FTIR and 1H NMR studies of the solubilization of pure and aqueous 1,2-ethanediol in the reverse aggregates of aerosol-OT

Solubilization of 1,2-ethanediol, ED, and its aqueous solution, ED-W, by the reverse aggregates of sodium bis(2-ethylhexyl) sulfosuccinate, Aerosol-OT or AOT, in n-heptane and isooctane has been studied by FTIR and H-1 NMR. Curve fitting of the v(OD) bands of the aggregate-solubilized (partially deuterated) ED and ED-W showed the presence of a main peak and a smaller one. The frequency of the former peak decreases, whereas its full width at half-height increases as a function of increasing [solubilizate]/[AOT]. The dependence on the later ratio of H-1 NMR chemical shifts, delta(proton), of solubilized water, ED, ED-W as well as the surfactant discrete protons showed monotonic increase or decrease. Results of both techniques indicated that ED and/or water interact with the surfactant by a similar mechanism, i.e., by solvating its head-ions. The magnitudes of \Delta v(OD)\ and \Delta delta(proton)\ showed, however, that AOT interacts more strongly with ED than with water. Over the entire range of [solubilizate]/[surfactant], the main von peak area corresponds to 85 +/- 2% (ED), and 88 +/- 2% (ED-W) of the total peak area. These results show that the aggregate-solubilized ED or ED-W does not seem to coexist in "layers" of different structures, as suggested by the multi-state water solubilization model.