In Situ Wetting State Transition on Micro- and Nanostructured Surfaces at High Temperature

Wang, Jingming; Liu, Meng; Ma, Rui; Wang, Qianbin; Jiang, Lei

doi:10.1021/am5034457

Cited by 30 publications

(20 citation statements)

References 49 publications

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“…In this context, it is worth exhibiting monostable Cassie states where even an accidental transition to the undesired Wenzel state, due to force fluctuations such as encountered in an impact (37) or to pressure applied on the liquid (16,17,33,(46)(47)(48)(49)(50), can be repaired owing to the absence of barrier between both states. Because reported Wenzel-to-Cassie (W2C) transitions generally involve either an external energy input (17,49,(51)(52)(53) or a potential energy release (35,(54)(55)(56), monostable Cassie states might be seen as unreal (57), but we describe here such situations and criteria for achieving them. Our hope is that these findings will shed new light on our fundamental understanding of water repellency.…”

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confidence: 99%

Monostable superrepellent materials

Quéré

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

104

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Superrepellency is an extreme situation where liquids stay at the tops of rough surfaces, in the so-called Cassie state. Owing to the dramatic reduction of solid/liquid contact, such states lead to many applications, such as antifouling, droplet manipulation, hydrodynamic slip, and self-cleaning. However, superrepellency is often destroyed by impalement transitions triggered by environmental disturbances whereas inverse transitions are not observed without energy input. Here we show through controlled experiments the existence of a "monostable" region in the phase space of surface chemistry and roughness, where transitions from Cassie to (impaled) Wenzel states become spontaneously reversible. We establish the condition for observing monostability, which might guide further design and engineering of robust superrepellent materials.repellency | Cassie state | monostability | interfaces | dewetting W ater repellency describes the ability of materials to repel water and make it flow with negligible friction and adhesion, compared with usual situations. It is achieved by combining chemical hydrophobicity with micro-and/or nanotextures (1, 2). Water meeting such materials remains at the textures' tops, which generates a composite interface made of hydrophobic solid and air trapped inside the textures (Cassie state) (3). As a consequence, water hardly contacts these solids on which its dynamical behaviors are spectacular (4-7). Repellency also holds if the liquid has a higher surface tension than water (salty water, mercury); using special texture designs, it can even be extended to liquids with smaller surface tension (8), and/or to water at small scale (such as dew) (9, 10), so it was proposed (11) to call such materials "superhygrophobic," from the Greek "hygros" meaning humid.Repellent materials are classically found in nature, in particular at the surface of many plants and insects, two situations where the control of water is crucial for surviving (1, 12). It was reported that these natural surfaces often (yet not always) exhibit dual structures, with microbumps on the scale of 10-100 μm coated by nanostructures of typically 100 nm (1). This results in an amplification of static (13-17) and dynamical (18) repellency, because we can then expect the generation of composite solid/air interfaces at different scales--where we mean by amplification an improved nonwettability (13-15, 17) and a smaller adhesion (16,18,19), two factors that contribute to the liquid mobility.This field of research has been very active for about 20 years, with theoretical, experimental, and computational viewpoints. Researchers discussed the surface energy of materials having different kinds of structures (20-23), various adhesion properties (24-26), diverse geometries of solid-liquid-vapor contact lines (27, 28), or flow interactions between the liquid and its substrate (29-32). In many studies, model hydrophobic textures (such as lines or pillars) were considered, and wetting was found to be usually "bistable": Depending on the history o...

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confidence: 99%

Monostable superrepellent materials

Quéré

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

104

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“…They also process a novel superhydrophobic surface preparation method to fabricate micro/nano structures on an Al mold with intensive conical holes by nanosecond laser drilling and HCl etching for droplet pancake bouncing [10]. Under the assistance of air film between water and hydrophobic solid surface, these structures can reduce the contact area between solid and liquid with obviously reducing the friction drag [11][12][13][14][15]. Therefore, achieving the favorable performance of the superhydrophobic surface has attracted more attentions of researchers while researches about drag reduction were still an urgent need in various fields [16,17].…”

Section: Introductionmentioning

confidence: 99%

Drag reduction of stable biomimetic superhydrophobic steel surface by acid etching under an oxygen-sufficient environment

Rong

Zhang

Mao

et al. 2020

Mater. Res. Express

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Superhydrophobic surfaces have shown utility applications in drag reduction field. A novel method based on simulation analysis and test experiments is proposed to fabricate a superhydrophobic surface with 3D flower-like micro and nano-structures on a steel ball under an O 2 rich environment. The superhydrophobic steel surface has water CA of 166±1.5°. The sliding angle is less than 2°. The experiment and the simulation of the superhydrophobic and the untreated steel ball fall under water are built to prove the validity of the method of reducing water resistance. The drag reduction ratio of the superhydrophobic steel ball is beyond 53% opposed to the untreated surface under water. A model simulation is built to simulate and analyze the solid-liquid interface drag reduction mechanism of superhydrophobic surface based on theoretical analysis. The result testifies the rationality of the drag reduction experiment.

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“…These include locally reduced pressure from above the surface 16 , vibration, 17 droplet coalescence, 18 back pressure from beneath the surface, 19 and high temperature. 20,21 However these have not been shown to be appropriate for reversing the wetting transition when the superhydrophobic surface is fully submersed.…”

Section: Introductionmentioning

confidence: 99%

Active gas replenishment and sensing of the wetting state in a submerged superhydrophobic surface

2017

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Previously superhydrophobic surfaces have demonstrated effective drag reduction by trapping a lubricious gas layer on the surface with micron-sized hydrophobic features. However, prolonged reduction of drag is hindered by the dissolution of the gas into the surrounding water. This paper demonstrates a novel combination of superhydrophobic surface design and electrochemical control methods which allow quick determination of the wetted area and a gas replenishment mechanism to maintain the desirable gas filled state. Electrochemical impedance spectroscopy is used to measure the capacitance of the surface which is shown to be proportional to the solid/liquid interface area. To maintain a full gas coverage for prolonged periods the surface is held at an electrical potential which leads to hydrogen evolution. In the desired gas filled state the water does not touch the metallic area of the surface, however after gas has dissolved the water touches the metal which closes the electrochemical circuit causing hydrogen to be produced replenishing the gas in the surface and returning to the gas filled state; in this way the system is self-actuating. This type of surface and electrochemical control shows promise for applications where the gas filled state of superhydrophobic surfaces must be maintained when submerged for long periods of time.

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In Situ Wetting State Transition on Micro- and Nanostructured Surfaces at High Temperature

Cited by 30 publications

References 49 publications

Monostable superrepellent materials

Monostable superrepellent materials

Drag reduction of stable biomimetic superhydrophobic steel surface by acid etching under an oxygen-sufficient environment

Active gas replenishment and sensing of the wetting state in a submerged superhydrophobic surface

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