Ref HAL: hal-02310531_v1
DOI: 10.1038/s41563-019-0464-7
WoS: 000486618800021
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Nanolaminate membranes made of two-dimensional materials such as graphene oxide are promising candidates for molecular sieving via size-limited diffusion in the two-dimensional capillaries, but high hydrophilicity makes these membranes unstable in water. Here, we report a nanolaminate membrane based on covalently functionalized molybdenum disulfide (MoS2) nanosheets. The functionalized MoS2 membranes demonstrate >90% and similar to 87% rejection for micropollutants and NaCl, respectively, when operating under reverse osmotic conditions. The sieving performance and water flux of the functionalized MoS2 membranes are attributed both to control of the capillary widths of the nanolaminates and to control of the surface chemistry of the nanosheets. We identify small hydrophobic functional groups, such as the methyl group, as the most promising for water purification. Methyl- functionalized nanosheets show high water permeation rates as confirmed by our molecular dynamic simulations, while maintaining high NaCl rejection. Control of the surface chemistry and the interlayer spacing therefore offers opportunities to tune the selectivity of the membranes while enhancing their stability

Ref HAL: hal-02319058_v1
DOI: 10.1063/1.5111621
WoS: 000489308600038
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The Raman modes of α-quartz-type boron phosphate were found to be extremely stable in frequency over a large temperature range from 300–1000 K. In order to determine the origin of this behavior, the material was also studied at high pressure up to 6 GPa. Upon compression, a classical behavior was observed with mode Grüneisen parameters ranging from −0.08(2) to 3.0(1). The present results indicate that the high temperature behavior in this material is an example of an unusual compensation effect between phonon–phonon interactions and implicit contributions due to thermal expansion. Phonon stability is of utmost importance for materials properties that are dependent on it such as dielectric and piezoelectric properties, for example. Boron phosphate belongs to the important class of α-quartz-type piezoelectric materials for which temperature stability is of primordial importance for resonator and sensor applications.

Ref HAL: hal-02302983_v1
DOI: 10.1021/acs.jpcc.9b04705
WoS: 000486360900040
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3 Citations

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L’existence d’une phase « Nematique twist Bend » (NTB) a été prédite par I.Dozov dès 2001 [1] mais n’a été observée expérimentalement qu’en 2010 [2]. Cette phase est assez originale car elle présente optiquement des défauts de type coniques focales sans réel ordre translationnel observable en diffusion des rayons X. Généralement cette phase est présente à des températures élevées (au-dessus de 100°C) dans les corps purs. L’ajout d’un nématogène [comme le 4-Cyano-4'-pentylbiphenyl (5CB)] à un composé NTB [tels que le 1,7-bis (4-cyanobiphényl-4-yl) heptane (CB7CB)] permet de diminuer fortement la plage d’existence de la phase NTB [3] tout en modifiant continûment les propriétés thermiques et diélectriques. Dans ce travail, nous avons exploré les modifications dues à l’ajout au CB7CB de smectogènes, et en particulier du 4′-octyl-4-biphénylcarbonitrile (8CB). Le diagramme de phase de ce dernier mélange binaire présente des caractéristiques surprenantes. Malgré leur ressemblance macroscopique, les phases SmA et NTB semblent ainsi incompatibles et restent séparées par une phase nématique s’étendant à très basse température (-20 ° C) pour une fraction CB7CB de ϕ_c≈20%. Nous avons par ailleurs caractérisé les propriétés optiques, thermiques, diélectriques et d’ancrage des phases N et NTB des mélanges. Les propriétés optiques sont très différentes de celles du CB7CB sur une large gamme de composition et de forts effets pré-transitionnels sont observables à l'approche de ϕ_c≈20%. Les propriétés d’ancrage (fig1) sont également significativement modifiées par l'ajout de 8CB au CB7CB ce qui facilite l'alignement homéotrope, très difficilement obtenu pour le CB7CB.

Ref HAL: hal-02290446_v1
PMID 35619482
DOI: 10.1021/acsmacrolett.9b00508
WoS: 000482521100019
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4 Citations
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This paper presents an efficient way to measure the curing kinetics and gel point, αgel, in epoxy resins from one single experiment. The epoxy curing reaction is herein monitored using in situ and time-resolved near-infrared absorption spectroscopy (NIR). The curing profiles over different isothermal conditions are in good agreement with DSC. Furthermore, the increase of the NIR absorption bands of aromatic rings (unreactive throughout curing) probe the cure shrinkage, as more and more aromatic rings are localized within the fixed sample volume. Therefore, the gel point is determined using the onset of the aromatic absorption increase. The results are in good agreement with the theoretical gel point, as well as DMA results. This innovative approach enables gelation measurements on epoxy neat resins and film composites with an easy-to-perform, accurate, robust, and versatile method.

Ref HAL: hal-02273078_v1
DOI: 10.1021/acs.jpcc.9b04806
WoS: 000474796600017
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The BiCuSeO-based compounds with very low thermal conductivity are among the most promising thermoelectric materials recently discovered. Their lattice dynamics, which remains mostly unexplored experimentally, is investigated in this paper. We report Raman experiments on BiCuSe1–xSxO solid solutions and infrared experiments on BiCuSeO and BiCuSO alloys coupled to first-principles-based calculations. We have observed that the high-energy A1g Raman-active mode strongly depends on the chalcogen content. We also report the density functional theory calculations of the dielectric and elastic constants, the phonons in the whole Brillouin zone, and the thermodynamic properties. We have determined the thermal expansion of BiCuSeO at room temperature from neutron diffraction experiments and evaluated its thermodynamic Grüneisen parameter and found a quite large value compared to other thermoelectric materials, which confirms the large anharmonicity of BiCuSeO.

Commentaires: jp9b04806_si_001.pdf (1.0 MB)

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To date, aqueous stable graphene flakes solutionscan be obtained by simple REDOX reactions.1–5 Most of the current applications regardinggraphene require ordered nanostructuredcomposites materials. Liquid crystal phases orderingrepresent an opportunity to arrange theminto macroscopic assemblies with long-rangeordering. 1,2 Preparing organized materials andthin films from these dispersions then requires agood control of the liquid crystal ordering duringthe deposition and the drying of the films. As amatter of fact, it turns out that graphene flakeseasily align at high shear.3,4 On the other hand,Graphene Flakes Liquid Crystals (GFLC) exhibita very interesting behaviour at low shear or undersmall displacements, thin films often showspeculiar patterns (such as the periodic texturesshown in Fig.72-72). We have shown how tocreate and stabilize large-sized periodic texturesin GFLC. The patterns have been characterizedunder optical and electronic microscopies. Theirstability can be explained by the competition betweenthe anchoring field of the substrate andthe presence of a yield stress resulting fromthe peculiar elastic and rheological properties ofthe GFLC. Our findings also clarify why longstandinghypotheses on the presence of exoticphases1 at large concentrations are present inthe literature.
References[1] Zakri, C.; Blanc, C.; Grelet, E.; Zamora-Ledezma, C.; Puech, N.; Anglaret, E.; Poulin, P. Philosophical Transactions of theRoyal Society A: Mathematical, Physical and Engineering Sciences 2013, 371, 20120499..
[2] Zamora-Ledezma, C.; Puech, N.; Zakri, C.; Grelet, E.; Moulton, S. E.; Wallace, G. G.; Gambhir, S.; Blanc, C.; Anglaret, E.;Poulin, P. The journal of physical chemistry letters 2012, 3, 2425–2430..
[3] Poulin, P.; Jalili, R.; Neri, W.; Nallet, F.; Divoux, T.; Colin, A.; Aboutalebi, S. H.; Wallace, G.; Zakri, C. Proceedings of theNational Academy of Sciences 2016, 113, 11088–11093..
[4] Zamora-Ledezma, C.; Jeridi, H.; Anglaret, E.; Blanc, C. Orientations and periodic textures in graphene liquid crystals. 27thInternational Liquid Crystal Conference (ILCC2018). 2018..
[5] Xu, Z.; Gao, C. Nature communications 2011, 2, 571.