Single-side etching for on-demand and versatile liquid diodes with opposite wettability in multiple systems

To achieve smart control of liquid penetration, liquid diodes have been widely studied in the recent years. However, most liquid diodes can only achieve opposite wettability in one or two systems, resulting in the loss of unidirectional liquid transportation property after they are wetted by immiscible liquids. This shortcoming will highly restrain the application areas of liquid diodes. Herein, a two-step single-side etching strategy have been adopted to develop opposite wettability on reverse sides of single-layered meshes. Opposite wettability forms not only in air but also under various liquids such as water and oil to realize unidirectional liquid penetration in these systems. More importantly, varied thickness of lyophobic layer was found to be crucial in liquid transportation in different systems, which was further demonstrated by the analysis of Laplace pressure on various meshes. Besides, the obtained liquid diodes were also competent in fog collection, liquid capture and oil/water separation, exhibiting great versatility. Thus, our findings not only propose on-demand and versatile liquid diodes but can also enlighten further study in smart valves in different systems.