Molecular Dynamics Simulation of Surfactant Microaggregates in the Apolar Medium of n-Octane

Molecular dynamics simulation of reverse micelles of a cationic surfactant and water clusters in n-octane is performed. The main structural and thermodynamic characteristics of the systems are obtained. On average, the micelles have a spherical shape. The partial ion distribution densities virtually coincide, indicating the formation of stable ion pairs. The local profiles of the component distribution densities make it possible to establish that both water and oil slightly penetrate into the region where the hydrophobic portion of the surfactant is located. Separate cation-anion complexes dissolve in the aqueous cavity of a micelle. The hydration shells of the ions overlap; at the same time, the first hydration shell contains up to three water molecules. The energy contributions of each of the components to their force interaction are characterized in detail. The principal contribution to the internal energy for micelles is due to electrostatic interaction between the surfactant molecules. The local normal pressure is calculated, and its value is used to estimate the effective surface tension for the systems in question.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 500–507.Original Russian Text Copyright © 2005 by Mudzhikova, Brodskaya.