REVERSIBLE ELECTROCHEMICAL REACTIONS IN CONDUCTING POLYMERS - A MOLECULAR APPROACH TO ARTIFICIAL MUSCLES

Electrical currents trigger oxidation or reduction reactions in conduc ting polymers. Changes in volume associated with these redox processes can be transformed into macroscopic movements of more than 180 degree s by the construction of a bilayer: polypyrrole-flexible and inactive polymer (artificial muscle). The effects of the applied potential, the nature of the solvent and the electrolyte concentration on the angula r movement of the free end of the bilayer were analysed. The movement accelerates with increasing anodic (or cathodic, when the movement is reversed) overpotentials, with increasing electrolyte concentration or by using more polar solvents, leading to the conclusion that the move ment is linked to electrochemically driven exchange of hydrated counte rions between the solution and the conducting polymer, Geometrical con siderations give a simple equation for both the microscopic and macros copic changes of volume associated to the penetration of counterions d uring oxidation, which is able to explain the experimental behaviour.