Electrochemical deposition of poly(o-anisidine) and polypyrrole at octadecanethiol coated gold electrodes

Abstract

The o-anisidine and pyrrole have been polymerized by the electrochemical oxidation of monomers on gold electrodes, covered with self-assembled monolayers. The obtained polymer–monolayer systems have been investigated by cyclic voltammetry in aqueous supporting electrolyte solutions containing K4Fe(CN)6 and Ru(NH3)6Cl3. The deposition of conducting polymers strongly depends on the integrity of a monolayer. In the case of a large number of SAM defects, the polymerization of o-anisidine and pyrrole leads to the formation of nuclei of the conducting polymer in the insulating matrix of the thiol monolayer. When the polymer is in the conducting (oxidized) form, the nuclei act as an array of microelectrodes. The polarogram-shaped voltammograms obtained for K4Fe(CN)6 confirm the hemispherical diffusion of redox species to the polymer nuclei. When the polymer is in the non-conducting (reduced) form, the polymer–octadecanethiol layer blocks the redox processes on the electrode. The exponential-type CV curves observed for Ru(NH3)6Cl3, when the polymer is in its non-conducting state, can be assigned to the tunnelling of electrons through the passivating layer. The use of monolayers with a low number of defects influences the mechanism of polymer growth. Thus, the polypyrrole grows on the layer of thiols, and the poly(o-anisidine) forms polymer nuclei.