Roles of Catanionic Surfactant Mixtures on the Stability of Foams in the Presence of Oil

The stability of foams in the presence of oil is a crucial factor for foam displacement process in enhanced oil recovery. After the test of foam stability in the presence of oil of the mixtures of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (C12TAB), “catanionic” surfactant mixtures are proposed as a novel agent to enhance the oil resistance of foam. Based on the investigations of the foam evolution and the interfacial properties, the mechanisms are demonstrated by means of approaches of multiple light scattering and interfacial dilational rheological experiments. Because of the electrostatic attraction between molecules with opposite charges, catanionic mixtures are highly close-packed and form dense adsorption layers, which possess high modulus. So when oil–aqueous and gas–aqueous interfaces are approaching each other, strong pseudoemulsion films are formed. The compact adsorption layers also inhibit the diffusion exchange between the interface and the bulk, and this is the key factor to decrease the interaction between the gas–aqueous and oil–aqueous interfaces of the pseudoemulsion film. These properties increase the enter barrier of the oil droplets to the film surface.