Ling Yang

Directional liquid transport has been widely observed in various species including cacti, spiders, lizards, the pitcher plant Nepenthes alata, and Araucaria leaves. However, in all these examples the liquid transport for a specific liquid is completely restricted in a fixed direction. We demonstrate that Crassula muscosa shoot surfaces have the ability to transport a specific liquid unidirectionally in either direction. This is accomplished through the presence of asymmetric reentrant leaves with varying reentrant angles, which yields the variation in liquid meniscus heterogeneity. These findings enable engineered biomimetic structures capable of selective directional liquid transport, with functions such as intelligent flow direction switching, liquid distribution, and mixing.

Reentrant feature widely exists in natural structures ranging from mushroom, overhang, undercut, trapezoid, sphere, spatula and taper to sharp edge, and has triggered a biomimetic design revolution of functional surfaces for extreme repellency to fluid foulants, directional fluid navigation, and strong adaptive adhesion. In this Review, we discuss how the bionic introduction of reentrant feature on a surface mediates fluid wetting, contact line motion, as well as solid adhesion. We briefly introduce nature-inspired design principles from representative reentrant surfaces on the springtail, gecko, and pitcher plant. Through quantitatively associating microscopic structural parameters of reentrant feature, including angle, shape, diameter, thickness, sharpness and anisotropy, with macroscopically visible wetting and adhesion properties, we evaluate how the design of reentrant feature can enable exceptional

Droplet impact is a ubiquitous phenomenon in nature, daily life, and industrial processes. It is thus crucial to tune the impact outcomes for various applications. As a special outcome of droplet impact, the bouncing of droplets keeps the form of the droplets after the impact and minimizes the energy loss during the impact, being beneficial in many applications. A unified understanding of droplet bouncing is in high demand for effective development of new techniques to serve applications. This review shows the fundamentals, regulations, and applications of millimeter‐sized droplet bouncing on solid surfaces and same/miscible liquids (liquid pool and another droplet). Regulation methods and current applications are summarized, and potential directions are proposed.