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

We present a study of polyaniline chemical deposition in situ on gold elect rodes coated with thiol monolayers containing different terminal groups: me thyl, hydroxy, and carboxy. The differences in the deposition rates of poly mers on various thiol monolayers were investigated with the quartz crystal microbalance (QCM) and UV-vis spectroscopy. It was found that the polymer i s formed in the bulk of the polymerization solution and subsequently precip itated on the electrode surface. The synthesized polymers were studied by c yclic voltammetry. A novel method allowing for the investigation of the inn er (thiol) layer integrity. was proposed. It is based on the electrochemica l oxidation of the gold substrate and formation of complexes with chloride ions incorporated in the polymer films. The observation of a characteristic AuCl4- 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 thi ol monolayers with terminal methyl and carboxy groups leads to the formatio n of sandwich-like systems with the thiol monolayer interposed between the polymer layer and the gold surface, while the chemical polymerization on hy droxy-ended thiols induces partial desorption of the monolayer; thus, the p olymer is directly adjacent to the bare gold over large areas of the electr ode surface. The morphology of the synthesized polymer was also investigate d by contact mode atomic force microscopy (AFM). (C) 2001 Elsevier Science B.V. All rights reserved.