Cation Effect On The Binary And Ternary Phase Behaviors Of Double-Tailed Methanesulfonate Amphiphiles

A series of symmetrical dialkyl methanesulfonate amphiphiles [DiC(n)CHSO(3)](m)M (n = 6, 7, 8) with different counter cations (Mm+ = H+, Li+, Na+, K+, Cu2+, Zn2+, Mg2+, Ca2+, Sc3+) were synthesized in five steps. Their solubility and critical micelle concentration (CMC) in water were determined highlighting a huge effect of the chain length and the nature of the cation. The hydrophilic-lipophilic balance of the surfactants were assessed with the phase inversion temperature (PIT)-slope method based on the deviation from the PIT of the reference C10E4/n-octane/0.01 M NaCl(aq) emulsion through addition of increasing amounts of the dialkyl methanesulfonates. The hydrophilicity of the surfactants was thus ranked in terms of dPIT/dx(sulfonate). A "cation" scan with the [DiC(6)CHSO(3)](m)M/benzene/water systems at f(w) = 0.5 was finally performed confirming the hydrophilicity ranking obtained with the PIT-slope method. It revealed that the [DiC(6)CHSO(3)](2)Mg behaves as a "Balanced Surfactant" able to form spontaneously a three-phase microemulsion system (Winsor III) just in the presence of water and oil, in the same way as the catalytic surfactant dimethyldioctylammonium molybdate, which has the same PIT-slope.