Thermodynamics of Micellization, Interfacial Behavior and Wettability Alteration of Aqueous Solution of Nonionic Surfactants

The present work deals with the physiochemical properties of polyoxyethylene sorbitan fatty acid esters (polysorbates), which are commonly known under the trade name Tween. Thermodynamics of micellization and adsorption at air-water interface for these nonionic surfactants solutions have been studied over a broad range of temperature. As the temperature of the surfactant solutions increases, the surface tension decreases whereas the critical micelle concentration (CMC) of each surfactant solution initially decreases and then increases. The free Gibb free energies of the micelle formation Delta G(m)(o), and the surfactant adsorption Delta G(ads)(o), are calculated for the CMC of each surfactant at different temperatures. The surface or expanding pressure (Pi(cmc)), minimum area per molecule (A(min)), maximum surface excess (Gamma(max)) are also calculated. The interfacial tension (IFT) between the aqueous surfactant solutions and the crude oil are measured at different concentrations of the surfactants using a spinning drop tensiometer. The contact angles are determined on an oil wet quartz surface to investigate the wettability alteration in the presence of Tween surfactants with varying salinity. FTIR analysis of quartz at dry and oil wet state, crude oil and COBRS (crude oil-brine-rock-surfactant) combinations are performed to identify the associated functional groups and their mutual interactions.