Molecular dynamics simulation study on π-π stacking of Gemini surfactants in oil/water systems

Abstract

• Water/n-octane interfacial properties with surfactants are studied by using MD simulation. • Three kinds of Gemini surfactants with or without pyrenyl groups are considered. • The π-π interaction and steric hindrance mutually determine the droplet coalescence. • The presence of pyrenyl group in surfactants helps to form microemulsion. Whereas the π-π stacking interactions at oil/water interfaces can affect interfacial structures hence the interfacial properties, the underlying microscopic mechanism remains largely unknown. We reported an all-atom molecular dynamics (MD) simulation study to demonstrate how the Gemini surfactants with pyrenyl groups affect the interfacial properties, structural conformations, and the motion of molecules in the water/ n -octane/surfactant ternary systems. It is found that the pyrenyl groups tend to be vertical to the interface owing to the π-π stacking interaction. Besides, a synergistic effect between the π-π interaction and steric hindrance is found, which jointly affects the coalescence of liquid droplets. Therefore, the existence of aromatic groups and a moderate number of surfactants helps to form microemulsion. This work provides a molecular understanding of Gemini surfactants with aromatic groups in microemulsion preparation and applications.