Wettability of solid/brine/n-dodecane systems: experimental study of the effects of ionic strength and surfactant concentration

The effects of aqueous phase ionic strength and surfactant concentration on the interfacial tension as well as on the advancing contact angle of glass/brine/n-dodecane, and polyacrylonitrile/brine/n-dodecane systems are measured. Ionic strength is varied between 0.0 and 1.5 M by means of sodium chloride, while the concentration of sodium dodecyl sulfate (an anionic surfactant) fluctuates from 1.39×10−4 to 1.12×10−4 M. The interfacial tension between n-dodecane and aqueous phase is measured over the same ionic strength and sodium dodecyl sulfate concentration ranges as the contact angle measurements. The main results of this work are: (i) increasing aqueous phase ionic strength as well as increasing surfactant concentration cause a decrease in the n-dodecane/aqueous phase interfacial tension; (ii) on a glass surface, even if there is a contact angle diminution when increasing the ionic strength, the solid surface remains at all times clearly hydrophilic; and (iii) on a polyacrylonitrile surface, although there is no a significant effect of the ionic strength on the contact angle behavior, there exists, nevertheless, a wettability quality change from hydrophobic to hydrophilic behavior due to an increase of the surfactant concentration in the aqueous phase. These results are discussed with respect to their implication on wettability behavior of solid/oil/brine systems.