DYNAMIC BEHAVIOR OF POWER-COMPENSATED DIFFERENTIAL SCANNING CALORIMETERS .4. THE INFLUENCE OF CHANGES IN MATERIAL PROPERTIES

The influence of sample material properties on the smearing of measured curves has been proved experimentally. As shown by model calculations, changes in material properties at the glass transition result in a change in Green's function for the liquid state compared to that for the glassy state. From experimental investigations, moreover, it follows that these effects are overlapped by influences of the change in the thermal contact between sample and pan. It was found that change in the thermal contact influences the determined Green's function more than changes in material properties do. The error in the desmeared curves, determined using a Green's function obtained via other materials properties, is within the limits of accuracy of the measurements. Therefore the Green's function estimated from the switch-on as well as from the switch-off behaviour can be used to desmear the whole measured curve, if the material properties do not change markedly, as is the case during the glass transition of polymer materials.