Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer

Duval, E.; Saviot, Lucien; David, Laurent; Étienne, S.; Jal, J. F.

doi:10.1209/epl/i2003-00573-x

Cited by 34 publications

(30 citation statements)

References 27 publications

(56 reference statements)

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“…(5.6), leading to ω AM > 0. In agreement with this idea, hyperquenched mineral glasses show a much stronger excess of modes [76] in comparison with normally cooled glasses, and annealed polymeric glasses expectedly show a smaller excess of modes [77].…”

Section: Infinite Quenchsupporting

confidence: 57%

On the rigidity of amorphous solids

2005

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We poorly understand the properties of amorphous systems at small length scales, where a continuous elastic description breaks down. This is apparent when one considers their vibrational and transport properties, or the way forces propagate in these solids. Little is known about the microscopic cause of their rigidity. Recently it has been observed numerically that an assembly of elastic particles has a critical behavior near the jamming threshold where the pressure vanishes. At the transition such a system does not behave as a continuous medium at any length scales. When this system is compressed, scaling is observed for the elastic moduli, the coordination number, but also for the density of vibrational modes. In the present work we derive theoretically these results, and show that they apply to various systems such as granular matter and silica, but also to colloidal glasses. In particular we show that: (i) these systems present a large excess of vibrational modes at low frequency in comparison with normal solids, called the "boson peak" in the glass literature. The corresponding modes are very different from plane waves, and their frequency is related to the system coordination; (ii) rigidity is a non-local property of the packing geometry, characterized by a length scale which can be large. For elastic particles this length diverges near the jamming transition; (iii) for repulsive systems the shear modulus can be much smaller than the bulk modulus. We compute the corresponding scaling laws near the jamming threshold. Finally, we discuss the implications of these results for the glass transition, the transport, and the geometry of the random close packing.

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Section: Infinite Quenchsupporting

confidence: 57%

On the rigidity of amorphous solids

2005

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“…Strong and fragile systems have very different molecular organisation and bonding. Although the intensity of vibrational anomalies is less important in fragile systems, it is well documented in experiments [6] on polymer glasses or in simulations of Lennard-Jones systems [22]. The observation of common features points to a universal framework for the description of low frequency vibrations in glassy systems.…”

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confidence: 99%

Inhomogeneous Elastic Response of Silica Glass

Léonforte¹,

Tanguy²,

Wittmer³

et al. 2006

Phys. Rev. Lett.

211

184

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Using large scale molecular dynamics simulations we investigate the properties of the non-affine displacement field induced by macroscopic uniaxial deformation of amorphous silica, a strong glass according to Angell's classification. We demonstrate the existence of a length scale ξ characterizing the correlations of this field (corresponding to a volume of about 1000 atoms), and compare its structure to the one observed in a standard fragile model glass. The "Boson-peak" anomaly of the density of states can be traced back in both cases to elastic inhomogeneities on wavelengths smaller than ξ where classical continuum elasticity becomes simply unapplicable.PACS numbers: 61.43.Fs, 62.20.Dc, 63.50.+x, 72.80.Ng The vibrational dynamics of glasses and in particular the vibrational anomaly known as the "Boson Peak", i.e. an excess of the low-energy density of state in glasses relative to the Debye model, have attracted considerable attention in condensed matter physics [1,2,3]. This anomaly is observed in Raman and Brillouin spectroscopy [4] and inelastic neutron scattering [5] experiments in many different systems (polymer glasses [6], silica [7], metallic glasses [8]) and the corresponding excitations are often associated with heat capacity or heat conductivity low temperature anomalies. Many interpretations of these vibrational anomalies have been put forward, and generally involve some kind of disorder generated inhomogeneous behavior [1], whose exact nature, however, is the subject of a lively debate [2,3,4,9].In this work, we argue that the natural origin of these anomalies in "fragile" as well as "strong" glasses lies in the inhomogeneities of the elastic response at small scales, which can be characterized through the correlation length ξ of the inhomogeneous or "non-affine" part of the displacement field generated in response to an elastic deformation imposed at the macroscopic scale. The existence of such a length has been suggested in a series of previous numerical studies [10,11,12] In practice, however, it appears that the only practical way to quantify this effect for a given material consists in direct molecular simulations [10,11]. The present contribution extends, for the first time, the numerical analysis to a realistic model of an amorphous silca melta "strong" glass according to Angell's classification [21]. Our results are compared to a previously studied "fragile" reference glass formed by weakly polydisperse LJ particles in 3D [12]. Strong and fragile systems have very different molecular organisation and bonding. Although the intensity of vibrational anomalies is less important in fragile systems, it is well documented in experiments [6] on polymer glasses or in simulations of Lennard-Jones systems [22]. The observation of common features points to a universal framework for the description of low frequency vibrations in glassy systems. One recent finding of particular interest, is the fact that, in these LJ systems, the Boson Peak anomaly appears to be located at the edge of the non-affine...

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“…glasses and substitution solid solutions) to the first van Hove singularity in crystal structures is noted in (Buchenau et al, 2004;Gospodarev et al, 2008). BPs are also observed in polymeric and metallic glasses (Duval et al, 2003;Arai et al, 1999). As is shown in Fig.4 shape of the first van Hove singularity can be seen on curves 6.…”

Section: Low-frequency Characteristics Of the Phonon Spectra Of Disormentioning

confidence: 56%