Symmetry-Breaking Drop Bouncing on Superhydrophobic Surfaces with Continuously Changing Curvatures.

Wooseok Choi,Sungchan Yun

doi:10.3390/polym13172940

Abstract

Controlling the residence time of drops on the solid surface is related to a wide spectrum of engineering applications, such as self-cleaning and anti-icing. The symmetry-breaking dynamics induced by the initial drop shape can promote drop bouncing. Here, we study the bouncing features of spherical and ellipsoidal drops on elliptical surfaces that continuously change curvatures inspired by natural succulent leaves. The bounce characteristics highly depend on the geometric relations between the ellipsoidal drops and curved surfaces. Numerical results show that ellipsoidal shapes of the drops amplify asymmetries of the mass and momentum in synergy with an influence of the surface curvature during the impact, which is verified by experiments. Effects of the surface anisotropy and drops’ ellipticity on the residence time are investigated under various surface morphologies and Weber numbers. The residence time is closely associated with an initial surface curvature at the apex. The underlying principle of modifying the residence time via the drops’ ellipticity and initial surface curvature is elucidated based on momentum asymmetry. The understanding of the bouncing features on curved surfaces will offer practical implications for enhanced heat transfer performances and controlled water repellency, etc.

Highlights

Bouncing dynamics of drops on solid surfaces have gained substantial attention over the last two decades for industrial applications, such as self-cleaning [1], anti-icing [2], low friction [3], and dropwise condensation [4]
The bouncing dynamics are highly affected by the geometric configurations between curved surfaces and drops
We suggest that the momentum asymmetry can be convincing evidence for for thethe decrease in in thethe residence time

Summary

Introduction

Bouncing dynamics of drops on solid surfaces have gained substantial attention over the last two decades for industrial applications, such as self-cleaning [1], anti-icing [2], low friction [3], and dropwise condensation [4]. The bounce characteristics are highly dependent on the surface roughness, temperature, wettability, and ambient conditions [5,6]. The residence time is considered essential because it determines the extent to which mass, momentum, and energy are exchanged between surfaces and drops. Drops impacting on superhydrophobic surfaces can lift off quickly because of the low wetting hysteresis at the contact line, inspired by effects of the lotus leaves and pitcher plant [7,8]. The emphases of recent works focus mainly on compelling drops to depart from the surfaces as fast as possible

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Conclusion