Apex structures enhance water drainage on leaves

Abstract

The rapid removal of rain droplets at the leaf apex is critical for leaves to avoid damage under rainfall conditions, but the general water drainage principle remains unclear. We demonstrate that the apex structure enhances water drainage on the leaf by employing a curvature-controlled mechanism that is based on shaping a balance between reduced capillarity and enhanced gravity components. The leaf apex shape changes from round to triangle to acuminate, and the leaf surface changes from flat to bent, resulting in the increase of the water drainage rate, high-dripping frequencies, and the reduction of retention volumes. For wet tropical plants, such as Alocasia macrorrhiza, Gaussian curvature reconfiguration at the drip tip leads to the capillarity transition from resistance to actuation, further enhancing water drainage to the largest degree possible. The phenomenon is distinct from the widely researched liquid motion control mechanisms, and it offers a specific parametric approach that can be applied to achieve the desired fluidic behavior in a well-controlled way.

Directional liquid dynamics of interfaces with superwettability

“…Besides water collection for survival, there are also many creatures using their unique structures to expel water directionally for preventing pollution, keeping dry, and walking quickly (7)(8)(9)(10)(11)(12)(37)(38)(39). For example, a butterfly wing obliquely inserted with periodic anisotropic nanotips can orientally expel raindrops to prevent wetting (37).…”

“…Liquids tend to exhibit many unique and interesting dynamic behaviors at superwetting interfaces (1,2), including asymmetrical spreading, steady rolling, full bounce, and directional transport (1)(2)(3)(4)(5). These fantastic dynamic behaviors (1,3) belong to one of the important categories of bionics, which have facilitated a series of innovations and revolutions in several application areas ranging from agricultural irrigation, lubrication, fog collection, to microfluidic operation (4)(5)(6)(7)(8). With nature as the source of wisdom, the directional liquid dynamics of typical living organism interfaces open the gate for new inspirations.…”

Anisotropy-induced directional self-transportation of low surface tension liquids: a review

“…The total resistance to droplet motion is the sum of contact line and viscous dissipation, but the extent to which each contributes may be found using the above velocity-force relations, eqn (6) and (7). Note that the resistance due to viscous forces is negligible at the onset of the motion (V z 0).…”

Bioinspired Surface with Superwettability for Controllable Liquid Dynamics

“…[ 1–4 ] By skillfully manipulating liquid dynamics, natural organisms can survive under harsh conditions. Examples of this phenomenon include the ability of lotus leaves to float on water via the superhydrophobic margin, [ 5 ] the ability of spiders to collect moisture from fog onto the silk of their webs for drinking, [ 6 ] the ability of pitcher plants to secrete a lubricant directionally onto the peristome to cause insects to slide, [ 7 ] the ability of leaf apex to drip with a high frequency to avoid damage under rainy days, [ 8 ] and the ability of bombardier beetles to aim a hot caustic spray as a response to danger. [ 9,10 ] In addition to organisms in nature, we also encounter liquid dynamic behaviors in daily life.…”

“…d) Reproduced with permission. [ 8 ] Copyright 2020, National Academy of Sciences. e) Reproduced with permission.…”