Direct Strain Measurement of Polypyrrole Actuators Controlled by the Polymer/Gold Interface

Electrochemically induced strain and actuation in a polypyrrole/Au/polyimide laminate was measured using a sensitive strain gage during oxidation and reduction (redox) of polypyrrole−ClO4-. The polyimide formed the top layer of the strain gage, allowing direct measurement of strain during redox switching in various electrolytes and potential windows. Strain increased in the order NaCl < NaNO3 < NaClO4. In the NaClO4 solution for oxidizing potentials between 0.1 and 0.5 V vs Ag/AgCl, strain and charge were linearly proportional to voltage. Lower polypyrrole deposition potentials also increased strain. The surface roughness of the Au was varied by electrochemically depositing Au (which we designate EcAu) on top of thermally evaporated Au (EvAu)/polyimide. Greater EcAu deposition times led to greater Au roughness. Strain increased with polypyrrole thickness and Au roughness, which correlated with better adhesion between the polypyrrole and the Au. Au roughness also improved the cycling stability of the actuators.