Principles for Differential Scanning Calorimetry (DSC):
In principle DSC is a very sensitive and elegant technique that measures the energy required to induce thermal transitions, or thermally initiated reactions, in a sample.
A sample and a reference are placed in a well controlled oven. The temperature in the reference and sample are measured separately and compared as the temperature in the oven is either ramped up, ramped down or kept constant.
As the temperature changes, the sample and reference will heat up at slightly different rate, if they are not identical. A thermal transition in the sample will slow the heating of the sample even further. The difference in temperature means that the oven element must be giving more heat to the sample in order to attempt to keep the sample at the same temperature as the oven.
This heat-work is measured and plotted as a function of time during the temperature change in the DSC. This can then be turned into a heat-flow versus temperature style graph, since the temperature at any given time is recorded during the run.
The instrument therefore records at what temperature the thermal transition occurs, and how much energy was required to do the transition.
Modulated DSC (TOPEM)
The DSC measures the energy difference it takes to change the temperature of the sample over the reference, in thermodynamics, this difference corresponds to the difference in heat capacity between the sample and the reference. Heat capacity is not a constant, as you were taught in general chemistry. Heat capacity is a response function (function of state) that depends on temperature in the system and how fast the system responds to temperature changes. How does this work? Consider a liquid near the boiling point. You can add a lot of energy to heat up the liquid without changing the actual temperature (the liquid is boiling). You can, however, put energy VERY fast into the system and super-heat the liquid above the boiling temperature, i.e. by using micro-waves.
DSC can extract the heat capacity function at various heat/cool rates. This is done by rattling the temperature in the oven up and down within a very small variation of temperatures, very fast. Simultaneously the temperature is brought up very slowly inside the DSC oven. From this TOPEM curve, we can extract the heat capacity (ingenious when it works).
About our instrument
Make: Mettler Toledo
Purchase: 2007 (Adalsteinsson)