Fragile glass-formers

Figure 2 Sketch of typical temperature dependencies of the viscosity r of glass-forming systems. The viscosimetric Tg of a material is defined by the viscosity reaching 1013 Poise. Strong glass formers show an Arrhenius temperature dependence, whereas fragile glass formers follow reasonably well a Vogel-Fulcher (VF) law predicting a diverging viscosity at some temperature T0.

An intimate connects exists between the shape of the relaxation function and steepness index [3,5,48,89,116,117], Strong liquids have less broad relaxation functions compared with fragile glass formers. The degree of nonexponentiality is reflected in the Kohlrausch exponent [1... 

Equation (4-5) typically applies up to temperatures of Tg + 50 C or so. For higher temperatures, an Arrhenius temperature-dependence often applies for small-molecule liquids, even if they are fragile glass formers. For example. Fig. 4-6 shows a plot of 1/ logio(/oo/fp) versus temperature for propylene carbonate, where fp = Incop is the peak frequency (in... 

Figure 12.2 Variation of the heat capacity for fragile glass formers in crystal (C), supercooled liquid (Lgc), equilibrium liquid (Leq) and glass (G) phases. is the Kauzmann temperature.

Fig. 11. Schematic illustration of the topographic distinction between energy landscapes for strong and fragile glass formers. Only one symmetry sector is represented. Potential energy increases upward the horizontal direction represents all configurational coordinates.

Stillinger, F. H., Enumeration of isobaric inherent structures for the fragile glass former o-terphenyl. J. Phys. Chem. B102,2807 (1998). 

Paluch, M., Gapihski, J., Patkowski, A., and Fischer, E. W. (2001) Does fragility depend on pressure A dynamic light scattering study of a fragile glass-former, J Chem. Phys. 114, 8048-8055. 

Rossler E, Sokolov A (1996) The dynamics of strong and fragile glass formers. Chem Geol 128 143-153 Routbort JL, Tomlins GW (1995) Atontic transport of oxygen in nonstoichiometric oxides. Radiation Effects and Defects in Solids 137 233-238... 

Bohmer R, Ngai KL, Angell CA, Plazek DJ (1993) Nonexponential relaxations in strong and fragile glass formers. J Chem Phys 99 4201-4209... 

Angell, C.A. (1985) in Strong and Fragile Glass Formers in Relaxation in Complex Systems, edited by K.I. Ngai and G.B. Wright, National Technical Information Service, U.S. Department of Commerce, Springfield, VA, 3. 

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