Continuous Directional Water Delivery on the 3D-Printed Arrowhead Microstructure Array

High-speed directional transport of condensate droplets on superhydrophobic saw-tooth surfaces

HYPOTHESIS

Most droplets on high-efficiency condensing surfaces have radii of less than 100 μm, but conventional droplet transport methods (such as wettability-gradient surfaces and structural-curvature-gradient surfaces) that rely on the unbalanced force of three-phase lines can only transport millimeter-sized droplets efficiently. Regulating high-speed directional transport of condensate droplets is still challenging. Therefore, we present a method for condensate droplet transportation, based on the reaction force of the superhydrophobic saw-tooth surfaces to the liquid bridge, the condensate droplets could be transported at high speed and over long distances.

EXPERIMENTS

The superhydrophobic saw-tooth surfaces are fabricated by femtosecond laser ablation and chemical etching. Condensation experiments and luminescent particle characterization experiments on different surfaces are conducted. Aided by the theoretical analysis, we illustrate the remarkable performance of condensate droplet transportation on saw-tooth surfaces.

FINDINGS

Compared with conventional methods, our method improves the transport velocity and relative transport distance by 1-2 orders of magnitude and achieves directional transport of the smallest condensate droplet of about 2 μm. Furthermore, the superhydrophobic saw-tooth surfaces enable multi-hop directional jumping of condensate droplets, leading to cross-scale increases in transport distances from microns to decimeters.

Water collection and transport in bioinspired nested triangular patterns

To address water shortages worldwide, proactive measures are needed to supplement the water supply. In arid regions, many plants and animals use fog or the moisture in air as a source of water. An important consideration for efficient water collection is to transport collected water droplets as rapidly as possible to storage/use before they are evaporated. Triangular geometry has been used for faster transport of water droplets. In the case of a triangular geometry, if a droplet is placed at its apex, the droplet is driven across the triangular region by the Laplace pressure gradient. However, the magnitude of the gradient decreases along the triangle. In this study, nested triangles were designed to provide a higher pressure gradient. Water condensation and transport studies were carried out on the nested pattern at a temperature below the dew point in ambient air. It was found that the nested pattern increases the droplet travel speed. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 3)'.