Actuator based on doping/undoping-induced volume change in anisotropic polypyrrole film

We propose an actuator using the cylindrical polypyrrole (PPy) film, with a n anisotropy of morphology and conductivity, can be polymerized electrochem ically in a Teflon slender pipe. The PPy actuator bends and reverts in a re gular direction upon electrochemical undoping/doping. The bending speed bec omes faster as the undoping potential is increased, but the magnitude of di splacement depends not on the undoping potential but on the amount of charg e or dopant concentration. The bending behavior strongly depends on the typ e of supporting salt in the electrolyte solutions, suggesting that cation t ransport into and out of the PPy plays a key role in the bending behavior a nd the size of the cation is a critical factor. It was also found that, the shape of the transient reduction current strongly depends on the type of c ation and that the current does not follow the diffusion law. A bending mec hanism based on the cation insertion and extraction, as well as on the anis otropic volume change upon doping/undoping, is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.