THEORETICAL-STUDY OF SORPTION-INDUCED BENDING OF POLYPYRROLE FILMS

Polypyrrole films containing perchlorate were electrochemically synthe sized and the bending and recovery motion of the films obtained has be en investigated. It was found that the thickness of the aim and ambien t relative humidity (RH) were crucial to the motion of film: An increa se of the film thickness decreased the displacement of the bending but increased the bending stress. On the other hand, an increase of the a mbient RH decreased both functions. The motion of film was caused by t he difference of expansion on both sides of the film owing to anisotro pic sorption of water vapor, which could he expressed by the diffusion -limited bending model. The diffusion coefficients calculated from the bending and recovery motion at 25 degrees C, RH 50% were 12.2 x 10(-8 ) cm(2) s(-l) and 3.5 x 10(-8) cm(2) s(-1), respectively. The maximum expansion of the film surface calculated from the bending curve was ab out 0.36%. (C) 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2237-2246, 1998.