Controlling the surface wettability represents an important challenge in the field of surface functionalization. Here, the wettability of a stainless-steel surface is modified by 30-ns pulses of a Nd:YAG marking laser (λ = 1064 nm) with peak fluences within the range 3.3–25.1 J cm⁻². The short- (40 days), intermediate- (100 days) and long-term (1 year) superhydrophilic-to-(super)hydrophobic transition of the laser-textured surfaces exposed to the atmospheric air is examined by evaluating its wettability in the context of the following parameters: (i) pulse fluence; (ii) scan line separation; (iii) focal position and (iv) wetting period due to contact angle measurements. The results show that using solely a short-term evaluation can lead to wrong conclusions and that the faster development of the hydrophobicity immediately after laser texturing usually leads to lower final contact angle and vice versa, the slower this transition is, the more superhydrophobic the surface is expected to become (possibly even with self-cleaning ability). Depending on laser fluence, the laser-textured surfaces can develop stable or unstable hydrophobicity. Stable hydrophobicity is achieved, if the threshold fluence of 12 J cm⁻² is exceeded. We show that by nanosecond-laser texturing a lotus-leaf-like surface with a contact angle above 150° and roll-off angle below 5° can be achieved.

In this work, we present functionalization of AISI 316 L surfaces by nanosecond Nd:YAG laser texturing and adsorption of superhydrophobic fluoroalkylsilane functionalized 30-nm silica nanoparticles. Surface modification by varying the distance between laser-produced micro(μ)-channels leads to different surface roughnesses. After nanosilica coating, the superhydrophilic laser-textured surfaces change into superhydrophobic surfaces with the same μ-roughness. A higher μ-channel density leads to more hydrophobic surfaces after coating. This enables a study of the combined effect of surface wettability and morphology on the friction coefficient and wear resistance. Experiments were performed in dry and water environments. In the case of dry friction, increased μ-roughness leads to a higher friction coefficient, and the water-repellency modification by nanosilica particles has no influence on the tribological behaviour. In contrast, in the water environment, the wettability presents an important contribution to the properties of contact surfaces: hydrophobic surfaces exhibit a lower friction coefficient, especially at higher densities of μ-channels. Energy-dispersive X-ray spectroscopy analysis of surfaces before and after the tribological experiments is performed, revealing the difference in weight % of Si in the worn surface compared to the unworn surface, which varies according to the nature of the surface morphology due to laser texturing in both dry and water environments.

Epoxy/TiO₂/epoxy and epoxy/FAS-TiO₂/epoxy coatings were applied to the surface of AISI 316L stainless steel with the aim to improve the biocompatibility and antibacterial properties. Contact-angle measurements were used to evaluate the wetting properties of the epoxy, epoxy/TiO₂/epoxy and epoxy/FAS-TiO₂/epoxy coatings. The epoxy and epoxy/TiO₂/epoxy coatings were hydrophilic compared with the strongly hydrophobic epoxy/FAS-TiO₂/epoxy coating. The average surface roughness (S_a) of the epoxy/FAS-TiO₂/epoxy coating was higher than that of the epoxy/TiO₂/epoxy coating due to the formation of agglomerates. The biocompatibility evaluation revealed that the cell attachment was significantly higher on the epoxy/FAS-TiO₂/epoxy and epoxy/TiO₂/epoxy coatings compared with the pure epoxy coating. We also observed improved antibacterial properties for the epoxy coatings with the addition of both TiO₂ and FAS-TiO₂ nanoparticles.

We present the modification of Ti-6Al-4V surfaces with a diode end-pumped Nd:YVO4 laser by varying the distance between laser-produced micro(μ)-channels. We analyzed the influence of laser texturing on the morphology, microstructure, surface and corrosion properties of Ti-6Al-4V. SEM imaging reveals a characteristic μ-channel pattern with different scan line separations, while electron backscatter diffraction (EBSD) indicates that laser texturing with the current parameters influences the microstructure up to 2 µm deep with the most significant influence at the tips, where melting and rapid solidification occur. The Vickers hardness test indicates a surface hardening effect of the laser-textured compared to the as-received Ti-6Al-4V surfaces. The XPS analysis showed that the oxide layer on the laser-textured samples was considerably thicker compared to the as-received sample, at 20 and 7 nm, respectively. We observed that the wettability was strongly correlated with the scan line separation. The results show increased hydrophobicity with increased scan line separation. The corrosion resistance was improved for laser-textured surfaces compared to the as-received surface and increased with the scan line separation.

We present the results of one year observation of wetting and corrosion properties of nanosecond fiber laser-textured stainless steel, uncoated and coated with epoxy or FAS (fluoroalkylsilane)-TiO₂/epoxy. A comparative study was performed on samples kept under ambient conditions and in reduced air pressure and humidity. The results show the ability to induce wettability conversion from initially superhydrophilic to final superhydrophobic state either indirectly by ageing the uncoated laser-textured surface or directly by application of FAS-TiO₂/epoxy coating. The storage conditions significantly influenced the wettability development of uncoated laser-textured steel, i.e., the process of ageing was slowed down in reduced air pressure and humidity. Detailed surface chemical analysis revealed that adsorption of the organic matters from the surrounding media influences the wettability conversion and ageing. However, the ageing of the coated surfaces was not affected by the storage conditions. Corrosion stability of uncoated laser-textured surfaces was enhanced over time due to the wettability transition, depending on their morphology. Coatings represent a superior barrier over the texture and wettability with the stable long-term surface protection against aggressive media.