Differential Scanning Colorimetry (DSC method)

In this course, students will be able to understand the working principle of the DSC method. It is a technique in which the energy necessary to establish a zero temp. difference between the sample & reference material is measured as a function of temp. Here, sample & reference material are heated by separate heaters in such a way that their temp is kept equal while this temperature is increased or decreased linearly. •These measurements provide quantitative and qualitative information about physical and chemical changes that involve endothermic or exothermic processes, or changes in heat capacity.

Endothermic reaction: if the sample absorbs some amount of heat during phase transition then the reaction is said to be endothermic. In an endothermic reaction, more energy is needed to maintain zero temp difference between sample & reference. E.g. Melting, boiling, sublimation, vaporization, and de-solvation.

Exothermic reaction: if the sample released some amount of heat during phase transition, then the reaction is said to be exothermic. In an exothermic reaction, less energy is needed to maintain zero temp difference between sample & reference. E.g. crystallization, degradation, polymerization.

DSC Is widely used to measure glass transition temp & characterization of polymer. There are five different types of DSC instruments: 1. Heat flux DSC 2. Power compensated DSC 3. Modulated DSC 4. Hyper DSC 5.Pressure DSC. Commonly used DSC instruments are Heat Flux DSC and Power Compensated DSC.

Factors Affecting DSC Curve- 1. Instrumental factors: Furnace heating rate, Recording or chart speed, Furnace atmosphere, Geometry of sample holder/location of sensors, Sensitivity of the recording system, Composition of sample containers.

2. Sample characteristics: Amount of sample, Nature of sample, Sample packing, Solubility of evolved gases in the sample, Particle size, Heat of reaction, Thermal conductivity.

Advantages of DSC- Instruments can be used at very high temperatures, Instruments are highly sensitive, Flexibility in sample volume/form and Characteristic transition or reaction temperatures can be determined, High resolution obtained, High sensitivity, Stability of the material.

Applications of DSC:

1. Determine the melting behavior of complex organic materials, both temperatures and enthalpies of melting can be used to determine the purity of a material. 2. Measurement of plastic or glassy material glass transition temperatures or softening temperatures, which change depending upon the temperature history of the polymer or the amount and type of fill material, among other effects. 3. Determines crystalline to amorphous transition temperatures in polymers and plastics and the energy associated with the transition. 4. Crystallization and melting temperatures and phase transition energies for inorganic compounds. 5. Oxidative induction period of an oil or fat. 6. It May be used as one of the multiple techniques to identify an unknown material or by itself to confirm that it is the expected material. 7. Determine the thermal stability of a material. 8. Determine the reaction kinetics of a material.