THE SURFACE FREE-ENERGY OF FLUORITE IN PRESENCE OF SODIUM DODECYL-SULFATE

Measurements of contact angle for water, glycerol, formamide, diiodomethane and bromoform on the surface of fluorite covered with a film of sodium dodecyl sulfate (SDS) were made. From these results the Lifshitz-van der Waals and the acid-base components of the surface free energy of fluorite covered with an SDS film were calculated. The electron-acceptor and the electron-donor parts of the acid-base component were also evaluated. On the basis of the measurements and the calculations carried out, a minimum wettability of fluorite and a minimum contribution of the acid-base intermolecular interaction to the surface free energy of fluorite were found when the fluorite surface was covered with an SDS monolayer. At higher SDS concentrations, a bilayer film can be formed on the fluorite surface, increasing the electron-donor proportion of the acid-base component of the surface free energy.