A Fourier Transform Infrared Study on the Structure of Water Solubilized by Reverse Aggregates of Sodium and Magnesium Bis(2-ethylhexyl)sulfosuccinates in Organic Solvents

Abstract

The structure of water (4% D2O in H2O, v/v) solubilized by the reverse aggregates of sodium bis(2-ethylhexyl) sulfosuccinate [Na(AOT)] in heptane and by magnesium bis(2-ethylhexyl) sulfosuccinate [Mg(AOT)2] in toluene has been probed by FT-IR. The νODband of solubilized HOD has been recorded as a function of the [water]/[surfactant] molar ratio, W/S, up to the phase separation boundary for Na(AOT), W/S of 60, and to W/S of 33 for Mg(AOT)2. Curve-fitting of this band showed the presence of main peaks at 2530 ± 19 and 2523 ± 7 cm−1, and small peaks at 2355 ± 43 and 2352 ± 18 cm−1for Na(AOT) and Mg(AOT)2, respectively. Over the entire W/S range, the main peak corresponds to 92 ± 3% (Na(AOT)) and 92 ± 2% (Mg(AOT)2) of the total peak area. For each surfactant, as a function of increasing W/S, the frequency of the main peak decreases, whereas its full width at half-height increases; values of both properties at W/S of 60 for Na(AOT) and at W/S of 33 for Mg(AOT)2are close to the corresponding ones for HOD in bulk aqueous phase. These results show that the aggregate-solubilized water, although different from bulk water, does not seem to coexist in “layers” of different structures, as suggested by the multistate water solubilization model.