Polymer sandwiches: polyaniline films deposited on thiol-coated gold by chemical in situ method

Abstract

We present a study of polyaniline chemical deposition in situ on gold electrodes coated with thiol monolayers containing different terminal groups: methyl, hydroxy, and carboxy. The differences in the deposition rates of polymers on various thiol monolayers were investigated with the quartz crystal microbalance (QCM) and UV-vis spectroscopy. It was found that the polymer is formed in the bulk of the polymerization solution and subsequently precipitated on the electrode surface. The synthesized polymers were studied by cyclic voltammetry. A novel method allowing for the investigation of the inner (thiol) layer integrity was proposed. It is based on the electrochemical oxidation of the gold substrate and formation of complexes with chloride ions incorporated in the polymer films. The observation of a characteristic AuCl 4 − reduction peak allows for the determination whether the polymer is adjacent just to the surface of gold or it is separated from the bare metal by thiol monolayer. It was found that the deposition of polymer on the thiol monolayers with terminal methyl and carboxy groups leads to the formation of sandwich-like systems with the thiol monolayer interposed between the polymer layer and the gold surface, while the chemical polymerization on hydroxy-ended thiols induces partial desorption of the monolayer; thus, the polymer is directly adjacent to the bare gold over large areas of the electrode surface. The morphology of the synthesized polymer was also investigated by contact mode atomic force microscopy (AFM).