Impact of moisture absorption on the performance of a polyurethane-based dielectric elastomer actuator

Abstract

Dielectric elastomer actuators (DEAs) have gained an increasing importance in various research applications. In literature the most explored dielectric elastomers (DEs) are silicones and acrylics. As promising alternatives, polyurethanes have been identified due to their inherent higher dielectric constant, higher dielectric strength, and appropriate response behavior. However, polyurethane systems are known to have hygroscopic properties that can lead to changes in the dielectric properties when they are exposed to moisture. In this work, a circular DEA composed of a thermosetting polyurethane film and carbon grease electrodes is exposed to four stabilized levels of relative humidity (RH = 22 %, 36 %, 56 %, 70 %) at a constant temperature of 22 °C. The actuation strain is measured to study the effect of moisture absorption on the DEA performance. In addition, impedance spectroscopy is performed on the DEA to investigate the influence of moisture on its dielectric properties. Impedance, phase angle and dielectric constant of the DEA are evaluated at the respective RH level. The results show a rise in the dielectric constant of 15 % with increasing the humidity from 22 % to 70 %. However, increasing the humidity does not necessarily lead to an increase in actuation strain.