Robust Hydrogel Coating with Oil-Repellent Property in Air, Water, and Oil Surroundings

Development of a robust self-cleaning oil-repellent surface in a cost-efficient and green manner is highly desirable, yet still difficult to realize. Herein, we develop a poly­(vinyl alcohol) (denoted as PVA) composite hydrogel on which the oily contaminations can be removed efficiently by water merely. Owing to its high affinity to water and resistance to oils, the water-wetted hydrogel establishes a slippery oil-repellent state in air, displays underwater superoleophobicity with ultralow adhesion to all probe oils, and blocks oil from permeating when immersed into an oil surrounding. Oily contaminations on the PVA hydrogel surface are removed just by titling or water immersion, with no oil residue left behind. This enhanced oil repellency was retained after hand-bending, water-jetting, and even 1000 cycles of sand abrasion, demonstrating mechanical robustness. Application of the PVA hydrogel-coated copper mesh is demonstrated to separate oil/water and oil/oil mixtures, with separation efficiency being greater than 98%.