A hybrid laser ablation and chemical etching process for manufacturing nature-inspired anisotropic superhydrophobic structures

The surface with anisotropic superhydrophobicity has great potential applications for drag reduction, drug delivery and microfluidic devices. Observation from natural biological surfaces proved that directional microstructures are indispensable to realize anisotropic superhydrophobicity. However, current lithography-based manufacturing approaches have limited capabilities to scale-up for real world industrial applications. This paper proposes a hybrid laser ablation and chemical etching process for manufacturing ratchet-like microstructures on 316L stainless steel for the first time. It harvests the advantages of both processes. The laser ablation will form specified recast layer and covered by oxide layer on the specimen, and these two layers can be easily removed in the chemical etching process hence to obtain the periodic ratchet-like microstructures. According to the experimental results, the direction of microstructures is same as with the laser beam feed direction. The width and depth of microstructures also can be well-controlled by laser power and pitch. The specimens with pith of 25 μm have contact angle larger than 150°. And the droplet easily rolls off along the laser beam feed direction but is pinned tightly in the opposite direction.