Bioinspired cone structures with helical micro-grooves for fast liquid transport and efficient fog collection

A cactus spine with a grooved cone structure provides an ideal model for designs capable of transporting liquids directionally. Inspired by the cactus spine, a lot of artificial liquid transport systems have been reported. In fact, aligned micro-grooves on natural cactus spines are helical rather than straight. Besides, helical structures are frequently found in plant xylem tissue and animal heart tissue, both of which relate closely to liquid transport. Nevertheless, the effect of helical microstructures on liquid transport has not been explored. Herein, we fabricate cones with helical micro-grooves, comparing their liquid transport ability with that of cones with straight micro-grooves. It turns out that the critical volume of a droplet starting to move has decreased from similar to 0.41 mu L to similar to 0.17 mu L and the motion velocity has increased from similar to 29.72 mu m s(-1) to similar to 96.73 mu m s(-1). Helical micro-grooves are speculated to have induced easier conformation transition of droplets from a clam-shell to a barrel state and prolonged the liquid-solid-vapor three phase contact line (TPCL), enlarging the Laplace pressure difference on the droplet and facilitating the droplet's directional motion. By integrating helical grooved cones with highly water-absorbing wood, we construct a fog collection system, demonstrating high efficiency. We envision that this novel helical grooved cone structure will offer new insights for the design of liquid manipulation systems.