MEASURING EQUILIBRIUM AND FREQUENCY DEPENDENT SPECIFIC HEATS OF POLYMERS BY A PULSED DSC TECHNIQUE

摘要

A new pulsed technique, based on moment analysis, is presented here for the measurement of equilibrium and frequency dependent specific heats of several materials. It is shown that the equilibrium specific heat can be estimated by the areas under the input temperature pulse and the output enthalpy change, provided both perturbations return to their initial baseline value. Fourier analysis of the data yields a frequency dependent complex specific heat, the modulus of which is directly comparable to that obtained by modulated differential scanning calorimetry (MDSC). It is further shown that MDSC is limited to providing a single frequency dependent specific heat, whereas the pulsed technique can yield the entire frequency spectrum in addition to the equilibrium specific heat in a single experiment. These results also highlight the influence of thermal lags in the instrument on the frequency response of the material's thermal properties. Experimental data is presented on a variety of materials such as indium, copper, sapphire, polycarbonate, polystyrene, poly(methyl methacrylate) and poly(ethylene terephthalate).