Effect of molecular structure on synergism in mixed zwitterionic/anionic surfactant system: An experimental and simulation study

The oil/water interfacial properties of different zwitterionic surfactant (N-dodecyl- N, N -dimethyl-3-ammonio-1-propanesulfonate, ASB; 3-(1-dodecyl-3- imidazolio)propanesulfonate, ImS3; 3-(1-dodecyl-3-benzimidazolio)propanesulfonate, BzImS3) combined with anionic surfactant (sodium dodecyl benzene sulfonate, SDBS) have been studied via experimental and simulation methods. Both experimental and simulation results indicate that the synergistic effect between surfactants is greatly affected by the aromatic cation part of the zwitterionic surfactants. For ASB/SDBS system, the SDBS and ASB molecules are adsorbed at same position of the oil/water interface, which generates competitive adsorption and resulting in a relatively loose surfactant monolayer. For ImS3/SDBS and BzImS3/SDBS systems, the additional π-π stacking interaction increases the compactness of surfactant monolayer, which contributes to the greatly reduced oil/water interfacial tension. The adsorption mechanism of mixed zwitterionic/anionic surfactant systems at oil/water interface is supplemented at a molecular level, which provides a fundamental guidance for an in-depth understanding of optimal selection of surfactant in enhancing oil recovery.