Bouncing transitions on microtextured materials

Reyssat, Mathilde; Pépin, A.; Marty, F.; Chen, Y.; Quéré, David

doi:10.1209/epl/i2005-10523-2

Cited by 380 publications

(410 citation statements)

References 15 publications

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“…Although a number of simpler models than Maitra's model (Equation 2) have been proposed in order to predict the pinning threshold based on balancing PL with either the dynamic or water hammer pressure, these models do not include the effect of the droplet diameter [15,38,39]. From our own experiments, we observed that water droplets of larger diameter are significantly more prone to pinning than smaller droplets, which is demonstrated in supporting Figure S4, in which one large droplet exhibits partial rebounding behaviour, while two smaller droplets concurrently exhibit complete rebounding.…”

Section: The Impalement Transition On Superhydrophobic Surfacesmentioning

confidence: 99%

Splashing Threshold of Oblique Droplet Impacts on Surfaces of Various Wettability

Aboud

Kietzig

2015

Langmuir

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Oblique drop impacts were performed at high speeds (up to 27 m/s, We>9000) with millimetric water droplets, and a linear model was applied to define the oblique splashing threshold. Six different sample surfaces were tested: two substrate materials of different inherent surface wettability (PTFE and aluminum), each prepared with three different surface finishes (smooth, rough, and textured to support superhydrophobicity). Our choice of surfaces has allowed us to make several novel comparisons. Considering the inherent surface wettability, we discovered that PTFE, as the more hydrophobic surface, exhibits lower splashing thresholds than the hydrophilic surface of aluminum of comparable roughness. Furthermore, comparing oblique impacts on smooth and textured surfaces, we found that asymmetrical spreading and splashing behaviours occurred under a wide range of experimental conditions on our smooth surfaces, however impacts 2 occurring on textured surfaces were much more symmetrical, and one-sided splashing occurred only under very specific conditions. We attribute this difference to the air-trapping nature of textured superhydrophobic surfaces, which lowers the drag between the spreading lamella and the surface. The reduced drag affects oblique drop impacts by diminishing the effect of the tangential component of the impact velocity, causing the impact behaviour to be governed almost exclusively by the normal velocity. Finally, by comparing oblique impacts on superhydrophobic surfaces at different impact angles, we discovered that although the pinning transition between rebounding and partial rebounding is governed primarily by the normal impact velocity, there is also a weak dependence on the tangential velocity. As a result, pinning is inhibited in oblique impacts. This led to the observation of a new behaviour in highly oblique impacts on our superhydrophobic surfaces which we named the stretched rebound, where the droplet is extended into an elongated pancake shape and rebounds while still outstretched, without exhibiting a recession phase.

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Section: The Impalement Transition On Superhydrophobic Surfacesmentioning

confidence: 99%

Splashing Threshold of Oblique Droplet Impacts on Surfaces of Various Wettability

Aboud

Kietzig

2015

Langmuir

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“…If the gravitational forces acting on the solid-liquid contact overcome the shear forces, the SL contact gets de-pinned from the apex of the roughness feature, and the corresponding mechanism is called depinning (figure 1b) 20,37 figure 2i and figure 2ii). On the other hand, case IV consists of an energetically favorable Wenzel state, i.e.…”

Section: Metastable Cassie State: Geometric Orientationmentioning

confidence: 99%

“…The value of k approaches a maximum value of 0.5 for nearly elastic collisions 48 . The experiments on droplet impingement typically use a droplet speed of the order of ms -1 , for which the water hammer coefficient is typically approximated as 0.2 20,22,49 . For low velocities and high droplet volumes, the collision is known to be inelastic, which lowers the coefficient k to the order of 0.001 (equation 23) 18 .…”

Section: Surface Design For Quasi-static Robustness: Pressure Balancementioning

confidence: 99%

Design of a robust superhydrophobic surface: thermodynamic and kinetic analysis

Sarkar

Kietzig

2015

Soft Matter

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The design of a robust superhydrophobic surface is a widely pursued topic. While many investigations are limited to applications with high impact velocities (for raindrops of the order of a few m/s), the essence of robustness is yet to be analyzed for applications involving quasi-static liquid transfer. To achieve robustness with high impact velocities, the surface parameters (geometrical details, chemistry) have to be selected from a narrow range of permissible values, which often entail additional manufacturing costs. From the dual perspectives of thermodynamics and mechanics, we analyze the significance of robustness for quasi-static drop impact, and present the range of permissible surface characteristics. For surfaces with a Young's contact angle greater than 90° and square micropillar geometry, we show that robustness can be enforced when an intermediate wetting state (sagged state) impedes transition to a wetted state (Wenzel state). From the standpoint of mechanics, we use available scientific data to prove that a surface with any topology must withstand a pressure of 117 Pa to be robust. Finally, permissible values of surface characteristics are determined, which ensure robustness with thermodynamics (formation of sagged state) and mechanics (withstanding 117 Pa).

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“…According to the Washburn's law for pressure entry in porous media [23], the order of magnitude of the entry pressure is inversely proportional to the typical size R of roughness: P w = 2γ cos θ/R. The quantitative measurements obtained on periodic arrays of micro-pilars evidenced that R ∼ s 2 L [18,19], with s and L stand for the space between pillars and their length, respectively. Therefore, our idea is to increase robustness by covering the surface with a forest of chemically-grown SiNWs of high aspect-ratio (from 30 to 100) and of about 50 to 100 nm in diameter, see Fig.…”

Section: Qualitative Analysis Of the Robustness Of A Surfacementioning

confidence: 99%

“…Drop impact experiment is a particularly versatile way to test this robustness [18][19][20][21][22]. During impact, the sudden vertical deceleration of the liquid particles leads to momentum transfer that applies an effective dynamical pressure P dyn = 1/2ρU 2 , with U being the impact velocity and ρ the liquid density.…”

Section: Qualitative Analysis Of the Robustness Of A Surfacementioning

confidence: 99%

Quantitative Testing of Robustness on Superomniphobic Surfaces by Drop Impact

et al. 2010

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The quality of a liquid-repellent surface is quantified by both the apparent contact angle θ0 that a sessile drop adopts on it, and the value of the liquid pressure threshold the surface can withstand without being impaled by the liquid, hence keeping a low-friction condition. We designed surfaces covered with nano-wires obtained by the vapor-liquid-solid (VLS) growth technique, that are able to repel most of the existing non-polar liquids including those of very low surface tension, as well as many polar liquids of moderate to high surface tension. These super-omniphobic surfaces exhibit apparent contact angles ranging from 125 to 160 • depending on the liquid. We tested the robustness of the surfaces against impalement by carrying out drop impact experiments. Our results show how this robustness depends on the Young's contact angle θ0 related to the surface tension of the liquid, and that the orientational growth of NWs is a favorable factor for robustness.

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Bouncing transitions on microtextured materials

Cited by 380 publications

References 15 publications

Splashing Threshold of Oblique Droplet Impacts on Surfaces of Various Wettability

Splashing Threshold of Oblique Droplet Impacts on Surfaces of Various Wettability

Design of a robust superhydrophobic surface: thermodynamic and kinetic analysis

Quantitative Testing of Robustness on Superomniphobic Surfaces by Drop Impact

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