Regulating water adhesion on superhydrophobic TiO₂ nanotube arrays

Bioinspired surfaces with special wettability have attracted a significant attention in recent years because of their potential applications for no loss liquid transfer, anti-icing, and self-cleaning. Herein, the realization of two extreme superhydrophobic states on 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane-modified TiO₂ nanotube arrays (NTAs) is described by changing the structural characteristics of nanotubes while keeping the surface chemical composition constant. The water adhesive force is regulated in a wide range from ≈4.4 to ≈89.6 μN by the nanotubular diameter, length, density, and surface roughness. The cooperation effect between the negative pressures induced by the volume change of sealed air-pockets and the van der Waals' attraction at solid-liquid interface contributes to the water adhesion. The superhydrophobic TiO ₂ NTAs with a high adhesive force is used as a "mechanical hand" to transfer water microdroplets without any loss, and the one with extremely low adhesive force is utilized as a self-cleaning and anti-icing surface.