Experimental demonstration of the active area model in extensional ionic polymer transducers

Abstract

Ionic polymer transducers (IPTs) also known as ionic polymer metal composites (IPMCs) are soft smart materials that are well characterized in bending actuation. A salient feature of an IPT is its ability to generate large strains of the order of 5% at moderate voltages ( < 2 V). The authors previously reported extensional actuation in IPTs, which in theory is supposed to generate larger energy densities as compared to bending actuation. The experiments in the previous study were limited to the measurement of an AC force response in IPTs. This paper presents DC and AC experimental measurements of the free displacement in extensional IPT actuators. The active area model presented in the previous study is employed in this study and is proven to accurately predict the displacement behavior. Moreover, the magnitudes of the α and β coupling coefficients in the active area model required to fit the displacement data are within the ranges reported in the previous study. Furthermore, the active area model is based on the assumption that the high surface area electrodes are the only active components, while the inner ionomer membrane acts as an ion transport medium and does not perform any electromechanical coupling. This assumption is proved in this study by replacing the central Nafion membrane with a passive AlO2 porous film filled with the EMI-TF ionic liquid. The actuator with the AlO2 membrane demonstrates electromechanical extensional response faster than that in the Nafion based transducer. The large stiffness of the AlO2 based transducer is expected to provide larger forces and results in an actuator with greater energy density.