Apparent Molar Volume of Solubilized Water in AOT/Isooctane/Water Reverse Micellar Aggregates

Abstract

States of the solubilized water in reverse micellar solution of aerosol-OT (AOT, bis(2-ethylhexyl) sodium sulfosuccinate) in isooctane were investigated by determining the apparent molar volume of water, Vw, through density measurements at different temperatures and water contents wo ([H2O]/[AOT]) of the solution. The low Vw values in the range up to wo = ∼ 2 are due to the strong interaction of H2O molecules with the ionic headgroup of AOT. Then, Vw exhibits a steep rise with water content in the range of wo = 2−6 owing to the swelling of the spherical reverse micelle, which is caused by the weaker binding of the additional water molecules to the ester group of AOT. In the range of wo = 6−12, Vw exhibits a complex behavior as a function of the water content with a distinct minimum in the vicinity of wo = 10. This nonmonotonic course of Vw as a function of water content in this range cannot be rationalized in terms of monotonic changes of the characteristics of the solubilized water in the micelle, or in ...