Molecular Dynamics Study of Nanoparticles and Non-Ionic Surfactant at an Oil/Water Interface

R. J. K. Udayana Ranatunga, Chuong T. Nguyen, Blake A. Wilson, Wataru Shinoda and Steven O. Nielsen

Soft Matter, 7, 6942-6952 (2011).

Nanoparticles (NPs) and surfactants can spontaneously concentrate at the interface between two immiscible liquids, such as oil and water. Systems of high oil/water interfacial area, such as emulsions, are the basis of many industries and consumer products. Although NPs and surfactants are currently incorporated into many of these applications, their mutual interfacial behavior is not completely understood. Here we present molecular dynamics simulations of NPs and non-ionic surfactant in the vicinity of an oil/water interface. It was found that in low concentration the surfactants and NPs show cooperative behavior in lowering the oil/water interfacial tension, while at higher surfactant concentration this synergy is attenuated. It was also found that binding of surfactants to the NP surface decreases the surfactant efficiency in lowering the interfacial tension, while concurrently creating a barrier to NP aggregation.