On the wetting behavior of laser-microtextured stainless steel using Direct Laser Interference Patterning

Microtextures generated by pulsed lasers allow for changing the surface properties of a wide palette of materials by replicating nature's most effective topographies. In the case of laser-induced microtextures, the surface's wetting properties evolve over time and eventually stabilize. The size of the fabricated features and the initial surface roughness strongly influence this transition and play a key role in the determination of the final wetting state. This work aims to study the wettability of textured stainless-steel with two different surface finishes. Nanosecond Direct Laser Interference Patterning was applied to fabricate a wide range of dot-like microtextures that were evaluated in terms of surface roughness. The water contact angle was monitored for up to 90 days, showing a transition from hydrophilic to hydrophobic. Applying the Wenzel model, the wettability transition was analyzed in regard to surface roughness, and the transition of the average Young contact angle could be extrapolated. In the steady-state, the textured surfaces exhibited the rose-petal effect, where contact angles up to 154.4° were attributed to the microtextures, while a simultaneous high drop adhesion could be related to the initial surface finish. Measurements with water and diiodomethane showed that the textures were both hydrophobic and oleophilic in the steady-state. The surface free energy was estimated and decreased on all textures compared to the untextured reference.