Amphiphiles at electrified interfaces

The adsorption of insoluble surfactants, spread as a monolayer at the gas-solution interface (GS), onto an electrified metal-solution (MS) interface of a gold single-crystal electrode has been investigated. A Langmuir trough converted into an electrochemical cell was employed in these studies and the adsorption of insoluble surfactants on the Au electrode surface was measured using electrochemical techniques. The results of these experiments have shown that the transfer of insoluble surfactants from GS onto the MS interface is strongly affected by the electrode potential and the transfer ratio is 1:1 only at the potential of zero charge (pzc). UV-Vis and light scattering experiments were employed to demonstrate that insoluble surfactants may be desorbed from the electrode surface at very negative potentials. The desorbed surfactants are trapped in the subsurface region in the form of aggregates, most likely micelles. When the electrode potential is changed to a value close to pzc the micelles spread back onto the electrode surface. The potential induced adsorption of micelles proceeds through a hemimicelle stage. We have shown that the shape and size of the hemimicelle may be conveniently controlled by the electrode potential.