Unidirectional Wetting of Liquids on "Janus" Nanostructure Arrays under Various Media

We report the unidirectional wetting behavior of liquids (water and oil) on Janus silicon cylinder arrays (Si-CAs) under various media (air, water, and oil). The Janus cylinders were prepared by chemical modification of nanocylinders with different molecules on two sides. Through adjusting surface energies of the modified molecules, the as-prepared surfaces could control the wetting behavior of different types of liquids under various media. We discuss the regularity systematically and propose a strategy for preparing anisotropic wetting surfaces under arbitrary media. That is, to find two surface modification molecules with different surface energies, one of the molecules is easy to be wetted by the liquid under the corresponding media, while the other one is difficult. Additionally, by introducing thermal-responsive polymer brushes onto one part of Janus Si-CAs, the surfaces show thermal-responsive anisotropic wetting property under various media. We believe that due to the excellent unidirectional wettability under various media, the Janus surfaces could be applied in water/oil transportation, oil-repellent and self-cleaning coatings, water/oil separation, microfluidics, and so on.