Electrochemical and spectroscopic studies of the mechanism of monolayer and multilayer adsorption of an insoluble surfactant at the Au(111)/electrolyte interface

The adsorption of an insoluble monolayer of 12-(9-anthroyloxy) stearic acid (12-AS) onto a single crystal gold electrode has been described. The spreading of the insoluble surfactant onto the metal/solution interface of the gold electrode was initially investigated with the help of cyclic voltammetry and differential capacity. Electrochemical studies indicate that the film of 12-AS molecules spreads onto the metal surface at potentials close to the potential of zero charge (pzc) and desorbs from the electrode surface at potentials that are sufficiently negative. The spreading of the film and its subsequent desorption are repeatable. The 12-AS molecule is a surfactant dye which may be used to perform spectroelectrochemical experiments. Electroreflectance spectroscopy, fluorescence spectroscopy and measurements of the light scattered by the desorbed surfactant molecules were employed to determine the mechanism by which molecules of the insoluble surfactant spread onto and desorb from the metal/solution interface of the gold electrode. With the help of the spectroelectrochemical experiments we have demonstrated that the repeatable potential-induced desorption and adsorption (spreading) of the insoluble molecules involves formation of micelles (or similar molecular organizations) in the subsurface region and spreading of the micelles onto the electrode surface.