Ref HAL: hal-01768107_v1
PMID 29443532
Ref Arxiv: 2007.15470
DOI: 10.1021/acs.langmuir.7b03932
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Ref. & Cit.: NASA ADS
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9 Citations
Résumé:

A new method based on the combination of small-anglescattering, reverse Monte Carlo simulations, and an aggregate recognition algorithm is proposed to characterize the structure of nanoparticle suspensions in solvents and polymer nanocomposites, allowing detailedstudies of the impact of different nanoparticle surface modifications.Experimental small-angle scattering is reproduced using simulated annealing of configurations of polydisperse particles in a simulation box compatible with the lowest experimental q-vector. Then, properties of interest likeaggregation states are extracted from these configurations and averaged. This approach has been applied to silane surface-modified silica nanoparticles with different grafting groups, in solvents and after casting into polymer matrices.It is shown that the chemistry of the silane function, in particular mono- or trifunctionality possibly related to patch formation, affects the dispersion state in a given medium, in spite of an unchanged alkylchain length. Our approach may be applied to study any dispersion or aggregation state of nanoparticles. Concerningnanocomposites, the method has potential impact on the design of new formulations allowing controlled tuning of nanoparticle dispersion.

Ref HAL: hal-01761380_v1
DOI: 10.1103/PhysRevLett.120.148003
WoS: 000429451000016
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5 Citations
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We investigate freely expanding sheets formed by ultrasoft gel beads, and liquid and viscoelastic drops, produced by the impact of the bead or drop on a silicon wafer covered with a thin layer of liquid nitrogen that suppresses viscous dissipation thanks to an inverse Leidenfrost effect. Our experiments show a unified behavior for the impact dynamics that holds for solids, liquids, and viscoelastic fluids and that we rationalize by properly taking into account elastocapillary effects. In this framework, the classical impact dynamics of solids and liquids, as far as viscous dissipation is negligible, appears as the asymptotic limits of a universal theoretical description. A novel material-dependent characteristic velocity that includes both capillary and bulk elasticity emerges from this unified description of the physics of impact.

Résumé:

Je présenterai le comportement de gels soumis à des contraintes mécaniques extrêmes. Deux types de gels (transitoires auto-assemblés et permanent réticulés) et deux configurations expérimentales imposant de grandes déformations extensionnelles seront explorés. D’une part, je présenterai la déformation biaxiale de nappes libres produites par impact d’une goutte ou perle sur une surface solide dans des conditions de dissipation minimisée. Ces expériences montrent un comportement unifié de la dynamique d’impact pour les solides, liquides et fluides viscoélastiques que nous rationalisons en prenant en compte les effets élasto-capillaires : une nouvelle vitesse caractéristique qui inclut à la fois l’élasticité en volume et l’élasticité de surface émerge de cette description unifiée de l’impact. D’autre part, je présenterai étude de fracture de gels transitoires produite sous déformation uniaxiale (étirement de filament). L’originalité de ce travail est de coupler suivi par imagerie rapide de la propagation d’une fracture et rhéométrie extensionnelle pour analyser et quantifier la nature des mécanismes de fracture.

Ref HAL: hal-01735760_v1
DOI: 10.1103/PhysRevE.97.012403
WoS: WOS:000423129000005
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2 Citations
Résumé:

Cilia are elastic hairlike protuberances of the cell membrane found in various unicellular organisms and in several tissues of most living organisms. In some tissues such as the airway tissues of the lung, the coordinated beating of cilia induce a fluid flow of crucial importance as it allows the continuous cleaning of our bronchia, known as mucociliary clearance. While most of the models addressing the question of collective dynamics and metachronal wave consider homogeneous carpets of cilia, experimental observations rather show that cilia clusters are heterogeneously distributed over the tissue surface. The purpose of this paper is to investigate the role of spatial heterogeneity on the coherent beating of cilia using a very simple one dimensional model for cilia known as the rower model. We systematically study systems consisting of a few rowers to hundreds of rowers and we investigate the conditions for the emergence of collective beating. When considering a small number of rowers, a phase drift occurs, hence a bifurcation in beating frequency is observed as the distance between rowers clusters is changed. In the case of many rowers, a distribution of frequencies is observed. We found in particular the pattern of the patchy structure that shows the best robustness in collective beating behavior, as the density of cilia is varied over a wide range.

Ref HAL: hal-01724008_v1
DOI: 10.1063/PT.3.3873
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Ref HAL: hal-01715256_v1
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With the demography growth, there is a huge pressure on protein demand, and the development of plant based proteins is required for a future sustainable food production. Plant proteins are efficient to stabilize interfaces in foams or emulsions, and the understanding of physical mechanisms at the origin of their interfacial behavior is important to develop new products. We investigate the adsorption of wheat grains (gliadin) and sunflower seeds (helianthinin) proteins, at air-water and oil-water interfaces, respectively. A combination of tensiometry, dilatational viscoelasticity and ellipsometry measurements is used to determine the adsorption mechanisms, and characterize the structure and properties of the interfacial protein films formed with different bulk protein concentrations. We demonstrate that a diffusion-controlled adsorption occurs at low bulk protein concentration for helianthinin whereas this mechanism occurs whatever the bulk concentration for gliadins. Surface pressure-induced film relaxation through conformation changes of proteins at the air-water interface is identified for gliadin whereas surface aggregation is observed at high helianthinin concentration. Overall, our experimental results highlight that structural flexibility of proteins appears as a key factor for their interfacial activity.

Ref HAL: hal-01703868_v1
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La possibilité pour un fluide viscoélastique de se fracturer a été mise en évidence pour la première fois dans les années 60 [1]] mais reste beaucoup moins documentée [2] que l’étude de la fracturation des matériaux solides Les hydrogels transitoires représentent une classe de matériaux viscoélastiques particulièrement bien adaptée pour l’investigation de fractures dans les fluides viscoélastiques, car leurs temps de relaxation et leur modules élastiques sont facilement modulables. Nous illustrons quelques aspects de la nucléation et de la propagation de fractures dans des réseaux transitoires modèles constitués de micelles se tensio-actifs pontées par des polymères téléchéliques en solution aqueuse. Deux géométrie seront considérées : cellule de Hele-Shaw [3] et rhéomètrie extensionnelle [4].[1] JF Hutton. Nature 200 (1963) 646
[2] C. Ligoure and S.Mora, Rheologica Acta, 52 (2013) 91-114 [3] , Foyart G., Ligoure C., Mora S., Ramos L. ACS Macro Letters, 5 (2016) 1080-1083 [4] , Arora S., Shabbir A., Hassager O., Ligoure C., Ramos L., JOR 61 (2017).1267-1275