Force detection with Donnan equilibrium in polypyrrole film

Mechanical stimuli to polypyrrole (PPy) composite film could be detected as a spike-wise current by applying or releasing a stepwise tensioning-load in electrochemical cell. The current polarity observed here varies with the film preparation. A negative current was observed in the PPy film electrodeposited in dodecylbenzene sulfonic acid (PPyDBS), besides a positive current was observed in the film electrodeposited in bis(trifluoromethane sulfonyl)imide (PPyTFSI) with applying a load. Reversal currents were observed with releasing a load from the films. Switching of the polarity of the induced current well corresponded to the film actuation polarity, indicating that the current induction is the phenomenological counterpart of the electrochemical actuation. Perturbation of Donnan equilibrium by external pressure possibly generates an ion flux across the film/electrolyte interface, resulting in (dis)charge of the PPy similar to the redox process.