Anisotropic Wetting Behavior on Gradient Surface Structures Fabricated by Direct Laser Interference Patterning on Stainless Steel

Abstract In this work, anisotropic line‐like textures with gradually increasing spatial periods from 2.0 to 4.8 µm are fabricated on stainless steel by two‐beam Direct Laser Interference Patterning using a ps‐laser source. Three manufacturing strategies are developed to fabricate these so‐called gradient structures achieving different surface roughness Rz and overall texture uniformity. The influence of unidirectional texture gradients on anisotropic wetting properties is studied by depositing 1 µL water droplets. The results show that the optimum‐designed gradient patterns induce in all cases the spontaneous motion of water droplets in the direction of increasing periodicity, or equivalently, increasing hydrophilicity. It is also observed a direct correlation between the gradient ratio and the traveling distance, which reaches a maximum of 0.99 mm for a period gradient of 2.24 µm mm⁻¹. Furthermore, multidirectional gradient textures are produced by combining gradient areas with opposing gradient orientations. The anisotropic wetting characteristics on such complex textures are measured, showing a strong local dependency of the water contact angle and droplet displacement. The findings from this work provide new design rules for customizing gradient surfaces able to realize predictable, position‐dependent wetting properties and directional movement of microliter water droplets.