Micellar interactions in water-in-oil microemulsions

The dielectric properties of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles in CCl4 and n-heptane have been measured in the frequency range 0.02-20 GHz as a function of W = [H2O]/[AOT]. A relaxation phenomenon has been observed reflecting some properties inherent the single particle dynamics. This dielectric relaxation has been found to be markedly affected by interparticle interactions. Our data, according to previous results, show that interactions in these systems depend on the oil chain length, on the molar ratio W and are significantly affected by the addition of small amounts of electrolyte. In order to achieve a deeper insight into the microscopic origin of these interactions, IR absorptions in the C=O stretching region of AOT molecules have been recorded to give information on the relative population of different AOT rotational isomers in the various examined systems. The data show a clear correlation between the presence of attractive interactions and the composition of AOT rotamers, supporting the hypothesis that the intermicellar interactions are favored by a particular orientation and packing of non-polar tails of AOT molecules in the micellar microaggregate.