Abstract :
Heat capacities are determined for the different frequencies generated as higher harmonics of the Fourier-transform of the heat-flow rate and sample temperature with quasi-isothermal, temperature-modulated differential scanning calorimetry (TMDSC). A complex sawtooth modulation was created using a TMDSC of the heat-flux type, controlled close to the heater. The complex sawtooth is designed to yield four harmonics of similar amplitudes. This new modulation method permits the determination of heat capacity with assurance of identical thermal history and sample geometry, which are important for the study of non-equilibrium processes as they exist, for example, in the glass transition region. Using a proper calibration by plotting the frequency dependence of the calorimeter response, heat capacities are determined approaching a 0.1% standard deviation for polymers. Best results were found for modulation with a complex sawtooth of 14 segments with a maximum amplitude of 1.0 K, a period of 420 s for 9–30 mg of polymer sample, and a sampling interval of one point per second.
