Charge reversal Behavior at the CaF2/H2O/SDS interface as studied by vibrational sum frequency Spectroscopy

We report in situ spectroscopic measurements of charge reversal behavior and surfactant bilayer formation at the salt/aqueous solution interface as the aqueous surfactant concentration is varied. The studies, which employ vibrational sum frequency spectroscopy to measure the vibrational response of sodium dodecyl sulfate and water at the CaF2/H2O interface, demonstrate the complex nature of the adsorption process which includes monomer adsorption, surfactant bilayer formation, surfactant restructuring, surface charge reversal, and water reorientation. These effects have been monitored directly for the first time by taking advantage of the spectroscopy and the nonlinear phase relationships between the CH and OH vibrational modes. The results provide important insight into the adsorption mechanism that is central to processes such as mineral ore flotation and separation, waste processing, and petroleum recovery.