ELECTROCHEMISTRY OF SURFACTANT-DOPED POLYPYRROLE FILM(I) - FORMATION OF COLUMNAR STRUCTURE BY ELECTROPOLYMERIZATION

Perpendicularly oriented columnar structure was obtained for electropo lymerized polypyrrole films formed from micellar solution of anionic s urfactants. The surfactants used as dopants were a class of anionic su rfactant, namely, sodium salts of dodecyl sulfate (SDS) and dodecylben zene sulfonate (SDBS). The formation process of polypyrrole films on e lectrode surfaces was studied with in situ atomic force microscopy (AF M) and electrochemical quartz crystal microbalance (EQCM) methods in o rder to monitor the submicron structure of the grown polymers. In EQCM measurement, the frequency shift (Delta f) and the resonance resistan ce (Delta R) of the quartz crystal electrode were obtained simultaneou sly. An abrupt increase in Delta R was observed for both PPy/DS- and P Py/DBS- films at about 60-100 mC cm(-2). Such a drastic change in Delt a R, which may be associated with the emergence of the viscoelastic pr operties of the films, could be explained by the formation of columnar structure. in situ AFM observation clearly indicated that such a stru cture started to form around these critical charges. The cyclic voltam mograms for the PPy/DS- and PPy/DBS- films showed sharp redox couples observed around -0.5 to 0.6 V. The redox corresponds to a cation dopin g/undoping process. The diffusion rate of cations for the resulting fi lms was studied with ac impedance measurement as a function of the con centration of surfactant dopants. As the PPy film was prepared in high er concentration of the surfactant dopant, where the micelles are form ed in solution, the resulting film showed a considerably higher (ca. t hree orders of magnitude) diffusion coefficient compared to ordinary P Py films so far reported. Such an enhanced diffusivity of ions could b e attributed to a special formation process of polypyrrole in micelle solution: the mechanism is discussed here.