Capacitive study of self-assembled alkylthiol monolayers: Surface charge effects and kinetics of surfactants adsorption

Adsorption and desorption kinetics of different surfactants onto/from the surface of gold electrodes covered by self-assembled monolayers of 1-octadecanethiol were monitored in aqueous solutions by means of capacitive measurements. Effects of temperature, surfactant concentration and of the surfactants hydrophobic chain length were studied. A linear dependence between the initial slope of the adsorption kinetics and surfactant concentration was observed. This effect can be used for analytical determination of surfactants. The adsorption kinetics suggests a fractal geometry of the surfactants adsorption. The influence of pH and ionic strength on the capacitance of gold electrodes covered by omega-terminated alkylthiols was studied. The curves obtained depend on the ionic strength and have minima near the pK of the terminal group.