External field-enhanced membrane demulsification: Dynamic interfacial behaviors and separation mechanisms

Membrane separation technology offers distinct advantages in the treatment of emulsions, enabling efficient oil-water separation through precise pore-size sieving and tunable interfacial interactions. However, membrane fouling leads to significant flux decline. In the membrane separation process, interfacial properties such as charge distribution, chemical characteristics, and micro/nanoscale topology between the material and the aqueous phase critically govern the system's separation performance and overall efficiency, and can be actively modulated by external fields. Recently, strategies incorporating external fields, including light, electricity, mechanical force, magnetism, gas, and heat, have demonstrated significant potential for enhancing membrane separation. These fields can actively destabilize emulsions, lower the separation energy barrier, and cooperate with antifouling and regeneration mechanisms to synergistically improve flux recovery and long-term operational stability. This review first outlines the fundamental principles of oil-water separation and the current state of membrane performance, followed by an analysis of key bottlenecks in membrane-based emulsion separation. It then elaborates on the mechanisms through which various external fields enhance separation, supported by examples illustrating how different fields regulate interfacial behavior, mass transfer processes, and membrane surface properties. Finally, future development pathways and application prospects for external-field-assisted membrane systems toward efficient and sustainable separation are discussed.