Solvation effects on ion exchange of conducting polymer, polypyrrole (PPy), films, electrodeposited in a mixture consisting of conducting polymer, poly(2-methoxyaniline-5-sulfonate) (PMAS) as a polyanion additive and dodecylbenzene sulfonic acid (DOS) as main supporting electrolyte, were investigated by means of the volume change of the film. PMAS incorporation into PPy film was found to show large water content, indicating that the PMAS incorporation increases porosity in PPy film. Dynamic volume change in the film with redox reaction was found to be influenced by both of the nature of solvent as well as supporting electrolyte. Solvents with small donor and small acceptor number were found to display cathodic and anodic film expansions, respectively. Charge screening effect by weak solvation probably decreases the interaction between dopant ions and PPy, promoting the reversible volume change of the film due to facile ion exchange during the redox process. The magnitude of film deformation has also been assigned to the exchange of substantial particles having a same order of Stokes radius. (C) 2010 Elsevier B.V. All rights reserved.