Fig. 1. Periodic surface structure and hydrophilic properties. (a) SEM image of prepared periodic surface structure under N=160 and F=0.26 J/cm²; (b) contact angle of smooth copper sheet; (c) contact angle of copper sheet after adding periodic surface structure

Fig. 2. SEM images of periodic surface structures prepared under different laser parameters. (a)‒(c) Periodic surface structures prepared under different energy densities when N=160; (d)‒(f) periodic surface structures prepared under different equivalent pulse numbers when F=0.26 J/cm²

Fig. 3. Morphologies of V-grooves with different depths. (a) a=12 μm; (b) a=25 μm; (c) a=50 μm; (d) cross-sectional profile curve

Fig. 4. Grooves under different β. (a)‒(c) Depth of 12 μm; (d)‒(e) depth of 25 μm; (g)‒(i) depth of 50 μm

Fig. 5. Diffusion properties of liquid droplets in grooves. (a) Diffusion of liquid droplet in smooth V-groove; (b) diffusion of liquid droplet in groove with 0° LIPSS; (c)‒(e) diffusion distance curves of grooves under different β

Fig. 6. Schematics of droplet diffusion. (a) Droplet diffusion when LIPSS stripes are parallel to x-axis direction; (b) droplet diffusion when LIPSS stripes are perpendicular to x-axis direction; (c) schematic of contact angle of smooth groove; (d) schematic of contact angle of LIPSS striped groove when β=90°; (e) schematic of contact angle of LIPSS striped groove when β=0°