In Situ and Ex Situ pH-Responsive Coatings with Switchable Wettability for Controllable Oil/Water Separation.

The development of stimuli-responsive materials with the ability of controllable oil/water separation is crucial for practical applications. Here, a novel pH responsive nonfluorine-containing copolymer was designed. The copolymer together with silica can be dip-coated on different materials including cotton fabric, filter paper, and polyurethane foam. The coated materials exhibit switchable superhydrophilicity and superhydrophobicity and can be applied in continuous separation of oil/water/oil three phase mixtures, different surfactant stabilized emulsion (oil-in-water, water-in-oil, and oil-in-acidic water) as well as oil uptake and release via in situ and ex situ pH change. We expect that the coatings highlight the practical applications because of the cost-effective preparation process and fluorine-free strategy.