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David Quéré

Publications and source records attributed to David Quéré.

13 recordsLinked to original sources
PubMed2004

Air entrainment by a viscous jet plunging into a bath.

A liquid jet plunging into a container of liquid often entrains a thin film of air with it, producing bubbles. This bubble production is detrimental to many industrial processes, such as filling a container with a molten glass or polymer, or in coating processes. Conversely, in making a foam, one uses this effect; hence it is important to control the rate of bubble production. Here, we measure the amount of air entrained by a viscous jet over a wide range of parameters and explain the phenomenon theoretically. Simple scaling arguments are shown to predict entrainment rates over 4 orders of magnitude in the dimensionless jet speed.

Journal Article↗
PubMed2004

Capturing drops with a thin fiber.

We study experimentally the dynamics of drops impacting horizontal fibers and characterize the ability of these objects to capture the drops. We first show that a drop larger than a critical radius cannot be trapped by a fiber whatever its velocity. We determine this critical size as a function of the fiber radius. Then we show that for smaller drops, different situations can occur: at a low impact velocity, the drop is entirely captured by the fiber, whereas some liquid is ejected when arriving faster. We quantify the threshold velocity of capture.

Journal Article↗
PubMed2004

Self-similar etching.

When a fiber is brought into contact with a soft etching liquid, a conical tip is generally shaped. We show here that the use of corrosive liquids which release gases during the etching reaction may lead to original self-similar shapes, because of successive pinning and detachment of the meniscus. The conditions for the formation of this shape and its evolution are described. In particular, we stress the effect of convection due to released bubbles.

Journal Article↗
PubMed2004

First steps in the spreading of a liquid droplet.

We describe the first steps of spreading of a liquid droplet brought in contact with a solid that it wets completely. Usually, it is assumed that the dynamics of the droplet results from a balance between the spreading forces and viscosity. But before this classical stage, inertia resists to the motion, which leads to a very different dynamic law. We study experimentally the nature of this law, compare our results with recent theoretical predictions, and determine the duration of this inertial regime.

Journal Article↗
PubMed2004

Model droplets.

Explore the source record for details and available documents.

Chemical Phenomena↗
PubMed2003

Drops impacting a sieve.

We study experimentally the impact of liquid drops against thin plates pierced with small holes. When the drop is larger than the hole, different situations can occur: (i) at a small velocity, the drop is entirely captured by the plate; (ii) above a threshold speed, some liquid is ejected below the surface. We characterize this critical speed and these two different situations, focusing on the forces able to slow down the drop. We also quantify the amount of liquid ejected out of the hole.

Journal Article↗
PubMed2003

Fracture of a viscous liquid.

When a viscous liquid hits a pool of liquid of the same nature, the impact region is hollowed by the shock. Its bottom becomes extremely sharp if increasing the impact velocity, and we report that the curvature at that place increases exponentially with the flow velocity, in agreement with a theory by Jeong and Moffatt. Such a law defines a characteristic velocity for the collapse of the tip, which explains both the cusplike shape of this region, and the instability of the cusp if increasing (slightly) the impact velocity. Then, a film of the upper phase is entrained inside the pool. We characterize the critical velocity of entrainment of this phase and compare our results with recent predictions by Eggers.

Journal Article↗
PubMed2003

Superhydrophobic states.

It is well known that the roughness of a hydrophobic solid enhances its hydrophobicity. The contact angle of water on such flat solids is typically of the order of 100 to 120 degrees, but reaches values as high as 160 to 175 degrees if they are rough or microtextured. This result is remarkable because such behaviour cannot be generated by surface chemistry alone. Two distinct hypotheses are classically proposed to explain this effect. On one hand, roughness increases the surface area of the solid, which geometrically enhances hydrophobicity (Wenzel model). On the other hand, air can remain trapped below the drop, which also leads to a superhydrophobic behaviour, because the drop sits partially on air (Cassie model). However, it is shown here that both situations are very different from their adhesive properties, because Wenzel drops are found to be highly pinned. In addition, irreversible transitions can be induced between Cassie and Wenzel states, with a loss of the anti-adhesive properties generally associated with superhydrophobicity.

Hydrophobic and Hydrophilic Interactions↗
PubMed2002

Contact time of a bouncing drop.

When a liquid drop lands on a solid surface without wetting it, it bounces with remarkable elasticity. Here we measure how long the drop remains in contact with the solid during the shock, a problem that was considered by Hertz for a bouncing ball. Our findings could help to quantify the efficiency of water-repellent surfaces (super-hydrophobic solids) and to improve water-cooling of hot solids, which is limited by the rebounding of drops as well as by temperature effects.

Journal Article↗
PubMed2002

Rise of liquids and bubbles in angular capillary tubes.

We discuss the rise of a liquid inside an angular capillary tube. It is shown that for a wetting liquid, the height of the rise is (as usually) inversely proportional to the length which characterizes the confinement. The exact laws deduced from energetic considerations are found to be in excellent agreement with the data. We then show how such tubes can be used to prevent bubbles from being trapped. The rising velocity of a bubble is finally discussed, in the particular case of a square tube.

Journal Article↗