Nature produces many examples of super-hydrophobic surfaces and these have been the source of many scientific developments in recent decades [1]. The industrial applications of super-hydrophobicity are numerous. We can mention anti-bacterial surfaces for the biomedical field, anti-icing surfaces for aeronautics, or self-cleaning surfaces. Super-hydrophobicity can be reached by controlling both the chemistry and the topography of the functionalized surfaces to mimic occurrences in nature. In order to avoid chemical treatments that are potentially not respectful of the environment and health, one of the challenges of super-hydrophobicity is to propose water repellency strategies without chemical treatments. In this study, femtosecond laser surface texturing is proposed to achieve super-hydrophobicity of stainless steel surfaces without any additive chemical treatment [2].
Inspired by Euphorbia leaves, two types of texturing designs are performed: the laser texturing of micrometric square pillars, and the laser texturing of micrometric square pillars on top of which static laser impacts are done to get a different topography in the nanometric scale. To study the effect of the texturing environment on the wetting properties of surfaces, both ambient air and CO2 constant flow irradiation conditions are investigated. Independently of the environment, both surfaces have similar topographic parameters, including height and width of the micrometric squares, and are visually consistent (Fig. 1). However, surfaces aged differently when textured in ambient air or under CO2 flow (Fig. 1). The hydrophilic-to-hydrophobic transition is faster when the surface is textured under CO2 environment. Moreover, the apparent contact angle reached after CO2-flow texturing is higher compared to ambient air: 142° vs 119° for the surface textured in ambient air. This difference in static contact angle implies that the surface chemistry during laser texturing plays a significant role on wetting even for long time after irradiation.

References
[1] W. Barthlott et al., Nano- Micro Lett. (2017) 9:23
[2] P. Bizi-Bandoki et al., App. Surf. Sc. 273 (2013) 399-407