Why liquids are fragile

Abstract

The fragilities (Tg-normalized temperature dependence of alpha-relaxation times) of 33 glass-forming liquids and polymers are compared for isobaric, mP, and isochoric, mV, conditions. We find that the two quantities are linearly correlated, mP = (37 +/- 3) + (0.84 +/- 0.5)mV. This result has obvious important consequences, since the ratio mV/mP is a measure of the relative degree to which temperature and density control the dynamics, Moreover, we show that the fragility itself is a consequence of the relative interplay of temperature and density effects near Tg. Specifically, strong behavior reflects a substantial contribution from density (jammed dynamics), while the relaxation of fragile liquids is more thermally-activated. Drawing on a scaling law, a physical interpretation of this result in terms of the intermolecular potential is offered.

15 pages 4 figures

References in corpus (4)

• Scaling the alpha-relaxation time of supercooled fragile organic liquids
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• Fragility and compressibility at the glass transition
• Effect of Chemical Structure on the Isobaric and Isochoric Fragility in Polychlorinated Biphenyls

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• Theory of the Structural Glass Transition: A Pedagogical Review
• Density scaling in viscous liquids: From relaxation times to four-point susceptibilities
• Superstrong nature of covalently bonded glass-forming liquids at select compositions
• Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids
• Local dielectric spectroscopy of near-surface glassy polymer dynamics
• Does the repulsive interatomic potential determine fragility in metallic liquids?
• Thermodynamic scaling of dynamics in polymer melts: Predictions from the generalized entropy theory
• On the experimental determination of the repulsive component of the potential from high pressure measurements: what is special about twelve?
• In search of invariants for viscous liquids in the density scaling regime: Investigations of dynamic and thermodynamic moduli
• Correlation between kinetic fragility and Poisson's ratio from analysis of data for soft colloids