Gradient meshes with Janus wettabilities are fabricated to stably separate and collect spilled oils from a range of flowing oily wastewater. Here, we demonstrate an overflow with separation methodology, which combines selective oil overflow and membrane separation, to separate low content oils from dynamic flowing oil-water mixtures by a curved gradient mesh that covered on a solid edge. The microscaled air-oil-water-solid four-phase wetting state during the oil-water separation process is visualized and demonstrated. The fundamental understanding of this overflow with separation system and the superior gradient mesh materials would enable us to construct a wide variety of separation devices out of traditional designs and advance related applications, such as wastewater treatment and fuel purification.
Keywords: Janus; hydrodynamic; oil−water separation; overflow; superoleophobicity.