Leaf-inspired surface enables different liquids to flow in different directions

Water on an Araucaria leaf moves in one direction while ethanol on the same leaf moves in another, a surprising finding that scientists in a new study took advantage of. Inspired by the unique liquid transport behavior they observed on the leaves of this plant, they developed a surface that can direct different liquids to flow in opposite directions. The approach could be used in a host of practical applications, from microfluidics to water desalination. Directional liquid transport on surfaces can be achieved using coatings that attract or repel liquids or textures with specific curvatures. However, in most cases, fluid transport is limited to a fixed direction. Shile Feng and colleagues examined how liquids flow along the Araucaria leaf, which consists of periodically arranged ratchets tilting toward the leaf tip. The authors demonstrate that low-surface-tension liquids, like ethanol, flow along the ratchet-tilting direction – towards the tips. On the other hand, high-surface-tension liquids, like water, flow in the opposite direction. Based on these observations, Feng et al. developed a dual reentrant surface with a similar asymmetric profile and properties. Through a series of experiments, they show how different liquids placed on their synthetic surfaces naturally steer in opposite directions. This approach could be used to promote liquid propagation or to inhibit it, depending on the need. The self-steering exhibited by liquids on their surfaces was also accompanied by self-propulsion and high-flow velocity.