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

Abstract

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 À2 ) laser scanning, whereas the micro/nanostructures for superhydrophobic ability were fabricated by smallenergy (0.08 J cm À2 ) laser scanning. The processed surface shows a sliding angle (SA) difference of 6 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. Fig. 1 Multi-level rice leaf surfaces with anisotropic sliding behavior and fabrication of the rice leaf-like biosurfaces. (a) The upside of rice leaf blades. (b) The top-view SEM image of the rice leaf upper surface. The inset is a magnified image of micropillars with nanostructures. (c) Hierarchical model of the rice leaf. (d) Schematic of the bionic rice leaf using a femtosecond laser. (e) Optical image of the processed PDMS film. (f) Top-view SEM of untreated PDMS. (g) Cross-sectional SEM image of the rice leaf-like wavy grooves. (h) Top-view SEM image of the processed PDMS surface, and the insert is a magnified image of micro-nanostructures.

Excellent Fog‐Droplets Collector via Integrative Janus Membrane and Conical Spine with Micro/Nanostructures

“…We demonstrate that a higher fog collection rate can be achieved effectively, which is attributed to a cooperation effect between the Laplace pressure in difference and the released surface energy in droplet coalescence, in addition to wettability force of superhydrophobic–hydrophilic difference in JM. Recently, there have been some outstanding works which utilize anisotropic wetting surface or single layer Janus membrane for water collection and they exhibit good results, e.g., 0.068 mL min −1 cm −2 ). The results of our experiment are as impressive in terms of collecting rate and this strategy of MNCS+JM offers an insight into surface of materials to control the droplet transport for water collection in efficiency, which is significant to be extended into the realms of applications such as high‐efficiency water collection system, microfluidics devices, and others.…”

Mechanically durable and long-term repairable flexible lubricant-infused monomer for enhancing water collection efficiency by manipulating droplet coalescence and sliding

“…6a for 5 s and 12 s. The micro-nano structures could capture more droplets and accelerate the growth rate of droplets on them. [41][42][43] Also, the lubricant layer has a superior heat transfer performance, which promoted the growth of the condensed droplets. As the fog continued to be captured, many droplets accumulated into larger droplets slowly.…”

The Design of Hydrophilic Nanochannel‐Macrostripe Fog Collector: Enabling Wicking‐Assisted Vertical Liquid Delivery for the Enhancement in Fog Collection Efficiency

“…Herein, we first present the fog collector inspired by grass leaves consisting of two different structures—nanochannels and macrostripes—enabling spontaneous droplet removal and preventing re‐entrainment of the droplets ( Figure a). [ 33–36 ] First, nanoscale grooves (i.e., “nanochannels”) of polymer substrates are prepared via nanoimprinting lithography (NIL), which is suggested for low‐cost, scalable fabrication. [ 37,38 ] Macrostripes are then patterned through laser cutting to provide desired openings.…”