INFRARED-ABSORPTION AND WATER-STRUCTURE IN AEROSOL OT REVERSE MICELLES

The structure of water in bis(2-ethylhexyl)sodium sulfosuccinate (AOT) micelles has been studied as a function of the [H2O]/[AOT] ratio (W) by using the absorption IR due to O-H stretching modes in the 3800-300 0 cm(-1) range. Three systems have been studied: water/AOT/carbon tetr achloride, water/AOT/ /n-heptane and water/AOT iso-octane. Experimenta l spectra are presented and discussed for the O-H stretching region bo th of H2O and isotopically diluted HDO molecules in D2O. We have restr icted ourselves to the region of small amounts of water (0 < W < 20) w here the properties of the systems change strongly with the water cont ent. The results show that IR spectra can be expressed as sum of contr ibutions from interfacial and bulk-like water. The fraction of water i n the two ''regions'' within the water pool was evaluated as a functio n of W. From the data a continuous variation appears in the water prop erties inside micellar cores rather than a two-steps hydration mechani sm. The solubilization of mater is described in terms of hydration of the AOT head group and Na+ counterions. The maximum hydration number o f AOT was found to be 3.5. The same behaviour has been observed in the three solvents studied.