Robust Superhydrophobic Conical Pillars from Syringe Needle Shape to Straight Conical Pillar Shape for Droplet Pancake Bouncing.

Superhydrophobic conical pillars have great industrial application potential in, for example, anti-icing of aircraft wings and protecting high voltage transmission lines from freezing rain because of their droplet pancake bouncing phenomenon, which is recognized to further reduce the liquid-solid contact time. However, there are still no methods that can fabricate robust superhydrophobic conical pillars in large scale. Here, a mold replication technology was proposed to realize the large-scale fabrication of superhydrophobic conical pillars with high mechanical strength. An Al mold with intensive conical holes decorated with micro/nanometer-scale structures was fabricated by nanosecond laser drilling and HCl etching. The conical shape originated from a near Gaussian spatial distribution of the energy and temperature in the radial direction in the laser drilling processes. Robust superhydrophobic conical pillars from syringe needle shape to straight conical pillar shape were easily fabricated through replication from the Al mold without any extra spray of superhydrophobic nanoparticles. It was also found that although all superhydrophobic conical pillars with different shapes could generate the droplet pancake bouncing, the shape had a great influence on the critical bottom space and the critical Weber number (We) to generate pancake bouncing. The pancake bouncing with the shortest contact time of a 68.5% reduction appeared on superhydrophobic straight conical pillars with the shape angle of 180°. Overcoming the difficulties in the large-scale fabrication and robustness of superhydrophobic conical pillars will promote practical applications of the droplet pancake bouncing phenomenon.