Wettability transition of metallic surfaces from laser-generated superhydrophilicity to water-induced superhydrophobicity via a facile and eco-friendly strategy

[Display omitted] •Eco-friendly preparation strategy was proposed for superhydrophobic metallic surfaces;•This strategy combines nanosecond laser and hygrothermal treatments (95%RH @ 80 °C);•Superhydrophobic surfaces were effectively fabricated for several engineering metals;•Laser-induced superhydrophilicity and transformed superhydrophobicity were explained;•Nanostructure transformation dominates the wettability transition of metallic surface. Superhydrophobic metallic surfaces exhibit superior self-cleaning and anti-corrosion properties, but facile and pollution-free preparation of such surfaces remains a challenge. Herein, we propose an eco-friendly strategy by using ns-laser treatment followed by simple hygrothermal treatment (95%RH @ 80 °C), and this strategy is applicable to facilely preparing superhydrophobicity for various metals. Immediately after ns-laser treatment, ultra-porous nano-fibers composed of amorphous Al-Al2O3 mixture were produced, and rendered aluminum surface superhydrophilic via local capillary forces. Counterintuitively, subsequent hydrothermal treatment accelerated wettability transition to superhydrophobicity, and comparative analysis and theoretical modelling strongly suggest that the mechanism of accelerated transition is deeply dominated by nanostructure transformation. A roughened but compact surface layer of spherical AlOOH nanocrystals was reconstructed to enable water droplet in Wenzel wetting state. Our results shed new insights into the origin of wettability evolution commonly reported at various processing/service stages, and demonstrate a novel method to construct superhydrophobic metallic surfaces.