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 cycles. That is, the anisotropic PPy film acts as an actuator or a “bending machine”. The PPy film can be prepared electrochemically as a fiber in a slender Teflon pipe. The response speed of the PPy fiber actuator depends on the speed and amount of dopant insertion and extraction; namely, it becomes faster when the reduction potential is more negative or the electrolyte concentration is higher. The bending behavior strongly depends on the type of supporting 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 volume change upon doping/undoping, is proposed.