Molecular Dynamics Simulation of an Aqueous Sodium Octanoate Micelle Using Polarizable Surfactant Molecules

Abstract

The inclusion of dynamic induced polarization in simulations of aqueous ionic systems can have important consequences. As a step toward performing analogous studies on aqueous surfactant systems, we have completed initial studies of the system sodium octanoate/water in which only the surfactant anions are polarizable, polarization effects in the solvent being treated via a mean-field model. Two simulations were performed: one of an aggregate of 15 sodium octanoate monomers and the other of a single octanoate ion in solution. The present simulations are compared to earlier results for nonpolarizable models. The behavior of the monomers is not appreciably changed by the addition of polarization. However, general structural characteristics of the micellar aggregate such as volume, shape, and hydration are different. Significantly, with the current parameterization, no contact ion pairs of the type found in the nonpolarizable model were present when the anion headgroups were allowed to polarize, a result that accords better with the interpretation of experiment. © 1993, American Chemical Society. All rights reserved.