Effect of the Polymerization Degree of Cardanol Polyoxyethylene Ether on the Oil–Water Interface: Experimental and Molecular Dynamics Simulation Study

The oil-water interface (OWIF) plays a significant role in the flotation process. By modification of the chemical properties of the OWIF, the interaction between bubbles and coal slime can be optimized to enhance the yield of clean coal. The addition of an appropriate amount of surfactant can modify the interfacial properties, thereby increasing the solubility of oil in water and enhancing its dispersity in the pulp, which is beneficial for reducing the dosage of hydrocarbon-oil collectors during flotation. The surfactant reduces the repulsion between oil and water phases and lowers the interfacial tension by acting as an interfacial bridge at the OWIF. This study focuses on cardanol polyoxyethylene ether (CPE), exploring its influence on interfacial properties through experiments and molecular dynamics simulations. Experimental studies on interfacial tension revealed that the effectiveness of CPE in reducing oil-water interfacial tension is ranked as CPE-15, CPE-12, and CPE-9, respectively. The stability time of the emulsion showed that the emulsifying capacity of CPE-15 was the greatest. The adsorption equilibrium configuration indicated that CPE adsorbs directionally at the OWIF, resulting in partial miscibility between the oil and water phases. The interfacial formation energy showed that CPE-15 had the highest absolute value. The coordination numbers with water molecules for CPE-9, CPE-12, and CPE-15 were 1.39, 1.45, and 1.70, respectively. In conclusion, as the number of ethoxy groups in CPE increases, the stability of the monolayer improves and the capacity to reduce the OWIF energy increases.