Glasses fragility parameter

Equation (3.9) clearly indicates that ionic conductivity could be improved by lowering the Tg of the system. The difference in the temperature dependences of ionic conductivity (and viscosity) for ion-conductive glass-forming materials has been discussed by Angell et al. using fragility parameters [115]. 

Fig. 3.53 Viscosity data from Fig. 3.51 plotted against the volume (normalized by the ambient-pressure volume). The curves are fits obtained by the free-volume theory (eqn 3.9.5), the resulting parameters being for methanol, B = 2.22 0.05 and V = 33.8 0.1 A for 1,2-propanediol, S = 6.7 0.3 and 14 = 71.9 0.5 A. Extrapolation of these fits to T = 10 Pa s gives the indicated glass-transition pressures, P. The strong curvature of the methanol data indicates the more fragile behavior of this fluid, which is reflected in the fragility parameters (calculated from equation 5 given by Cook et a .)F For methanol mp = 289 6 and for 1,2-propanediol mp = 123 5.

Figure 9 Diagrammatic representations of typical DSC scans of the glass transition showing the quantities required for the determination of the fragility parameter and To. The first scan, usually taken after storage (annealing), reveals an endotherm of the relaxation enthalpy, which disappears after recooling and immediate reheating...

A best-fit of the data in Fig. 3 to Eq. (2) yields the characteristic temperature. To = (509 18K) (error estimate is based on a 95% confidence interval through out this chapter) and below we compare the ratio, D= Qy lk To, the fragility parameter in glass-forming liquids, for our GB dynamics to D for appropriate... 

Appendix A. Objective Measures of Fragility and an Order Parameter for Glass Formation Acknowledgments References... 

APPENDIX A OBJECTIVE MEASURES OF FRAGILITY AND AN ORDER PARAMETER FOR GLASS FORMATION... 

Interaction frustration has also been found to be a control parameter for fragility in a spin model of glass formation. 

An explicit expression relating kinetic fragility to thermodynamic behavior of supercooled liquids was accomplished for the first time by Mohanty and coworkers [55,56] and independently by Speedy [54], These authors derived an expression for the steepness parameter, a measure of kinetic fragility, from the temperature variation of the relation time or viscosity, with the ratio of excess entropy and heat capacity changes at the glass transition temperature [54-56]. A detailed description of this work will be provided later in the review chapter. 

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