Simulating adsorbed layers of surfactant mixtures at an oil-water interface

The molecular dynamics technique is used to investigate the structure of ad sorbed layers of surfactant mixtures at an oil-water interface. Simulations have been performed on a simple water-oil-surfactant model to mimic the fa vourable interaction of head groups with water and hydrocarbon tails with o il. The oil-water interfacial tension (IFT) is calculated for a system cons isting of 50-50 mixtures of surfactants and cosurfactants. The IFT is a min imum when the chain length of the oil molecules is approximately equal to t he difference between the chain lengths of the surfactant and the cosurfact ant. This minimum is due to the competition between the penetration of oil molecules in the interfacial layer, and the flattening of the longer-tailed surfactants at the interface.