Molecular array behavior and synergistic effect of sodium alcohol ether sulphate and carboxyl betaine/sulfobetaine in foam film under high salt conditions

Abstract In this paper, the molecular array behavior of the mixed systems of anionic–nonionic surfactant sodium alcohol ether sulphate (AES) and zwitteroinic surfactants carboxyl betaine (CAB) or sulfobetaine (DSB) at the gas/water interface in foam films was investigated by molecular dynamics simulation approach, which helped to understand in microscopic view how salts effected the foam stability of the mixed surfactants and their synergistic effect. It was found that the multivalent inorganic cations could be bounded to the negatively charged head groups of the surfactants and participated in the formation of the interface layer directly, not only influenced the interfacial adsorption behavior of the surfactant molecules, but also changed the state of the water molecules in the foam films. Foam decay method was utilized to determine the foam stability experimentally. The experimental results agreed very well with the simulation results. The knowledge about how the microscopic character of the surfactant mixtures at the interface with multivalent cations coexisting effect the foam properties could provide useful guidance for the application of surfactants under high salinity condition, such as the formula design for foam flooding system used in offshore enhanced oil recovery (EOR).