Thermodynamics glass transition

All in all- at this time a first order thermodynamic glass transition can definitely be excluded. However, the controversy over the existence of a second order transition (even though a hypothetical one) in the... 

The kinetic theories are dealt with in section 5.3.2. According to these theories there is no true thermodynamic glass transition. The kinetic theories predict that the glass transition is a purely kinetic phenomenon and that it appears when the response time for the system to reach equilibrium is of the same size as the time-scale of the experiment. The theory predicts that a lowering of the cooling rate will lead to a decrease in the kinetic glass transition temperature. 

Together, equations (10), (12) and (13) have led to much discussion over the thermodynamics of the glass transition event. This is because, depending upon how the experiments are carried out, one can attain agreement, i.e. R = 1, or not with the prediction for a second-order thermodynamic transition. In this author s view, much of the discussion is unnecessary because the experiments measure a kinetic phenomenon (perhaps a manifestation of an underlying thermodynamic event) and, therefore, cannot test whether or not there is a true thermodynamic glass transition. 

Interestingly, it was found that the thermodynamic glass transition matched not only the change in coefficient of expansion which accompanies the glass transition found by thermomechanical analysis (TMA), but also the heat distortion temperature as measured on macroscopic test bars. This finding permitted the use of DSC data with confidence for cure checks, in preference to the more complex and time-consuming preparation of heat distortion test bars. 

Figure 5.4 Thermodynamic glass transition of two cast epoxy samples showing the increase in Tg (lower...

These predictions represent a complete dynamic scenario that has been investigated by numerous experiments [65]. Indeed, such MCT predictions have been able to describe properly the relaxation processes in supercooled liquids, even if the experimental results locate the MCT critical transition. To, at temperatures higher than the thermodynamical glass transition. 

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