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(2) 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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