Tunable Capillary Wicking of 316L Stainless-Steel Hierarchical Microgrooves Fabricated by Master Oscillator Power Amplifier Nanosecond Laser Texturing

Laser-induced recast ridges can create auxiliary capillary spaces but may also restrict the main liquid-transport channels. How these competing structural effects influence capillary transport remains insufficiently understood. Capillary pressure depends on surface tension, wettability, and meniscus curvature, whereas viscous resistance depends on fluid viscosity, the available flow cross-section, and channel connectivity. Hierarchical microgroove wicks were fabricated on 316L stainless steel using master oscillator power amplifier (MOPA) nanosecond laser texturing, with scanning passes, groove spacing, and pulse width varied systematically. Scanning electron microscopy and three-dimensional surface profilometry were combined with apparent water contact-angle and capillary-rise measurements to relate structural development to liquid transport. At a groove spacing of 0.1 mm and a pulse width of 200 ns, increasing the scanning passes from 15 to 25 reduced the main-microgroove width from 60 to 55 μm and was accompanied by a decrease in the capillary factor from 30.859 to 29.024 mm·s−0.5. The observations indicate that the presence of secondary microgrooves alone is insufficient for improved wicking. Open main–secondary connections are associated with enhanced capillary transport, while excessive recast accumulation restricts channel openings and may increase viscous resistance. These findings provide an experimental basis for controlling recast geometry and channel connectivity in directly textured stainless-steel wicks for potential use in ultrathin vapor chambers.