arXiv subjects

David Quéré

Publications and source records attributed to David Quéré.

12 recordsLinked to original sources

arXiv2026

Static friction of liquid marbles

Liquid marbles, droplets coated with a granular layer, are highly mobile as particles prevent capillary adhesion to the substrate. Yet their coating creates a static rolling friction, which we measure and model. Motion requires shear within the shell so that it is governed mainly by the grain density. This density controls yielding via a logistic function emerging as the particle network approaches percolation and increasing rapidly at close packing. More broadly, our system offers a simple platform for probing granular-raft mechanics and measuring their effective surface tension.

cond-mat.soft↗

arXiv2022

Leidenfrost flows: instabilities and symmetry breakings

Leidenfrost drops were recently found to host strong dynamics. In the present study, we investigate both experimentally and theoretically the {flows structures and stability} inside a Leidenfrost water drop as it evaporates, starting with a large puddle. As revealed by infrared mapping, the drop base is warmer than its apex by typically 10$^{\circ}$C, which is likely to trigger bulk thermobuoyant flows and Marangoni surface flows. Tracer particles unveil complex and strong flows that undergo successive symmetry breakings as the drop evaporates. We investigate the linear stability of the baseflows in a non-deformable, quasi-static, levitating drop induced by thermobuoyancy and effective thermocapillary surface stress, using only one adjustable parameter. The stability analysis of nominally axisymmetric thermoconvective flows, parametrized by the drop radius $R$, yields the most unstable, {thus, dominant, azimuthal modes (of wavenumber $m$). Our theory predicts well the radii $R$ for the mode transitions and cascade with decreasing wavenumbers from $m=3$, $m=2$, down to $m=1$ (the eventual rolling mode that entails propulsion) as the drop shrinks in size}. The effect of the escaping vapor is not taken into account here, which may further destabilize the inner flow and couple to the liquid/vapor interface to give rise to motion Bouillant et al. (2018) [8] and Brandao et al. (2020) [9].

physics.flu-dyn↗

arXiv2019

Superhydrophobic frictions

Contrasting with its sluggish behavior on standard solids, water is extremely mobile on superhydrophobic materials, as shown for instance by the continuous acceleration of drops on tilted water-repellent leaves. For much longer substrates, however, drops reach a terminal velocity that results from a balance between weight and friction, allowing us to question the nature of this friction. We report that the relationship between force and terminal velocity is non-linear. This is interpreted by showing that classical sources of friction are minimized, so that the aerodynamical resistance to motion becomes dominant, which eventually explains the matchless mobility of water. Our results are finally extended to viscous liquids, also known to be unusually quick on these materials.

cond-mat.soft↗

arXiv2019

Two recipes for repelling hot water

Although a hydrophobic microtexture at a solid surface most often reflects rain owing to the presence of entrapped air within the texture, it is much more challenging to repel hot water. As it contacts a colder material, hot water generates condensation within the cavities at the solid surface, which eventually builds bridges between the substrate and the water, and thus destroys repellency. Here we show that both "small" (~100 nm) and "large" (~10 μm) model features do reflect hot drops at any drop temperature and in the whole range of explored impact velocities. Hence, we can define two structural recipes for repelling hot water: drops on nanometric features hardly stick owing to the miniaturization of water bridges, whereas kinetics of condensation in large features is too slow to connect the liquid to the solid at impact.

cond-mat.soft↗

arXiv2018

Drop Trampoline

Rigid superhydrophobic materials have the ability to repel millimetric water drops, in typically 10 ms. Yet, most natural water-repellent materials can be deformed by impacting drops. To test the effect of deformability, we perform impacts of non-wetting drops onto thin ($\sim$ 10 \micro m), circular PDMS membranes. The bouncing mechanism is markedly modified compared to that on a rigid material: the liquid leaves the substrate as it is kicked upwards by the membrane. We show that the rebound is controlled by an interplay between the dynamics of the drop and that of the soft substrate, so that we can continuously vary the contact time by playing on the membrane's characteristics and reduce it up to 70\%.

cond-mat.soft↗

arXiv2016

Monostable Superantiwettability

Superantiwettability, including superhydrophobicity, is an enhanced effect of surface ruggedness via the Cassie-Baxter wetting state, and has many applications such as antifouling, drop manipulation, and self-cleaning. However, superantiwettability is easily broken due to Cassie-Baxter to Wenzel wetting state transition caused by various environmental disturbances. Since all observed reverse transitions required energy inputs, it was believed that the Cassie-Baxter state couldn't be monostable. Here we show that there is a regime in the phase space of the receding contact angle and ruggedness parameters in which a Wenzel state can automatically transit into the Cassie-Baxter one without an external energy input, namely the Cassie-Baxter state in this regime is monostable. We further find a simple criterion that predicts very well experimentally observed Wenzel to Cassie-Baxter transitions for different liquids placed on various pillar-structured substrates. These results can be used as a guide for designing and engineering durable superantiwetting surfaces.

cond-mat.soft↗

arXiv2013

Wicking in a powder

We investigate the wicking in granular media by considering layers of grains at the surface of a liquid, and discuss the critical contact angle below which spontaneous impregnation takes place. This angle is found to be on the order of 55° for monodisperse layers, significantly smaller than 90°, the threshold value for penetrating assemblies of tubes: owing to geometry, impregnating grains is more demanding than impregnating tubes. We also consider the additional effects of polydispersity and pressure on this wetting transition and discuss the corresponding shift observed on the critical contact angle.

physics.flu-dyn↗

arXiv2013

Reshaping and Capturing Leidenfrost drops with a magnet

Liquid oxygen, which is paramagnetic, also undergoes Leidenfrost effect at room temperature. In this article, we first study the deformation of oxygen drops in a magnetic field and show that it can be described via an effective capillary length, which includes the magnetic force. In a second part, we describe how these ultra-mobile drops passing above a magnet significantly slow down and can even be trapped. The critical velocity below which a drop is captured is determined from the deformation induced by the field.

physics.flu-dyn↗

arXiv2013

Particles accelerate the detachment of viscous liquids

During detachment of a viscous fluid extruded from a nozzle a filament linking the droplet to the latter is formed. Under the effect of surface tension the filament thins until pinch off and final detachment of the droplet. In this paper we study the effect of the presence of individual particles trapped in the filament on the detachment dynamics using granular suspensions of small volume fractions (ϕ < 6%). We show that even a single particle strongly modifies the detachment dynamics. The particle perturbs the thinning of the thread and a large droplet of fluid around the particle is formed. This perturbation leads to an acceleration of the detachment of the droplet compared to the detachment ob- served for a pure fluid. We quantify this acceleration for single particles of different sizes and link it to similar ob- servations for suspensions of small volume fractions. Our study also gives more insight into particulate effects on de- tachment of more dense suspensions and allows to explain the accelerated detachment close to final pinch off observed previously (Bonnoit et al 2012)

cond-mat.soft↗

arXiv2012

Surface explosion cavities

We present a fluid dynamics video on cavities created by explosions of firecrackers at the water free surface. We use three types of firecrackers containing 1, 1.3 and 5 g of flash powder. The firecrackers are held with their center at the surface of water in a cubic meter pool. The movies are recorded from the side with a high-speed video camera. Without confinement the explosion produces an hemispherical cavity. Right after the explosion this cavity grows isotropically, the bottom then stops while the sides continue to expand. In the next phase the bottom of the cavity accelerates backwards to the surface. During this phase the convergence of the flow creates a central jet that rises above the free surface. In the last part of the video the explosion is confined in a vertical open tube made of glass and of centimetric diameter. The explosion creates a cylindrical cavity that develops towards the free end of the tube. Depending on the charge, the cavity can either stop inside the tube or at its exit, but never escapes.

physics.flu-dyn↗

arXiv2012

Liquid Hertz Contact: softness of weakly deformed drops on non-wetting substrates

The behavior of weakly deformed drops on non wetting surfaces is usually described using linear models. We show that these simple pictures cannot account for measurements of the dynamics of droplets that oscillate or bounce on super-hydrophobic substrates. We demonstrate that several peculiar experimental observations observed in previous works can be understood through a logarithmic correction of the linear model.

cond-mat.soft↗

arXiv2010

Paramagnetic Leidenfrost Drops

We present a fluid dynamics video showing the behavior of drops of liquid oxygen, at room temperature. Due to their low boiling point, these drops levitate on a cushion of their own vapour. This property gives them a high mobility, as known more generally in such Leidenfrost situations. But liquid oxygen is also paramagnetic, and thus likely to be manipulated using a magnet. It is first shown that the shape of the drop can be modified by changing the drop/magnet distance; approaching the magnet acts as reinforcing gravity, so that the drops get flattened by this action. The transformation is of course reversible: as the magnet is withdrawn, the liquid recovers its quasi-spherical shape. Magnets can also be used to trap the oxygen drops. As they pass above a magnet, they slow down significantly, a consequence of their deformation: despite a very low friction, the vibrations induced by the drop deformations represent an important source of dissipation: below a well-defined velocity, drops can even be stopped in the magnetic trap. Quicker ones can be decelerated and then captured by series of magnets. Oberving the same events from the top reveals the complex shapes adopted by the liquid as it crosses the traps.

physics.flu-dyn↗