In-situ spectroscopic investigations of surfactant adsorption and water structure at the CaF2/aqueous solution interface

We report in-situ spectroscopic measurements of the structure and orientation of molecules in the interfacial region between the semi-soluble ionic solid CaF2 (fluorite) and an aqueous phase. This paper integrates a series of new experiments with earlier results to give a comprehensive understanding of this very dynamic interface. We employ the surface specific technique, vibrational sum-frequency spectroscopy (VSFS), to study the effect that alterations in the aqueous phase composition, such as pH, surfactant ion concentration, and ion composition have on the bonding interactions, ion exchange behavior, and electrical properties in the interfacial region. These studies demonstrate the complex nature of the interactions of semi-soluble solids with an aqueous phase and the complexity of the surfactant adsorption process. Fundamental studies such as these are essential for understanding the mechanisms involved in surfactant adsorption and interfacial charge reversal; information which is important for industrially relevant processes such as mineral ore flotation, waste processing and petroleum recovery.