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

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 nu(OD) band 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(-1) for Na(AOT) and Mg(AOT)(2), respectively. Over the entire W/S range, the main peak corresponds to 92 +/- 3% (Na(AOT)) and 92 F 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)(2) are 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. (C) 1998 Academic Press.