Anisotropic Hemiwicking Behavior on Laser Structured Prismatic Microgrooves

Abstract

The wicking phenomenon, including wicking and hemiwicking, has attracted increasing attention for its critical importance to a wide range of engineering applications, such as thermal management, water harvesting, fuel cells, microfluidics, and biosciences. There exists a more urgent demand for anisotropic wicking behaviors since an increasing number of advanced applications are significantly complex. For example, special-shaped vapor chambers and heating atomizers in some electronic cigarettes need liquid replenishing with various velocities in different directions. Here, we report two-dimensional anisotropic hemiwicking behaviors with elliptical shapes on laser structured prismatic microgrooves. The prismatic microgrooves were fabricated via one-step femtosecond laser direct writing, and the anisotropic hemiwicking behaviors were observed when utilizing glycerol, glycol, and water as the test liquid. Specifically, the ratios of horizontal wicking distance in directions along short and long axes were tan 0°, tan 15°, tan 30°, and tan 45° for samples with cross-angles of 0°, 30°, 60°, and 90°, respectively. The vertical water wicking front displayed corresponding angles under the guidance of laser structured prismatic microgrooves. Theoretical analysis shows that the wicking distance is mainly dependent on the cross-angle θ and surface roughness, in which the wicking distance is proportional to cos­(θ/2). Driven by the capillary pressure forming in the narrow microgrooves, the liquid initially filled the valleys of microgrooves and then surrounded and covered the prismatic ridges with laser-induced nanoparticles. The abundant nanoparticles increased the surface roughness, leading to the enhancement of wicking performance, which was further evidenced by the larger wicking speed of the sample with more nanoparticles. The mechanism of anisotropic hemiwicking behaviors revealed in this work paves the way for wicking control, and the proposed prismatic microgrooved surfaces with two-dimensional anisotropic hemiwicking performance and superhydrophilicity could serve in a broad range of applications, especially for the advanced thermal management with specific heat load configurations.

Revisiting an ecophysiological oddity: Hydathode‐mediated foliar water uptake in Crassula species from southern Africa

“…We observed hemiwicking (i.e., capillarity-driven spread of liquid on a rough hydrophilic surface; Kim et al, 2016;Quéré, 2008;Telecka et al, 2018) in the two Crassula species with the most hydrophilic leaf surfaces. This phenomenon occurred very rapidly on the asymmetrically sculptured leaf surface of C. tecta and led to efficient spread of the water film (Supporting Information: Video S1) (Jiang et al, 2022;Shin et al, 2016), as previously reported (Fradera-Soler et al, 2021;Tölken, 1974Tölken, , 1977, while it was rather slow and barely noticeable in and Nosonovsky, 2010;Okulova et al, 2018;Schneider et al, 2016), which is likely caused by the hierarchical sculpturing of leaf surfaces, involving epicuticular waxes (Figure 5) (Barthlott et al, 2017;Riglet et al, 2021).…”

Self-induced interface enhanced moisture-harvesting and light-trapping toward high performance electric power generation

“…Then, at the interface between the ME and PSSA-Kc film, directional microgrooves in the textured ME could guide coalescent water spreading to fill the channel space of the microgrooves and to fully touch with the PSSA-Kc film. 10,11 Such moisture adsorption will result in the surface of the PSSA-Kc film transforming to a soft gel. When the ME forms conformal contact with the PSSA-Kc gel, the peaks of regular microgrooves on the ME acting as a template for constructing duplicate morphology will squeeze the gel, and the smaller top end width in the sinusoidal structure of the ME creates adequate room for continuous infusing and shaping of the PSSA-Kc surface due to capillary pressure (Fig.…”

Superhydrophobic microstructures for better anti-icing performances: open-cell or closed-cell?

“…Ultrafast laser direct writing, as a top-down processing strategy, can facilely fabricate tunable micro-nanostructures on nearly any material 42,43 and own ultrahigh structural repeatability. Taking these advantages, micro-nanostructures with tunable patterns were prepared on aviation aluminum alloy surfaces.…”