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(33) Production(s) de l'année 2020
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How much information is in my scattering data? Some recent approaches to the structure of microgels, polymers and nanoparticles
Auteur(s): Oberdisse J.
Conférence invité: MZL User Meeting (Munich (online), DE, 2020-12-08)
Ref HAL: hal-03371654_v1
Exporter : BibTex | endNote
Résumé: Recent progress with soft nanostructures will be reviewed. Traditionally, data analysis follows two approaches, roughly depending on your geographic position with respect to the Rhine river. While “inversion” predominates in the east, “modeling” is more western. In short, “inversion” minimizes the use of a-priori knowledge, while modeling starts with an idea of what the structure might be, which may be wrong … and fit perfectly. Of course many implementations ignoring geography have been developed, and we advocate a mixed approach based on known ingredients: e.g., assembling nanoparticles in nanocomposites, or monomers within microgels. In polymer nanocomposites, we will show that SANS can be used to analyze the polymer interfacial region within a nm to NPs – which impacts dynamics as measured by BDS and NSE. On micron scales, thousands of NP are embedded in the polymer, and their dispersion affects both I(q) and the mechanics of the material. A statistical method based on RMC of this many-parameter problem will be presented, showing that key features like percolation can be described. Finally, the structure of core-shell microgels has been studied by SANS using deuteration. A model describing the polymer density profiles has been developed, and the surprising result is that the shell may not necessarily be where the intuition of the synthetic chemist located it. This leads to new nanostructures of striking mechanical properties, the study of which is an on-going endeavor.
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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 Fast Dynamics in Conductivity of Polymerized Ionic Liquids
Auteur(s): Bocharova Vera, Genix A.-C., Kisliuk Alexander, Sala Gabriele, Osti Naresh C., Mamontov Eugene, Sokolov Alexei P.
(Article) Publié:
Journal Of Physical Chemistry B, vol. 124 p.10539-10545 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-03131544_v1
DOI: 10.1021/acs.jpcb.0c07549
WoS: WOS:000592964600024
Exporter : BibTex | endNote
Résumé: Polymerized ionic liquids (PolyILs) are promising candidates for a broad range of technologies. However, the relatively low conductivity of PolyILs at room temperature has strongly limited their applications. In this work, we provide new insights into the roles of various microscopic parameters controlling ion transport in these polymers, which are crucial for their rational design and practical applications. Using broadband dielectric spectroscopy and neutron and light scattering techniques, we found a clear connection between the activation energy for conductivity, fast dynamics, and high-frequency shear modulus in PolyILs at their glass transition temperature (Tg). In particular, our analysis reveals a correlation between conductivity and the amplitude of fast picosecond fluctuations at Tg, suggesting the possible involvement of fast dynamics in lowering the energy barrier for ion conductivity. We also demonstrate that both the activation energy for ion transport and the amplitude of the fast fluctuations depend on the high-frequency shear moduli of PolyILs, thus identifying a practically important parameter for tuning conductivity. The parameters recognized in this work and their connection to the ionic conductivity of PolyILs set the stage for a deeper understanding of the mechanism of ion transport in PolyILs in the glassy state.
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Chemical-Physical Characterization of a Binary Mixture of a Twist Bend Nematic Liquid Crystal with a Smectogen
Auteur(s): Aouini A., Nobili M., Chauveau E., Dieudonne-George P., Dameme Gauthier, Stoenescu Daniel, Dozov I., Blanc C.
(Article) Publié:
Crystals, vol. 10 p.1110 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-03113887_v1
DOI: 10.3390/cryst10121110
WoS: WOS:000601985600001
Exporter : BibTex | endNote
Résumé: Nematic twist-bend phases (N-TB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature N-TB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to N-TB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4 ',4 '-(heptane-1,7-diyl)bis(([1 ',1 ''-biphenyl]4 ''-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T approximate to 104 degrees C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4 '-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable N-TB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.
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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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