Synergistic Interactions in Mixed W/O Microemulsions of Cationic Gemini and Anionic Surfactants

The synergic effect between cationic Gemini imidazolium surfactant [C12(Bim) 2-2Br] and anionic surfactant sodium dodecyl sulfate (SDS) on the physicochemical properties of the W/O microemulsions was studied. The properties include the molar fraction of the alcohol at the interfacial layer (X-a(i)), the molar fraction of the alcohol in the oil phase (X-a(o)), and the Gibbs free energy change (-Delta G(o -> i)(o)) of transferring alcohol from the continuous oil phase to the interfacial layer. The W/O microemulsion systems contain C-12(Bim)(2)-2Br-SDS/butan-1-ol/octane/5 % NaCl solution. The values of X-a(i) and X-a(o) obtained from the W/O microemulsions containing the mixed surfactants are smaller than that of the microemulsion systems containing the single surfactant C-12(Bim)(2)-2Br or SDS, while the values of -Delta G(o -> i)(o) are larger. This showed the existence of synergism between [C-12(Bim)(2)-2Br] and SDS. The effects of alcohols, alkanes and NaCl concentrations on the values of X-a(i), X-a(o) and -Delta G(o -> i)(o), in the W/O microemulsions stabilized by C-12(Bim)(2)-2Br and SDS were also investigated and discussed.