Nature always uses its special wisdom to construct elegant and suitable projects. On account of this, organisms in the flora and fauna have been with fine hierarchical structures (HS) to adapt to the harsh environment over many years of evolution. Water is one of the most important sources and the biggest challenges for human beings.  Clean water resources are vital to our human society. The leakage and discharge of oily wastewater not only destroys the economy, but also disrupts our living and living environment. Efficient oil-water separation technology has become a pressing need. Surfaces with switchable superwetting behavior have attracted much attention due to their importance for basic research and practical applications. Therefore, the basic principles of wettability in oil-water separation process, the basic theory of switchable wettability and the mechanism of oil-water separation were introduced in this review, respectively. Next, the research progress and the problems and challenges faced by three types of conventional special wettability materials (superhydrophobic/superoleophilic materials, superhydrophilic/superoleophobic materials, and superhydrophilic/underwater superoleophobic materials) were discussed. Most importantly, recent advances in switchable wettability smart materials (stimulus-responsive smart materials, pre-wetting-induced materials and Janus materials) as organic combinations of conventional special wettability materials were presented in detail, such as the main response factors, representative works reported in detail, design ideas and fabrication strategies. Finally, a comprehensive summary of switchable superwetting smart materials was presented.

Biomimetic, Tribology, Wettability