Coalescence-Induced Jumping of Multiple Condensate Droplets on Hierarchical Superhydrophobic Surfaces

Xuemei Chen,Suresh V Garimella,Justin A Weibel,Ravi S Patel

doi:10.1038/srep18649

Abstract

Coalescence-induced jumping of condensate droplets from a superhydrophobic surface with hierarchical micro/nanoscale roughness is quantitatively characterized. Experimental observations show that the condensate droplet jumping is induced by coalescence of multiple droplets of different sizes, and that the coalesced droplet trajectories typically deviate from the surface normal. A depth-from-defocus image processing technique is developed to track the out-of-plane displacement of the jumping droplets, so as to accurately measure the droplet size and velocity. The results demonstrate that the highest jumping velocity is achieved when two droplets coalesce. The jumping velocity decreases gradually with an increase in the number of coalescing droplets, despite the greater potential surface energy released upon coalescence. A general theoretical model that accounts for viscous dissipation, surface adhesion, line tension, the initial droplet wetting states, and the number and sizes of the coalescing droplets is developed to explain the trends of droplet jumping velocity observed in the experiments.

Highlights

Of multiple size droplets[22], and they showed that the jumping velocity increased with number of coalescing droplets
All models reported in the literature are based on the assumption that coalescence occurs for sized spherical droplets; in reality, the bulk of condensate is removed from superhydrophobic surfaces via stochastic coalescence processes that occur for groups of droplets having different radii[11,12,13,14,15]
A general theoretical model that takes into account the viscous dissipation, surface adhesion, line tension, droplet wetting state, and the number and size differences of the initial coalescing droplets is developed to explain the underlying jumping mechanisms that lead to the observed behavior

Summary

Introduction

Of multiple size droplets[22], and they showed that the jumping velocity increased with number of coalescing droplets. We investigate the behavior of multiple-droplet coalescence-induced jumping during condensation on hierarchical superhydrophobic surfaces featuring nanostructured truncated microcones. On such surfaces, synergy between the micro- and nano-structures favors the formation of condensate droplets suspended on the inclined planes of neighboring cones, where the Laplace pressure assists the upward movement of the droplets[12,13]. A general theoretical model that takes into account the viscous dissipation, surface adhesion, line tension, droplet wetting state, and the number and size differences of the initial coalescing droplets is developed to explain the underlying jumping mechanisms that lead to the observed behavior

Methods

Results

Conclusion