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Chimie et Matériaux
(9) Production(s) de l'année 2020
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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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Rejuvenating the structure and rheological properties of silica nanocomposites based on natural rubber
Auteur(s): Boonsomwong Kanyarat, Genix A.-C., Chauveau E., Fromental J.-M., Dieudonne-George P., Sirisinha Chakrit, Oberdisse J.
(Article) Publié:
Polymer, vol. 189 p.122168 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-03004917_v1
Ref Arxiv: 2011.07820
DOI: 10.1016/j.polymer.2020.122168
WoS: WOS:000513011400007
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: The antagonistic effect of processing and thermal annealing on both the filler structure and the polymer matrix is explored in polymer nanocomposites based on natural rubber with precipitated silica incorporated by coagulation from aqueous suspension followed by roll-milling. Their structure and linear and non-linear rheology have been studied, with a particular emphasis on the effect of high temperature thermal treatment and the number of milling passes. Small-angle X-ray scattering intensities show that the silica is organized in small, unbreakable aggregates containing ca. 50 primary nanoparticles, which are reorganized on a larger scale in filler networks percolating at the highest silica contents. As expected, the filler network structure is found to be sensitive to milling, more milling inducing rupture, as evidenced by the decreasing Payne effect. After thermal treatment, the nanocomposite structure is found to be rejuvenated, erasing the effect of the previous milling on the low-strain modulus. In parallel, the dynamics of the samples described by the rheology or the calorimetric glass-transition temperature remain unchanged, whereas the natural latex polymer network structure is modified by milling towards a more fluid-like rheology, and cannot be recovered.
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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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Efectul levigării asupra betonului – partea a ii-a: evoluția comportării mecanice a itz în timpul levigării la scară locală
Auteur(s): Gîrboveanu Andrei, Jebli Mouad, Jamin Frédéric, Huon Vincent, Bonnet L., El Youssoufi Moulay Saïd, Georgescu Dan
(Article) Publié:
Romanian Journal Of Materials, vol. p. (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02953521_v1
Exporter : BibTex | endNote
Résumé: Legătura dintre pasta de ciment și agregat influențează durabilitatea betonului supus levigării, din cauza existenței unei anumite zone mai vulnerabile în pasta de ciment, adiacentă agregatelor-Zona de Tranziție Inter facială (ITZ). Pentru a evalua comportamentul mecanic al betonului la scara locală a legăturii pastă de ciment/agregat, s-au efectuat încercări de întindere pe eșantioane din pastă de ciment și compozite pastă/agregat. Relația dintre degradarea chimică și proprietățile mecanice (modulul lui Young și rezistența la întindere) a fost exprimată prin noțiunea de degradare chimică. Alte aspecte discutate, cum ar fi cinetica de levigare, dizolvarea chimică și fisurarea au fost evocate pentru a evidenția originea pierderii proprietăților mecanice ale pastei de ciment și a legăturii pastă / ciment. În ceea ce privește legătura pastă/agregat, după o dizolvare importantă în cadrul ITZ, se produce treptat o pierdere totală de aderență între pasta de ciment și agregat. În ceea ce privește pasta de ciment, aceasta suferă o scădere mai mică a modulului lui Young și a rezistenței la întindere în comparație cu compozitele, fiind de asemenea mai puțin afectată de fisurare. În general, acest studiu evidențiază mecanismul prin care comportamentele mecanice ale pastei de ciment și ale legăturii de pastă de ciment / agregate sunt afectate de levigare.
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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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Biaxial extensional viscous dissipation in sheets expansion formed by impact of drops of Newtonian and non-Newtonian fluids
Auteur(s): Louhichi A., Charles C.-A., Phou T., Vlassopoulos Dimitris, Ramos L., Ligoure C.
(Article) Publié:
Physical Review Fluids, vol. 5 p.053602 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02884674_v1
Ref Arxiv: 2004.04825
DOI: 10.1103/PhysRevFluids.5.053602
WoS: WOS:000530638500002
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We investigate freely expanding liquid sheets made of either simple Newtonian fluids or solutions of high molecular water-soluble polymer chains. A sheet is produced by the impact of a drop on a quartz plate covered with a thin layer of liquid nitrogen that suppresses shear viscous dissipation thanks to an inverse Leidenfrost effect. The sheet expands radially until reaching a maximum diameter and subsequently recedes. Experiments indicate the presence of two expansion regimes: the capillary regime, where the maximum expansion is controlled by surface tension forces and does not depend on the viscosity, and the viscous regime, where the expansion is reduced with increasing viscosity. In the viscous regime, the sheet expansion for polymeric samples is strongly enhanced as compared to that of Newtonian samples with comparable zero-shear viscosity. We show that data for Newtonian and non-Newtonian fluids collapse on a unique master curve where the maximum expansion factor is plotted against the relevant effective \textit{biaxial extensional} Ohnesorge number that depends on fluid density, surface tension and the biaxial extensional viscosity. For Newtonian fluids, this biaxial extensional viscosity is six times the shear viscosity. By contrast, for the non-Newtonian fluids, a characteristic \textit{Weissenberg number}-dependent biaxial extensional viscosity is identified, which is in quantitative agreement with experimental and theoretical results reported in the literature for biaxial extensional flows of polymeric liquids.
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Structural identification of percolation of nanoparticles
Auteur(s): Musino D., Genix A.-C., Chauveau E., Bizien Thomas, Oberdisse J.
(Article) Publié:
Nanoscale, vol. 12 p.3907-3915 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02564183_v1
DOI: 10.1039/C9NR09395H
WoS: 000515391000035
Exporter : BibTex | endNote
Résumé: We propose a method relying on structural measurements by small-angle scattering to quantitatively follow aggregation of nanoparticles (NPs) in concentrated colloidal assemblies or suspensions up to percolation, regardless of complex structure factors arising due to interactions. As experimental model system, the dispersion of silica NPs in a styrene-butadiene matrix has been analyzed by small-angle X-ray scattering and transmission electron microscopy (TEM), as a function of particle concentration. A reverse Monte Carlo analysis applied to the NP scattering compared favorably with TEM. By combining it with an aggregate recognition algorithm, series of representative real space structures and aggregation number distribution functions have been determined up to high concentrations, taking into account particle polydispersity. Our analysis demonstrates that the formation of large percolating aggregates on the scale of the simulation box (of linear dimension 1/qmin, here micron-sized) can be mapped onto the macroscopic percolation characterized by rheology. Our method is thus capable of determining aggregate structure in dense NP systems with strong – possibly unknown – interactions visible in scattering. It is hoped to be useful in many other colloidal systems, beyond the case of polymer nanocomposites exemplarily studied here.
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