Dynamics of strong and fragile glass formers: Differences and correlation with low-temperature properties

Sokolov, Alexei P.; Rössler, E. A.; Kisliuk, A.; Quitmann, D.

doi:10.1103/physrevlett.71.2062

Cited by 380 publications

(298 citation statements)

References 22 publications

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“…Fragility in polymers has been related and/or correlated to the nonexponentiality (breadth) of segmental relaxation function, [4][5][6] rates of physical aging 7,8 and peculiarity of the fast dynamics. 9,10 It has been realized that behavior of structural (segmental) relaxation in many polymers deviates from regularities known for structural (R-) relaxation in small molecular liquids. 4,[11][12][13] There seems to be a "polymer specific" contribution to fragility of polymeric systems.…”

Section: Introductionmentioning

confidence: 99%

Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture

et al. 2008

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Understanding microscopic parameters that control steepness of the temperature variations of segmental relaxation (fragility) and the glass transition phenomenon remains a challenge. We present dielectric and mechanical relaxation studies of segmental dynamics in various polymers with different side groups and backbone structures. The results have been analyzed in terms of flexibility of backbone and side groups of polymeric molecules, as suggested by the recent theoretical works by Dudowicz et al. A comparison of structures with identical backbones and varying side groups and identical side groups but different backbones reveals that the flexibility of side groups relative to the flexibility of the backbone is the most important factor controlling fragility in polymers, while the glass transition temperature T g depends primarily on the backbone flexibility and the side group bulkiness (occupied volume). Based on these results and analysis of literature data we formulated a modified approach to understand the role of chemical structure in segmental dynamics: (i) Polymers with stiff backbones always have high T g and fragility, while (ii) polymers with flexible backbones and no side groups are the strongest; (iii) however, for the most common type of polymeric structure, C-C or Si-O backbone with side groups, fragility increases with increasing "relatiVe" stiffness of side groups versus the backbone. In this class of polymers, lowest fragility is expected when the side groups are of similar chemical structure (or flexibility) as the backbone, as in the case of polyisobutylene, one of the strongest polymers known.

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Section: Introductionmentioning

confidence: 99%

Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture

et al. 2008

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“…Many studies have evidenced the existence of correlations between the values of the fragility and other properties of the supercooled liquids, such as: i) the "visibility" of the Boson Peak [6,7]; ii) the T -dependence of the shear elastic modulus in liquids (shoving model) [8,9,10,11]; iii) the stretching of the decay of the correlation functions at the glass transition temperature [12,13]; iv) the nonlinearity of the relaxation functions [14] and, very recently, v) the vibrational properties of the glass at T → 0 [15]. Other works have tried to extract physical information on the nature of the glass transition from the existence of these correlations [16,17].…”

Section: Introductionmentioning

confidence: 99%

Landscapes and fragilities

Ruocco

Sciortino

Zamponi

et al. 2004

The Journal of Chemical Physics

141

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The concept of fragility provides a possibility to rank different supercooled liquids on the basis of the temperature dependence of dynamic and/or thermodynamic quantities. We recall here the definitions of kinetic and thermodynamic fragility proposed in the last years and discuss their interrelations. At the same time we analyze some recently introduced models for the statistical properties of the potential energy landscape. Building on the Adam-Gibbs relation, which connects structural relaxation times to configurational entropy, we analyze the relation between statistical properties of the landscape and fragility. We call attention to the fact that the knowledge of number, energy depth and shape of the basins of the potential energy landscape may not be sufficient for predicting fragility. Finally, we discuss two different possibilities for generating strong behavior.

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“…Despite the huge range of time scales older [34] and recent theoretical [35][36][37][38][39][40][41] studies addressed the rattling process in the cage to understand the structural relaxation -the escape process -gaining support from numerical [8, 15, 41-59, 61? , 62] and experimental works on glassforming liquids [41,63,64] and glasses [38,[65][66][67][68][69][70].…”

Section: Introductionmentioning

confidence: 99%

Cage rattling does not correlate with the local geometry in molecular liquids

Bernini

Puosi

Leporini

2015

Journal of Non-Crystalline Solids

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Molecular-dynamics simulations of a liquid of short linear molecules have been performed to investigate the correlation between the particle dynamics in the cage of the neighbors and the local geometry. The latter is characterized in terms of the size and the asphericity of the Voronoi polyhedra. The correlation is found to be poor. In particular, in spite of the different Voronoi volume around the end and the inner monomers of a molecule, all the monomers exhibit coinciding displacement distribution when they are caged (as well as at longer times during the structural relaxation). It is concluded that the fast dynamics during the cage trapping is a non-local collective process involving monomers beyond the nearest neighbours.PACS numbers:

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Dynamics of strong and fragile glass formers: Differences and correlation with low-temperature properties

Cited by 380 publications

References 22 publications

Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture

Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture

Landscapes and fragilities

Cage rattling does not correlate with the local geometry in molecular liquids

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