Comment on “Direct determination of kinetic fragility indices of glassforming liquids by differential scanning calorimetry: Kinetic versus thermodynamic fragilities” [J. Chem. Phys. 117, 10184 (2002)]

Abstract

Recently Wang et al. [J. Chem. Phys. 117, 10184 (2002)] reported fragilities for various molecular liquids, as determined by calorimetry. The technique is based on measuring the change in fictive temperature with cooling rate. We point out that the same method was previously applied to polymers [Robertson, Santangelo, and Roland, J. Non-Cryst. Solids 275, 153 (2000)], yielding good agreement with fragility values obtained by mechanical or dielectric spectroscopy.

Enthalpy relaxation in hyperquenched glasses of different fragility

“…Originally the fragility was suggested to be connected to the size of the jump in heat capacity observed in DSC measurements at T g [31]. Later on this has been opposed based on measurements on a range of substances [33,34]. Because of the large amount of standard measurements of C p on each composition available from the second upscans performed, we have the possibility to investigate the connection between the fragility and the calorimetric glass transition closer.…”

“…Several suggestions to a possible connection between parameters extracted from the thermodynamic glass transition and the kinetic fragility have been proposed [31][32][33][34]. Originally the fragility was suggested to be connected to the size of the jump in heat capacity observed in DSC measurements at T g [31].…”

Composition–structure–property relationships in boroaluminosilicate glasses

“…There have been several attempts to connect the kinetic fragility index m determined from viscosity measurements with thermodynamic property changes at the glass transition determined using DSC [20,33,[41][42][43][44]. "Fragile" liquids have dramatic viscosity changes at the glass transition, and they are thus expected to have large configurational heat capacities, as a consequence of their configurational entropy changing rapidly with temperature [42].…”

Determination of Fragility in Organic Small Molecular Glass Forming Liquids: Comparison of Calorimetric and Spectroscopic Data and Commentary on Pharmaceutical Importance

“…For example, Ngai has argued that although thermodynamics (degree of change of volume or entropy) does play a role in change of either η or τ as a function of temperature at T > T g , the extent of this contribution will also depend on the chemical and physical structure of the molecule and will thus differ from one group of glass formers to another . Kinetic factors such as α-relaxation as well as time/temperature dependent distribution of this relaxation time are influenced by many-body relaxation dynamics and thus cannot be completely explained by thermodynamics alone. , Similarly, glass transition cannot be viewed strictly as a thermodynamic parameter since there may be other underlying factors contributing to this phenomenon that are not thermodynamic in nature. While it is certainly attractive to calculate thermodynamic fragility from easily and readily measurable parameters, based on the data and the arguments presented, the use of “thermodynamic fragility” is questionable at best.…”

“…45 Kinetic factors such as α-relaxation as well as time/temperature dependent distribution of this relaxation time are influenced by many-body relaxation dynamics and thus cannot be completely explained by thermodynamics alone. 45,46 Similarly, glass transition cannot be viewed strictly as a thermodynamic parameter since there may be other underlying factors contributing to this phenomenon that are not thermodynamic in nature. While it is certainly attractive to calculate thermodynamic from easily and readily measurable parameters, based on the data and the arguments presented, the use of "thermodynamic fragility" is questionable at best.…”