Visualizing Dynamic Actuation of Ultrathin Polypyrrole Films

We report on the use of electrochemical atomic force microscopy (EC-AFM) to visualize the dynamic actuation of ultrathin polypyrrole films doped with polystyrene sulfonate. By varying the film thickness over 3 orders of magnitude from the micrometer to the nanometer range and measuring their actuation height displacement as a function of the applied potential and its change in frequency, we are able to differentiate between diffusion and current limiting processes that determine the rate at which charge balancing ions move in and out of the polymer during actuation. In particular, we observe a 100-350% increase in strain and strain rate when the film thickness is reduced below 100 nm and provide unique insight into how the nanoscale architecture of these ultrathin films is correlated to their actuation performance.