Abstract
Achieving the directional and long-range droplet transport on solid surfaces is widely preferred for many practical applications but has proven to be challenging. Particularly, directionality and transport distance of droplets on hydrophobic surfaces are mutually exclusive. Here, we report that drain fly, a ubiquitous insect maintaining nonwetting property even in very high humidity, develops a unique ballistic droplet transport mechanism to meet these demanding challenges. The drain fly serves as a flexible rectifier to allow for a directional and long-range propagation as well as self-removal of a droplet, thus suppressing unwanted liquid flooding. Further investigation reveals that this phenomenon is owing to the synergistic conjunction of multiscale roughness, structural periodicity, and flexibility, which rectifies the random and localized droplet nucleation (nanoscale and microscale) into a directed and global migration (millimeter-scale). The mechanism we have identified opens up a new approach toward the design of artificial rectifiers for broad applications.
Highlights
Billions of years’ evolution has endowed many living organisms with a high level of sophistication in the directional transport of mass, momentum, and energy on their surfaces [1–4]
The directional droplet transport observed on natural hydrophilic surfaces elegantly takes advantage of gradients in surface energy or Laplace pressure [7, 8, 12]
It remains elusive to achieve a directional and long-range liquid transport on hydrophobic surfaces [27, 28], which are preferred for many applications including thermal power generation and conversion, antifogging/anti-icing, and desalination [29–40]
Summary
Billions of years’ evolution has endowed many living organisms with a high level of sophistication in the directional transport of mass, momentum, and energy on their surfaces [1–4]. Adhesion, friction, and energy conversion have been widely exploited by cactus, pitcher plant, gecko, spider, lizard, and others [5–13]. The directional droplet transport observed on natural hydrophilic surfaces elegantly takes advantage of gradients in surface energy or Laplace pressure [7, 8, 12]. It remains elusive to achieve a directional and long-range liquid transport on hydrophobic surfaces [27, 28], which are preferred for many applications including thermal power generation and conversion, antifogging/anti-icing, and desalination [29–40]. It remains a far prospect to fabricate new materials that endow the directed and long-range transport of liquid in a wide spectrum of working environments
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