Computer simulation of the surface layer of an ionic micelle with explicit allowance for the contribution of water

Ionic micelles have been simulated in an aqueous solution of single-charged counterions using the molecular dynamics method. It has been demonstrated that the contribution of water molecules needs to be explicitly taken into account when computing the electrical field strength of a micelle. This contribution results in a complex local dependence of the electric charge and gives rise to a charge reversal region in the immediate vicinity of the micelle crown, thereby causing a nonmonotonic behavior of the electric potential. The computations have been performed for both cationic and anionic micelles. A model micelle consists of a rigid hydrocarbon core (impenetreable to water molecules and counterions) and cationic fragments of a surfactant. Data obtained for three molecular models of water (SPC, TIP5P, and two-centered S2 models) have been compared with the results of the continual description of the solvent. For all water models, its local contribution to the electric field around micelles is significant even at large distances from the particle surface.