Bridging local to global dynamics of drop impact onto solid substrates

Lastakowski, Henri; Boyer, François; Biance, Anne‐Laure; Pirat, Christophe; Ybert, Christophe

doi:10.1017/jfm.2014.108

Cited by 57 publications

(57 citation statements)

References 33 publications

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“…We find that R h increases linearly with time, with a constant opening velocity V c = (1.64 ± 0.16) m/s, which results from a balance between the rim inertia and surface tension in the film as predicted by Taylor [15] and Culick [16] for the rupture of a soap film: V c = 2γ/(ρh), with ρ the density of the liquid, γ its surface tension, and h the film thickness. Although a constant velocity is not expected here as the thickness decreases with time [19], we quantitatively show in the Supplemental Material [20] that this effect is negligible for the time-and length-scales considered here. Numerically, one considers for h the thickness experimentally measured in the outside periphery of the hole, h out = The evolution of the pre-hole radius, R ph , with the time elapsed since its formation, T = t − t ph , is plotted in Fig.…”

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confidence: 71%

“…The sheet formation and destabilization are recorded from the top with a fast camera (Phantom V7.3) run at an acquisition rate of 10 kHz. The thickness field of the sheet loaded with dye is determined (range of measurable thicknesses (5 − 450) µm with an uncertainty of 5 µm) thanks to a time-and space-resolved measurement of the adsorbance of the sheet [14,19]. Figure 1(a) displays the destabilization process of a dyed emulsion-based liquid sheet (see movies in the Supplemental Material [20]).…”

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Bursting of Dilute Emulsion-Based Liquid Sheets Driven by a Marangoni Effect

2015

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We study the destabilization mechanism of thin liquid sheets expanding in air and show that dilute oil-in-water emulsion-based sheets disintegrate through the nucleation and growth of holes that perforate the sheet. The velocity and thickness fields of the sheet outside the holes are not perturbed by holes and hole opening follows a Taylor-Culick law. We find that a pre-hole, which widens and thins out the sheet with time, systematically precedes the hole nucleation. The growth dynamics of the pre-hole follows the law theoretically predicted for a liquid spreading on another liquid of higher surface tension due to Marangoni stresses. Classical Marangoni spreading experiments quantitatively corroborate our findings.The destabilization of free liquid films is of great importance for aerosol dispersions, and is involved in many practical situations [1,2] [6], and dilute oil-in-water emulsions [7]. However, despite its relative ubiquity, the bursting of liquid sheets through perforation events have not yet been carefully investigated nor modeled. The occurrence of perforation events in a spray directly decreases the fraction of small drops issued from the spray [8] as illustrated in the case of dilute emulsions, which are prone to induce the bursting of liquid sheets [7]. Dilute emulsions are also recognized as anti-drift adjuvants [8][9][10][11] and therefore commonly used as carrier fluids for pesticides delivery. Controlling the perforation processes would therefore allow one to finely tune the size distribution of drops issued from sprays, a goal of uttermost importance in many industrial processes. In this optics, a physical description of the mechanisms at play in perforation processes is desired. The commonly invoked conditions for perforation include a dewetting of inclusions by the fluid and an inclusion diameter equal to, or larger than, the thickness of the liquid sheet, so that inclusions cause perforation by puncturing both interfaces of the sheet [3]. But, to the best of our knowledge, those conditions have never been confronted to robust experimental facts. To unambiguously clarify the physical mechanisms at play, rationale experiments on individual perforation events are therefore required.In this Letter, we investigate the perforation mechanisms of an emulsion-based free liquid sheet issued from a single-drop experiment; resulting from the impact of one drop of fluid onto a small target [12][13][14]. During the sheet expansion, holes nucleate and grow. We show that each perforation event is preceded by the formation of a pre-hole that thins out the sheet and widens with time. We demonstrate that the pre-hole growth is governed by a Marangoni effect. The entry of emulsion oil droplets at the air/water interface leads to a spreading of the oil due to a surface tension gradient stress. This stress is counterbalanced by a viscous stress that drags the subsurface fluid, whose flow causes a local film thinning which ultimately lead to the rupture of the film. We show that the growth kinetics of pre-holes ...

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Bursting of Dilute Emulsion-Based Liquid Sheets Driven by a Marangoni Effect

2015

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“…A first method, already described elsewhere (Lastakowski et al 2014) is based on light absorption, a dye (Brilliant Black BN, Sigma, 60%, No. 211842, 5g/L) being added to the solution.…”

Section: Thickness Profile Measurementsmentioning

confidence: 99%

On the generation of a foam film during a topological rearrangement

Petit

Seiwert²,

Cantat³

et al. 2014

J. Fluid Mech.

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(Received ?; revised ?; accepted ?. -To be entered by editorial office) T1 topological rearrangement, i.e. switching of neighboring bubbles in a liquid foam, is the elementary process of foam dynamics, and it involves film disappearance and generation. It has been extensively studied as it is crucial in foam rheology or foam collapse. T1 dynamics depends mainly on the surfactants used to generate the foam, and several models taking into account surface viscosity and/or elasticity have been proposed. By performing experiments in a cubic assembly of films, we go a step forward in this global analysis and investigate experimentally the mechanism of formation of the new film. In particular, the flow velocity field is probed by particle tracking and the film thickness is measured by light absorption and interferometric measurements. Two limit behaviors for the film are reported: it may 1) undergo an homogeneous extension, or 2) resist elongation and remain at rest, new film being created from liquid exchange with connecting meniscus. Both T1 dynamics and film thickness are shown to depend on the competition between these two behaviors. Interestingly, their balance is set by the surfactant solution used, but it is also shown to vary during a single T1 relaxation process.

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“…At low impact velocities, the upper T L boundary is also lower than for ethanol, but it increases with U and reaches almost the same level as that for ethanol at U ≈ 4 m=s. Several models for the spreading diameter D max of an impacting drop have been developed [9,11,29,30]. For the so-called pancake model [11], D max and D 0 =U are considered to be the relevant length and time scales [11].…”

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Dynamic Leidenfrost Effect: Relevant Time and Length Scales

et al. 2016

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When a liquid droplet impacts a hot solid surface, enough vapor may be generated under it to prevent its contact with the solid. The minimum solid temperature for this so-called Leidenfrost effect to occur is termed the Leidenfrost temperature, or the dynamic Leidenfrost temperature when the droplet velocity is non-negligible. We observe the wetting or drying and the levitation dynamics of the droplet impacting on an (isothermal) smooth sapphire surface using high-speed total internal reflection imaging, which enables us to observe the droplet base up to about 100 nm above the substrate surface. By this method we are able to reveal the processes responsible for the transitional regime between the fully wetting and the fully levitated droplet as the solid temperature increases, thus shedding light on the characteristic time and length scales setting the dynamic Leidenfrost temperature for droplet impact on an isothermal substrate. DOI: 10.1103/PhysRevLett.116.064501 Boiling and spreading of droplets impacting on hot substrates have been extensively studied since both phenomena strongly affect the heat transfer between the liquid and the solid. Applications include spray cooling [1], spray combustion [2], and others [3].At room temperature, an impacting droplet spreads on a solid surface and entraps a bubble under it [4][5][6]. At temperatures higher than the boiling temperature T b , vapor bubbles appear which disturb and finally rupture the free surface, resulting in the violent spattering of tiny droplets [7,8]. On even hotter surfaces, however, beyond the socalled Leidenfrost temperature T L , the droplet interface becomes smooth again without any bubbles inside it. In this regime the droplet lives much longer, as now it levitates on its own vapor layer: the well-known Leidenfrost effect [9,10].In order to determine the Leidenfrost temperature T L and its dependence on the impact velocity U, phase diagrams have been experimentally produced for various impacting droplets with many combinations of substrates and liquids: water on smooth silicon [8], water on microstructured silicon [11], FC-72 on carbon nanofiber [12], water on aluminium [13], and ethanol on sapphire [14]. All of these phase diagrams show a weakly increasing behavior of T L with U. When theoretically deriving T L , one needs to determine the vapor thickness profile. In the case of a gently deposited droplet, this can be accomplished since the shape of the droplet is fixed except for the bottom surface, which reduces the problem to a lubrication flow of vapor in the gap between the substrate and the free surface [15][16][17][18][19][20]. For impacting droplets on an unheated surface at high Weber number We ≡ ρU 2 D 0 =σ (here, D 0 is the equivalent diameter of the droplet and ρ and σ are the density and the surface tension of the liquid, respectively), it is known that the neck around the dimple beneath the impacting droplet rams the surface. In this cold impact case, the neck propagates outwards like a wave [21]. For impact on a superheated s...

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Bridging local to global dynamics of drop impact onto solid substrates

Cited by 57 publications

References 33 publications

Bursting of Dilute Emulsion-Based Liquid Sheets Driven by a Marangoni Effect

Bursting of Dilute Emulsion-Based Liquid Sheets Driven by a Marangoni Effect

On the generation of a foam film during a topological rearrangement

Dynamic Leidenfrost Effect: Relevant Time and Length Scales

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