Fragility and Its Estimation

An estimate of the fragility of a given glassy preparation is required to enable a reliable calculation of its shelf life to be made. The estimation of the fragility parameter itself requires a number of thermoanalytical measurements to be performed. Three methods, in decreasing order of experimental rigour, are given below. 

The entropy change on crystal-melting, ASm, may be taken to represent Sc at the melting point T, hence Equation (7) may be written as 

For many organic glass formers, = (constant/7) and can therefore be calculated at Tg (or any single temperature), permitting Tito be estimated. 

Tg is the temperature region where an undercooled liquid deviates from, or returns to equilibrium, and it describes the relationship between relaxation time and temperature. The measured Tg depends upon the applied experimental heating (or cooling) rate, as described by Mo-ynihan et 

This can lead to significant experimental errors unless careful calibration is carried out throughout the course of experimental runs. 

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