Nonspecular Reflection of Droplets

Pingan Zhu; Chengmin Chen; Krishnaswamy Nandakumar; Liqiu Wang

doi:10.1002/smll.202006695

Nonspecular Reflection of Droplets

Small. 2021 Jan;17(3):e2006695. doi: 10.1002/smll.202006695. Epub 2020 Dec 21.

Authors

Pingan Zhu^{1

2

3}, Chengmin Chen^{4

5}, Krishnaswamy Nandakumar⁶, Liqiu Wang^{1

3}

Affiliations

¹ Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China.
² Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, China.
³ HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), Hangzhou, Zhejiang, 311300, China.
⁴ Energy Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan, Shandong, 250014, China.
⁵ School of Energy and Power Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan, Shandong, 250014, China.
⁶ Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA, 70803, USA.

PMID: 33345437
DOI: 10.1002/smll.202006695

Abstract

The bouncing of droplets on super-repellent surfaces normally resembles specular reflection that obeys the law of reflection. Here, the nonspecular reflection of droplet impingement onto solid surfaces with a dimple for energy-efficient, omnidirectional droplet transport is reported. With the dimple of the radius being comparable to that of the droplet, all the symmetries in the law of reflection can be broken down so that the droplet is endowed with a translational velocity finely tunable in both its direction and magnitude simply by varying the radii of the droplet and the dimple, the impinging position, and droplet Weber number. Tailoring the initial and translational velocity of impinging droplets would steer their reflected trajectories at will, thus enabling versatile droplet manipulation including trapping, shedding, antigravity transport, targeted positioning, and on-demand coalescence of droplets.

Keywords: droplet impact; liquid repellency; nonspecular reflection of droplets; omnidirectional droplet transport; symmetry breaking.

Publication types

Research Support, Non-U.S. Gov't