Water Droplets’ Internal Fluidity during Horizontal Motion on a Superhydrophobic Surface with an External Electric Field

Sakai, Munetoshi; Kono, Hiroki; Nakajima, Akira; Sakai, Hideki; Abe, Masahiko; Fujishima, Akira

doi:10.1021/la903730k

Cited by 19 publications

(15 citation statements)

References 19 publications

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“…The dielectrophoretic force is important when the electric field is unequal for water droplets. 41 It is commonly remarkable at the instant of applying voltage. However, the initial position of the water droplet was at the middle position between electrodes on the SLBC.…”

Section: Resultsmentioning

confidence: 99%

Static and dynamic hydrophobicity of alumina-based porous ceramics impregnated with fluorinated oil

et al. 2014

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Using phase separation, alumina-based porous ceramics with three-dimensional frameworks were prepared, with fine structural roughness created by subsequent hot-water treatment. The pore volume of the porous alumina and its specific surface area increased concomitantly with increasing hot-water treatment time. Porous alumina/fluorinated oil bulk composites were prepared by coating hydrophobic silane onto the porous ceramic surface and subsequently impregnating fluorinated oil. A wetting ridge formed at the bottom of the water droplets on the composites. Partial contact between the water and solid surface was inferred from a comparison of interface energies in the system. The composites provided a smaller sliding angle (SA) than that of the sample without impregnating fluorinated oil. The composite with fine roughness exhibited longer sustainability of a small SA than that without fine roughness. Particle image velocimetry revealed that the dominant sliding mode for water droplets on this composite was slipping. The droplets moved on the surface under an external electric field. Coulombic force contributes to this motion.

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Section: Resultsmentioning

confidence: 99%

Static and dynamic hydrophobicity of alumina-based porous ceramics impregnated with fluorinated oil

et al. 2014

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“…In their system, the Coulomb force of the electric charge provided to the water from the solid surface was the dominant driving force for water droplet movement. Recently, the internal fl uidity of water droplets during transportation on superhydrophobic surface by an external electric fi eld has also been analyzed using a particle image velocimetry system, revealing that the droplet undergoes slipping motion and that dielectrophoretic force plays an important role in movement by an electric fi eld [96].…”

Section: Control Of Water Droplets On Solid Surfacesmentioning

confidence: 99%

Design of hydrophobic surfaces for liquid droplet control

Nakajima

2011

NPG Asia Mater

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During rainfall, small water droplets can be observed to roll off hydrophobic umbrella surfaces at diff erent speeds. A droplet on a round hydrophobic surface does not always slide down on the surface easily at a small tilt angle, but even if it does, large moving acceleration is not always observed. What determines the motion of droplets on solid surfaces?Diff erences in droplet shape on solid surfaces are often explained by variations in wettability. Th e wetting of a solid surface has persisted through the ages as a research subject at the border between physics and chemistry. Wettability control of a solid against a liquid has been widely explored in industry for application in daily life because it can engender various physical and chemical phenomena related to solids and liquids. Wettability is an important property of solid surfaces from both fundamental and practical aspects. Th e degree of adhesion of liquid droplets onto a solid surface is commonly described in terms of the contact angle (θ), which is given by Young's equation aswhere γ sv , γ sl , and γ lv represent the interfacial free energies per unit area of the solid-gas, solid-liquid and liquid-gas interfaces. Although the defi nition and measurement of the contact angle are simple and easy, the nature of wettability is complex because it is related to three phases: solid, liquid and gas. Moreover, various factors aff ect the surface wettability of a solid. When one factor of a solid surface such as roughness is altered, other factors such as the surface topography or its chemical composition often change simultaneously. Th erefore, it is usually diffi cult to discuss the results of surface wettability obtained from experiments while retaining academic rigor. Th e main research interest for industrial materials is the behavior of millimeter-size droplets on a solid surface of more than a few centimeters in area. Th erefore, the discussion of wettability among samples with great diff erences in surface character is sometimes conducted with ignorance of the infl uence of other characteristics.Hydrophobic coatings are extremely important for wettability control. Th e coatings are anticipated for various industrial uses such as anti-wetting, anti-snow (or ice), anti-rust and reduced friction resistance by reducing solid-liquid interaction. Generally, a hydrophobic surface is one on which water forms a round droplet that is easily removed. Recent advances in probe microscopy and surface spectroscopy and the wider availability of such techniques have revealed that macroscopic surface hydrophobicity, especially dynamic hydrophobicity, is aff ected by nanolevel characteristics such as structure, chemical composition and their alignment and homogeneity. Th e expected properties for a hydrophobic surface cannot always be obtained unless precise design and control of the solid surface are applied. Th is report presents the results of recent studies on the design of hydrophobic surfaces for droplet removal or control from the viewpoint of materials science....

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“…The interactions between the droplet and the microstructures at the edge of the contact area during sliding have been investigated using high-speed cameras [12][13][14]. Moreover, the rolling motion inside the sliding droplets has also been observed by mixing nanoparticles with the droplet [15,16]. Nevertheless, it remains difficult to clarify the interaction between the droplet and each microstructure inside of the contact area because the inner contact area during sliding motion cannot be observed.…”

Section: Introductionmentioning

confidence: 99%

Two-axis MEMS-based force sensor for measuring the interaction forces during the sliding of a droplet on a micropillar array

Nguyen

Takahashi

Matsumoto

et al. 2015

Sensors and Actuators A: Physical

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Water Droplets’ Internal Fluidity during Horizontal Motion on a Superhydrophobic Surface with an External Electric Field

Cited by 19 publications

References 19 publications

Static and dynamic hydrophobicity of alumina-based porous ceramics impregnated with fluorinated oil

Static and dynamic hydrophobicity of alumina-based porous ceramics impregnated with fluorinated oil

Design of hydrophobic surfaces for liquid droplet control

Two-axis MEMS-based force sensor for measuring the interaction forces during the sliding of a droplet on a micropillar array

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