Synthesis, Aggregation Behavior, Interfacial Properties and Oil Displacement Performance of a Maleic Anhydride-Derived Nonionic Gemini Surfactant.

To enhance the recovery efficiency of heavy oil, a nonionic Gemini surfactant (MOP-10) was successfully synthesized through a one-step reaction between maleic anhydride and octylphenol polyoxyethylene ether (OP-10). The surfactants before and after modification were systematically characterized and analyzed by means of surface tension measurement, interfacial tension test, contact angle measurement, diffusion-ordered proton nuclear magnetic resonance (1H NMR DOSY), and multiple light scattering (Turbiscan). The results demonstrated that MOP-10 exhibited a significantly lower critical micelle concentration (0.072 g/L) and superior interfacial activity, achieving an low interfacial tension of 8.04 × 10-2 mN/m, compared with OP-10. Meanwhile, MOP-10 shows a stronger wettability regulation capability at the solid-liquid interface, reducing the contact angle of the hydrophobic quartz surface to 14.81°. Furthermore, DOSY technology was employed to deeply investigate the molecular behavior of the surfactant prior to reaching the CMC, and the existence of preaggregates was confirmed. Microscopic oil displacement experiments demonstrate that MOP-10 can significantly enhance the heavy oil recovery rate to 73.69%, which is 14.23 percentage points higher than that of OP-10. The excellent performance of MOP-10 is mainly attributed to its Gemini structure, which endows the surfactant with stronger interfacial adsorption capacity, lower interfacial tension, and more efficient wettability reversal ability. This study reveals that MOP-10 has considerable application potential in heavy oil exploitation and provides a theoretical basis for the design and development of high-efficiency oil displacement agents.