Ion exchange, anisotropic structure and thermal stability of polypyrrole films

Summary form only given. The thermal stability of electrochemically prepared polypyrrole films with p-toluene sulphonate or perchlorate counterions (PPy/pTS and PPy/CI0/sub 4-/) are improved by simple treatment with aqueous sulphuric acid, sodium sulphate or sodium bisulphate. The degree of stabilisation achieved depends on the solution, temperature and duration of treatment. PPy/pTS is easily stabilised and thick films (40 /spl mu/m) retain 90% of the initial conductivity after long periods (200 h) at 150 /spl deg/C, while thinner films (12 /spl mu/m) retain slightly less (70%). PPy/Cl0/sub 4-/ is not as sensitive as PPy/pTS to the composition of the solution. Although the mechanism of improvement of stability is not yet clear it is apparent that the level of ion exchange and the polymer microstructure are important. The early stages of ion exchange are not symmetrical and diffusion is facilitated at the electrode side of the film. Furthermore X-ray diffraction shows no evidence of morphological change after treatment of thick PPy/pTS but in thin film an additional peak is indicative of more ordered structure following treatment. These observations may imply that there is a higher density of crosslinks and branching at the growth side than at the electrode side of the film.