Biomimetic surfaces with anisotropic sliding wetting by energy-modulation femtosecond laser irradiation for enhanced water collection

Biological rice leaf surfaces show a distinct anisotropic sliding property by means of three-level macrogrooves and micro/nanostructures, and they have many potential applications in biomimetic cell movement control, water transportation, and microfluidic devices. However, fabricating artificial threelevel biosurfaces with a controllable anisotropic sliding property by a simple and effective method remains a challenge. Herein, we report a simple method to prepare hierarchical groove structures (macro and micro/nano) on polydimethylsiloxane (PDMS) films using energy-modulation femtosecond laser scanning. The macrogrooves for anisotropic control were realized by larger-energy (> 0.40 J cm(-2)) laser scanning, whereas the micro/nanostructures for superhydrophobic ability were fabricated by smallenergy (0.08 J cm(-2)) laser scanning. The processed surface shows a sliding angle (SA) difference of 6 degrees between the perpendicular and parallel directions, which is comparable to that of the natural rice leaf. To quantitatively investigate the anisotropic wettability, surfaces with a different period (100 to 600 mm) and height (30 to 100 mm) were systematically fabricated by adjusting the scanning space and pulse energy. Finally, the distinct ability of the dynamic water droplet anisotropic sliding and size-constrained fog deposition on the anisotropic biosurfaces was demonstrated. The collection efficiency of water on the anisotropic surface with a rotation of 5 and 10 degrees is four times and eighty times higher than that on an isotropic surface.