Modeling of the bending of an electroactive polymer strip

Abstract

Ionic electro-active polymer (Nafion for example) can be used as sensor or actuator. To this end, a thin film of the water-saturated material is sandwiched between two electrodes. Water saturation causes a quasi-complete dissociation of the polymer and the release of small cations. The application of an electric field across the thickness results in the bending of the strip. Conversely, a voltage can be detected between the two electrodes when the strip is bent. This phenomenon involves multiphysics couplings of electro-mechanical-chemical type. We have previously modeled this system and determined its constitutive equations using the thermodynamics of linear irreversible processes.We applied this model to the case of a cantilevered PEA strip subjected to a continuous voltage between its two faces (static case). The applied forces and the tip displacement are calculated using a beam model in large displacements. We have also studied the force to be exercised on the free end to prevent its displacement (blocking force).Numerical simulations were performed in the case of Nafion. We have drawn the profiles of cations concentration, pressure, electric field and potential in the thickness of the strip. These quantities, which are almost constant in the central part of the strip, vary drastically near the electrodes. The obtained values of the tip displacement and the blocking force are in good agreement with the experimental data published in the literature. These two quantities are linear functions of the imposed electrical potential ; the tip displacement varies as the length square, and the blocking force is proportional to the width and inversely proportional to the length.