Zipping Effect on Omniphobic Surfaces for Controlled Deposition of Minute Amounts of Fluid or Colloids

Dufour, Renaud; Brunet, Philippe; Harnois, Maxime; Boukherroub, Rabah; Thomy, V.; Senez, V.

doi:10.1002/smll.201101895

Cited by 76 publications

(56 citation statements)

References 24 publications

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“…Superhydrophobic coatings can enhance (16) or reduce (17) adsorption of cells or proteins. Minute amounts of proteins or biomolecules can be deposited on arrays of micropillars, offering promising routes to sensitive high-throughput analysis on laboratory-on-chip benches (18). Patterned superhydrophobic coatings provide new strategies to guide drops (19) or to tune drop adhesion (20).…”

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confidence: 99%

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How superhydrophobicity breaks down

Papadopoulos

Mammen

Deng

et al. 2013

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

432

442

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A droplet deposited or impacting on a superhydrophobic surface rolls off easily, leaving the surface dry and clean. This remarkable property is due to a surface structure that favors the entrainment of air cushions beneath the drop, leading to the so-called Cassie state. The Cassie state competes with the Wenzel (impaled) state, in which the liquid fully wets the substrate. To use superhydrophobicity, impalement of the drop into the surface structure needs to be prevented. To understand the underlying processes, we image the impalement dynamics in three dimensions by confocal microscopy. While the drop evaporates from a pillar array, its rim recedes via stepwise depinning from the edge of the pillars. Before depinning, finger-like necks form due to adhesion of the drop at the pillar's circumference. Once the pressure becomes too high, or the drop too small, the drop slowly impales the texture. The thickness of the air cushion decreases gradually. As soon as the water-air interface touches the substrate, complete wetting proceeds within milliseconds. This visualization of the impalement dynamics will facilitate the development and characterization of superhydrophobic surfaces.micropillars | pinning | wetting transition | contact angle | lithography | self-cleaning | hysteresis

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confidence: 99%

“…Even the timescale of the impalement transition remains unclear. So far, most detailed information was obtained by highspeed video microscopy (18,40) and scanning electron microscopy (18,25). However, neither of these techniques provides quantitative 3D information.…”

mentioning

confidence: 99%

How superhydrophobicity breaks down

Papadopoulos

Mammen

Deng

et al. 2013

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

432

442

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“…In most of the cases, a liquid Cassie-Baxter state drop evaporating on a superhydrophobic surface will eventually suffer a wetting transition into a Wenzel state, i.e., it will get impaled into the structure and loose its spherical shape (14,15). Here, however, we use a surface that combines overhanging pillared structures (16,17) with a hierarchical nanostructure (Fig. 2C).…”

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confidence: 99%

Building microscopic soccer balls with evaporating colloidal fakir drops

Marin

Gelderblom

Susarrey-Arce

et al. 2012

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

124

104

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Evaporation-driven particle self-assembly can be used to generate three-dimensional microstructures. We present a unique method to create colloidal microstructures in which we can control the amount of particles and their packing fraction. To this end, we evaporate colloidal dispersion droplets on a special type of superhydrophobic microstructured surface, on which the droplet remains in Cassie-Baxter state during the entire evaporative process. The remainders of the droplet consist of a massive spherical cluster of the microspheres, with diameters ranging from a few tens up to several hundreds of microns. We present scaling arguments to show how the final particle packing fraction of these balls depends on the dynamics of the droplet evaporation, particle size, and number of particles in the system. superhydrophobicity | microparticle deposition E vaporation-driven particle self-assembly is an ideal mechanism for constructing micro-and nanostructures at scales where direct manipulation is impossible. For example, in colloidal dispersion droplets with pinned contact lines, evaporation gives rise to the so-called coffee stain effect (1): A capillary flow drags the particles toward the contact line to form a ring-shaped stain. Such a flow not only aggregates the particles, but is also able to organize them in crystalline phases (2-5). Similar mechanisms such as the convective assembly (6, 7) are currently successfully used to produce two-dimensional colloidal crystal films. To obtain three-dimensional clusters of microparticles, colloidal dispersion droplets can be dried suspended in emulsions (8-10), in spray dryers (11, 12), or kept in Leidenfrost levitation (13). The main drawback of these three-dimensional assembly techniques, however, is the lack of control on both the amount of particles and the particle arrangement in the remaining structures.In this work, we devise a unique, controlled way of generating on-demand self-assembled spherical microstructures via droplet evaporation on a superhydrophobic surface (Fig. 1). We present scaling arguments to predict the particle arrangement in the microstructures formed, based on the dynamics of the evaporation process. To generate the microstructures, we evaporate colloidal dispersion droplets on a special type of superhydrophobic substrates. In most of the cases, a liquid Cassie-Baxter state drop evaporating on a superhydrophobic surface will eventually suffer a wetting transition into a Wenzel state, i.e., it will get impaled into the structure and loose its spherical shape (14, 15). Here, however, we use a surface that combines overhanging pillared structures (16, 17) with a hierarchical nanostructure (Fig. 2C). These surface properties impose a huge energy barrier for the wetting transition to occur, and therefore the droplet will remain almost floating over the structure in a Cassie-Baxter state during its entire life (18).A typical result can be observed in Fig. 1 (see also Movie S1: A water droplet containing 1 μm soluble polystyrene particles (initial concen...

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“…9 and 10 originates from the fact that our model is built on experimental observation where water meniscus cleanly detached from hydrophobic microstructures before jumping to the next. On super-repellent surfaces made of hydrophilic materials, in contrast, the meniscus is known to be pinched off before jumping 34 phenomenon not accounted for in our current model. To investigate such an unusual case, one would need a repellent surface made of hydrophilic microstructures with unambiguous liquidsolid fraction 33 and the ability to measure the local angle at pinching-off on the microstructures.…”

Section: Figurementioning

confidence: 86%