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This work shows that after creating certain dual scale roughness structures by femtosecond laser irradiation different metal alloys initially show superhydrophilic behavior with complete wetting of the structured surface. However, over time, these surfaces become nearly superhydrophobic with contact angles in the vicinity of 150 degrees and superhydrophobic with contact angles above 150 degrees. The contact angle hysteresis was found to lie between 2 and 6 degrees. The change in wetting behavior correlates with the amount of carbon on the structured surface. The explanation for the time dependency of the surface wettability lies in the combined effect of surface morphology and surface chemistry.
Kietzig et al. (Fri,) studied this question.