Wrinkles, folds and plasticity in granular rafts

We investigate the mechanical response of a compressed monolayer of large and dense particles at a liquid-fluid interface: a granular raft. Upon compression, rafts first wrinkle; then, as the confinement increases, the deformation localizes in a unique fold. This characteristic buckling pattern is usually associated to floating elastic sheets and as a result, particle laden interfaces are often modeled as such. Here, we push this analogy to its limits by comparing the first quantitative measurements of the raft morphology to a theoretical continuous elastic model of the interface. We show that although powerful to describe the wrinkle wavelength, the wrinkle-to-fold transition and the fold shape, this elastic description does not capture the finer details of the experiment. We describe an unpredicted secondary wavelength, a compression discrepancy with the model and a hysteretic behavior during compression cycles, all of which are a signature of the intrinsic discrete and frictional nature of granular rafts. It suggests also that these composite materials exhibit both plastic transition and jamming dynamics.Comment: 10 pages, including Supplementary Information. Submitted to Physical Review Material

The liquid helix

From everyday experience, we all know that a solid edge can deflect a liquid flowing over it significantly, up to the point where the liquid completely sticks to the solid. Although important in pouring, printing and extrusion processes, there is no predictive model of this so-called "teapot effect". By grazing vertical cylinders with inclined capillary liquid jets, we here use the teapot effect to attach the jet to the solid and form a new structure: the liquid helix. Using mass and momentum conservation along the liquid stream, we first quantitatively predict the shape of the helix and then provide a parameter-free inertial-capillary adhesion model for the jet deflection and critical velocity for helix formation.Comment: Accepted in Physical Review Letters, author versio

Curvature Regularization near Contacts with Stretched Elastic Tubes

Bringing a rigid object into contact with a soft elastic tube causes the tube to conform to the surface of the object, resulting in contact lines. The curvature of the tube walls near these contact lines is often large and is typically regularized by the finite bending rigidity of the tube. Here, we show using experiments and a F\"{o}ppl--von K\'{a}rm\'{a}n-like theory that a second mechanism of curvature regularization occurs when the tube is axially stretched. The radius of curvature obtained is unrelated to the bending rigidity of the tube walls, increases with the applied stretching force and decreases with sheet thickness, in contrast with the effects of finite bending rigidity. %Moreover, the axial force decreases the contact area between the tube and the intruding object, potentially reducing the drag necessary to propel the object through the tube. We show that these features are due to an interplay between geometry and mechanics specific to elastic tubes, but one that is absent from both planar sheets and spherical shells

ANGELITO [Material gráfico]

ÁLBUM FAMILIAR CASA DE COLÓNCopia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201

Membranes plissées à la surface de l'eau : des films élastiques aux radeaux granulaires

This thesis is concerned with the buckling of a model particle laden interface: a monolayer of dense, athermal particles at a planar liquid-fluid interface that we call a granular raft. Under compression granular rafts wrinkle and fold like elastic sheets. We investigate this buckling instability experimentally and theoretically for these two systems under the continuum mechanics framework. We first look at folds in custom made dense floating elastic sheets. We highlight the influence of the sheet's own weight in the fold formation and shape. Then we explore the regime of very large deformations, after the sheet contacts itself. Depending on the sheet density, the fold in self-contact either bends back toward the interface or sinks down toward the bottom of the tank. We then look at wrinkles and folds in granular rafts. Our experimental apparatus allows us to compress the rafts uniaxially and extract their morphology. As compression increases, we observe two distinct wrinkling patterns, then the deformations localise in a unique fold. We develop an elastic model that we solve numerically to predict the fold shape and size. We then highlight the limitations of the model and show that the granular nature of these rafts cannot always be neglected. Finally, we deposit water droplets on top of granular rafts. If the particles are hydrophobic and large enough, the raft can inhibit coalescence indefinitely via particle bridging. When we vary the size of these floating drops, they take unusual shapes which depend on the raft properties. These drops can then be encapsulated in a thin composite oil-particle layer leading to water droplets in water.Cette thèse porte sur le flambement d'une interface chargée en particules: une monocouche de grains denses et athermaux à une interface liquide-fluide plane que l'on appelle radeau granulaire. Ces radeaux se rident et se plient lorsqu'ils sont compressés comme des films élastiques. Nous étudions cette instabilité de flambement expérimentalement et théoriquement dans ces deux systèmes dans le cadre de la mécanique des milieux continus. Nous commençons par examiner les plis dans des films élastiques denses. Nous soulignons l'influence du poids du film dans la formation du pli. Puis nous explorons le régime des très grandes déformations, après que le film soit entré en contact avec lui-même. Suivant la densité du film, le pli se replie vers l'interface ou s'enfonce vers le fond de la cuve. Ensuite nous étudions les rides et les plis dans les radeaux granulaires compressés uniaxialement. A mesure que la compression augmente, nous observons deux motifs de ride distincts, puis la déformation se localise en un unique pli. Nous prédisons la forme et la taille des plis avec un modèle élastique résolu numériquement. Nous insistons sur les limitations de ce modèle et montrons que le caractère granulaire de ces radeaux n'est pas toujours négligeable. Enfin, nous déposons des gouttes d'eau à la surface des radeaux. Lorsque les particules sont hydrophobes et suffisamment grandes, elles capturent un film d'huile qui sépare la goutte du bain et empêche la coalescence. Puis nous modifions la taille de ces gouttes qui prennent des formes inhabituelles. Ces gouttes peuvent ensuite être encapsulées dans une fine couche de particules et d'huile conduisant à des gouttes d'eau dans l'eau

Phase separated active protein droplets

International audienc

Stains from Freeze-Dried Drops

The evaporation of droplets of colloidal suspensions onto a surface is a common tool to achieve surface coatings and self-assembly. However, because of the spontaneous flow developing within an evaporating drop, the deposit is difficult to control, and an unwanted ring-like structure often forms, with particles aggregating along the drop edge. Here, by freezing the drops before sublimating them in dry air we propose a new approach that produces a different kind of stain where most particles are clustered in the center of the drops instead. We demonstrate that these deposits can be continuously tuned from wide but thin to concentrated and thick by varying the droplet's aspect ratio. Unlike evaporated liquid drops, stains from freeze-dried drops do not depend on the drying conditions or substrate roughness and possess a porous and branched microstructure somewhat reminiscent of freeze-casted ceramics. With these stains being governed by the freezing process rather than the drying, this opens alternative ways to control colloidal deposits

Folds in floating membranes : from elastic sheets to granular rafts

Cette thèse porte sur le flambement d'une interface chargée en particules: une monocouche de grains denses et athermaux à une interface liquide-fluide plane que l'on appelle radeau granulaire. Ces radeaux se rident et se plient lorsqu'ils sont compressés comme des films élastiques. Nous étudions cette instabilité de flambement expérimentalement et théoriquement dans ces deux systèmes dans le cadre de la mécanique des milieux continus. Nous commençons par examiner les plis dans des films élastiques denses. Nous soulignons l'influence du poids du film dans la formation du pli. Puis nous explorons le régime des très grandes déformations, après que le film soit entré en contact avec lui-même. Suivant la densité du film, le pli se replie vers l'interface ou s'enfonce vers le fond de la cuve. Ensuite nous étudions les rides et les plis dans les radeaux granulaires compressés uniaxialement. A mesure que la compression augmente, nous observons deux motifs de ride distincts, puis la déformation se localise en un unique pli. Nous prédisons la forme et la taille des plis avec un modèle élastique résolu numériquement. Nous insistons sur les limitations de ce modèle et montrons que le caractère granulaire de ces radeaux n'est pas toujours négligeable. Enfin, nous déposons des gouttes d'eau à la surface des radeaux. Lorsque les particules sont hydrophobes et suffisamment grandes, elles capturent un film d'huile qui sépare la goutte du bain et empêche la coalescence. Puis nous modifions la taille de ces gouttes qui prennent des formes inhabituelles. Ces gouttes peuvent ensuite être encapsulées dans une fine couche de particules et d'huile conduisant à des gouttes d'eau dans l'eau.This thesis is concerned with the buckling of a model particle laden interface: a monolayer of dense, athermal particles at a planar liquid-fluid interface that we call a granular raft. Under compression granular rafts wrinkle and fold like elastic sheets. We investigate this buckling instability experimentally and theoretically for these two systems under the continuum mechanics framework. We first look at folds in custom made dense floating elastic sheets. We highlight the influence of the sheet's own weight in the fold formation and shape. Then we explore the regime of very large deformations, after the sheet contacts itself. Depending on the sheet density, the fold in self-contact either bends back toward the interface or sinks down toward the bottom of the tank. We then look at wrinkles and folds in granular rafts. Our experimental apparatus allows us to compress the rafts uniaxially and extract their morphology. As compression increases, we observe two distinct wrinkling patterns, then the deformations localise in a unique fold. We develop an elastic model that we solve numerically to predict the fold shape and size. We then highlight the limitations of the model and show that the granular nature of these rafts cannot always be neglected. Finally, we deposit water droplets on top of granular rafts. If the particles are hydrophobic and large enough, the raft can inhibit coalescence indefinitely via particle bridging. When we vary the size of these floating drops, they take unusual shapes which depend on the raft properties. These drops can then be encapsulated in a thin composite oil-particle layer leading to water droplets in water