Strain response of polypyrrole actuators induced by redox agents in solution

We report on the chemical actuation of a polypyrrole (PPy) artificial muscle by redox agents in solution without external power supply, such as a battery, connected to the actuator. In particular, hexacyanoferrate and L-ascorbic acid are employed to analyse the strain responses of PPy. The redox agents establish a certain potential at the polymer electrode, which results in a corresponding strain change. The results are in accordance with the strain generated by an external voltage via a potentiostat. We use a bending beam of polyimide/gold/PPy to observe the strain of PPy inside a liquid flow cell. By adding different relative concentrations of the hexacyanoferrate couple to the electrolyte, we achieve a repeatable linear transition in strain without significant hysteresis. Strain changes are induced by redox pairs as well as redox moieties in solution.