Differential Scanning Calorimetry

In-depth explanation of Differential Scanning Calorimetry

Differential scanning calorimetry measures the difference in heat flow between a sample and an inert reference as both are heated or cooled at a controlled rate. Endothermic events such as melting appear as peaks in one direction, and exothermic events such as crystallization or curing appear in the opposite direction. The glass transition appears as a step change in the baseline heat capacity, marking the change from a glassy to a rubbery state in an amorphous polymer. The area under a peak is proportional to the enthalpy change, which allows the heat of fusion or reaction to be determined. DSC is used extensively for polymers, pharmaceuticals and food materials.

Going deeper: Differential Scanning Calorimetry

Key ideas: Enthalpy of transition = peak area divided by sample mass and heating rate calibration, in J/g, and percent crystallinity = delta H measured/delta H of 100 percent crystalline polymer x 100. Melting is endothermic and crystallization exothermic. Tg is taken at the midpoint of the step. Use sealed aluminium pans, small samples (3 to 10 mg), a first heating to erase thermal history and then a second heating.

Common mistakes and connections: Students confuse a peak (first-order transition with latent heat) and a step (second-order, such as the glass transition). The direction of endo or exo depends on the instrument convention, so check the label. Heating rate changes peak positions, and a poor baseline gives wrong areas. Related to enthalpy of fusion, heat capacity, polymers and TGA.

Visualization of Differential Scanning Calorimetry

A PET scan shows a baseline step at the glass transition near 75 C, an exothermic crystallization peak, then the endothermic melting peak near 250 C. The interactive lesson shows this as a live animation or chart.

Worked example and use case

The glass transition of polyethylene terephthalate (PET) appears as a step in the DSC heating curve near 75 C.

Where Differential Scanning Calorimetry fits in Analytical, Lab & Spectroscopy

Differential Scanning Calorimetry is topic 82 of 99 in Analytical, Lab & Spectroscopy.

Related topics

• Boiling Point DeterminationIntermediate
• Flash PointIntermediate
• Thermogravimetric AnalysisAdvanced
• Computational ChemistryAdvanced
• Density Functional TheoryAdvanced
• Molecular DynamicsAdvanced

Browse all 99 topics in Analytical, Lab & Spectroscopy