Quasi-Isothermal Kinetics of the Glass Transition

The kinetics in the glass transition and melting regions are of interest for a better understanding of the materials, prediction of their performance and analysis of their history. To describe the glass transition, following the 

In the glass transition region, the approach to equilibrium may be approximated by a first-order kinetics as long as the distance from equilibrium is not too large. The instantaneous number of high-energy configurations is then represented by N and the relaxation time by t  

Under quasi-isothermal conditions and at steady state, the solution of Eq. (20) can be written with constants An = Aa/No and A-c = Asj/(RT ), where A is the amplitude of temperature modulation. 

From Eq. (22), one sees that the large-amplitude motion contributes fully in the liquid state where y = 0, and not at all in the glassy state where y = itH. The glass transition temperature, defined at the temperature of half-vitrification or devitrification, occurs at y = TtlZ. 

This observation points to an important difference between MTDSC and dynamic mechanical analysis (DMA). In DMA, the stress or strain is modulated, keeping the temperature, and with it the relaxation time, constant (as long as the strain is sufficiently small to keep the sample in the range of 

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