Adsorption and aggregation of sodium dodecyl sulfate on gold(111) electrode surfaces

Electrochemical measurements, scanning probe microscopy and neutron reflectivity experiments have been combined to present a complete description of the adsorption and aggregation of sodium dodecyl sulfate at the Au(111) interface. The various states of adsorption are found to be a function of bulk solution surfactant concentration and the charge on the electrode surface. At low surfactant concentrations, SDS adsorbs to form two-dimensional arrays of “dimer pairs”. At higher concentrations, additional SDS molecules adsorb on the surface resulting in the formation of hemimicellar surfactant aggregates. This work presents the first direct images of the potential controlled phase transition between the hemimicellar and condensed states of a dodecyl sulfate (SDS) film at the Au(111) electrode surface. The adsorbed SDS forms stripe-shaped hemimicellar aggregates at small or moderate charge densities at the electrode. Adsorbed SDS molecules are ordered and form a long range two-dimensional lattice. It is proposed that each unit cell contains two flat-lying SDS molecules. (Abstract shortened by UMI.).