title: Ion exchange in reverse micelles.
abstract: The distribution and dynamics of alkali cations inside Na-AOT reverse micelles have been investigated using Monte Carlo and molecular dynamics simulations. Water is modeled using the extended simple point charge (SPC/E) model. Simulations were carried out for alkali salts of Li+, Na+, K+, and Cs+ placed into the aqueous core of the reverse micelle, for situations corresponding to one and three molecules of added salt. In all cases, we observe that the larger K+ and Cs+ ions exchange with the Na+ counterion; however, the smaller Li+ ion prefers to remains solvated within the core of the reverse micelle. Our study reveals that the oil-water interface of the Na-AOT reverse micelle has the greatest selectivity toward Cs+ followed by K+ and Li+. A model based on enthalpic contributions illustrates that the solvation energies of the different cations in water control the ion-exchange process. The hydration number of the first water shell for Li+ situated in the aqueous core of the reverse micelle with radius R = 14.1 A was similar to that observed at infinite dilution in bulk water.
authors.affiliation: Department of Chemical Engineering, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Pal
authors.forename: G
authors.initials: G
authors.lastname: Vishal
authors.forename: K S
authors.initials: KS
authors.lastname: Gandhi
authors.forename: K G
authors.initials: KG
authors.lastname: Ayappa