Monte Carlo simulations of reverse micelles and other ionic clusters

Abstract

The primary focus of this study is the size and shape of reverse micelles of sodium AOT at low hydration levels. We predict that completely dry sodium ACT in a nonpolar solvent would be insoluble, forming rods of macroscopic length which aggregate to the hexagonal phase. It is shown that these long rods are broken up by waters of hydration. The water molecules hydrate the cations on the exterior of the micelle. and the dipolar repulsion of these aligned water molecules ruptures the long rods. At the lowest experimentally achievable hydration levels, excellent agreement is found between the observed micelle sizes and the predictions based on the calculated energies. Both the long rods and the normal micelles are three coordinated polyhedral structures. Results on the aggregation and dissociation dynamics of the micelles are also presented with predictions of the energetics manifested in the simulations.

The observed three coordinated polyhedral structures are also shown to be the ground state in the general case of charged ionic hard spheres with sufficient ion asym— metry and in the specific case of silver iodide. A series of density functional theory calculations is also presented, which probe the boundary between the six coordinated and four coordinated crystalline structures and demonstrate anomalies between the ground state crystals predicted.