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(394) Production(s) de l'année 2014
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On the structure of sodium-borosilicate glasses: Insight from ab initio
simulations
Auteur(s): Kob W.
Conférence invité: 1st Joint Meeting of DGG – ACerS GOMD (Aachen, DE, 2014-05-25)
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Crossovers in the dynamics of supercooled liquids probed by an amorphous wall
Auteur(s): Hocky Glen M, Berthier L., Kob W., Reichman David R.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 89 p.052311 (2014)
Texte intégral en Openaccess :
Ref HAL: hal-00998409_v1
PMID 25353804
Ref Arxiv: 1402.5974
DOI: 10.1103/PhysRevE.89.052311
WoS: 000336765000003
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
37 Citations
Résumé: We study the relaxation dynamics of a binary Lennard-Jones liquid in the presence of an amorphous wall generated from equilibrium particle configurations. In qualitative agreement with the results presented in Nature Phys. {\bf 8}, 164 (2012) for a liquid of harmonic spheres, we find that our binary mixture shows a saturation of the dynamical length scale close to the mode-coupling temperature $T_c$. Furthermore we show that, due to the broken symmetry imposed by the wall, signatures of an additional change in dynamics become apparent at a temperature well above $T_c$. We provide evidence that this modification in the relaxation dynamics occurs at a recently proposed dynamical crossover temperature $T_s > T_c$, which is related to the breakdown of the Stokes-Einstein relation. We find that this dynamical crossover at $T_s$ is also observed for a system of harmonic spheres as well as a WCA liquid, showing that it may be a general feature of glass-forming systems.
Commentaires: 9 pages, 7 figures
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Life cycle assessment of nanocomposites made of thermally conductive graphite nanoplatelets
Auteur(s): Metz R., Bantignies J.-L.
(Article) Publié:
International Journal Of Life Cycle Assessment, vol. 19 p.1226-1232 (2014)
Ref HAL: hal-00996082_v1
DOI: 10.1007/s11367-014-0733-2
WoS: 000337062400006
Exporter : BibTex | endNote
33 Citations
Résumé: Purpose Polymers typically have intrinsic thermal conductivity much lower than other materials. Enhancement of this property may be obtained by the addition of conductive fillers. Nanofillers are preferred to traditional ones, due to their low percolation threshold resulting from their high aspect ratio. Beyond these considerations, it is imperative that the development of such new fillers takes place in a safe and sustainable manner. A conventional life cycle assessment (LCA) has been conducted on epoxy-based composites, filled with graphite nanoplatelets (GnP). In particular, this study focuses on energy requirements for the production of such composites, in order to stress environmental hot spots and primary energy of GnP production process (nano-wastes and nanoparticles emissions are not included). Methods A cradle-to-grave approach has been employed for this assessment, in an attributional modeling perspective. The data for the LCA have been gathered from both laboratory data and bibliographic references. A technical LCA software package, SimaPro (SimaPro 7.3), which contains Ecoinvent (2010) life cycle inventory (LCI) database, has been used for the life cycle impact assessment (LCIA), studying 13 midpoint indicators. Sensitivity and uncertainty analyses have also been performed. Results and discussion One kilogram of GnP filler requires 1,879 MJ of primary energy while the preparation of 1 kg of epoxy composite loaded with 0.058 kg of GnP 303 MJ. Besides energy consumption in the filler preparation, it is shown that the thermoset matrix material has also a nonnegligible impact on the life cycle despite the use of GnP: the primary energy required to make epoxy resin is 187 MJ, i.e., 62 % of the total energy to make 1 kg of composite. Conclusions Raw material extraction and filler and resin preparation phase exhibit the highest environmental impact while the composite production is negligible. Thermosetting resin remains the highest primary energy demand when used as matrix for GnP fillers. The result of the sensitivity analysis carried out on the electricity mix used during the GnP and the composite production processes does not affect the conclusions.
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Tuning Structure and Rheology of Silica-Latex Nanocomposites with the Molecular Weight of Matrix Chains: A Coupled SAXS-TEM-Simulation Approach
Auteur(s): Banc A., Genix A.-C., Chirat M., Dupas C., Caillol Sylvain, Sztucki Michael, Oberdisse J.
(Article) Publié:
Macromolecules, vol. 47 p.3219-3230 (2014)
Texte intégral en Openaccess :
Ref HAL: hal-00993789_v1
Ref Arxiv: 1405.5411
DOI: 10.1021/ma500465n
WoS: 000336020900052
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
34 Citations
Résumé: The structure of silica-latex nanocomposites of three matrix chain masses (20, 50, and 160 kg/mol of poly(ethyl methacrylate)) are studied using a SAXS/TEM approach, coupled via Monte Carlo simulations of scattering of fully polydisperse silica nanoparticle aggregates. At low silica concentrations (1 vol. %), the impact of the matrix chain mass on the structure is quantified in terms of the aggregation number distribution function, highest mass leading to individual dispersion, whereas the lower masses favor the formation of small aggregates. Both simulations for SAXS and TEM give compatible aggregate compacities around 10 vol. %, indicating that the construction algorithm for aggregates is realistic. Our results on structure are rationalized in terms of the critical collision time between nanoparticles due to diffusion in viscous matrices. At higher concentrations, aggregates overlap and form a percolated network, with a smaller and lighter mesh in the presence of high mass polymers. The linear rheology is investigated with oscillatory shear experiments. It shows a feature related to the silica structure at low frequencies, the amplitude of which can be described by two power laws separated by the percolation threshold of aggregates.
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Elasticité des verres et des liquides surfondus
Auteur(s): Ruffle B.
Conférence invité: Atelier GDR-Verres et USTV : Propriétés vs structure des verres et liquides à haute température (Paris, FR, 2014-05-26)
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Développements récents en spectroscopie Brillouin : applications en science des matériaux
Auteur(s): Ruffle B.
Conférence invité: XXèmes journées du Groupe Français de Spectroscopie Vibrationnelle (Paris, FR, 2014-05-21)
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Revealing the fast atomic motion of network glasses
Auteur(s): Ruta B., Baldi G., Chushkin Y., Ruffle B., Cristofolini L., Fontana A., Zanatta M., Nazzani F.
(Article) Publié:
Nature Communications, vol. 5 p.3939 (2014)
Texte intégral en Openaccess :
Ref HAL: hal-00993301_v1
DOI: 10.1038/ncomms4939
WoS: 000337505200004
Exporter : BibTex | endNote
83 Citations
Résumé: Still very little is known on the relaxation dynamics of glasses at the microscopic level due to the lack of experiments and theories. It is commonly believed that glasses are in a dynamical arrested state, with relaxation times too large to be observed on human time scales. Here we provide the experimental evidence that glasses display fast atomic rearrangements within a few minutes, even in the deep glassy state. Following the evolution of the structural relaxation in a sodium silicate glass, we find that this fast dynamics is accompanied by the absence of any detectable aging, suggesting a decoupling of the relaxation time and the viscosity in the glass. The relaxation time is strongly affected by the network structure with a marked increase at the mesoscopic scale associated with the ion-conducting pathways. Our results modify the conception of the glassy state and asks for a new microscopic theory.
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