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 studi ed. The pH ranged from 7.0 to 10.0. Sodium dodecyl sulfate (SDS), an anioni c surfactant, was the surfactant used in this study. Two different surfacta nt concentrations were used, one concentration near the critical micelle co ncentration (cmc) and one concentration significantly above the cmc. The in terfacial tension between the oil and surfactant solutions was measured ove r the same pH and concentration ranges as the contact angle measurements. I ncreasing 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, increa sing the pH and surfactant concentration above the cmc hinders the change i n the contact angle of the oil on both the stainless steel and glass surfac es despite the decrease in the interfacial tension.