Differential scanning calorimetry is a powerful and sensitive thermoanalytical technique. In this destructive technique, the difference in the amount of heat required to increase the temperature of a sample and a reference is measured as a function of temperature. DSC is used to measure the energy transferred to or from a sample undergoing a physical or chemical change, hence it determines alterations in structural properties of a sample as a function of time and temperature.
DSC is widely used in several industries such as polymers and composites, nanomaterials, membranes and films, biological materials, pharmaceuticals, food industry and research, electronics, drug delivery and interactions.
Figure 1: SC thermogram of bisphenol A/aniline benzoxazine monomer.
Figure 2: Schematic of the combined DSC/SAXS/WAXS experiment
Types of Differential Scanning Calorimetry
There are two types of DSCs based on the mechanism of operation.
- Heat-flux DSC. In this type, the sample and empty reference pans are placed on a thermoelectric disk enclosed in a furnace. The furnace is heated at a linear rate, transferring heat to the pans through the disk. The temperature difference between both the pans is measured by thermocouples and is converted into a heat flow signal via a calibration procedure.
- Power-compensated DSC: In this type, separate furnaces house the sample and reference pans while maintaining them at the same temperature. Temperature is changed according to a predetermined programme. The difference in thermal power needed to keep them at the same temperature is determined and plotted as a function of time or temperature.
Uses of Differential Scanning Calorimetry
This versatile technique is operated in a dry state and is quite useful in characterizing the crystals between size range 1–100 nm. DSC provides information about the wide range of structural aspects such as arrangement of the crystal components, and macroscopic information like mean shape and size of crystalline samples. DSC is also used to phase transition temperatures (Tg, Tm) and heat capacities (Cp) of analytes.
Other uses involve determination of heat of fusion and extent of crystallization for the crystalline materials, the cure behavior of thermoset monomers or oligomers oxidative stability, thermal degradation, and water loss in a sample.
DSC is also used to evaluate thermal reversibility of protein degradation; eutectic point and construction of phase diagrams; effect of hardeners on the thermal properties of cured materials; heat and degree of curing reaction, and residual cure.
Other uses of DSC involves determination of drug–lipid interactions, the status of the lipid, and melting and recrystallization behaviors of the nanostructured lipid carriers (NLCs), determination of thermodynamics of nucleic acid-folding transitions (DNA and RNA), analysis of physicochemical transformation during starch gelatinization process,prediction of the storage life of food products and determination of glass transition temperature (Tg) to determine the miscibility of biopolymer blends.
Strengths and Limitations of Differential Scanning Calorimetry
DSC is a convenient and low cost method of studying thermal transitions in various materials. It can be used for a wide range of temperatures (−90 to 550°C) and utilizes a low amount of sample. This is quite a sensitive method where the slightest phase transitions are captured.
On the other hand, DSC is a destructive analysis technique, so analysis of heterogeneous materials is difficult. This does not detect generation of gases and cannot be used for elemental analysis purposes. Sensitivity of the methods reduces in the instances of overlapping in some phase transitions. Samples that might sublime or evaporate during the procedure are most likely to give inaccurate results as a constant mass of the sample is required throughout the test.
