Recording thermal transitions with differential scanning calorimetry

Differential scanning calorimetry measures the thermodynamic parameters associated with thermally induced phase transitions. Here, the sample of interest and an inert reference are heated or cooled independently at a programmed rate, and in tandem, such that their temperatures change in unison and the differential temperature is maintained at zero. If the sample undergoes a thermally induced transition, heat must be applied to or withdrawn from the sample in order to maintain the same temperature in both sample and reference compartments. The instrument measures the heat flow into the sample relative to the reference and this dijferential heat flow (or excess specific heat) is recorded as a function of temperature, resulting in a trace, as shown in Fig. 1... 

Differential Scanning Calorimetry. Differential scanning calorimetry is in some respects a modification of differential thermal analysis, and the schematic diagram of a differential scanning calorimeter (dsc) is similar to that of the dta device shown in Figure 12. The essential difference, however, is that the measured quantity here is the differential power supplied to the two wells, rather than the temperature difference. In other words, the dsc device maintains the same programmed temperature in each well and records the power required to achieve this. If a transition takes place in the sample, a characteristic excursion in the measured differential power is observed. The nature of these excursions can be related to the transitional properties of the sample. Furthermore, by proper calibration with a reference material of known thermal properties, the specific heat capacity of the sample may be obtained. 

Thermal characterization of an emulsion polymer essentially means the measurement of the glass transition temperature Tg, that is the temperature above which the hard, glass-like polymer film becomes viscous or rubber-like. Polymers whose Tg lies well above room temperature are designated as hard , those with a Tg much lower than room temperature as soft . Normally Tg is measured by differential scanning calorimetry (DSC [25]). In this technique, the difference between the heat absorbed per unit time by the polymer film to that absorbed by a thermally inert reference material is recorded during a linear temperature ramp. The sample and the reference are placed on a sensor plate of defined thermal resistance R, and the temperature difference AT between the sample and the reference is then recorded over the temperature ramp. Usually, the heat flow difference, which is the negative quotient of AT and R, is plotted as a function of temperature (Fig. 3-11). 

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