Bioinspired Azimuthally Varying Nanoscale Cu Columns on Acupuncture Needles for Fog Collection

Abstract

Inspired by the natural fog collection of the Namib beetles and desert cacti, a bioinspired design (BID) needle with a remarkable wettability gradient is introduced. Previous studies about directional water transport have rarely investigated wettability gradients along the azimuthal direction of a needle. Here, we have reported on the fast droplet transportation on a BID needle improved by azimuthally varying Cu nanocolumns on a steel acupuncture needle. We have employed glancing angle deposition (GLAD) to produce gradient porous Cu nanocolumns directly on the curved surface of an acupuncture needle. Due to the engineered gradient on such a surface, a high-speed fog collection of V = 134.8 mm·s–1 and a remarkable acceleration of a = 848.3 mm·s–2 were observed for the droplets on the needle surface. All periodically created droplets were easily swept along the 40 mm needle path in less than 0.5 s. Such efficient fog collection and fast droplet transportation in the proposed azimuthally nonuniform structure have many potential applications, from fog collection in low water regions to water transportation in microsystems.

Wetting Ridge‐Guided Directional Water Self‐Transport

“…In nature, lots of creatures have evolved unique microscaled structures with the ability to spontaneous and directional liquid transport. [ 14 , 15 , 16 , 17 , 18 , 19 ] For instance, the Araucaria leaf, which is composed of periodically arranged 3D ratchets with transverse and longitudinal reentrant curvatures, allows the fluids with different surface tension to spread along different directions. [ 20 ] Namib desert beetle can harvest water droplets from the fog by using their heterogeneous wettability structured back that consists of wax‐coated hydrophobic regions and non‐waxy hydrophilic bumps.…”

Fabric Comprised of Cotton Impregnated with Graphene Oxide and Coated with Polystyrene for Personal Moisture and Thermal Management

“…The breakthrough pressure on the GO side was lower than that on the PS side, as illustrated in Figure c, and therefore electronic diode operation was simulated. The increase in the breakthrough pressure on the PS side occurred because the PS layer had smaller apertures, which increased the Laplace pressure ( P L ), thereby repelling the water droplets . The Laplace pressure was calculated using the Young–Laplace equation in eq , P normalL = 2 γ 0.25em cos nobreak0em.25em⁡ θ r where γ represents the surface tension of the liquid, θ is the advancing WCA on the inner surfaces of the capillaries in the material, and r represents the radii of the pores in the material (Figure S7).…”

“…The increase in the breakthrough pressure on the PS side occurred because the PS layer had smaller apertures, which increased the Laplace pressure (P L ), thereby repelling the water droplets. 42 The Laplace pressure was calculated using the Young−Laplace equation in eq 6 43,44 = P r…”

Biomimetic directional transport for sustainable liquid usage

“…(b) Composition of the superhydrophilic‐hydrophobic integrated conical stainless steel needle [45]. (c) The growth of nanocolumns on the tip of the needle and cross‐sectional field emission SEM (FESEM) images of the Cu nanocolumns on two different points of the needle [44]. (d) Composition and function of the fabric [42]…”