Bending of polyelectrolyte membrane platinum composites by electric stimuli: Part II. Response kinetics

In previous papers, it was reported that a solid polymer electrolyte membrane-platinum (SPM-Pt) composite bent in response to electric stimuli. In this paper, a model, in which electric fields can induce mechanical deformation in the SPM via electrokinetically induced pressure gradients, was applied to the kinetics of the bending response. In order to compare the theoretical model with the experimental result, simultaneous measurement was carried out with the displacement and the electrochemical properties for the composites prepared from membranes of different thickness in various kinds of salt solution. The curvature response was simulated by the empirical equations having one characteristic time. The characteristic time was linearly proportional to the square of the thickness of the membrane. The parameter which means curvature per unit charge was linearly proportional to the reciprocal of the square of the membrane thickness, and the water transference coefficient of the membrane of various ionic forms. The results support the theoretical model. In addition to the electrokinetic effect, the model includes the effect of the interfacial stress between the Pt electrode and the SPM. The bending behavior after the characteristic time can be explained successfully by the model including the interfacial effect.