Phase behavior and solubilization of microemulsion systems containing Gemini imidazoliums and their monomeric analogues

The Gemini imidazolium surfactants with a four-methylene spacer group [C n (Bim) 2 -2Br, n = 12, 14, 16] and their corresponding monomers [C n mimBr, n = 12, 14, 16] were synthesized and characterized. The phase behavior and solubilization of microemulsion systems containing C n (Bim) 2 -2Br/butan-1-ol/octane/brine as well as microemulsion systems containing C n mimBr/butan-1-ol/octane/brine were studied and compared. The C n (Bim) 2 -2Br-based microemulsion systems have greater solubilization ability than that of the corresponding mono surfactants C n mimBr-based systems. As the carbon chain lengths of the surfactants [C n (Bim) 2 -2Br and C n mimBr] increase, the mass fraction of the alcohol in the interfacial layer A S would decrease, whereas the solubilization ability ( SP* ) would increase. The maximum solubilization ability ( SP* ) of the two microemulsion systems was attained when the oil/water mass ratio ( α ) approaches 0.5. The solubilization ability of both microemulsion systems would increase with increasing NaCl concentrations in aqueous phase. In C n (Bim) 2 -2Br-based microemulsion systems, the alcohol is significantly more soluble in aqueous phase than in the oleic phase. And it was noted that the alcohol is more soluble in C n (Bim) 2 -2Br-based systems than in C n mimBr-based systems in both aqueous and oleic phases.