The Kinetics of the α- and β-Relaxations in Indomethacin as Measured by DSC

摘要

Differential scanning calorimetry has been used to study the α-relaxation (glass transition) as well as β-relaxation (sub-Tg relaxation) in indomethacin. The β-relaxations have been measured as a small endothermic sub-Tg peak that appears on reheating the samples previously annealed in the temperature region -20 – +5°C. The activation energy of the β-relaxation is ～57 kJ mol-1 and shows an increase with temperature as approaching the glass transition region. In the glass transition region the effective activation energy of relaxation decreases with temperature from 320 to 160 kJ mol-1. The heat capacity measurements have allowed for evaluating of cooperative rearranging region in terms of linear size (3.2 nm) and number molecules (90). The β-relaxation fades below -30°C that provides a practical estimate for the lower temperature limit of physical instability in indomethacin. Experimental evidence is provided that the glassy indomethacin undergoes active nucleation in the temperature region of the β- relaxation.