Abstract:

Microemulsions are widely used in tertiary oil recovery, cosmetics, food industry and other fields due to their excellent properties. By mixing anionic and cationic surfactants, a microemulsion system with excellent performance could be prepared. The factors influencing the phase behavior of the microemulsion system of mixed anionic/cationic surfactants, such as the molar ratio of SDBS to （C₁₂-4-C₁₂）Br₂, salinity, surfactant mass fraction, and oil-water ratio, were studied. The results show that, for the SDBS-（C₁₂-4-C₁₂）Br₂/n-butanol/NaCl/water/kerosene system, the solubilization parameter shows a trend of first increase and then decrease with the increase of the molar ratio. The optimal molar ratio of SDBS to （C₁₂-4-C₁₂）Br₂ is 0.7∶1. In the experiments to investigate the effects of salt, the oil-water ratio was fixed to 1∶1, and the mass fractions of mixed surfactants were 2%, 3%, 4% and 5%, respectively. With the increase of NaCl mass fraction, all systems show the phase transition from Winsor Ⅰ→Winsor Ⅲ→Winsor Ⅱ. In the experiments to investigate the effects of oil, the mass fraction of mixed surfactants was fixed to 4%, and the mass fractions of NaCl were 0.50%, 1.30% and 1.65%, respectively. With the increase of the oil-water ratio, when the NaCl mass fraction was 0.50%, the system changed from micellar solution to Winsor Ⅰ type; when the NaCl mass fractions were 1.30% and 1.65%, the two systems showed the phase transition from Winsor Ⅱ→Winsor Ⅲ→Winsor Ⅰ. When the NaCl mass fraction was fixed to 1.30% and the mass fractions of mixed surfactants were 3%, 4% and 5% respectively, with the increase of the oil-water ratio, all systems showed the phase transition from Winsor Ⅱ→Winsor Ⅲ→Winsor Ⅰ. In addition, the amounts of oil required for the formation and disappearance of Winsor Ⅲ microemulsion increased with the mass fractions of NaCl and mixed surfactants.

Key words: microemulsion, surfactant mixture, oil-water ratio, phase change