Interfacial tension of methane plus water with surfactant near the hydrate formation conditions

Interfacial tension of methane + water with surfactant near the hydrate formation conditions were measured using the pendant-drop method at 273.2 K and 278.8 K and in the pressure range of (0.4 to 9.5) MPa. The concentrations of sodium dodecyl sulfate (SDS) were 100 ppm, 300 ppm, 500 ppm, 700 ppm, and 1000 ppm. It was found that the interfacial tension of the solutions decreases steeply with the addition of SDS. When the SDS concentration is about 500 ppm, the surfactant concentration reaches a critical micellar concentration of the methane + water solution. Surfactant molecules associate as micelles, and the interfacial tension remains constant with further increase in SDS concentration.