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Glossary

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Modulated differential scanning calorimetry (mDSC)

It is a synonymous of Oscillating Differential Scanning Calorimetry (oDSC).

In calorimetry there are three established temperature modulation methods:

1. The sample is heated with a periodically changing heat flow from a electrical heater or chopped light beam, and the temperature change of the sample (magnitude and phase shift) is measured as the response signal (AC calorimetry).

2. A thermal wave is sent into the sample from a metallic film that is evaporated onto its surface and which heats it periodically. The temperature change is measured by using the same metal film as a resistance thermometer. The third harmonic of the resulting temperature oscillations is proportional to the power input and depends on the product of the heat capacity and thermal conductivity of the sample in a characteristic way (3 method).

3. The sample (or furnace) temperature is controlled to follow a set course with superimposed periodical changes, and the heat flow rate is measured via the differential temperature between sample and reference (temperature-modulated differential scanning calorimetry, TMDSC).

In all three cases, both the magnitude of the periodic part of the response signal and its phase shift with respect to the stimulating signal are measured, and this results in a complex quantity (temperature, heat flow rate, and heat capacity, respectively). As heat transport always requires time, the frequency of temperature modulation is normally limited to a maximum of 0.2 Hz to allow the heat to flow through the sample properly. For the 3 method, however, frequencies of several kilohertz are possible because the heat source and the temperature probe are identical in this case. At the lower end, the frequency range is only limited by the noise threshold (sensitivity) of the sensors in question. As a rule only two decades are available. Consequently, only time-dependent processes with timescales within this window can be followed in the calorimeter.

References:

  • Thermal Analysis and Calorimetry, G?nther W. H. H?hne, Dutch Polymer Institute, Eindhoven University of Technology, Eindhoven, The Netherlands. Ullmann's Encyclopedia of Industrial Chemistry
 

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