Wenzel to Cassie transition during droplet impingement on a superhydrophobic surface

Clavijo, Cristian; Crockett, Julie; Maynes, Daniel

doi:10.1103/physrevfluids.1.073902

Cited by 14 publications

(7 citation statements)

References 54 publications

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“…However, an approximately elliptical morphology of a droplet was also observed, and the droplet was found to be more likely to spread along the groove direction rather than the perpendicular direction from the overhead perspective at We = 14.4. This finding corresponds well to droplet behavior on other anisotropic substrates [32][33][34][35] , as shown in Figure S5B (see Supporting Movie 3).…”

Section: Coupling Effect Of the Translational Motion And Oriented Included Anglesupporting

confidence: 86%

Nonwet Kingfisher Flying in the Rain: The Tumble of Droplets on Moving Oriented Anisotropic Superhydrophobic Substrates

Zheng

Zhang

Wang

et al. 2020

ACS Appl. Mater. Interfaces

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Extensive studies of anti-wetting have been restricted to stationary substrates, while dewetting mechanisms on moving interfaces are still poorly understood. Due to the hydrophobic and anisotropic surface characteristics of kingfishers, they are able to easily change flight direction even under highintensity precipitation. The present study aims to mechanistically analyze how the synergy of interfacial movement, anisotropy, and superhydrophobicity affects rapid dehydration. We have designed a droplet-conveyor system to simulate the bouncing of droplets on moving anisotropic superhydrophobic targets and performed simulations via the lattice Boltzmann algorithm. The moving interface can induce a directional tumbling behavior of the droplet and effectively avoid continuous wetting in the same region. We found that droplet tumbling is essentially caused by transformed depinning velocity vectors at interface the downstream. Also, the hang time of a tumbling droplet is positively related to the angle between the motion vector and the texture. The oriented anisotropic motion facilitates the tumbling of droplets and decreases their hang time by up to 23% as compared to that on a stationary inclined superhydrophobic surface. Similar interfacial process dehydration also occurs on a non-wet kingfisher flying in the rain, and we believe that these findings provide valuable new insights for high-efficiency water repellency of surfaces.

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Section: Coupling Effect Of the Translational Motion And Oriented Included Anglesupporting

confidence: 86%

Nonwet Kingfisher Flying in the Rain: The Tumble of Droplets on Moving Oriented Anisotropic Superhydrophobic Substrates

Zheng

Zhang

Wang

et al. 2020

ACS Appl. Mater. Interfaces

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“…Minimized atomization during contact boiling is attributed to the hydrophobic texture (micro-pillars) and rationalized as follows. First, the pillars do not permit liquid intrusion into the open space between them (even if liquid penetrates at the impingement point due to stagnation pressure, it is likely that the liquid returns to the Cassie state due to the elevated temperature of the surface [38]). The prevailing Cassie state results in a reduction of contact area between solid and liquid (solid fraction is 11% for the current case) and thus heat transfer to the liquid is decreased.…”

Section: High Speed Imaging Of Atomizationmentioning

confidence: 99%

Hydrodynamics of droplet impingement on hot surfaces of varying wettability

Clavijo

Crockett

Maynes

2017

International Journal of Heat and Mass Transfer

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This work presents on the hydrodynamics of water droplet impingement on superheated solid surfaces across the entire wettability spectrum: superhydrophilic, hydrophilic, hydrophobic and superhydrophobic. While a large body of work exists on droplet impingement on hydrophilic and superhydrophilic surfaces, impingement on the latter two has been largely neglected and the present results show that dynamics are dramatically different. Experiments ranging in surface temperature from 125 • C to 415 • C and Weber numbers from 10 to 225 were performed and analyzed using high-speed imaging. Some of the most striking differences are as follows. While atomization is always present for impingement on the hydrophilic and superhydrophilic surfaces at temperatures below the Leidenfrost point, atomization is absent at low Weber numbers and at low excess surface temperatures on the hydrophobic surface. At high surface temperatures, the attraction of vapor bubbles on the hydrophobic surface allows a vapor blanket to form more readily thus leading to Leidenfrost behavior at a much lower temperature than classically observed on a hydrophilic surface. One of the most interesting phenomenon that will be discussed includes what will be described as a "pseudo-Leidenfrost" state for impingement on the superhydrophobic surface. Because water can be suspended at the peaks of the roughness on a superhydrophobic interface, vapor escapes from underneath the droplet thus mimicking Leidenfrost behavior for all excess temperatures. This results in minimal atomization for superhydrophobic impingement over the entire regime explored. Finally, maximum spread diameters for Leidenfrost impingement are tabulated as a function of the Weber number for all surfaces and are shown to be larger on the smooth surfaces than on the textured ones indicating that droplet spreading at the Leidenfrost point is not independent

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“…θ a and θ a,0 are respectively the apparent advancing angle of the rough surface (e.g., the prepared Surf_1 and Surf_2 in this work) and the true advancing angle for a smooth substrate (as seen in the supporting information of Table S1). Of note the expressions by the two equations were derived without consideration of external disturbances such as phase change [46], hydraulic pressure [42], kinetic impact [47], etc. Direct experimental evidences have shown that a rough surface satisfying the two criteria can still undergo wetting transition from Cassie's mode to Wenzel's mode upon a small external disturbance [48].…”

Section: Theoretical Analysismentioning

confidence: 99%

Wetting transition of sessile and condensate droplets on copper-based superhydrophobic surfaces

Zhao

Zhang

Wang

et al. 2018

International Journal of Heat and Mass Transfer

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Wenzel to Cassie transition during droplet impingement on a superhydrophobic surface

Cited by 14 publications

References 54 publications

Nonwet Kingfisher Flying in the Rain: The Tumble of Droplets on Moving Oriented Anisotropic Superhydrophobic Substrates

Nonwet Kingfisher Flying in the Rain: The Tumble of Droplets on Moving Oriented Anisotropic Superhydrophobic Substrates

Hydrodynamics of droplet impingement on hot surfaces of varying wettability

Wetting transition of sessile and condensate droplets on copper-based superhydrophobic surfaces

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