Apex structures enhance water drainage on leaves

Significance

Liquid manipulation is of significance not only for industrial spraying and drainage facilities, but also for the survival of creatures. Plant leaves perform excellently in rainwater drainage and leaf drying at the apex to avoid damage. Here we demonstrate that apex structure enhances water shedding with high dripping frequencies and low retention volumes. Based on the understanding of the tiny apex structure in controlling water delivery at the plant leaf, the evolutionary law of leaf apex shape could be further revealed. The shape-controlled liquid manipulation mechanism would improve the microfluidic and drainage systems.

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.