Molecular Dynamics Simulation of the Effects of Anionic–Nonionic Surfactants on Interfacial Properties of the Oil–Water Interface

Surfactant oil drive is a crucially enhanced oil recovery method that improves oil recovery rates. The aggregation behavior of surfactant molecules at the oil-water interface significantly influences oil repulsion. In this study, a molecular dynamics simulation is used to investigate this repellent behavior of single and binary surfactants of alkanolamides (6501) and fatty alcohol polyoxyethylene ether sodium sulfate (AES). The oil-water interface is characterized by density distribution, interfacial thickness, radial distribution function, interfacial tension, and interfacial generation energy. The results reveal that the dodecanolamide surfactant (126501) and AES effectively reduce interfacial tension. In the binary 126501/AES system, the interfacial film thickness increases to 18.08 Å, and the diffusion coefficient increases to 0.186 Ų/ps. The radial distribution function shows that oil molecules are located 4.2 Å from the anionic head of AES, which weakens the intermolecular forces within the oil layer. In the 126501/AES system, the interfacial energy of -96.12 kJ/mol indicates a stable interface. Moreover, both the 126501/AES and tetradecanolamide surfactant (146501)/AES systems exhibit excellent resistance to metal ions. The molecular-level mechanism provides useful guidance for designing the surfactant systems for enhanced oil recovery.