Electro-responsive polypyrrole film based on reversible sorption of water vapor

Polypyrrole films containing tetrafluoroborate were electrochemically synthesized and electrically driven motion of the film was investigated. It was found that application of dc voltage brought about reversible contraction of the film in ambient air, where the contraction increased with increasing applied voltage and ambient relative humidity (RH). The degree of contraction was 1.2% under 2 V (25°C, 50% RH), while the value decreased at voltages higher than 5 V. In contrast, the film in a vacuum underwent elongation by the electric field. The results allowed us to consider that the apparent strain of the film under the electric field was expressed by two processes: one was the contraction due to the desorption of water vapor and the other was the thermal expansion of polymer chains both caused by Joule heating. Under isometric conditions, the film generated contractile stress of 4.8 MPa under 2 V, which was four orders of magnitude larger than its own weight.