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(33) Production(s) de l'année 2020
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Stress transmission in cemented bidisperse granular materials
Auteur(s): Heinze K., Frank Xavier, Lullien-Pellerin Valerie, George M., Radjai Farhang, Delenne Jean-Yves
(Article) Publié:
Physical Review E, vol. 101 p. (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02573271_v1
DOI: 10.1103/PhysRevE.101.052901
WoS: 000530027900010
Exporter : BibTex | endNote
Résumé: We analyze stress distributions in a two-dimensional bidisperse cemented granular packing for a broad range of the values of particle-size ratio, the volumes of large and small particles, and the amount of cementing matrix. In such textured porous materials, the stress concentration, which controls the fracture and fragmentation of the material under tensile loading or in grinding processes, reflects not only the porosity but also the contact network of the particle phase and the resulting stress chains. By means of peridynamic simulations under tensile loading, we show how both the texture and stress distribution depend on size ratio, volume ratio, and the amount of the cementing matrix. In particular, the volume fraction of the class of small particles plays a key role in homogenizing stresses across the system by reducing porosity. Interestingly, the texture controls not only the porosity but also the distribution of pores inside the system with its statistical variability, found to be strongly correlated with the homogeneity of stresses inside the large particles. The most homogeneous stress distribution occurs for the largest size ratio and largest volume fraction of small particles, corresponding to the lowest pore size dispersion and the cushioning effect of small particles and its similar role to the binding matrix for stress redistribution across the packing. At higher porosity, the tensile stresses above the mean stress fall off exponentially in all phases with an exponent that strongly depends on the texture. The exponential part broadens with decreasing matrix volume fraction and particle-size ratio. These correlations reveal the strong interplay between size polydispersity and the cohesive action of the binding matrix for stress distribution, which is significant for the behavior of textured materials in grinding operations.
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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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Recent advances in stimuli-responsive core-shell microgel particles: synthesis, characterisation, and applications
Auteur(s): Oberdisse J., Hellweg Thomas
(Article) Publié:
Progress In Colloid And Polymer Science, vol. 298 p.TBA (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02566998_v1
Ref Arxiv: 2011.07823
DOI: 10.1007/s00396-020-04629-0
WoS: WOS:000521913700001
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: Inspired by the path followed by Matthias Ballauff over the past 20 years, the development of thermosensitive core-shell microgel structures is reviewed. Different chemical approaches, from hard nanoparticle cores to double stimuli-responsive microgels have been devised and successfully implemented by many different groups. Some of the rich variety of these systems is presented, as well as some recent progress in structural analysis of such microstructures by small-angle scattering of neutrons or X-rays, including modeling approaches. In the last part, again following early work by the group of Matthias Ballauff, applications with particular emphasis on incorporation of catalytic nanoparticles inside core-shell structures – stabilizing the nanoparticles and granting external control over activity – will be discussed, as well as core-shell microgels at interfaces.
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Contrast variation SANS measurement of shell monomer density profiles of smart core-shell microgels
Auteur(s): Cors M., Wiehemeier Lars, Wrede Oliver, Feoktystov Artem, Cousin Fabrice, Hellweg Thomas, Oberdisse J.
(Article) Publié:
Soft Matter, vol. 16 p.1922-1930 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02566985_v1
PMID 31995091
DOI: 10.1039/c9sm02036e
WoS: WOS:000527137300020
Exporter : BibTex | endNote
Résumé: The radial density profile of deuterated poly(N,n-propyl acrylamide) shell monomers within core-shell microgels has been studied by small angle neutron scattering in order to shed light on the origin of their linear thermally-induced swelling. The poly(N-isopropyl methacrylamide) core monomers have been contrast-matched by the H2O/D2O solvent, and the intensity thus provides a direct measurement of the spatial distribution of the shell monomers. Straightforward modelling shows that their structure does not correspond to the expected picture of a well-defined external shell. A multi-shell model solved by a reverse Monte Carlo approach is then applied to extract the monomer density as a function of temperature and of the core crosslinking. It is found that most shell monomers fill the core at high temperatures approaching synthesis conditions of collapsed particles, forming only a dilute corona. As the core monomers tend to swell at lower temperatures, a skeleton of insoluble shell monomers hinders swelling, inducing the progressive linear thermoresponse.
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New interaction potentials for borate glasses with mixed network formers
Auteur(s): Sundararaman Siddharth, Huang L., Ispas S., Kob W.
(Article) Publié:
The Journal Of Chemical Physics, vol. 152 p.104501 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02563181_v1
DOI: 10.1063/1.5142605
WoS: 000519911600001
Exporter : BibTex | endNote
Résumé: We adapt and apply a recently developed optimization scheme used to obtain effective potentialsfor aluminosilicate glasses to include the network former boron into the interaction parameter set.As input data for the optimization, we used the radial distribution functions of the liquid at hightemperature generated by ab initio molecular dynamics simulations, and density, coordination andelastic modulus of glass at room temperature from experiments. The new interaction potentials areshown to reproduce reliably the structure, coordination and mechanical properties over a widerange of compositions for binary alkali borates. Furthermore, the transferability of these newinteraction parameters allows mixing to reliably reproduce properties of various boroaluminateand borosilicate glasses.
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Determining the Mesh Size of Polymer Solutions via the Pore Size Distribution
Auteur(s): Sorichetti V., Hugouvieux Virginie, Kob W.
(Article) Publié:
Macromolecules, vol. 53 p.2568-2581 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02540128_v1
Ref Arxiv: 1908.01484
DOI: 10.1021/acs.macromol.9b02166
WoS: 000526399500029
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
1 Citation
Résumé: In order to determine in polymeric systems the geometrical mesh size ξ, we simulate a solution of coarse-grained polymers with densities ranging from the dilute to the concentrated regime and for different chain lengths. We determine the monomer density fluctuation correlation length ξc from the monomer structure factor as well as the radial distribution function, showing that the identification ξ = ξc is not justified outside of the semidilute regime. In order to better characterize ξ, we compute the pore size distribution (PSD) following two different definitions, one by Torquato et al. and one by Gubbins et al. We find that the mean values of the two distributions, ⟨r⟩T and ⟨r⟩G, display the behavior predicted for ξ by scaling theory, and argue that ξ can be identified with either one of these quantities. This identification allows to interpret the PSD as the distribution of mesh sizes, a quantity which conventional methods cannot access. Finally, we show that it is possible to map a polymer solution on a system of hard or overlapping spheres, for which Torquato’s PSD can be computed analytically and reproduces accurately the PSD of the solution. We give an expression that allows ⟨r⟩T to be estimated with high accuracy in the semidilute regime by knowing only the radius of gyration and the density of the polymers.
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