on the behavior of IPMC in an electric field strongly establish the presence of water movement due to electrophoretic migration of hydrated counter-ions or simply cations. In this paper, the effects of counter-ions on the performance of IPMCs in sensing and actuation are discussed. Samples of IPMCs were carefully prepared in a standard size of 0.25 x 1 inch strip containing various monovalent and divalent metal cations including Na+, Li+, K+, H+, Ca++, Mg++ and Ba++. Given a sinusoidal wave input of 1.2 volts with 1/2 Hz, the IPMC having Li+ shows the best performance in terms of force generation. Such results strongly indicate that sulfonate exchange sites are the relatively low charge sites and therefore the hydration process (rather than electrostatic field interaction) plays a much more important role. It is noted that water absorptivity and the phenomenon of exchange site clustering depend on the type of cations. Furthermore, the experimental results strongly indicate the importance of the hydration process. Muscle performance characteristics are reported and a simple phenomenological model for forces and fluxes is also presented.