Dropwise condensation on superhydrophobic surfaces with two-tier roughness

Chen, Chuan‐Hua; Cai, Qingjun; Tsai, C. C.; Chen, Chung‐Lung; Xiong, Guangyong; Yu, Ying; Z, Ren

doi:10.1063/1.2731434

Cited by 322 publications

(300 citation statements)

References 18 publications

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“…Note that, recently, Boreyko and Chen [29] reported a spontaneous drop removal as a result of surface energy released due to the drop coalescence during condensation. In contrast to our study, those coalescing water drops have large contact angle ≈170 o (as can be estimated from their movie and [22]), hence the pinning forces on the surface of the drop contact line are quite small, making possible spontaneous drop removal. In addition, the critical angle is Â c (≈94 o ) < Â (≈101 o ) [22], which means that the Cassie-Baxter state is the most favorable state.…”

Section: Resultsmentioning

confidence: 43%

“…In contrast to our study, those coalescing water drops have large contact angle ≈170 o (as can be estimated from their movie and [22]), hence the pinning forces on the surface of the drop contact line are quite small, making possible spontaneous drop removal. In addition, the critical angle is Â c (≈94 o ) < Â (≈101 o ) [22], which means that the Cassie-Baxter state is the most favorable state. In contrast, in our case, the critical angle is Â c (≈135 o ) > Â (≈75 o ) , making the Wenzel state the most favorable state.…”

Section: Resultsmentioning

confidence: 43%

“…In contrast, and although this process is of major importance for the evaluation of corrosion, the studies of condensation-induced wetting on superhydrophobic surface and their corresponding wetting properties (self-cleanliness, different wetting states), are much less documented [18][19][20][21][22][23][24][25][26][27][28][29]. The aim of the present work is thus to study condensation of water on a multiscale rough superhydrophobic surface where the contact angle is varied in a wide range (70-150 • ).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Water condensation on zinc surfaces treated by chemical bath deposition

Narhe

González-Viñas

Beysens

2010

Applied Surface Science

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a b s t r a c tWater condensation, a complex and challenging process, is investigated on a metallic (Zn) surface, regularly used as anticorrosive surface. The Zn surface is coated with hydroxide zinc carbonate by chemical bath deposition, a very simple, low-cost and easily applicable process. As the deposition time increases, the surface roughness augments and the contact angle with water can be varied from 75 • to 150 • , corresponding to changing the surface properties from hydrophobic to ultrahydrophobic and superhydrophobic. During the condensation process, the droplet growth laws and surface coverage are found similar to what is found on smooth surfaces, with a transition from Cassie-Baxter to Wenzel wetting states at long times. In particular, it is noticeable in view of corrosion effects that the water surface coverage remains on order of 55%.

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Section: Resultsmentioning

confidence: 43%

Section: Resultsmentioning

confidence: 43%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Water condensation on zinc surfaces treated by chemical bath deposition

Narhe

González-Viñas

Beysens

2010

Applied Surface Science

View full text Add to dashboard Cite

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“…In principle, any sub-microscale structures with a small feature size (tip size and interspace) and a certain height (or depth) can become effective candidates for creating CMDSP surfaces. In fact, except for arrays of closely packed nanotips, including nanocones, [22,27,50,69,70] nanoneedles, [21,28,31,66,71] nanopencils, [23] and tip-like nanotubes, [72,73] other architectures such as nano wires, [24,74] nanosheet arrays, [20,29,62,75] nanorod-capped nano pores, [68,76] the porous structure of nanoparticles, [67] nanoparticle aggregates, [73,[77][78][79][80] and two-tier structures [25,57,63,[81][82][83][84][85][86][87][88][89] have all been verified to be effective in endowing material surfaces with the desired CMDSP functionality as long as they follow these basic construction rules.…”

Section: Construction Rules Of Bionic Cmdsp Surfacesmentioning

confidence: 99%

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

2017

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interest has focused on utilizing the lowadhesivity nature of superhydrophobic surfaces for the rapid removal of condensate microdrops, as this has significance in fundamental research and technological innovation. Example applications are the enhancement of condensation heat transfer for high-efficiency thermal management and energy utilization, [20][21][22][23][24][25] energy-effective antifreezing for airconditioner heat exchangers and aircraft wings, [26][27][28] and electrostatic energy harvesting. [29] In general, condensate drops on typical flat hydrophobic surfaces are only shed off under gravity when their sizes are comparable to the capillary length (≈2.7 mm for water), [30] which creates undesirable effects such as large thermal resistance [20][21][22][23][24][25] and the freezing of subcooled drops. [26][27][28] Clearly, a great challenge is the timely removal of condensate drops at the microscale where the gravitational effect does not work. The latest research has indicated that these small-scale condensate microdrops may self-remove via mutual coalescence as long as the coalescence-released excess surface energy is larger than the interface adhesion-induced energy dissipation. [31] Much effort has been devoted to exploring the utilization of knowledge of bionic low-adhesivity superhydrophobicity to develop innovative condensate microdrop self-propelling (CMDSP) surfaces. Different from traditional superhydrophobic surfaces, which are characterized by the bouncing or rolling off of deposited millimeter-size large drops, [32,33] CMDSP surfaces support the self-removal capability of smallscale condensate microdrops. It has been reported that classical superhydrophobic lotus leaves (Figure 1a), [34][35][36][37] as well as artificial surfaces consisting of hierarchical micro-and nanostructures, [38] one-tier microstructures, [39][40][41][42][43] or nanostructures [44,45] with larger characteristic interspaces, present a low-adhesivity property to the deposited water macrodrops, but become highly adhesive to condensed microdrops (Figure 1b). This is because moisture easily penetrates the microscale valleys or cavities. Clearly, superhydrophobic surfaces with irrationally designed surface structures can enhance the solid-liquid interfacial adhesion instead of promoting the rapid removal of condensed drops. Accordingly, it is still a challenge to design and fabricate very effective low-adhesivity superhydrophobic surfaces with the self-removal ability of condensate microdrops. Recently, there has been a large breakthrough in understanding the mechanism and construction rules of bionic CMDSP surfaces, leading to the exploration of fabrication methods for the surface functionalization of widely used metal materials and the Bionic condensate microdrop self-propelling (CMDSP) surfaces are attracting increased attention as novel, low-adhesivity superhydrophobic surfaces due to their value in fundamental research and technological innovation, e.g., for enhancing heat transfer, energy-effective antifreezing, and...

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“…Therefore, the third condition for realizing hydrophobicity is to lower the surface energy of the solid and reduce the contact area of the liquid-solid interface as much as possible so as to reduce the flow resistance of liquid droplets on the solid surface. At present, this characteristic is often represented by the size of the rolling angle or the retardation angle [18], of which the two calculation methods are related to the values of the advance angle and the receding angle of the liquid droplets [19,20]. The authors of this study believe that this representation method did not reflect the internal causes affecting the hydrophobicity.…”

Section: The Effective Work Of Adhesionmentioning

confidence: 79%

Hydrophobic mechanism and criterion of lotus-leaf-like micro-convex-concave surface

2011

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According to the principle that the contact angle of liquid droplet always increases on a limited liquid-solid interface, it is suggested that the integration of many small-size limited liquid-solid interfaces results in the increase of the hydrophobicity of lotus-leaf-like micro-convex-concave surfaces. Mathematical equations of the stability of liquid-droplets on the surface of lotus-leaf-like structure were established. The relationship between the theoretical critical-radius of the void of micro-convex-concave surface and the nature of the solid and the liquid was drawn. The three conditions of realizing hydrophobicity were described. The result of computation has shown that when the radius of the void of micro-concave-convex surface is less than the theoretical critical-radius r c, the droplets may always be in a stable state on the solid surface with the contact angle greater than 90°. The minimum area of the liquid-solid interface and low surface energy of solids are important factors in realizing hydrophobicity. The effective work of adhesion W a ′ was proposed as a criterion for measuring the hydrophobic ability of the solid surface. Water droplets fall on lotus leaf surface to form free rolling water globules. The exploration on hydrophobic mechanism of the lotus leaf surface has become a hot spot in the field of artificially preparing bionic hydrophobic and self-cleaning materials. In recent years, the research on new hydrophobic materials has continually achieved remarkable achievements in the fields of chemical engineering, daily use sanitary wares, clothing, fluid drag reduction, mechanical anti-corrosion and so on. After long-term observations, the researchers have found [1-3] that there are very complex multiple micron and nano-scale structures on the lotus leaf surface. It can be clearly seen under the scanning electron microscope that the lotus leaf surface has many small papillae, on the surface of each of which there are a lot of "hill" shaped convex top with the diameter of about 200 nm. The sunken parts between the papillae and the "hills" are filled *Corresponding author (email: zdy7081@163.com) with air. When rainwater lands on the leaf surface, it only constitutes partial point contact with the "hill" shaped convex top on the leaf surface. Researches have shown that, the micro-nano-structured morphology exists not only in the lotus leaf surface but also in the surface of other plants and skin of some animals [4]. However, the current research only clarifies the special constructs of the surface of hydrophobic materials, that is, the hydrophobic material should have a rough surface and low surface energy [5,6]. However, researches on the reason why the contact angle of rough surface is greater than that of smooth surface and the quantitative researches on the microstructure size are not sufficient. Wenzel [7] proposed that water droplets were completely wetted on the rough surface, whose apparent contact angle could be expressed as: cosθ r =rcosθ, where r was the surface roughness. He ...

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Dropwise condensation on superhydrophobic surfaces with two-tier roughness

Cited by 322 publications

References 18 publications

Water condensation on zinc surfaces treated by chemical bath deposition

Water condensation on zinc surfaces treated by chemical bath deposition

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

Hydrophobic mechanism and criterion of lotus-leaf-like micro-convex-concave surface

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