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Dynamique et rhéologie des fluides complexes (gels, polymères, mousses, colloïdes)
(23) Production(s) de l'année 2021
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Experimental Test of the Edwards Volume Ensemble of Tapped Granular Packings
Auteur(s): Yuan Ye, Xing Yi, Zheng Jie, Li Zhifeng, Yuan Houfei, Zhang Shuyang, Zeng Zhikun, Xia Chengjie, Tong Hua, Kob W., Zhang Jie, Wang Yujie
(Article) Publié:
Physical Review Letters, vol. 127 p.018002 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03287898_v1
PMID 34270306
DOI: 10.1103/PhysRevLett.127.018002
Exporter : BibTex | endNote
Résumé: Using x-ray tomography, we experimentally investigate granular packings subject to mechanical tapping for three types of beads with different friction coefficients. We validate the Edwards volume ensemble in these three-dimensional granular systems and establish a granular version of thermodynamic zeroth law. Within the Edwards framework, we also explicitly clarify how friction influences granular statistical mechanics by modifying the density of states, which allows us to determine the entropy as a function of packing fraction and friction. Additionally, we obtain a granular jamming phase diagram based on geometric coordination number and packing fraction.
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Effect of Chain Polydispersity on the Elasticity of Disordered Polymer Networks
Auteur(s): Sorichetti V., Ninarello A. S., Ruiz-Franco José, Hugouvieux Virginie, Kob W., Zaccarelli Emanuela, Rovigatti Lorenzo
(Article) Publié:
Macromolecules, vol. 54 p.3769 - 3779 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03234741_v1
DOI: 10.1021/acs.macromol.1c00176
Exporter : BibTex | endNote
Résumé: Due to their unique structural and mechanical properties, randomly cross-linked polymer networks play an important role in many different fields, ranging from cellular biology to industrial processes. In order to elucidate how these properties are controlled by the physical details of the network (e.g., chain-length and end-to-end distributions), we generate disordered phantom networks with different cross-linker concentrations C and initial densities ρ init and evaluate their elastic properties. We find that the shear modulus computed at the same strand concentration for networks with the same C, which determines the number of chains and the chain-length distribution, depends strongly on the preparation protocol of the network, here controlled by ρ init. We rationalize this dependence by employing a generic stress−strain relation for polymer networks that does not rely on the specific form of the polymer end-to-end distance distribution. We find that the shear modulus of the networks is a nonmonotonic function of the density of elastically active strands, and that this behavior has a purely entropic origin. Our results show that if short chains are abundant, as it is always the case for randomly cross-linked polymer networks, the knowledge of the exact chain conformation distribution is essential for correctly predicting the elastic properties. Finally, we apply our theoretical approach to literature experimental data, qualitatively confirming our interpretations.
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First-principles study of the surface of silica and sodium silicate glasses
Auteur(s): Zhang Z., Kob W., Ispas S.
(Article) Publié:
Physical Review B, vol. 103 p.184201 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03223925_v1
DOI: 10.1103/PhysRevB.103.184201
Exporter : BibTex | endNote
Résumé: We use ab initio molecular dynamics simulations to investigate the properties of the dry surface of pure silicaand sodium silicate glasses. The surface layers are defined based on the atomic distributions along the direction(z direction) perpendicular to the surfaces. We show that these surfaces have a higher concentration of danglingbonds as well as two-membered (2M) rings than the bulk samples. Increasing the concentration of Na 2 O reducesthe proportion of structural defects. From the vibrational density of states, one concludes that 2M rings have aunique vibrational signature at a frequency ≈850 cm −1 , compatible with experimental findings. We also findthat, due to the presence of surfaces, the atomic vibration in the z direction is softer than for the two otherdirections. The electronic density of states shows clearly the differences between the surface and interior and wecan attribute these to specific structural units. Finally, the analysis of the electron localization function allows toget insight on the influence of local structure and the presence of Na on the nature of chemical bonding in theglasses.
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Connecting real glasses to mean-field models
Auteur(s): Nandi U. k., Kob W., Bhattacharyya S.m.
(Article) Publié:
The Journal Of Chemical Physics, vol. 154 p.094506 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03171939_v1
DOI: 10.1063/5.0038749
Exporter : BibTex | endNote
Résumé: We propose a novel model for a glass-forming liquid which allows to switch in a continuous manner froma standard three-dimensional liquid to a fully connected mean-field model. This is achieved by introducingk additional particle-particle interactions which thus augments the effective number of neighbors of eachparticle. Our computer simulations of this system show that the structure of the liquid does not changewith the introduction of these pseudo neighbours and by means of analytical calculations, we determine thestructural properties related to these additional neighbors. We show that the relaxation dynamics of thesystem slows down very quickly with increasing k and that the onset and the mode-coupling temperaturesincrease. The systems with high values of k follow the MCT power law behaviour for a larger temperaturerange compared to the ones with lower values of k. The dynamic susceptibility indicates that the dynamicheterogeneity decreases with increasing k whereas the non-Gaussian parameter is independent of it. Thus weconclude that with the increase in the number of pseudo neighbours the system becomes more mean-field like.By comparing our results with previous studies on mean-field like system we come to the conclusion that thedetails of how the mean-field limit is approached are important since they can lead to different dynamicalbehavior in this limit.
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Relaxation dynamics of non-Brownian spheres below jamming
Auteur(s): Nishikawa Y., Ikeda A., Berthier L.
(Article) Publié:
Journal Of Statistical Physics, vol. p.37 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03138225_v1
Ref Arxiv: 2007.09418
DOI: 10.1007/s10955-021-02710-8
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We numerically study the relaxation dynamics and associated criticality of non-Brownian frictionless spheres below jamming in spatial dimensions $d=2$, $3$, $4$, and $8$, and in the mean-field Mari-Kurchan model. We discover non-trivial finite-size and volume fraction dependences of the relaxation time associated to the relaxation of unjammed packings. In particular, the relaxation time is shown to diverge logarithmically with system size at any density below jamming, and no critical exponent can characterise its behaviour approaching jamming. In mean-field, the relaxation time is instead well-defined: it diverges at jamming with a critical exponent that we determine numerically and differs from an earlier mean-field prediction. We rationalise the finite $d$ logarithmic divergence using an extreme-value statistics argument in which the relaxation time is dominated by the most connected region of the system. The same argument shows that the earlier proposition that relaxation dynamics and shear viscosity are directly related breaks down in large systems. The shear viscosity of non-Brownian packings is well-defined in all $d$ in the thermodynamic limit, but large finite-size effects plague its measurement close to jamming.
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