Interfacial composition and solubilization of microemulsion systems containing mixed surfactants C₁₂mimBr and Brij35: effects of surfactant composition, temperature, and salinity

The composition of the interfacial layer and solubilization of the microemulsions containing mixed cationic and nonionic surfactants (C₁₂mimBr-Brij35) were studied and compared based on the mass and the number of moles of the surfactants, respectively. As \( {X}_{C_{12}\mathrm{mimBr}} \) (mole fractions of C₁₂mimBr in C₁₂mimBr-Brij35 mixture) increases, the total masses of the surfactants (\( {m}_S^s \)) decrease, whereas the total number of moles of surfactants (\( {n}_S^S \)) increases in the interfacial layer. This opposite pattern of change between \( {m}_S^s \) and \( {n}_S^S \) against \( {X}_{C_{12}\mathrm{mimBr}} \) is due to the significant difference in the molecular mass between the two surfactants. The mass solubilization parameter of the microemulsions, \( {\mathrm{SP}}_m^{\ast } \), increases and follows a curve that concaves downward as \( {X}_{C_{12}\mathrm{mimBr}} \) values increase. However, the molar solubilization parameter, \( {\mathrm{SP}}_n^{\ast } \), would decrease as \( {X}_{C_{12}\mathrm{mimBr}} \) increases. The physicochemical properties of the microemulsions are less sensitive to both temperature and salinity.