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Jamming, plasticité et défaillance des matériaux
(12) Production(s) de l'année 2020
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Polypyrrole nanostructures modified with mono- and bimetallic nanoparticles for photocatalytic H2 generation
Auteur(s): Yuan Xiaojiao, Dragoe Diana, Beaunier Patricia, Uribe Daniel Bahena, Ramos L., Méndez-Medrano Maria Guadalupe, Remita Hynd
(Article) Publié:
Journal Of Materials Chemistry A, vol. 8 p.268-277 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-03437340_v1
DOI: 10.1039/C9TA11088G
Exporter : BibTex | endNote
Résumé: Conjugated polymer polypyrrole nanostructures modified with bimetallic (Pt–Ni) nanoparticles are very active for hydrogen generation and a synergetic effect is obtained by alloying Pt with Ni.
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Role of Normal Stress in the Creep Dynamics and Failure of a Biopolymer Gel
Auteur(s): Pommella A., Cipelletti L., Ramos L.
(Article) Publié:
Physical Review Letters, vol. 125 p.268006 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-03139495_v1
DOI: 10.1103/PhysRevLett.125.268006
WoS: WOS:000604249900023
Exporter : BibTex | endNote
Résumé: We investigate the delayed rupture of biopolymer gels under a constant shear load by simultaneous dynamic light scattering and rheology measurements. We unveil the crucial role of normal stresses built up during gelation: All samples that eventually fracture self-weaken during the gelation process, as revealed by a partial relaxation of the normal stress concomitant to a burst of microscopic plastic rearrangements.Upon applying a shear stress, weakened gels exhibit in the creep regime distinctive signatures in their microscopic dynamics, which anticipate macroscopic fracture by up to thousands of seconds. The dynamics in fracturing gels are faster than those of nonfracturing gels and exhibit large spatiotemporal fluctuations. A spatially localized region with significant plasticity eventually nucleates, expands progressively, and finally invades the whole sample, triggering macroscopic failure.
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Role of normal stress in the creep dynamics and failure of a biopolymer gel
Auteur(s): Pommella A., Cipelletti L., Ramos L.
(Document sans référence bibliographique) 2020-12-17Texte intégral en Openaccess :
Ref HAL: hal-03081334_v1
Ref Arxiv: 2012.09827
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We investigate the delayed rupture of biopolymer gels under a constant shear load by simultaneous dynamic light scattering and rheology measurements. We unveil the crucial role of normal stresses built up during gelation: all samples that eventually fracture self-weaken during the gelation process, as revealed by a partial relaxation of the normal stress concomitant to a burst of microscopic plastic rearrangements. Upon applying a shear stress, weakened gels exhibit in the creep regime distinctive signatures in their microscopic dynamics, which anticipate macroscopic fracture by up to thousands of seconds. The dynamics in fracturing gels are faster than those of non-fracturing gels and exhibit large spatio-temporal fluctuations. A spatially localized region with significant plasticity eventually nucleates, expands progressively, and finally invades the whole sample triggering macroscopic failure.
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Microstructure Characterization of Oceanic Polyethylene Debris
Auteur(s): Rowenczyk Laura, Dazzi Alexandre, Deniset-Besseau Ariane, Beltran Victoria, Goudounèche Dominique, Wong-Wah-Chung Pascal, Boyron Olivier, George M., Fabre P., Roux C., Mingotaud Anne-Françoise, ter Halle Alexandra
(Article) Publié:
Environmental Science And Technology, vol. 54 p.4102-4109 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02990067_v1
DOI: 10.1021/acs.est.9b07061
Exporter : BibTex | endNote
Résumé: Plastic pollution has become a worldwide concern. It was demonstrated that plastic breaks down to nanoscale particles in the environment, forming so-called nanoplastics. It is important to understand their ecological impact, but their structure is not elucidated. In this original work, we characterize the microstructure of oceanic polyethylene debris and compare them to the nonweathered objects. Cross-sections are analysed by several emergent mapping techniques. We highlight deep modifications of the debris within a layer a few hundred microns thick. The most 2 intense modifications are macromolecule oxidation and a considerable decrease in the molecular weight. The adsorption of organic pollutants and trace metals is also confined to this outer layer. Fragmentation of the oxidized layer of the plastic debris is the most likely source of nanoplastics. Consequently nanoplastic chemical nature differ greatly from plastics.
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Texturing edible oil with crystals of phenolic compounds: Platelets versus rods
Auteur(s): Pommella A., Mathonnat M., In M.
(Article) Publié:
Journal Of Food Engineering, vol. 283 p.110039 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-03049250_v1
DOI: 10.1016/j.jfoodeng.2020.110039
Exporter : BibTex | endNote
Résumé: Cinnamic acid and acetosyringone recrystallize in vegetable oil as platelets and rods respectively. After dissolution at high temperature(100°C) and upon cooling down to room temperature, their crystallites aggregate into a tenuous network which spans the entire volume of the system even at low mass fraction such as 1%. The whole system behaves as a soft solid characterized by an elastic modulus reaching 1MPa for mass fraction below 10% in the linear regime. The elastic modulus of cinnamic acid based oleogels varies with mass fraction as (-0) 2. For acetosyringone based oleogels, the elastic modulus varies non monotonically with concentration. This has been correlated to a morphological crossover from jammed spherulites at low mass fraction to entangled rods at higher mass fraction. Spherulite formation is related to the presence of branching points along the rods that result from secondary nucleation events. A new empirical parameter is defined from rheological data which reflects how far from equilibrium the solidification proceeds in nonisothermal conditions. This parameter accounts for the different concentration regimes of morphology and rheological properties that have been observed experimentally for acetosyringone.
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Tailoring the viscoelasticity of polymer gels of gluten proteins through solvent quality
Auteur(s): Costanzo S., Banc A., Louhichi A., Chauveau E., Wu Baohu, Morel Marie-Hélène, Ramos L.
(Article) Publié:
Macromolecules, vol. 53 p.9470-9479 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-03003151_v1
Ref Arxiv: 2010.10317
DOI: 10.1021/acs.macromol.0c01466
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We investigate the linear viscoelasticity of polymer gels produced by the dispersion of gluten proteins in water:ethanol binary mixtures with various ethanol contents, from pure water to 60% v/v ethanol. We show that the complex viscoelasticity of the gels exhibits a time/solvent composition superposition principle, demonstrating the self-similarity of the gels produced in different binary solvents. All gels can be regarded as near critical gels with characteristic rheological parameters, elastic plateau and characteristic relaxation time, which are related one to another, as a consequence of self-similarity, and span several orders of magnitude when changing the solvent composition. Thanks to calorimetry and neutron scattering experiments, we evidencea co-solvency effect with a better solvation of the complex polymer-like chains of the gluten proteins as the amount of ethanol increases. Overall the gel viscoelasticity can be accounted for by a unique characteristic length characterizing the crosslink density of the supramolecular network, which is solvent composition-dependent. On a molecular level, these findings could be interpreted as a transition of the supramolecular interactions, mainly H-bonds, from intra- to interchains, which would be facilitated by the disruption of hydrophobic interactions by ethanol molecules. This work provides new insight for tailoring the gelation process of complex polymer gels.
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Spinning elastic beads: a route for simultaneous measurements of the shear modulus and the interfacial energy of soft materials
Auteur(s): Carbonaro A., Chagua-Encarnacion Kennedy-Nexon, Charles C.-A., Phou T., Ligoure C., Mora S., Truzzolillo D.
(Article) Publié:
Soft Matter, vol. 16 p.8412 - 8421 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02947316_v1
DOI: 10.1039/d0sm01024c
Exporter : BibTex | endNote
Résumé: Large deformations of soft elastic beads spinning at high angular velocity in a denser background fluid are investigated theoretically, numerically, and experimentally using millimeter-size polyacry-lamide hydrogel particles introduced in a spinning drop tensiometer. We determine the equilibrium shapes of the beads from the competition between the centrifugal force and the restoring elastic and surface forces. Considering the beads as neo-Hookean up to large deformations, we show that their elastic modulus and surface energy constant can be simultaneously deduced from their equilibrium shape. Also, our results provide further support to the scenario in which surface energy and surface tension coincide for amorphous polymer gels.
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