Behavior of the 2,4-distyryl saturated cardanol PPO-PEO-SO3- surfactant at the oil/water interface through molecular dynamics simulations

Cardanol, a natural biophenol, is expected to be used in tertiary oil recovery due to its environmental protection and abundant synthetic products. In this study, five anionic-nonionic surfactants prepared using 2,4-distyryl and different numbers of polyoxypropylene (PPO) and polyoxyethylene (PEO) chains were designed using saturated cardanol as the base structure. Molecular dynamics simulations were used to study the interfacial behavior. Our results showed that anionic-nonionic surfactants prepared with a 2,4-distyryl and PPO-PEO-SO3- structure had good interfacial properties at the oil/water interface. Furthermore, the PPO/PEO ratio can significantly affect the interfacial behavior of the surfactants. When the PPO/PEO ratio increased, the interfacial tension decreased, and the interfacial thickness gradually increased. The hydrophobicity increased with the PPO/PEO ratio because it affected the hydrogen bond distribution of the surfactant. The morphological changes in the hydrophilic and hydrophobic chains during surfactant emulsification indicate that the higher PPO/PEO ratio made the surfactants more compressible. At the same time, the mechanism for the emulsification of PPO-PEO-SO3- at the oil-water interface can be explained from the perspective of molecular morphology by analyzing the data obtained for the radius of gyration and tilt angle of the propylene oxide (PO) and ethylene oxide (EO) chains. The innovative structure of this study provides a theoretical basis and reference data for designing oil-displacement surfactants.