Infrared and dielectric study of Ca(AOT)(2) reverse micelles

In this paper, we report on IR and dielectric spectroscopy of Ca(AOT)(2) re verse micelles containing water pools of different sizes. We investigate th e effect of changing the nature of the counterion (Na+ --> Ca2+) on the hyd ration mechanisms and dynamics of AOT microaggregates. The hydration has be en studied as a function of the molar ratio W = [H2O]/[AOT] by means of IR absorption of O-H stretching modes in the 3800-3000 cm(-1) frequency range. The dynamical properties of the system have been investigated by dielectri c permittivity measurements performed in the range 0.02-3 GHz, as a functio n of W. A relaxation phenomenon has been observed in this region, and a clo se connection between the behavior of the relaxation time vs W and the prog ressive hydration of AOT polar headgroups has been found, similar to the ca se of the NaAOT micellar system. These results could be interpreted in term s of two coexisting diffusion mechanisms: the reorientation of the whole mi cellar aggregate and the free rotational diffusion of the completely hydrat ed AOT headgroups.