Smart and soft electroactive polymer actuators as building blocks for soft robotics have
many beneficial properties that could make them useful in future biomimetic and biomedical
applications. Gelatin—a material exploited for medical applications—can be used to make a fully
biologically benign soft electroactive polymer actuator that provides high performance and has
been shown to be harmless. In our study, these polypyrrole-gelatin trilayer actuators with choline
acetate and choline isobutyrate showed the highest strain difference and highest efficiency in strain
difference to charge density ratios compared to a reference system containing imidazolium-based
ionic liquid and a traditional polyvinylidene fluoride (PVdF) membrane material. As neither the
relative ion sizes nor the measured parameters of the ionic liquids could explain their behavior in the
actuators, molecular dynamics simulations and density functional theory calculations were conducted.
Strong cation-cation clustering was found and the radial distribution functions provided further
insight into the topic, showing that the cation-cation correlation peak height is a good predictor of
strain difference of the actuators.