Surface properties and solubility enhancement of Gemini/conventional surfactant mixtures based on sulfonate Gemini surfactant

Abstract

The synergistic effect of sulfonate Gemini surfactant (SGS12) with different kinds of conventional surfactants on surface properties and solubility enhancement was investigated. Results indicated that the absolute values of βm were in the following order: SGS12/BQAS > SGS12/DTAB > SGS12/rhamnolipid > SGS12/SDS > SGS12/Triton X-100. The cationic/anionic surfactant mixtures formed micelles at a low concentration, which resulted from the strong attraction among different charged hydrophilic headgroups. Moreover, the molar solubilization ratio and lnKm values indicated that the solubility of SGS12/BQAS, SGS12/Triton X-100, and SGS12/DTAB mixtures toward pyrene was higher than that of either component. The micelle's hydrodynamic sizes of cationic/anionic surfactant mixtures were larger than that of either component, so the hydrophobic space to dissolve additional pyrene was large. Furthermore, dynamic surface tension determination suggested that cationic/anionic surfactant mixtures had a relatively short induction period, and the n values for SGS12/BQAS and SGS12/DTAB mixtures were slightly larger than those for either component. At the total surfactant concentration of 1 μmol·L−1, the plots of γt versus t1/2 for all surfactant mixtures were linear, indicating that the initial adsorption was controlled by diffusion. The values of Dt→0 for SGS12/BQAS, SGS12/DTAB, and SGS12/rhamnolipid mixtures were higher than those of either pure component. Therefore, the mixture of these surfactants accelerated the adsorption process and lowered the adsorption energy barrier, and the mixing of cationic and anionic surfactants was beneficial for dynamic surface activity. In conclusion, the cationic/anionic surfactant mixtures demonstrated good potential for the remediation of polycyclic aromatic hydrocarbon-contaminated soils from equilibrium and dynamic viewpoints.