Direct Laser Interference Patterning for Wettability Modification and Bubble Nucleation on Conventional and Additively Manufactured Metals

In addition to surface chemistry, surface roughness plays a critical role regarding wettability and solid-liquid as well as solid-gas interactions. Additive manufacturing produces substrates with unique characteristics (such as inherent roughness and porosity) that differ significantly from those of conventionally fabricated materials. In this study, conventionally manufactured Ti64 and stainless steel 316L substrates are compared with additively manufactured stainless steel 316L in their as-fabricated state, as well as after the application of direct laser interference patterning to introduce additional micro- and nanostructures. Surface morphology and topography are characterized using confocal microscopy and scanning electron microscopy. Wettability development is evaluated after storage in ambient air and aqueous environments, and the observed behaviors are correlated with different wetting states. Furthermore, the influence of these wetting states on bubble dynamics in O₂-oversaturated aqueous solutions is investigated. The results indicate that the intrinsic roughness of AM substrates significantly enhances gas nucleation, primarily due to increased surface area and the presence of Harvey nuclei. Additional laser structuring by direct laser interference patterning not only increases the surface area but also oxidizes the surface and can induce rapid changes in surface chemistry, thereby affecting solid-gas interactions. Notably, the laser treatment of Ti64 substrates led to the formation of surfaces with very high water contact angles, characterized by the rose petal wetting regime. Despite the apparent superhydrophobic character, these surfaces did not promote solid-gas interactions. Other obtained wetting states turned out to be more beneficial for enhancing bubble nucleation. This work underscores the complex interplay between surface topography and chemical modification in achieving specific wetting states and highlights their collective impact on solid-gas interfacial phenomena.