Additive Effects on the Phase Behavior of Cationic Surfactant ([C16mim]Br) Stabilized Hydrophobic Ionic Liquid Based Middle-Phase Microemulsions

The e-β fishlike phase diagram of the system [C16mim]Br/[Omim]Tf2N/water was constructed in the presence of different additives (alcohol and inorganic salt). From the diagram some additive-dependent characteristic physicochemical parameters were obtained. Results show that with the increase of the alkyl chain length of alcohols, the solubility of the alcohol in [Omim]Tf2N, and the optimum solubilization parameter (SP*) decrease, while the maximum alcohol width (△e) for the phase inversion and the mass fraction of the alcohol in the balanced interfacial film (Ain) increase. For inorganic salts, an increase in [NaCl], or an increase of the radius of halides (X–) at constant [NaX], or the substitution of the divalent anion SO42– by the same molar concentration of monovalent anion Cl– makes both SP* and △e increase, but Ain decrease. Overall, the alcohol effect on the phase behavior of the microemulsion is greater than the salt effect, and the composition effect of an inorganic salt is greater than the concen...