Bending machine using anisotropic polypyrrole films

We have found that a polypyrrole (PPy) film with anisotropy of conductivity and morphology bends in a regular direction and reverts during redox cycle s. That is, the anisotropic PPy film acts as an actuator or a "bending mach ine". The PPy film can be prepared electrochemically as a fiber in a slende r Teflon pipe. The response speed of the PPy fiber actuator depends on the speed and amount of dopant insertion and extraction; namely, it becomes fas ter when the reduction potential is more negative or the electrolyte concen tration is higher. The bending behavior strongly depends on the type of sup porting salt in the electrolyte solutions, suggesting that cation transport into and out of PPy plays a key role in the bending behavior and that the size of the cation is also a critical factor. A bending behavior mechanism based on cation insertion and extraction, as well as on the anisotropic vol ume change upon doping/undoping, is proposed.