Capillary-inertial colloidal catapults upon drop coalescence

Chavez, Roger L.; Liu, Fangjie; Feng, James J.; Chen, Chuan‐Hua

doi:10.1063/1.4955085

Cited by 20 publications

(13 citation statements)

References 29 publications

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“…In addition to liquid-mediated phenomena, the developed platform presented here lends itself to studies of self-cleaning, ,− where coalescence-induced droplet jumping can remove solid particles from the surface. On the vapor side, recent numerical studies have shown the importance of the surrounding vapor/gas density and flow field on the coalescence and detachment process .…”

Section: Discussionmentioning

confidence: 99%

Droplet Jumping: Effects of Droplet Size, Surface Structure, Pinning, and Liquid Properties

et al. 2019

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Coalescence-induced droplet jumping has the potential to enhance the efficiency of a plethora of applications. Although binary droplet jumping is quantitatively understood from energy and hydrodynamic perspectives, multiple aspects that affect jumping behavior, including droplet size mismatch, droplet−surface interaction, and condensate thermophysical properties, remain poorly understood. Here, we develop a visualization technique utilizing microdroplet dispensing to study droplet jumping dynamics on nanostructured superhydrophobic, hierarchical superhydrophobic, and hierarchical biphilic surfaces. We show that on the nanostructured superhydrophobic surface the jumping velocity follows inertial-capillary scaling with a dimensionless velocity of 0.26 and a jumping direction perpendicular to the substrate. A droplet mismatch phase diagram was developed showing that jumping is possible for droplet size mismatch up to 70%. On the hierarchical superhydrophobic surface, jumping behavior was dependent on the ratio between the droplet radius R i and surface structure length scale L. For small droplets (R i ≤ 5L), the jumping velocity was highly scattered, with a deviation of the jumping direction from the substrate normal as high as 80°. Surface structure length scale effects were shown to vanish for large droplets (R i > 5L). On the hierarchical biphilic surface, similar but more significant scattering of the jumping velocity and direction was observed. Droplet-size-dependent surface adhesion and pinning-mediated droplet rotation were responsible for the reduced jumping velocity and scattered jumping continued...

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Section: Discussionmentioning

confidence: 99%

Droplet Jumping: Effects of Droplet Size, Surface Structure, Pinning, and Liquid Properties

et al. 2019

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“…Such a dominance gives rise tô ' Ã T 1, which is impressive considering that the capillaryinertial velocity is about the best attainable in self-propelled motion powered by surface energy. The effectiveness will be significantly reduced if the drop coalescence is symmetric instead, as shown in a related capillary -inertial colloidal catapult where the merged drop has a predominantly oscillatory motion [31].…”

Section: Role Of Asymmetric Coalescencementioning

confidence: 99%

“…ballistic launching systems for small projectiles [32 -34] and self-cleaning systems for colloidal contaminants [31,35,36]. Competing interests.…”

mentioning

confidence: 99%

Asymmetric drop coalescence launches fungal ballistospores with directionality

Liu

Chavez

Patek

et al. 2017

J. R. Soc. Interface.

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Thousands of fungal species use surface energy to power the launch of their ballistospores. The surface energy is released when a spherical Buller's drop at the spore's hilar appendix merges with a flattened drop on the adaxial side of the spore. The launching mechanism is primarily understood in terms of energetic models, and crucial features such as launching directionality are unexplained. Integrating experiments and simulations, we advance a mechanistic model based on the capillary-inertial coalescence between the Buller's drop and the adaxial drop, a pair that is asymmetric in size, shape and relative position. The asymmetric coalescence is surprisingly effective and robust, producing a launching momentum governed by the Buller's drop and a launching direction along the adaxial plane of the spore. These key functions of momentum generation and directional control are elucidated by numerical simulations, demonstrated on spore-mimicking particles, and corroborated by published ballistospore kinematics. Our work places the morphological and kinematic diversity of ballistospores into a general mechanical framework, and points to a generic catapulting mechanism of colloidal particles with implications for both biology and engineering.

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“…When two microdroplets coalesce on superhydrophobic surfaces (SHSs), the coalesced droplet will jump out of the plane spontaneously . This jumping phenomenon is observed not only on natural materials, such as lotus leaf, gecko skin, and cicada wings, but also on fabricated SHSs with nanoscale or hierarchical structures. − The coalescence-induced droplet jumping has showed its great potential in thermal management, , self-cleaning surfaces, − anti-icing surfaces, condensation heat transfer enhancement, − and energy harvest …”

Section: Introductionmentioning

confidence: 99%

Effect of a Superhydrophobic Surface Structure on Droplet Jumping Velocity

Wang

Chen

et al. 2021

Langmuir

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The coalescence-induced droplet jumping on superhydrophobic surfaces is fundamentally significant from an academic or practical viewpoint. However, approaches to enhance droplet jumping velocity are very limited. In this work, the effect of structural parameters of the triangular prism on droplet jumping is studied systematically. The results indicate that droplet jumping velocity can be greatly increased by exploiting structure effects, which is a promising reinforcement method. When the height and apex angle of the triangular prism are fixed, the droplet jumping velocity increases with the length of the triangular prism until a plateau is reached. The ratio of translational kinetic energy to released surface energy during droplet jumping is determined by the apex angle and the height of the triangular prism, which is more effective with a smaller apex angle and a larger height. The results are supposed to provide guidelines for optimization of superhydrophobic surfaces.

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Capillary-inertial colloidal catapults upon drop coalescence

Cited by 20 publications

References 29 publications

Droplet Jumping: Effects of Droplet Size, Surface Structure, Pinning, and Liquid Properties

Droplet Jumping: Effects of Droplet Size, Surface Structure, Pinning, and Liquid Properties

Asymmetric drop coalescence launches fungal ballistospores with directionality

Effect of a Superhydrophobic Surface Structure on Droplet Jumping Velocity

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