Molecular simulation and experimental studies on the interfacial properties of a mixed surfactant SDS/C4mimBr

Mixed surfactants have potential applications in various fields. The understanding and prediction of their macro- and microscopic properties are of great importance in the designing of these materials. We used molecular dynamics (MD) and experiments to study the interfacial tension and the microscopic structures of the sodium dodecyl sulfate (SDS)/C₄mimBr mixed surfactant at the water/hexane interface. The interfacial tension, density profile, radial distribution function (RDF), orientation distribution of the tails and order parameters have been examined. It seems that the addition of C₄mimBr decreased the interfacial tension; a higher C₄mimBr concentration resulted in a thicker interface, a smaller droplet, and more disordered SDS tails. The competition between free volume and electrostatic shielding seems to be the primary mechanism behind these phenomena.