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

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.