Entropy, glass-forming liquids

C. Adam-Gibbs Relation Between the Configurational Entropy Sc and Relaxation in Glass-Forming Liquids... 

As will be discussed in more detail later, the kinetic fragility can be correlated with excess entropy for a wide class of glass-forming liquids... 

Lennard-Jones binary mixture of particles is a prototypical model that describes glass-forming liquids [52,53,158,162-165]. The temperature and the density dependence of diffusivity D(T, p) have been obtained by computer simulations for the Lennard-Jones binary mixture in the supercooled state. To relate fragility of binary Lennard-Jones mixture to thermodynamic properties necessitates determination of the configurational entropy SC(T, p) as well as the vibration entropy Sv,h(T, p) at a given temperature and density. 

Fig. 12. Adam-Gibbs plots of the dielectric relaxation time of 2-methyltetrahydrofuran (2-MTHF) and 3-bromopentane (3-BP) versus (Tsconi) . The lines are VTF fits, 7 fus is the fusion temperature, and Tb is the temperature below which the VTF equation applies. /I ag and Avf are prefactors in the Adam-Gibbs and VTF equations, respectively. Tk is the calorimetri-cally determined Kauzmann temperature, and To is the VTF singular temperature, which were set equal in the VTF (line) fits. (Reprinted with permission from R. Richer and C. A. Angell. Dynamics of glass-forming liquids. V. On the link between molecular dynamics and configurational entropy. J. Chem. Phys. (1998) 108 9016. Copyright 1998, American Institute of Physics.)...

Richert, R., and Angell, C. A., Dynamics of glass-forming liquids. V. On the link between molecular dynamics and configurational entropy. J. Chem. Phys. 108, 9016 (1998). 

In many examples, particularly in fragile glass-forming liquids discussed in detail in chapter 3, the entropy lost by the time the system arrives at Tg is such a large fraction of AS m that the entropy crisis is imminent in just under 20 K below Tg. Therefore, any suggestion that the remaining entropy may be lost so slowly that Tk becomes equal to 0 K appears impossible. Kauzmann s own resolution of this paradox has been... 

Table 3.2 Measured and caleulated values of entropies for several glass forming liquids (After Johari, 2000).

Kauzmann4 noted that if the entropies of simple glass-forming liquids were extrapolated to low temperatures, they would go to zero long before the... 

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