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

In this paper, we report on IR and dielectric spectroscopy of Ca(AOT)(2) reverse micelles containing water pools of different sizes. We investigate the effect of changing the nature of the counterion (Na+ --> Ca2+) on the hydration mechanisms and dynamics of AOT microaggregates. The hydration has been 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 dielectric permittivity measurements performed in the range 0.02-3 GHz, as a function of W. A relaxation phenomenon has been observed in this region, and a close connection between the behavior of the relaxation time vs W and the progressive hydration of AOT polar headgroups has been found, similar to the case of the NaAOT micellar system. These results could be interpreted in terms of two coexisting diffusion mechanisms: the reorientation of the whole micellar aggregate and the free rotational diffusion of the completely hydrated AOT headgroups.