Water uptake and migration effect on IPMC (ion-exchange polymer metal composite) actuator

The low actuating voltage and quick bending responses of ion-exchange polymer metal composite (IPMC) are considered very attractive for the construction of various types of actuators. The principle of IPMC actuation under electric field has been believed to be the ion cluster flux and electro-osmotic drag of water from anode to cathode direction through the hypothetical hydrophilic channels in the perfluorinated sulfonic acid polymer chains. In this study, the effect of water content residing in the perfluorinated polymer was investigated in terms of CV (cyclic voltammetry response, deformation, and bending moment. As a preliminary result of DSC thermal analysis, the water residing in the IPMC actuator seems to reside as free water and bound water, each corresponding to interstitial and hydrogen-bonded water molecules. Using the classical lamination theory (CLT), a modeling methodology was developed to predict the deformation, bending moment, and residual stress distribution of anisotropic IPMC thin plates. In this modeling methodology, the internal stress evolved by the unsymmetric distribution of water inside IPMC was quantitatively calculated and subsequently the bending moment and the curvature were estimated for various geometry of IPMC actuator. The model prediction and experimental results were compared well with practical observation and experimental results demonstrating the validity of the developed modeling methodology.