Infrared absorption and water structure in aerosol OT reverse micelles |
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Authors: | P Amico M D’Angelo G Onori A Santucci |
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Institution: | (1) Unità di Perugia, INFM, Perugia, Italy;(2) Dipartimento di Fisica, Università di Perugia, Via A. Pascoli, I-06100 Perugia, Italy |
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Abstract: | Summary 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 3800–3000 cm−1 range. Three systems have been studied: water/AOT/carbon tetrachloride, water/AOT/n-heptane and water/AOT iso-octane. Experimental spectra are presented and discussed for the O−H stretching region both of
H2O and isotopically diluted HDO molecules in D2O. We have restricted ourselves to the region of small amounts of water (0<W<20) where the properties of the systems change strongly with the water content. The results show that IR spectra can be expressed
as sum of contributions from interfacial and bulk-like water. The fraction of water in the two “regions” within the water
pool was evaluated as a function ofW. From the data a continuous variation appears in the water properties inside micellar cores rather than a two-steps hydration
mechanism. The solubilization of water is described in terms of hydration of the AOT head group and Na+ counterions. The maximum hydration number of AOT was found to be 3.5. The same behaviour has been observed in the three solvents
studied. |
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Keywords: | Disperse systems PACS 78 30 Infrared and Raman spectra and scattering |
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