Dissipative particle dynamics simulation and experimental analysis of the effect of anionic/cationic mixed surfactants on the stability of emulsions

Hydrogen bond shaping plays a very important role in the stability of emulsions and cannot be ignored when developing highly stable emulsions. Mixed systems of anionic and cationic surfactants can greatly reduce interfacial tension. In this study, we introduced different amounts of hydroxyl groups in Gemini surfactant spacers through dissipative particle dynamics simulations and evaluated the effect on the oil–water interface. In addition, Gemini cationic surfactants were mixed with anionic surfactants and the emulsification effect of the mixed system was evaluated, as well as the effect on the emulsion-formation and emulsion-breaking processes. We found that the anionic and cationic surfactants have a strong synergistic effect that significantly reduces interfacial tension and effectively transforms the oil–water interface into an emulsion state, but the effect of the interaction between the anion and the cation is affected by the spacer group. This work provides theoretical guidance and ideas for designing efficient emulsifiers and improving emulsion stability in the future.