Directional droplet bouncing on a moving superhydrophobic surface

Meng Wang; Yanzhao Shi; Shun Wang; Huanlin Xu; Hui Zhang; Min Wei; Xiaopeng Wang; Wanxi Peng; Hang Ding; Meirong Song

doi:10.1016/j.isci.2023.106389

Directional droplet bouncing on a moving superhydrophobic surface

iScience. 2023 Mar 11;26(4):106389. doi: 10.1016/j.isci.2023.106389. eCollection 2023 Apr 21.

Authors

Meng Wang¹, Yanzhao Shi², Shun Wang¹, Huanlin Xu¹, Hui Zhang¹, Min Wei¹, Xiaopeng Wang¹, Wanxi Peng¹, Hang Ding², Meirong Song¹

Affiliations

¹ College of Science and College of Forestry, Henan Agricultural University, Zhengzhou, Henan 450002, P. R. China.
² Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230022, P. R. China.

Abstract

Droplets directionally bouncing off moving superhydrophobic solid surfaces are universal in nature and are crucial in many biological, sustainable, environmental, and engineering applications. However, their underlying physics and regulation strategies remain relatively unknown. This paper demonstrates that the maximum directional acceleration of a post-impact droplet mainly occurs in the spreading stage and that the orientational velocity of the droplet mainly originates in the early impingement process. Furthermore, it clarifies the underlying physics based on momentum transfer process imposed by the boundary layer of impacts and proposes a strategy for regulating the directional droplet velocity using a comprehensive formula. Finally, it shows that directional bouncing reduces the flight momentum of a small flying device by 10%-22%, and the experimental values agree closely with the predicted values. This study reveals the droplet bounce orientation mechanism imposed by moving substrates, provides manipulation methods, and makes positive and meaningful discussions of practical applications.

Keywords: Fluidics; Surface; Surface property.