Effects of chain length of surfactants on the interfacial tension: molecular dynamics simulations and experiments

In this letter a simple oil/water/surfactant model is presented.This model allows us to study systematically, using the molecular dynamics technique, the relation between the structure of surfactants and various thermodynamic properties.Specifically, the effect of increasing the hydrophobic tail length on the interfacial tension has been studied.Experimental results on various model surfactants are also presented and compared with molecular dynamics calculations.The experimental data as well as the simulations indicate that increasing the tail length makes the surfactants more effective in decreasing the interfacial tension at low concentration.' Koninklijke/Shell-Laboratorium.Amsterdam.* Koninklijke/Shell Exploratie en Prcduktie Laboratorium. Model and Computational DetailsIn our model, which is based on an early model of Telo da Gama and Gubbins,l1*l2 we assume the existence of two types of particles: "oillike" and uwaterlike".These two types of particles are used to model three types of molecules, namely, oil molecules, water molecules, and surfactant molecules.An oil molecule consists of a single oillike particle, and a water molecule consists of a single waterlike particle.A surfactant molecule is made up of one waterlike particle and one or more oillike particles; these are joined