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(254) Production(s) de RAMOS L.
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Instabilities in freely expanding sheets of associating viscoelastic fluids
Auteur(s): Arora S., Louhichi A., Vlassopoulos D., Ligoure C., Ramos L.
(Article) Publié:
Soft Matter, vol. 2021 p.10935 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03672529_v1
Ref Arxiv: 2111.06144
DOI: 10.1039/d1sm01075a
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We use the impact of drops on a small solid target as a tool to investigate the behavior of viscoelastic fluids under extreme deformation rates. We study two classes of transient networks: semidilute solutions of supramolecular polymers and suspensions of spherical oil droplets reversibly linked by polymers. The two types of samples display very similar linear viscoelastic properties, which can be described with a Maxwell fluid model, but contrasting nonlinear properties due to different network structure. Upon impact, weakly viscoelastic samples exhibit a behavior qualitatively similar to that of Newtonian fluids: A smooth and regular sheet forms, expands, and then retracts. By contrast, for highly viscoelastic fluids, the thickness of the sheet is found to be very irregular, leading to instabilities and eventually formation of holes. We find that material rheological properties rule the onset of instabilities. We first provide a simple image analysis of the expanding sheets to determine the onset of instabilities. We then demonstrate that a Deborah number related to the shortest relaxation time associated to the sample structure following a high shear is the relevant parameter that controls the heterogeneities in the thickness of the sheet, eventually leading to the formation of holes. When the sheet tears-up, data suggest by contrast that the opening dynamics depends also on the expansion rate of the sheet.
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Food as complex soft matter physics systems - Is gluten a polymer gel like any others? A journey into the complexity of wheat proteins?
Auteur(s): Ramos L.
Conférence invité: 1st International Seminar on Soft Matter & Food: 1st Polish-Slovenian Edition. Physico-Chemical mode (hybride (Lasek and on-line), PL, 2021-11-22)
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Rheology of model gluten gels
Auteur(s): Ramos L.
Conférence invité: Probing out-of-equilibrium soft matter (Fribourg, CH, 2021-10-22)
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Sunflower Proteins at Air–Water and Oil–Water Interfaces
Auteur(s): Poirier A., Stocco A., Kapel Romain, In M., Ramos L., Banc A.
(Article) Publié:
Langmuir, vol. 37 p.2714 - 2727 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03189744_v1
DOI: 10.1021/acs.langmuir.0c03441
Exporter : BibTex | endNote
Résumé: The adsorption of a sunflower protein extract at two air− water and oil−water interfaces is investigated using tensiometry, dilational viscoelasticity, and ellipsometry. For both interfaces, a three step mechanism was evidenced thanks to master curve representations of the data taken at different aging times and protein concentrations. At short times, a diffusion limited adsorption of proteins at interfaces is demonstrated. First, a two-dimensional protein film is formed with a partition of the polypeptide chains in the two phases that depends strongly on the nature of the hydrophobic phase: most of the film is in the aqueous phase at the air−water interface, while it is mostly in the organic phase at the oil−water interface. Then a three-dimensional saturated monolayer of proteins is formed. At short times, adsorption mechanisms are analogous to those found with typical globular proteins, while strong divergences are observed at longer adsorption times. Following the saturation step, a thick layer expands in the aqueous phase and appears associated with the release of large objects in the bulk. The kinetic evolution of this second layer is compatible with a diffusion limited adsorption of the minor population of polymeric complexes with hydrodynamic radius R H ∼ 80 nm, evidenced in equilibrium with hexameric globulins (R H ∼ 6 nm) in solution. These complexes could result from the presence of residual polyphenols in the extract and raise the question of the role of these compounds in the interfacial properties of plant protein extracts.
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Competition between shear and biaxial extensional viscous dissipation in the expansion dynamics of Newtonian and rheo-thinning liquid sheets
Auteur(s): Louhichi A., Charles C.-A., Arora S., Bouteiller Laurent, Vlassopoulos Dimitris, Ramos L., Ligoure C.
(Article) Publié:
Physics Of Fluids, vol. 33 p.10.1063/5.0057316 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03324137_v1
Ref Arxiv: 2107.13348
DOI: 10.1063/5.0057316
WoS: 000691864900008
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
2 Citations
Résumé: When a drop of fluid hits a small solid target of comparable size, it expands radially until reaching a maximum diameter and subsequently recedes. In this work, we show that the expansion process of liquid sheets is controlled by a combination of shear (on the target) and biaxial extensional (in the air) deformations. We propose an approach toward a rational description of the phenomenon for Newtonian and viscoelastic fluids by evaluating the viscous dissipation due to shear and extensional deformations, yielding a prediction of the maximum expansion factor of the sheet as a function of the relevant viscosity. For Newtonian systems, biaxial extensional and shear viscous dissipation are of the same order of magnitude. On the contrary, for thinning solutions of supramolecular polymers, shear dissipation is negligible compared to biaxial extensional dissipation and the biaxial thinning extensional viscosity is the appropriate quantity to describe the maximum expansion of the sheets. Moreover, we show that the rate-dependent biaxial extensional viscosities deduced from drop impact experiments are in good quantitative agreement with previous experimental data and theoretical predictions for various viscoelastic liquids.
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Viscoelasticity and elastocapillarity effects in the impact of drops on a repellent surface
Auteur(s): Charles C.-A., Louhichi A., Ramos L., Ligoure C.
(Article) Publié:
Soft Matter, vol. 17 p.5829 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03254324_v1
PMID 34037061
Ref Arxiv: 2105.09244
DOI: 10.1039/d1sm00438g
WoS: 000653939000001
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
5 Citations
Résumé: We investigate freely expanding viscoelastic sheets. The sheets are produced by the impact of drops on a quartz plate covered with a thin layer of liquid nitrogen that suppresses shear viscous dissipation as a result of the cold Leidenfrost effect. The time evolution of the sheet is simultaneously recorded from top and side views using high-speed cameras. The investigated viscoelastic fluids are Maxwell fluids, which are characterized by low elastic moduli, and relaxation times that vary over almost two orders of magnitude, thus giving access to a large spectrum of viscoelastic and elastocapillary effects. For the purposes of comparison, Newtonian fluids, with viscosity varying over three orders of magnitude, are also investigated. In this study, d(max), the maximal expansion of the sheets, and t(max) the time to reach this maximal expansion from the time at impact, are measured as a function of the impact velocity. By using a generalized damped harmonic oscillator model, we rationalize the role of capillarity, bulk elasticity and viscous dissipation in the expansion dynamics of all investigated samples. In the model, the spring constant is a combination of the surface tension and the bulk dynamic elastic modulus. The time-varying damping coefficient is associated to biaxial extensional viscous dissipation and is proportional to the dynamic loss modulus. For all samples, we find that the model reproduces accurately the experimental data for d(max) and t(max).
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Impact of the protein composition on the structure and viscoelasticity of polymer-like gluten gels
Auteur(s): Ramos L., Banc A., Louhichi A., Pincemaille J., Jestin Jacques, Fu Zhendong, Appavou Marie-Sousai, Menut Paul, Morel Marie-Hélène
(Article) Publié:
Journal Of Physics: Condensed Matter, vol. 33 p.144001 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03139486_v1
Ref Arxiv: 2101.07322
DOI: 10.1088/1361-648X/abdf91
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We investigate the structure of gluten polymer-like gels in a binary mixture of water/ethanol, $50/50$ v/v, a good solvent for gluten proteins. Gluten comprises two main families of proteins, monomeric gliadins and polymer glutenins. In the semi-dilute regime, scattering experiments highlight two classes of behavior, akin to standard polymer solution and polymer gel, depending on the protein composition. We demonstrate that these two classes are encoded in the structural features of the proteins in very dilute solution, and are correlated with the presence of proteins assemblies of typical size tens of nanometers. The assemblies only exist when the protein mixture is sufficiently enriched in glutenins. They are found directly associated to the presence in the gel of domains enriched in non-exchangeable H-bonds and of size comparable to that of the protein assemblies. The domains are probed in neutron scattering experiments thanks to their unique contrast. We show that the sample visco-elasticity is also directly correlated to the quantity of domains enriched in H-bonds, showing the key role of H-bonds in ruling the visco-elasticity of polymer gluten gels.
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