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

Abstract

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.