Water repellency of hierarchical superhydrophobic Ti6Al4V surfaces improved by secondary nanostructures

Micro-nanostructures were successfully synthesized on a Ti6Al4V alloy and then coated with a monolayer of hydrophobic groups to obtain the superhydrophobic surfaces. The effect of secondary nanostructures (nanotube, nanowire and nanomesh) on superhydrophobic performance was investigated by the characterization of contact process of a falling water droplet onto the superhydrophobic surface via a high-speed camera. Meanwhile, the apparent contact angle and sliding angle of the water droplet were measured by a contact angle analyzer. The results indicated that the superhydrophobic surface with micro-nanostructures (microscale pits and nanowire) exhibited robust superhydrophobic properties (apparent contact angle 161° and sliding angle approximately 3°) due to the large amount of flowing air being trapped underneath the droplet. Moreover, it was observed that once the impacting droplet contacted with the superhydrophobic surface, it spread uniformly before retracting and finally lifted off the surface within 13 ms.