Increase in effective activation energy during physical aging of a glass

The novel technique of multi-frequency temperature modulated differential scanning calorimetry is employed to measure a decrease in the heat capacity under quasi-isothermal conditions. The effect is used to monitor the kinetics of physical aging in glassy maltitol at ∼5–8 °C below the glass transition temperature. The heat capacity relaxation is analyzed by an isoconversional method that yields effective activation energy for different extents of relaxation. The early stages of aging demonstrate an activation energy ∼145 kJ mol−1 that is significantly smaller than the activation energy of α-relaxation (413 kJ mol−1), which is closely approached at the final stages of aging.