Temperature-modulated differential scanning calorimetry. Part II. Determination of activation energies

Alternating differential scanning calorimetry (ADSC), which is a commercial implementation (Mettler–Toledo) of temperature-modulated differential scanning calorimetry (TMDSC), is used to evaluate the activation energy associated with the relaxation processes in polycarbonate in the region of the glass transition. This is achieved by varying the frequency of the temperature modulation over a range of approximately one decade and evaluating the mid-point of the step change in the complex heat capacity. These experiments were performed for two different amplitudes of the temperature modulation. The calculated activation energy for both sets of data was the same (790 kJmol-1) and in good agreement with values found in the literature. The quality of the ADSC data is discussed with reference to ripples seen on the Fourier-transformed signals and these ripples are attributed solely to the mode of the data analysis, and are not noise on the data.