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Structure, vibration, relaxations dans les systèmes désordonnés
(4) Production(s) de l'année 2024
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Hyper-Raman scattering from the LO modes of perovskite ferroelectric relaxors 
Auteur(s): Hehlen B. , Al-Zein A.
(Article) Publié:
Physical Review B, vol. 110 p.024313 (2024)
DOI: 10.1103/PhysRevB.110.024313
Résumé: Hyper-Raman scattering is used to study the temperature dependence of the longitudinal optic (LO) modes
of three prototypical ferroelectric relaxors in a broad temperature range from 20 to 800 K. The three LO bands
observed in all spectra of the three materials are linked to the three transverse optic (TO) modes in cubic relaxors
where LOi is linked to TOi , with i = 1 to 3. The Last, Slater, and Axe eigenvector pictures of the TO modes are
consistent with our observations on LO1, LO2, and LO3, respectively. Within this framework, the splitting of
LO2 would mostly be linked to a structural disorder on the B site while the strength of an anomaly of LO1 near
the freezing temperature Tf relies on the ability of the material to develop a long-range ordering. Moreover, the
more pronounced the splitting, the more important the structural disorder and the lower the value of the dielectric
constant.
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Structural and mechanical properties of bio-inspired polymer networks
Auteur(s): Hugouvieux Virginie, Kob W.
Conférence invité: Network dynamics: Synthesis, structure and mechanical properties (Les Houches School of Physics, FR, 2024-02-26)
Ref HAL: hal-04661726_v1
Exporter : BibTex | endNote
Résumé: We use molecular dynamics simulations to study the structural and mechanical properties of bead-spring polymer networks. In this study we deal with systems which are biologically-relevant as they result from the action of enzymes, i.e. biological catalysts. The latter convert repulsive monomers into attractive ones and hence, starting from a polymer solution, trigger the formation of a physically-crosslinked polymer network. This gel has a remarkably regular mesostructure in the form of a cluster phase. We simulate uniaxial tension of these networks. The evolution of their structural and mechanical properties during deformation is monitored by computing quantities such as the anisotropic pair correlation functions, Poisson's ratio, elastic moduli and stress-strain curves, and the effects of temperature and system composition (i.e. fraction of attractive monomers) are investigated.
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From creep to flow: Granular materials under cyclic shear
Auteur(s): Yuan Ye, Zeng Zhikun, Yuan Houfei, Zhang Shuyang, Kob W., Wang Yujie
(Article) Publié:
Nature Communications, vol. 15 p.3866 (2024)
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Creating equilibrium glassy states via random particle bonding
Auteur(s): Ozawa M., Barrat Jean-Louis, Kob W., Zamponi Francesco
(Article) Publié:
Journal Of Statistical Mechanics: Theory And Experiment, vol. 2024 p.013303 (2024)
Texte intégral en Openaccess : 
Ref HAL: hal-04721895_v1
Ref Arxiv: 2311.08079
DOI: 10.1088/1742-5468/ad17b6
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: Abstract Creating amorphous solid states by randomly bonding an ensemble of dense liquid monomers is a common procedure that is used to create a variety of materials, such as epoxy resins, colloidal gels, and vitrimers. However, the properties of the resulting solid do a priori strongly depend on the preparation history. This can lead to substantial aging of the material; for example, properties such as mechanical moduli and transport coefficients rely on the time elapsed since solidification, which can lead to a slow degradation of the material in technological applications. It is therefore important to understand under which conditions random monomer bonding can lead to stable solid states, that is, long-lived metastable states whose properties do not change over time. This work presents a theoretical and computational analysis of this problem and introduces a random bonding procedure that ensures the proper equilibration of the resulting amorphous states. Our procedure also provides a new route to investigate the fundamental properties of glassy energy landscapes by producing translationally invariant ultrastable glassy states in simple particle models.
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