An experimental study of the change in the contact angle of an oil on a solid surface

The effects of pH and surfactant concentration on the change in the contact angle of an oil on both stainless steel and glass surfaces have been studied. The pH ranged from 7.0 to 10.0. Sodium dodecyl sulfate (SDS), an anionic surfactant, was the surfactant used in this study. Two different surfactant concentrations were used, one concentration near the critical micelle concentration (cmc) and one concentration significantly above the cmc. The interfacial tension between the oil and surfactant solutions was measured over the same pH and concentration ranges as the contact angle measurements. Increasing the pH as well as increasing the surfactant concentration causes a decrease in the oil/surfactant solution interfacial tension for solutions of SDS. Over the range of pH values and SDS concentrations studied, increasing the pH and surfactant concentration above the cmc hinders the change in the contact angle of the oil on both the stainless steel and glass surfaces despite the decrease in the interfacial tension.