Relaxation time configurational entropy model

On the other hand, some phenomenological distributions of relaxation times, such as the well known Williams-Watts distribution (see Table 1, WW) provided a rather good description of dielectric relaxation experiments in polymer melts, but they are not of considerable help in understanding molecular phenomena since they are not associated with a molecular model. In the same way, the glass transition theories account well for macroscopic properties such as viscosity, but they are based on general thermodynamic concepts as the free volume or the configurational entropy and they completely ignore the nature of molecular motions. 

The major tenet of the model is that there is a direct relationship between the configuration entropy and the rate of molecular transport. In other words, it is postulated that as the blocks become larger, it takes more time for them to switch configurations. It follows that the relaxation... 

Finally, it is worth noting that the values of Tq or needed to fit the viscosity data are close to the temperature at which the Kauzmann temperature, Tkau is estimated from extrapolations of other properties such as those shown in Fig. 9.8, lending credence to the model. This model also provides a natural way out of the Kauzmann paradox, since not only do the relaxation times go to infinity as T approaches 7)., but also the configuration entropy vanishes since in glass at T = T only one configuration is possible. 

While borrowing from the classical models, these phenomenological approaches have also helped to clarify and refine the concepts of free-volume and configurational entropy and have focused attention on the nature of the relaxation spectrum (7-10,109,110). When a hquid in equiUbrium at a temperature Ti is suddenly cooled to a temperature, T2, its structure has no time to adjust and its properties (such as volume V, enthalpy H, or index of refraction n) exhibit instantaneous, solidlike changes characteristic of the glassy state as illustrated in Figure 9. For example, the instantaneous change in the enthalpy H may be written as follows ... 

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