Wettability transition of structured steel surface by femtosecond laser after annealing

Abstract

Textured steel surfaces with self-organized structures were fabricated by femtosecond laser ablation. All of these surfaces exhibited high hydrophilicity right after laser ablation, but transferred to hydrophobicity or superhydrophobicity after a low temperature annealing. The chemical features of the surfaces were investigated by X-ray photoelectron spectroscopy. The results show that annealing improves polar substance detachment from laser-ablated steel surface, such as C-O-C and -OH, and adsorption of non-polar substances that repel water and improve surface hydrophobicity, such as C-C, -CH3, and -CH2, thereby improving hydrophobicity. The enhanced hydrophobicity facilitates gas film formation in the self-organized structures that further improves hydrophobicity.