Effect of Ethylene Oxide Group in the Anionic–Nonionic Mixed Surfactant System on Microemulsion Phase Behavior

Abstract

AbstractThe phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12‐14 alcohol ethoxylate (C12 − 14Ej) that contains an ethylene oxide (Ej) group number, j, of either 1, 5, or 9 was investigated for oil remediation. The oil–water interfacial tension (IFT) and optimal salinity of the microemulsion systems with different equivalent alkane carbon numbers (EACN) were examined. The anionic–nonionic surfactant ratio was found to play a pivotal role in the phase transition, IFT, and optimal salinity. The minimum IFT of mixed SDHS − C12 − 14Ej systems were about three times lower than those of neat SDHS systems. A hydrophilic–lipophilic deviation (HLD) empirical model for the mixed anionic–nonionic surfactant system with the characteristic parameter was proposed, as represented in the excess free energy term . The results suggested that the mixed system of SDHS − C12 − 14E1 was more lipophilic, while SDHS − C12 − 14E9 was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C12 − 14E5 system was close to the ideal mixture. The findings from this work provide an understanding of how to formulate mixed anionic–nonionic microemulsion systems using the HLD model for oils that possess a wide range of EACN.