Fast and environmentally friendly fabrication of superhydrophilic-superhydrophobic patterned aluminum surfaces

The superwettability patterned aluminum surface has been shown considerable attention for emerging applications. However, the available techniques are time-consuming and require hazardous chemicals, especially toxic fluoride. In this work, the superhydrophilic-superhydrophobic patterned surface of aluminum was successfully fabricated by using nanosecond laser (λ=1065 nm) and fluorine-free N-Octyltriethoxysilane (OcTES). The time required to make superhydrophilic surfaces is only a few minutes and switch it into superhydrophobic is only 30 min. The patterned surface had both superhydrophilicity (apparent water contact angle (WCA) closed to 0°) and superhydrophobicity (WCA of 156° and roll-off angle of 2.9°), which achieved the droplet arrays and the fluid channels with special patterns. The results indicated that the synergy between the rough surface and the dominant presence of polar Al-OH groups induced by laser ablation was critical for superhydrophilicity. The OcTES molecules containing non-polar C-C(H) groups were assembled on the rough surface by the formation of Si-O-Al bonds, which transformed the laser-treated surface from superhydrophilic into superhydrophobic. This work is of significance for the eco-friendly fabrication of superwettability patterned aluminum surface and shows potential applications in fluidic systems and liquid controls.