Structure of the surfactant-water interface

Abstract

The microscopic characteristics of the surfactant-water interface are studied using computer simulation. The water region near the flat surface formed by the -COOH polar head groups of surfactant molecules is considered. We calculate the density profile of water molecules and probability distributions for their orientations, distribution functions for pair interaction energies, and atom-atom and dipole-dipole pair correlation functions for the carboxylate head groups. The average number of nearest neighbours in the head group subsystem is four, two of which form linear hydrogen bonds with the central head group, so that their dipole moments are parallel to that of the central head group, while the other two, situated on each side of the central head group, are directed antiparallel to its dipole moment. The water molecules of the first hydration monolayer are squeezed into the spaces between head groups, and are built themselves into the surfactant monolayer structure. At a surface density for surfactant ...