Controlling wetting properties of functional metal surfaces can provide benefits for a wide variety of industrial applications, such as influencing biocompatibility, ice adhesion and achieving self-cleaning effects. Many research studies were inspired by natural examples, such as the lotus leaf, where superhydrophobicity is achieved through a combination of micro- and nanoscale surface texture and a layer of wax that alters the surface chemistry [1]. When it comes to metal surfaces, laser-texturing methods provide a flexible and robust approach to modify both the chemistry and microtopography in a single processing step and mimic the wettability found in nature [2,3]. In this work, using the technique of direct laser interference patterning (DLIP) with four interfering beams, periodic dot-like micro-textures are applied to stainless steel surfaces. Experiments are conducted on high initial roughness specimen to investigate how microtexturing can influence wetting on not specifically prepared surfaces, which are often found in technical surfaces. Rough as-built and pre-grinded samples are used to represent two types of initial surface finishes. By systematically varying different laser parameters during the texture fabrication, the influence of these parameters on the achieved topography and wetting behaviour is investigated. The textured surfaces show a transition from hydrophilic to hydrophobic wetting over the course of 90 days, achieving water contact angles up to 154.4°. Using the Wenzel model for wetting of rough surfaces, the transition of the Young contact angle is estimated for both types of initial surface finishes. In the steady-state, water and diiodomethane contact angle measurements show that surfaces are hydrophobic and oleophilic, with diiodomethane contact angles as low as 0°. Measurements of contact angle hysteresis reveal that textured surfaces exhibit the rose-petal effect, where water contact angles are high while drops adhere strongly to the surface with undefined sliding angle. It was shown that the high adhesion forces originate from the initial surface roughness, while the high water contact angle was a consequence of the DLIP texturing.

[1] Barthlott, W. and Neinhuis, C., “Purity of the sacred lotus, or escape from contamination in biological surfaces,” Planta 202, 1–8, (1997).
[2] Cai, Y., Chang, W., Luo, X., Sousa, A. M. L., Lau, K. H. A. and Qin, Y., “Superhydrophobic structures on 316L stainless steel surfaces machined by nanosecond pulsed laser,” Precision Engineering, 52, 266–275, (2018).
[3] Milles, S., Voisiat, B., Nitschke, M. and Lasagni, A. F., “Influence of roughness achieved by periodic structures on the wettability of aluminum using direct laser writing and direct laser interference patterning technology,” Journal of Materials Processing Technology, 270, 142–151, (2019).