Thermodynamics of the Glass Transition: Empirical Aspects*

Abstract

tThis choice will somewhat underestimate the value at high temperatures where the liquid "instantaneous" structure will be considerably loosened with respect to the crystal structure (and to that of the liquid at T g ) , but the difference will be of the nature of an anharmonicity correction, and should be small.

Landscapes and fragilities

“…Similarly, in a very recent work [65], Tarjus and coworkers show that -in alcohols-the change in density only slightly affects the fragility, thus indicating that under the experimentally accessible density changes the landscape suffers only minor modifications. For other systems, on the contrary, it has been observed a large deviation (≈ 40%) between constant density and constant pressure fragilities [46]. This ongoing discussions, however, does not affect the conclusions of the present work since all the formalism could have been based on the enthalpy landscape, instead of energy landscape, without any changes in the results.…”

“…For thirty years it has been realized [46] that the temperature dependence of the (constant volume) excess specific heat can be described by a hyperbolic law (C ≈ const + const ′ /T ), and this law is commonly used to represent the experimental data [27]. The "landscape model" that gives rise to such a temperature dependence for the excess specific heat is the so called hyperbolic model, recently introduced and discussed in detail by Debenedetti, Stillinger and Lewis [47].…”

Absence of molecular mobility on nano-second time scales in amorphous ice phases

“…A comparable T g has been deduced from DSC studies of different aqueous solutions, whose specific T g s extrapolate upon dilution toward the single value of 135 K [27,28].…”

Nonuniversality of the Specific Heat in Glass Forming Systems

“…We explain the physics of the two specific heat peaks by the micro-melting of two types of clusters. While this physics is easily accessible, the consequences are that one should not expect any universality in the temperature dependence of the specific heat in glass formers.The thermodynamic properties of glass-formers near the glass transition have been a subject of intensive and far from settled research for more than half a century [1][2][3][4]. The temperature dependence of the entropy and how the entropy extrapolates to low temperatures gave rise to the so-called Kauzmann paradox [1] that remains confusing to the present time.…”