Nanostructures in superhydrophobic Ti6Al4V hierarchical surfaces control wetting state transitions

This paper mainly reports the wetting state of liquid droplets on a Ti6Al4V micro-nanoscale hierarchical structured hydrophobic surface. In this work, the detailed action mechanism of the secondary nanostructure in the hierarchical structure on the wetting-state transition (from the Wenzel state to the Cassie state) was revealed and discussed. The variation of micro-morphology of the sample surface was observed using a field emission scanning electron microscope (FE-SEM). Furthermore, the apparent contact angle and sliding angle of the droplets on the surfaces were measured via a contact angle measurement instrument. The theoretical and experimental results indicated that the one-dimensional nanowire structure, which was planted on the microstructure surface by the hydrothermal method, effectively changed the wetting state of liquid droplets on the surface from the Wenzel state to the Cassie state owing to its good size synergies with microscale structure. This process not only increased the apparent contact angle of liquid droplets on the solid surface (to 161°), but also decreased the sliding angle significantly (to 3°) and contact angle hysteresis (to ∼2°), demonstrating the robust non-wetting property.