Universal wetting transition of an evaporating water droplet on hydrophobic micro- and nano-structures

Bussonnière, Adrien; Bigdeli, Masoud Bozorg; Chueh, Di-Yen; Chen, Peilin; Tsai, Peichun Amy

doi:10.1039/c6sm02287a

Cited by 46 publications

(50 citation statements)

References 62 publications

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“…It has been previously argued that the surface energy of any liquid on a real SH surface is distributed according to the Cassie–Baxter and Wenzel components. 32 It is plausible that with the onset of evaporation the ratio of latter may increase over the former, which may then allow for a sessile drop that initially exhibited predominant Cassie–Baxter behavior to transition toward a more predominant Wenzel character. A quantitative analysis to determine this in the current context will be challenging as the surface structures are hierarchical.…”

Section: Resultsmentioning

confidence: 99%

Drops on a Superhydrophobic Hole Hanging On under Evaporation

Chung¹,

Huynh²,

Katariya³

et al. 2017

ACS Omega

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Drops with larger volumes placed over a superhydrophobic (SH) surface with a hole do not fall through unless they are evaporated to a size that is small enough. This feature offers the ability to preconcentrate samples for biochemical analysis. In this work, the influence of pinning on the behavior of drops placed on a 0.1 mm thick SH substrate with a 2 mm diameter hole as they evaporated was investigated. With 16 μL of water dispensed, the sessile drop component volume was initially higher than that of the overhanging drop component and maintained this until the later stages where almost identical shapes were attained and full evaporation was achieved without falling off the hole. With 15 μL of water dispensed, the volume of the sessile drop was initially higher than that of the overhanging drop component but the liquid body was able to squeeze through the hole after 180 s due to the contact line not having sufficient pinning strength when it encountered the edge of the hole. This resulted in the liquid body either falling through the hole or remaining pinned with an oval-like shape. When it did not fall-off, the liquid body had volume and contact angle characteristics for the sessile drop and overhanging drop components that were reversed. In the later stages, however, nearly identical shapes were again attained and full evaporation was achieved without falling off the hole. The effects of pinning, despite the substrate being SH, offer another path toward achieving practical outcomes with liquid bodies without the need for chemical surface functionalization. Similarities and differences could be seen in the behavior of a sessile drop on a SH plate that was inclined at 30° to the horizontal and evaporated.

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Section: Resultsmentioning

confidence: 99%

Drops on a Superhydrophobic Hole Hanging On under Evaporation

Chung¹,

Huynh²,

Katariya³

et al. 2017

ACS Omega

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“…Although the kinetic energy of rainfall is the predominant factor in the foliar washing process 70 , leaf surfaces features like wax layer, trichomes and other protrusions can result in different contact angle between water droplet and different leaf surfaces 71 . These factors create different water-repellent performances between species 72 . Moreover, the hydraulic pressure change due to the impaction of raindrop can change the contact angle and thus the leaf wettability 73 which could also contribute to the PM 2.5 rainfall removal patterns.…”

Section: Discussionmentioning

confidence: 99%

Variation in Tree Species Ability to Capture and Retain Airborne Fine Particulate Matter (PM2.5)

Chen

Liu

Lü

et al. 2017

Sci Rep

221

149

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Human health risks caused by PM2.5 raise awareness to the role of trees as bio-filters of urban air pollution, but not all species are equally capable of filtering the air. The objectives of this current study were: (1) to determine the foliar traits for effective PM2.5-capture and (2) explore species-to-species differences in foliar PM2.5-recapture capacity following a rain event. The study concluded that overall, the acicular needle shape made conifers more efficient with PM2.5 accumulation and post-rainfall recapture than broadleaved species. The foliar shape and venation of broadleaved species did not appear to influence the PM2.5 accumulation. However, the number of the grooves and trichomes of broadleaved species were positively related to foliar PM2.5 accumulation, suggesting that they could be used as indicators for the effectiveness of tree PM2.5 capture. Furthermore, the amount of PM2.5 removal by rainfall was determined by the total foliar PM2.5. Not all PM2.5 remained on the foliage. In some species, PM2.5 was resuspended during the growing season, and thus reduced the net particular accumulation for that species. These findings contribute to a better understanding of tree species potential for reducing PM2.5 in urban environments.

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“…The only difference being the droplet base radius (r base ) and the number of micropillars beneath it. Most of the wetting-transition models (either based on the energy barrier 29,32,40 or the force balance 30 ) have considered the entire droplet base in their models. However, the droplet is not intelligent to see the whole picture and take care of everything.…”

Section: Resultsmentioning

confidence: 99%

“…Several wetting-transition mechanisms 39 are proposed based on the energy barrier 29,32,40 or the critical Laplace pressure 30,41 . Despite many efforts, there are still some discussions on the droplet wetting mechanism 41,42 .…”

Section: Introductionmentioning

confidence: 99%

Explaining Evaporation-Triggered Wetting Transition Using Local Force Balance Model and Contact Line-Fraction

Annavarapu

Kim

Wang

et al. 2019

Sci Rep

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Understanding wettability and mechanisms of wetting transition are important for design and engineering of superhydrophobic surfaces. There have been numerous studies on the design and fabrication of superhydrophobic and omniphobic surfaces and on the wetting transition mechanisms triggered by liquid evaporation. However, there is a lack of a universal method to examine wetting transition on rough surfaces. Here, we introduce force zones across the droplet base and use a local force balance model to explain wetting transition on engineered nanoporous microstructures, utilizing a critical force per unit length (FPL) value. For the first time, we provide a universal scale using the concept of the critical FPL value which enables comparison of various superhydrophobic surfaces in terms of preventing wetting transition during liquid evaporation. In addition, we establish the concept of contact line-fraction theoretically and experimentally by relating it to area-fraction, which clarifies various arguments about the validity of the Cassie-Baxter equation. We use the contact line-fraction model to explain the droplet contact angles, liquid evaporation modes, and depinning mechanism during liquid evaporation. Finally, we develop a model relating a droplet curvature to conventional beam deflection, providing a framework for engineering pressure stable superhydrophobic surfaces.

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Universal wetting transition of an evaporating water droplet on hydrophobic micro- and nano-structures

Cited by 46 publications

References 62 publications

Drops on a Superhydrophobic Hole Hanging On under Evaporation

Drops on a Superhydrophobic Hole Hanging On under Evaporation

Variation in Tree Species Ability to Capture and Retain Airborne Fine Particulate Matter (PM2.5)

Explaining Evaporation-Triggered Wetting Transition Using Local Force Balance Model and Contact Line-Fraction

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