Self-Enhancement of Coalescence-Induced Droplet Jumping on Superhydrophobic Surfaces with an Asymmetric V-Groove

Abstract

Coalescence-induced droplet jumping on superhydrophobic surfaces have recently received significant attention owing to their potential in a variety of applications. Previous studies demonstrated that the self-jumping process is inherently inefficient, with an energy conversion efficiency η ≤ 6% and dimensionless jumping velocity V j* ≤ 0.23. To realize a quick removal of droplets, increasing effort has been devoted to breaking the jumping velocity limit and inducing droplets sweeping. In this work, we used superhydrophobic surfaces with an asymmetric V-groove to experimentally achieve an enhanced coalescence-induced jumping velocity V j* ≈ 0.61, i.e., more than 700% increase in energy conversion efficiency compared with droplets jumping on flat superhydrophobic surfaces, which is the highest efficiency reported thus far. Moreover, the enhanced jumping direction shows a deviation as high as 60° from the substrate normal. The induced in-plane motion is conducive to remove a considerable number of droplets along the sweeping path and significantly increase the speed of droplet removal. Numerical simulation indicated that the jumping enhancement is a joint effect resulting from the impact of the liquid bridge on the corner of the V-groove and the suppression of droplet expansion by the sidewall of the V-groove. The transient variation of the droplet velocity and the driving force of the coalescing droplets on a surface with and without the asymmetric V-groove were revealed and discussed. Furthermore, effects of groove angle, droplet pair positions, and size mismatches on the jumping velocity and direction have been studied. The novel mechanism of simultaneously increasing the coalescence-induced droplet jumping velocity and changing the jumping direction can be further studied to enhance the efficiency of various applications.

Coalescence-Induced Droplet Jumping

“…Nevertheless, the methodology of the droplets’ dividing process for coalescence-jumping behavior is similar. The stages are usually divided according to the changes in the shape of the droplets and the contact angles between the droplets and the substrate surface (with a variation of three to five stages). − …”

A Superhydrophobic Droplet‐Based Magnetoelectric Hybrid System to Generate Electricity and Collect Water Simultaneously

“…Bioinspired superhydrophobic materials have low surface energy and micro‐ or nano‐scale surface roughness, [ 7–9 ] rendering their unique capability to manipulate water droplets. By carefully designing and controlling the superhydrophobic surfaces, water drops can pin, [ 10 ] roll, [ 11 ] separate, [ 12 ] jump, [ 13 ] and react [ 14 ] and, therefore, can possess a variety of applications, such as self‐cleaning coatings on solar cells, [ 15 ] oil/water separation, [ 16–18 ] microfabrication, [ 19,20 ] and anti‐biofouling. [ 21 ] Recently, superhydrophobic surfaces have facilitated the development of high‐efficiency triboelectric nanogenerators for harvesting rainwater energy.…”

Spontaneous Motion and Rotation of Acid Droplets on the Surface of a Liquid Metal

“…7,29 Moreover, the spontaneous spreading−retraction are studied thoroughly, 21,30,31 and a classification of the interfacially induced motions is summarized. 31 The selfjumping of droplets can also be realized through the coalescence of droplets 8,32,33 or the pressure difference between the top and the bottom of the droplet. 34 These productive studies all promote the development of droplet selfpropulsion and show significant application prospects.…”

“…The self-propulsion of droplets has attracted increasing interests from the scientific community − and shows significant application prospects, for example, microfluidics chips, self-cleaning surfaces, heat transformation, , and foldable devices . Up to now, the self-translation of droplets can be effectively achieved by employing the Leidenfrost effect on asymmetrically structured surfaces, − the unbalanced surface tension due to the asymmetrical morphology, ,, specially designed chemical conditions, ,, active particles, and field gradient − including temperature, , concentration, , and inhomogeneity of chemical properties of the droplet. , Moreover, the spontaneous spreading–retraction are studied thoroughly, ,, and a classification of the interfacially induced motions is summarized .…”

“…Up to now, the self-translation of droplets can be effectively achieved by employing the Leidenfrost effect on asymmetrically structured surfaces, − the unbalanced surface tension due to the asymmetrical morphology, ,, specially designed chemical conditions, ,, active particles, and field gradient − including temperature, , concentration, , and inhomogeneity of chemical properties of the droplet. , Moreover, the spontaneous spreading–retraction are studied thoroughly, ,, and a classification of the interfacially induced motions is summarized . The self-jumping of droplets can also be realized through the coalescence of droplets ,, or the pressure difference between the top and the bottom of the droplet . These productive studies all promote the development of droplet self-propulsion and show significant application prospects.…”