Effect of ionic liquid on soft epoxy-amine electroactuators

Energy conversion represents a challenge in various fields of applications such as soft robotics or microfluidics technologies, particularly in terms of electromechanical coupling for actuators. The dielectric elastomers are a variety of electroactive polymers (EAP) which require high electric fields to be used as actuators. It is well-known that the presence of ionic impurities can have an influence of their electro-mechanical response under high electric field (i.e. above 1 MV/m). More precisely, it can be responsible for the bending of the sample under constant electric field. Here, we investigate the impact of a small content, i.e. from 0.1 wt% to 10 wt% of an imidazolium Ionic Liquid (IL) on the electromechanical response of a soft epoxy-amine network. The interest of this study therefore lies in its position at the frontier between dielectric polymers and ionic polymers. Dielectric spectroscopy revealed a significant increase of electric conductivity (≈2 orders of magnitude) when adding only 0.1 wt% of IL and up to 4 orders of magnitude with 10 wt% of IL at T = 20 °C for f = 10 Hz. It also evidenced the presence of the electrode polarization for all the samples doped with IL. The bending test carried out at E = 0.1 MV/m revealed no bending for pure epoxy-amine and a slow kinetics of bending for all the samples doped with IL with displacement evolving throughout the experiment (i.e. over 4 h). As evidenced by dielectric spectroscopy and bending tests, it is clear that the presence of a small quantity of ionic moieties (whether doping agent or impurity) can strongly modify the electromechanical behavior of elastomer commonly described as dielectric.