Kinetics of enthalpy recovery studied by temperature-modulated differential scanning calorimetry

An analyzing method using periodic temperature modulation is applied to the kinetics of enthalpy recovery that occurs when an amorphous material in the glassy state devitrifies during heating. In particular, this study demonstrates that an analytical expression of the kinetic response can be formulated by assuming temperature modulation with a periodic temperature jump and isothermal holding. This analysis provides a reasonable interpretation for the well-known fact that the magnitude of the dynamic heat capacity of complex quantity obtained by temperature modulation does not exhibit a large peak corresponding to the enthalpy recovery peak. Furthermore, it is demonstrated that the phase angle peak of the dynamic heat capacity was affected by the kinetics. Its quantitative evaluation provides useful information on the relaxation time during glass transition. Numerical simulations and experimental results of atactic polystyrene examined by conventional differential scanning calorimetry and fast scanning calorimetry confirm these findings.