Electro-triggered interfacial reconfiguration for automatic membrane fouling cleaning: Fighting surfactants with...

The application of membrane separation technology in oil‒water emulsions is restricted owing to the membrane fouling caused by surfactants and oil droplets. These stubborn contaminants cannot be completely removed through passive dragging by conventional cleaning methods. Here, we developed a surfactant-doped polypyrrole electro-triggered wettability switching membrane (SP-EWM) via electropolymerization, enabling automatic cleaning of membrane fouling. The SP-EWM exhibited large wettability switching (WCA 136.5°↔6.8°), a rapid response (300 s), and stable cycling performance. It effectively demulsified various actual waste emulsions from the oilfield, coking, and machining industries. More importantly, automatic cleaning under positive‒negative charging was achieved, resulting in a high flux recovery rate (FRR∼100 %) and zero fouling accumulation over ten cycles, surpassing most previous studies. Essentially, under positive potential, the surfactants doped within the membrane rotated their hydrophilic groups (0.6 nm) and partially migrated, enabling wettability switching. This led to surfactants occupying the membrane‒water interface, reconfiguring the membrane‒water‒oil interface and promoting oil droplet coalescence (from 2.60 μm to 3.45 μm). Inverting the negative potential achieved the removal of surfactant and contaminant molecules. This study proposes an innovative automatic cleaning method, distilled as "fighting surfactants with surfactants". It fundamentally achieves membrane fouling removal by regulating the orientation of surfactant molecules within the membrane and the behavior of surfactant molecules in the cleaning solution at the membrane-liquid interface through an electric field.