Electrochemistry of Surfactant‐Doped Polypyrrole Film(I): Formation of Columnar Structure by Electropolymerization

Abstract

Perpendicularly oriented columnar structure was obtained for electropolymerized polypyrrole films formed from micellar solution of anionic surfactants. The surfactants used as dopants were a class of anionic surfactant, namely, sodium salts of dodecyl sulfate (SDS) and dodecylbenzene sulfonate (SDBS). The formation process of polypyrrole films on electrode surfaces was studied with in situ atomic force microscopy,(AFM) and electrochemical quartz crystal microbalance (EQCM) methods in order to monitor the submicron structure of the grown polymers. In EQCM measurement, the frequency shift (Δf) and the resonance resistance (ΔR) of the quartz crystal electrode were obtained simultaneously. An abrupt increase in ΔR was observed for both PPy/DS− and PPy/DBS− films at about . Such a drastic change in ΔR, which may be associated with the emergence of the viscoelastic properties of the films, could be explained by the formation of columnar structure. In situ AFM observation clearly indicated that such a structure started to form around these critical charges. The cyclic voltammograms 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 doping/undoping process. The diffusion rate of cations for the resulting films was studied with ac impedance measurement as a function of the concentration of surfactant dopants. As the PPy film was prepared in higher concentration of the surfactant dopant, where the micelles are formed in solution, the resulting film showed a considerably higher (ca. three orders of magnitude) diffusion coefficient compared to ordinary PPy films so far reported. Such an enhanced diffusivity of ions could be attributed to a special formation process of polypyrrole in micelle solution: the mechanism is discussed here.