Séminaires Matière Molle et Complexe


Séminaire dépt MMC : Stéphanie Deboeuf « Granular flows over a slope: experiments and models »

Date et lieu: Vendredi 17 novembre, 11h, bât. 11E, salle 120

Intervenant: Stéphanie Deboeuf

(par ailleurs et pour rappel, Stéphanie Deboeuf est membre du jury de soutenance de these de Thai Binh Nguyen qui aura lieu la veille, 16/11 à 14h, amphithéâtre N, Bat 42)

Laboratoire: Institut Jean Le Rond d’Alembert, Paris

Résumé: Granular material flowing on complex topographies are ubiquitous in industrial and geophysical situations (food-processing industry, civil engineering, rock avalanches, …). Even model granular flows are difficult to understand and predict. Recently, the frictional rheology mu(I) — describing the ratio of the shear stress to the normal stress as a function of the inertia number I that compares inertial and confinement effects — allows unifying different configurations of granular flows [GDR MiDi 2004]. However, it does not succeed in
describing some phenomenologies: creep flow, deposit height, … Is it attributable to the rheology, to non-local effects, to the choice of the function mu(I), …? To study these questions, our general approach is to compare experimental results, numerical simulations and analytical solutions. In this talk, I will present some experiments of a granular layer flowing on a slope (in 3D, in 2D,…) and I will focus on the front of the flow [Saingier et al 2016] and on its stopping dynamics. Comparisons are made with computations of St-Venant equations (depth-averaged mass and momentum equations) of the same configuration for a fluid of rheology mu(I).

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire dépt MMC : Stéphanie Deboeuf « Granular flows over a slope: experiments and models »

Séminaire MMC : 9 Novembre 2017 – Laurence LINS et Magali DELEU

JEUDI 9 novembre 2017 a 14h en salle 120 du 11E

Intervenant: Laurence LINS et Magali DELEU
Laboratoire: Gembloux Agro-Bio Tech, Liege.

Titre: « Complementary biophysical tools to investigate lipid specificity in the interaction between bioactive molecules and the plasma membrane »

 

 

 

Publié dans Départements, Matière molle, Non classé, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : 9 Novembre 2017 – Laurence LINS et Magali DELEU

Séminaire MMC : Anton PESHKOV – 9 Novembre 2017

JEUDI 9 novembre 2017 a 11h en salle 120 du 11E

Intervenant: Anton PESHKOV
Laboratoire: University of Maryland

Titre: « Systèmes actifs et hors équilibre: des bactéries aux granulaires »

 

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Anton PESHKOV – 9 Novembre 2017

Séminaire MMC : Ludovic Keiser & José Bico « Instabilités interfaciales: deux illustrations »

Date et lieu: Vendredi 20 octobre, 11h. bât. 11E, salle 120.

Intervenants : Ludovic Keiser & José Bico / Laboratoire PMMH, ESPCI Paris

– Détergence
Comment peut-on extraire de l’huile d’un milieu confiné? Nous étudions une expérience de détergence dans laquelle de l’huile piégée dans un coin formé par deux plaques est chassée par une solution de tensio-actif, mouillant préférentiellement les plaques. La rencontre des deux liquides conduit à une déstabilisation de l’interface, des doigts réguliers apparaissent progressivement et des gouttes finissent par se détacher. Ces gouttes fuient la partie confinée de la cellule et l’huile peut facilement être collectée.

– Étalements fleuris de Marangoni
Déposons une goutte d’un mélange d’eau et d’alcool à la surface d’un bain d’huile. Si la goutte est suffisamment alcoolisée, elle s’étale et éclate spontanément en une myriade de gouttelettes. La taille des gouttelettes éjectées dépend fortement de la concentration initiale d’alcool. Tout comme dans l’effet « larmes de vin », l’évaporation plus rapide de l’alcool induit des gradients de tension de surface (effet Marangoni) qui eux-mêmes engendrent un écoulement.  Le couplage complexe entre hydrodynamique interfaciale, mouillage et évaporation peut être appréhendé par des lois d’échelle analytiques.

Nous tenterons d’illustrer ces deux phénomènes par des démonstrations en direct.

 

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Ludovic Keiser & José Bico « Instabilités interfaciales: deux illustrations »

Séminaire MMC : Angelo POMMELLA « The role of the microstructure in soft systems : from dynamics to rupture »

DATE : Vendredi 6 octobre 2017 – 11h00
               Salle 050 Bat 11B

Intervenant : Angelo Pommella, Laboratoire Charles Coulomb, Université de Montpellier

Résumé :
Structural changes and rupture phenomena are ubiquitous in soft matter systems under stress, beingoften related and central to determine the final properties of medical, food, and personal care products. Indeed, some bio-applications deal with soft objects (e.g. vesicles) under flow while othersrequire specific supports (bio-gels) in static stressed conditions. In both cases, the dynamics and the rupture strongly depend on the time-dependent evolution of the internal structure. In this talk, I will present three studies aiming to elucidate some key mechanisms of the dynamics and rupture of
vesicles and bio-gels under different stress conditions. In the first part of the talk, I will focus on multilamellar vesicles. Giant vesicles (typical diameter 10 – 100 microns) are usually generated by the folding of a lamellar phase made of amphiphilic molecules and can be either unilamellar (made of a single bilayer) or multilamellar (made of a stack of bilayers). Their collective behaviour has been studied extensively but experimental results on the flow behaviour of individual multilamellar ve- sicles are lacking. We used a simple shear flow to investigate the dynamic behaviour of multilamellar
vesicles. We compared the results with the well-known dynamics of unilamellar vesicles and emulsion droplets finding surprisingly analogies with both systems. We explained these analogies analysing the evolution of the vesicle microstructure under flow. In the second part of the talk I will present a study on unilamellar vesicles. While the flow-induced dynamics upon small deformation of giant vesicles is well-known, the behaviour upon large deformation, such that unilamellar vesicles break, has rarely been studied for the case of flow-induced deformation. We investigated how break-up of unilamellar vesicles is affected by the mechanical properties of vesicle membranes under flow. We
used an acoustic microstreaming flow, a complex flow generated by an ultrasound-driven bubble, to probe the effect of the excess area and the area stretching modulus. We demonstrated that selective break-up based only on the mechanical properties of different vesicle populations can be achieved opening the way to vesicle sorting mechanism under flow. In the last part of the talk, I will show an investigation on the failure of agarose gels. So far, many studies approached the failure of soft systems from a macroscopic point of view while, very few focussed on the microscopic structure and, usually, only after failure takes place. We investigated the time-evolution of the dynamics of the gel microstructure when a constant stress is imposed to the gel leading to the material failure. We used a novel experimental setup combining rheology and dynamic light scattering. The results show the presence of a heterogeneous dynamic activity in the gel microstructure predicting the imminent failure. These dynamic events are not present in the rheological macroscopic behaviour.

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Angelo POMMELLA « The role of the microstructure in soft systems : from dynamics to rupture »

Séminaire MMC : Emilie Verneuil « Polymer powder dissolution : wetting, dilution and shear »

Date et lieu: Vendredi 29 septembre, 11h, bât. 11E, salle 120

Emilie Verneuil, Laboratoire SIMM/ESPCI/CNRS, Paris

Résumé: Powders of large molar mass polymers are known to readily form lumps when poured in water: chocolate powder in cold milk, baby formula in water, polymer additives for drilling fluids,… to give a few examples. The powder dissolution process can be divided into two steps: (i) Wetting of the powder grains by water, and capillary penetration into the grains porosity; (ii) Swelling of the polymer by water down to a dilute aqueous solution of polymer.
In a first part, I will discuss the wetting dynamics of water on soluble polymer substrates that controls step (i). Second, I will identify the physical properties controlling the swelling of the gel layer that forms between the dry solid and the aqueous solution, and show how shear contributes to its erosion, giving scaling laws to describe lumps dissolution (ii).

 

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Emilie Verneuil « Polymer powder dissolution : wetting, dilution and shear »

Séminaire MMC : Pascal PANIZZA « Formation of labyrinthine drying patterns in 2D model porous media »

 

DATE : Vendredi 22 septembre, 11h, bât. 11E, salle 120

Intervenant: Pascal PANIZZA ,  Département Matière Molle, IPR

Résumé: The evaporation of liquid dispersions is important in civil engineering as salt weathering damages the built environment and in material science for the design of novel smart materials at the micro- and nano-scale. Yet, this issue has remained elusive notably because of complex couplings between the formation of solid deposits and the various transport phenomena that occur during drying. To address this problem, we investigate drying of colloidal suspensions or surfactant solutions confined in 2D porous model media allowing us to overcome optical limitation inherent to bulk systems. We observe the formation of thin solid films that connect adjacent posts to form a maze. Our experiments show that the formation dynamics of these out of equilibrium patterns is controlled by a regular succession of Haines jumps. Identifying the elementary mechanisms yielding the formation of the deposits at the pore scale, we establish a pore-network model that well captures the final topology and formation dynamics of the  observed labyrinthine structures. Using simple arguments, we predict the topological changes in the drying pattern at the pore scale as a function of the relevant geometrical parameters (sample thickness and contact angle that the liquid makes with the substrate). Our experiments confirm our theoretical predictions.

 

Publié dans Actualités, Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Pascal PANIZZA « Formation of labyrinthine drying patterns in 2D model porous media »

Séminaire Etienne BARTHEL : How triple line pinning affects wetting on textured surfaces

 DATE : 15 septembre 2017,  11H, salle 120, Bât 11E

Intervenant : Etienne BARTHEL
Laboratoire:
SIMM/ESPCI/CNRS, Paris

 

Résumé: We have explored the role of triple line pinning on various surfaces. We have first considered periodic superhydrophobic surfaces. We have found that the receding contact angle is controlled by “point” defects : when the triple line adjusts between consecutive rows, it forms kinks which turn out to be the weakest pinning points. We have shown that such these kinks explain : 1) reduced receding contact angles 2) jerky line motion 3) surface fraction scaling. A linear relation with surface fraction is found only for large surface fractions (the Cassie relation) ; it is superseded by a singular behavior at low surface fractions. These results most likely solve the issue of the applicability of the Cassie relation to superhydrophobic surfaces. Then, we have explored the impact of texture inclination in the Wenzel state. We show that for inclined textures, the triple line can unexpectedly move only “against the
nap”, i.e. opposite the direction in which the textures point. The evolution of the advancing contact angle with inclination can only be explained by a 3D calculation of pinning. In both cases, simple rules of mixture do not satisfactorily account for the data.

 

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire Etienne BARTHEL : How triple line pinning affects wetting on textured surfaces

Séminaire MMC : Michel Louge « Statistical mechanics of hysteretic capillary phenomena: predictions of contact angle on rough surfaces and liquid retention in unsaturated porous media »

DATE : le Mardi 27 Juin prochain en salle 120 à 11H bâtiment 11E.

Intervenant : Michel Louge, de l’Université de Cornell,

Résumé :
We describe a statistical mechanics approach to hysteretic capillary phenomena with two examples: the retention of a liquid in an unsaturated porous medium; and the behavior of the triple gas-solid-liquid contact line on a rough surface. In both cases, random geometry of pores or cavities produces a frozen disorder that is subject to the collective release of capillary energy in first-order phase transitions. In unsaturated porous media, this may lead to Haines jumps. For the advancing and receding contact line, the analysis predicts six distinct regimes that include the classical Cassie-Baxter state, metastability, and other behavior observed in experiments

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Michel Louge « Statistical mechanics of hysteretic capillary phenomena: predictions of contact angle on rough surfaces and liquid retention in unsaturated porous media »

Séminaire MMC : Anne MARTEL « Neutrons for Structural Biology: Emphasis on SANS »

DATE : 16 juin 2017, 14h00, salle 120

Intervenante : Anne MARTEL, Institut Laue Langevin, Grenoble

A range of neutron-using techniques are usefull for structural biology: namely, Small Angle Scattering, Laue Diffractometry, high- and low- resolution diffractometry, Reflectometry and Inelastic Scattering.  Each of them can be used to tacles specific aspect: such as the role of hydrogens in an enzymatic reaction, the relative position of partners in a macromolecular complex or the global dynamic of a system. This presentation will list them, insisting on their common features and their unique contribution to solve biological questions. The Small Angle Neutron Scattering will be further detailed, with several examples illustrating our recent developments in sample environment dedicated to biology.

 

Publié dans Départements, Matière molle, Séminaires Matière Molle et Complexe | Commentaires fermés sur Séminaire MMC : Anne MARTEL « Neutrons for Structural Biology: Emphasis on SANS »