Amphiphiles at oil-water interfaces: simulation study of their tension-reducing properties

Molecular dynamics simulations of amphiphiles at a mock oilwater interface have been carried out using a simple well-known model which represents amphiphiles as conglomerates of water and oil particles connected together with harmonic potentials. We studied the tension reduction properties of amphiphiles composed of one water and one or more oil particles connected in a series; we varied the length of the series and placement of the water particle within it. In comparing amphiphiles of fixed length, we find that those with a terminal water particle are most effective at reducing the tension; these molecules mimic single-chained (the others, double-chained) amphiphiles. We find that at low concentrations, all amphiphiles examined behaved as insoluble monolayers. In this regime, we attempted to apply two-dimensional equations of state to predict their tension-reduction properties. At higher concentrations. the amphiphiles exhibit an increased solubility in the bulk oil phase, but are believed not to be in their most stable state.