Structure and electrostatics of the surfactant-water interface

Abstract

Molecular dynamics simulations using nonpolarizable and polarizable models have been conducted on columnar micelles of sodium octanoate in the liquid crystalline (E) mesophase. In the simulation using a nonpolarizable model, most of the Na⁺ ions are in direct contact with the carboxylate headgroups while for the simulations using our polarizable models the Na⁺ ions are mostly solvent separated, in better agreement with experiment. For all models the hydrocarbon/ water interface is only about 4 Å wide and the electric double layer is clearly distinguishable. In a detailed demonstration of the collective nature of dielectric screening, significant cancellation occurs between the contributions to the electrostatic potential from the different components in the system resulting in a relatively small net electrostatic potential.