Surfaces with controllable super-wettability and applications for smart oil-water separation

Surfaces with controllable super-wettability are of interest. Recently, although various methods have been carried out to achieve the super-wettability transition, long processing time, high temperature or special/ complex equipment combined with special/complex micro/nano structure based materials can hardly be avoided, thus limited the applications. In this study, a facile wetting-displacing method to reversibly transit super-hydrophobicity to super-hydrophilicity by a rapid switch between the Cassie and Wenzel state without any modification of the surface materials is proposed based on super-hydrophobic fabrics. The initially super-hydrophobic fabrics with a water contact angle of 168 degrees turned into super-hydrophilicity/underwater superoleophobicity rapidly (within 10 s) with nearly unlimited reversibility (no obvious change after 100 cycles). Interestingly, after the wetting-displacing process, the initially super-hydrophobic fabrics can show good super-hydrophilicity without any hydrophilic groups on it. Free light oil-water mixture and free heavy oil-water mixture can be gravitationally separated by the same prepared super-hydrophobic fabrics with extremely high flux, before and after the wetting-displacing process, respectively. Moreover, the super-wettability transition can be achieved by the wetting-displacing process on different super-hydrophobic surfaces, such as coated glass, steel mesh and cotton. The separation of water in oil and oil in water emulsions based on the superhydrophobic cotton are also carried out as the examples of application.