Study on the Behavior of Saturated Cardanol-Based Surfactants at the Crude Oil/Water Interface through Molecular Dynamics Simulations

Cardanol is a green biosurfactant with broad application prospects, which is expected to be used to enhance oil recovery (EOR). This paper designed two types of surfactants (extended and nonextended), including six kinds of nonionic and anion-nonionic surfactants. The position changes of PO and EO chains and the effects of different hydrophilic groups on the interface properties were studied with molecular dynamics simulations by constructing a model of crude oil (containing four components) and water molecules. The results of interfacial tension and solvent-accessible surface area showed that the interfacial properties of sulfate were better than those of sulfonates and nonionic surfactants. Meanwhile, the interface properties of nonextended surfactants were better than those of extended surfactants. The gyration radius (R_g) and tilt angle data demonstrated that when EO chains were located between hydrophobic groups and PO chains (nonextended surfactants), the adsorption capacity of surfactants at crude oil and water interfaces could be effectively improved. The radial distribution function of the hydrophilic group and hydrophobic group of surfactants with water molecules and four components of the crude oil molecule, respectively, explained that surfactants (8EO8POSO₄) had better emulsification performance when the intermolecular interactions between crude oil and water two phases were relatively balanced. This study provides a theoretical reference for the design of oil-displacement surfactants and the mechanism analysis of emulsification properties.