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 measure d curves has been proved experimentally. As shown by model calculation s, changes in material properties at the glass transition result in a change in Green's function for the liquid state compared to that for t he glassy state. From experimental investigations, moreover, it follow s that these effects are overlapped by influences of the change in the thermal contact between sample and pan. It was found that change in t he thermal contact influences the determined Green's function more tha n changes in material properties do. The error in the desmeared curves , determined using a Green's function obtained via other materials pro perties, is within the limits of accuracy of the measurements. Therefo re the Green's function estimated from the switch-on as well as from t he switch-off behaviour can be used to desmear the whole measured curv e, if the material properties do not change markedly, as is the case d uring the glass transition of polymer materials.