Study of the Synergistic Effect of Sodium Dodecyl Sulfate and Betaine at the Air/Water and Oil/Water Interfaces

Abstract

In this paper, the molecular array behavior of anionic surfactant sodium dodecyl sulfate SDS and zwitterionic surfactant Betaine at the air/water and oil/water interfaces were investigated by molecular simulation approaches, which helped to understand the effects of temperature, salts and the proportion of components on the interfacial activity and foam stability of the mixed binary systems, especially how the multivalent inorganic cations influence the interfacial adsorption behavior of the surfactants and the synergistic effect. The oil/water interfacial tension was not only measured experimentally using TEXAS500 spinning drop interface tension meter, but also calculated theoretically using dissipative particle dynamic (DPD) method. Foam decay method was utilized to determine the foam stability. The array behavior of surfactant molecules at the air/water and oil/water interfaces was described by molecular dynamics (MD) simulation method. It was found that the oil/water interfacial activity of mixed binary system was significantly better than unitary system. The synergistic effect be- tween SDS and Betaine was enhanced when there was Ca 2 + or Mg 2 + existed in the solution. The radial distribution function of head groups of surfactants around inorganic ions showed that there was very strong interaction between the Ca 2 + or Mg 2 +