Load dependence of soft actuators based on polypyrrole tubes

Isotonic load stress dependence of biomimetic soft actuators based on polypyrrole tubes has been studied to elucidate the work behaviour. Polypyrrole (PPy) tubes were electrochemically prepared on gold coated acryl resin in an aqueous solution of pyrrole and dodecylbenzensulfonic acid (DBS). The tubes were operated electrochemically in aqueous 1 M LiCl, and the change of tube length was measured under various load stresses. It was found that with increasing load stresses the response time slowed down and the contraction ratio reduced. Hence, the current decreased and lasted longer, indicating that the tube was sensing the load stress. During contraction of the tube, the conversion efficiency was estimated from the electrical input and mechanical output energies to be 0.12%. The maximum volumetric work was approximately 120 kJ/m3. The results were discussed taking the dynamics of ion migration into consideration.