Molecular dynamics simulation of gaseous-liquid phase transitions of soluble and insoluble surfactants at a fluid interface

The formation of gaseous and liquid expanded phases of surfactants on a liquid/vapor interface was studied using molecular dynamics simulations. Models of both soluble and insoluble surfactants as freely jointed chains in a monatomic solvent with appropriate Lennard-Jones interactions were presented. Results showed, for both soluble and insoluble cases, that the surface tension as a function of coverage showed a plateau close to the clean interface value until a critical surface concentration. Beyond this critical surface concentration, the suraface tension lowered steeply. An adsorption isotherm and a complete Gibbs construction for the surface excess was reported for the soluble case.