Anisotropic strain and memory effect in conducting polymer soft actuators under high tensile stresses

Electrochemomechanical strain (ECMS) under tensile stresses up to 5 MPa in polypyrrole films doped with dodecylbenzene sulfonate (PPy/DBS) has been studied in aqueous LiCl electrolytes. The ECMS of about 2% showed cation driven behavior and decreased with increasing the tensile stress. At higher tensile stresses, a nonlinear deformation against the injected charges was observed, as well as creeping associated with conformation change, slipping and/or breaking of polymer chains. After the removal of high tensile stresses, the creeping was recovered to some extent. The results were discussed in terms of the relaxation of anisotropic strain and memory effect introduced during the creeping. The conversion efficiency from electrical to mechanical energies was 0.04% being the maximum at around 3 MPa.