Double‐Defense Design of Super‐Anti‐Fouling Membranes for Oil/Water Emulsion Separation

Abstract Oil fouling threatens the water flux stability of membranes for oil/water separation. Simple hydrophilic modification fights for an opportunity to prevent oil contamination but fails to eliminate severe water flux decline. In essence, a “single‐defense” mechanism is insufficient to build a potent barrier against accumulated cake layer under a filtration environment. This work reports a “double‐defense” design by integrating hydrophilic polymer brushes and hydrogel layer on oil/water separation membranes for desired anti‐oil‐fouling property, where a poly(vinylidene fluoride) porous membrane is first covered by a layer of poly(hydroxyethyl methylacrylate) hydrogel and then controllably grafted with poly(sulfobetaine) brushes. The spatially hierarchical structure establishes a highly covered “double‐defense” barrier for the membrane surface to efficiently repel oil adhesion and the formation of an accumulated cake layer. When separating various surfactant‐stabilized oil‐in‐water emulsions, the permeating flux displays a nearly zero decline throughout the whole filtration period. Most importantly, the permeating flux of the membrane is almost the same when filtrating pure water and filtrating oil‐in‐water emulsions, which is difficult to be achieved by the general membranes, indicating that the membrane has excellent anti‐oil‐fouling property superior to the currently reported membranes.