Effect of surfactant hydrophobic chain equivalence on the oil-water interface and emulsion stability: A dissipative particle dynamics and experimental study

Gemini surfactants have shown great potential and have become a popular topic of research and are considered a novel alternative to conventional surfactants because of their extraordinary physical and chemical properties. In this study, a series of surfactants with similar structures but different numbers of hydrophobic chains were constructed, and their effects on an oil-water interface were systematically investigated using dissipative particle dynamics (DPD) simulations. The effects of these surfactants on the behavior of the oil-water interface were further analyzed when the surfactant concentrations in the system were the same and when the numbers of hydrophobic chains in the system were the same. The effects of surfactant structure on the stability of the emulsion were further investigated on the basis of an analysis of the effects of the surfactants on the behavior of the oil-water interface. The results showed that Gemini and tri-cationic surfactants transitioned the oil-water interface from a lamellar structure to an emulsion form at lower concentrations compared to conventional single-chain surfactants, (e.g., 39.0% for SC-21, 33.0% for DC-21, and 15.0% for TC-21), but this superiority may be due to the absolute advantage of concentration rather than structural properties. The use of Gemini and tri-cationic surfactants have a positive effect on emulsion stabilization when the surfactant concentrations are the same. However, the use of Gemini and tri-cationic surfactants, which have more complex synthetic routes, is not necessary. The present work provides a theoretical basis for the rational selection of surfactants for emulsion applications.