Capacitive Detection of Surfactant Adsorption on Hydrophobized Gold Electrodes

Abstract

Nonspecific adsorption of surfactants on polycrystalline gold electrodes, covered by a chemically adsorbed monomolecular layer of octadecanethiol, was studied by means of capacitive measurements. Homologous series of fatty acids (from decane to tetradecane acids) and dodecanepyridinium chloride were used as surfactants. The behavior of the electrode was completely different in the first and subsequent cycles of adsorption/desorption. In the first adsorption cycle, an initial capacitance jump at low concentrations (<10 μM) occurs, while later the curves show the usual saturation behavior. The first surfactant layer could not be completely desorbed; only the electrode capacitance shown after the jump was reached. Subsequent cycles do not reveal any capacitance jumps and were completely reversible. Adsorption curves in the series of monoalkyl acids are shifted according to the Traube rule. A comparison with the surfactant adsorption at the air/water interface has been done.