The fastest drop climbing on a wet conical fibre

Li, Erqiang; Thoroddsen, Sigurður T.

doi:10.1063/1.4805068

Cited by 23 publications

(17 citation statements)

References 22 publications

(18 reference statements)

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“…2D and Fig. S2), and thus an asymmetric surface energy landscape, which permits a motion (12)(13)(14)(15). A simple argument allows us to understand the origin of the driving force.…”

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confidence: 99%

Self-removal of condensed water on the legs of water striders

Wang

Yao

Liu

et al. 2015

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

216

175

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The ability to control drops and their movements on phobic surfaces is important in printing or patterning, microfluidic devices, and water-repellent materials. These materials are always micro-/nanotextured, and a natural limitation of repellency occurs when drops are small enough (as in a dew) to get trapped in the texture. This leads to sticky Wenzel states and destroys the superhydrophobicity of the material. Here, we show that droplets of volume ranging from femtoliter (fL) to microliter (μL) can be self-removed from the legs of water striders. These legs consist of arrays of inclined tapered setae decorated by quasi-helical nanogrooves. The different characteristics of this unique texture are successively exploited as water condenses, starting from selfpenetration and sweeping effect along individual cones, to elastic expulsion between flexible setae, followed by removal at the anisotropic leg surface. We envision that this antifogging effect at a very small scale could inspire the design of novel applicable robust water-repellent materials for many practical applications.water strider | water repellency | self-propulsion | antifogging | breath figure W hen a vapor condenses on a rough hydrophobic surface, liquid nuclei naturally appear within the roughness, forming tiny droplets stuck in the texture (1-3). Without the assistance of external forces, dew tightly adheres to the surface in the so-called Wenzel state, which most often destroys the superhydrophobicity of the material (4, 5). An applicable robust water-repellent surface thus requires an additional mechanism to expel these condensates from the texture (6). It has been reported in the literature that nanotextures (such as found on the surface of lotus leaves or cicada wings) might generate adhesion forces small enough to permit an efficient conversion of surface energy (coming from droplet coalescence) into kinetic energy, so that droplets can be mobilized (7-9). However, contact angle hysteresis effects are generally dominant at a small scale, so that a key challenge for antifogging materials lies in the generation of a force able to expel droplets from microtextures.Water striders (Gerris remigis, Fig. 1A) living at the water surface in a highly humid environment offer a remarkably simple solution to this problem. Without any external force, tiny condensed droplets in the range of femtoliters (fL) to microliters (μL) get removed from striders' legs, owing to the presence of oriented conical setae. A Gerris leg is a centimeter-size cylinder (of typical diameter 150 μm) decorated by an array of inclined tapered hairs characterized in Fig. 1 B and C by micro X-ray computed tomography (XCT) and scanning electron microscopy (SEM). Individual setae have a length L = 40-50 μm, a maximum diameter of ∼3 μm, and an apex angle of ∼5°. They make regular arrays with a mutual distance of 5-10 μm, and are tilted by an angle β = 25-35°to the base of the leg (Fig.

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“…2D and Fig. S2), and thus an asymmetric surface energy landscape, which permits a motion (12)(13)(14)(15). A simple argument allows us to understand the origin of the driving force.…”

mentioning

confidence: 99%

Self-removal of condensed water on the legs of water striders

Wang

Yao

Liu

et al. 2015

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

216

175

View full text Add to dashboard Cite

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“…Most of the previous studies consider the motion of axisymmetrical barrel shape droplets moving on conical substrates. The models are based on a driving force coming from a gradient of the Laplace pressure along the surface of the droplet [19,22]. In our case, the barrel shape is not axisymmetrical due to gravitational effects.…”

Section: A Barrel Shapementioning

confidence: 99%

“…Those cones were created by pulling a cylindrical copper wire out of an acid bath. Other studies used different ways to manufacture conical fibers like pulling glass [22][23][24][25], using an electrochemical corrosion gradient [26] or even polishing brass [27]. According to the relative size of the fiber and of the droplet, the droplet on cylindrical and conical fibers can present two distinct geometries: barrel or clamshell [28].…”

Section: Introductionmentioning

confidence: 99%

Capillary transport from barrel to clamshell droplets on conical fibers

et al. 2021

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Droplets spontaneously move when they are placed at the tip of a cone surface. Using three dimensionally printed structures, we experimentally explore a large panel of configurations regarding the aperture angle of the cone. We evidence a change of the droplet geometry while moving along the conical fiber. This transition is a switch of configuration from barrel to clamshell shape. The consequence is a change in the droplet dynamics. We estimate the position of this geometrical transition and we propose two models to describe the motion of the barrel and the clamshell droplets. While both shapes are driven by capillary forces, the dissipation is dependent on the geometrical configuration. For barrel shape droplets the main dissipation appears to be in the liquid wedge. For clamshell shape droplets the dissipation occurs mainly in the liquid film close to the conical fiber.

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“…Common to fluid coating processes is that they often require an external driving force to displace the fluid. However, when a droplet with a size smaller than the capillary length comes in contact with a conical fibre, it moves spontaneously from the tip to the base of the cone due to capillarity (Lorenceau & Quéré 2004;Li & Thoroddsen 2013). In nature, this self-propelled mechanism has been exploited by plants (Liu et al 2015) and animals (Zheng et al 2010;Wang et al 2015) to facilitate water transport at small scales.…”

Section: Introductionmentioning

confidence: 99%