Effect of Ethylene Oxide Group in the <scp>Anionic–Nonionic</scp> Mixed Surfactant System on Microemulsion Phase Behavior
Virin Kittithammavong, Ampira Charoensaeng, Sutha Khaodhiar
Abstract
Abstract The phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12‐14 alcohol ethoxylate (C 12 − 14 E j ) that contains an ethylene oxide (E j ) 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 − C 12 − 14 E j 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 − C 12 − 14 E 1 was more lipophilic, while SDHS − C 12 − 14 E 9 was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C 12 − 14 E 5 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.