Dynamics of glass-forming liquids. V. On the link between molecular dynamics and configurational entropy

Abstract

We compare dielectric relaxation τ(T) data of several low molecular weight glass-forming liquids with the predictions of the Adam–Gibbs theory using experimental data for the configurational entropy Sc(T). Combination of Adam–Gibbs and Vogel–Fulcher equations yields an expression for Sc(T) which can be compared with experimental data. Good agreement is found for a range of temperatures near Tg<T<TB which depends on the fragility of the liquid and on the presence of a β relaxation. For fragile liquids, TB coincides with a qualitative change in the temperature dependence of the relaxation time scale or viscosity, with the temperature Tβ, where Johari–Goldstein-type β processes tend to merge into the α process, and with other crossover temperatures. For nonfragile liquids, TB/Tg increases, and the deviations from the Adam–Gibbs equation weaken or disappear altogether. The significance of TB, and of the Sc(T) temperature dependence implied by the Vogel–Fulcher theory fitting, are discussed in terms of the landscape paradigm.

Fragility and elasticity: Description of flow in highly viscous liquids

“…16 The relation to the nonergodicity factor is understandable because a low nonergodicity factor means a low level of density fluctuations, which in turn means that one is close to the ideal glass of the Kauzmann paradoxon and expects a high thermodynamic fragility. 17 Very recently, 18 it has been pointed out that there are exceptions from the nonergodicity rule due to a strong influence of secondary relaxations, 19 a reasoning which is parallel to the one in the present work, a second fragility influence which requires not only a knowledge of the fast motion but also of the relaxations themselves.…”

Glassy dynamics in three-dimensional embryonic tissues

“…We 21 . This is about 25 times smaller than that seen in experiments, where g ¼ 0.8 + 0.2 dyn cm 21 (n ¼ 6) and indicates that our model is not quantitatively capturing the surface tension effects in real tissues.…”

“…However, embryonic tissues share several properties with another class of materials called supercooled fluids-they are tightly packed in disordered structures and display elastic behaviour on short timescales and fluid behaviour on long timescales. Supercooled fluids have a viscoelastic relaxation timescale that is controlled by their proximity to a glass transition [18,21] and display glassy dynamics such as anomalous slowing of individual motions and 'caging' behaviour [22,23]. Caging behaviour occurs when the motion of a single element ( particle, atom or cell) is trapped and impeded from motion by a surrounding 'cage' of its nearest neighbours due to the dense packing of the system; only rare, high-energy fluctuations allow the element to be released from the cage and permitted to move a new location.…”

Structure Evolution in Amylopectin/Ethylene Glycol Mixtures by H-bond Formation and Phase Separation Studied with Dielectric Relaxation Spectroscopy

“…According to reference data 23 our m values are at the lower limit, which qualify AP/EG as a very strong glass former, corresponding to a low degree of SCHEME 1: Cluster Model of Amylopectin 30…”