Thermal analysis has undergone significant improvements since the first thermometric measurements on clays by Henry Louis Le Chatelier in 1887 and the first differential temperature measurements by British scientist Roberts-Austen in 1899. Nowadays thermal analysis has developed to a range of different techniques that have become essential for the characterisation of polymers, pharmaceuticals, biomaterials, metals, study of food and food ingredients, inorganics and materials in general.
Main techniques.
There are different thermal analysis techniques depending on the material property or effect you want to measure. The following table gives an overview of the best and alternative techniques:
| Category | Property | DSC | TGA | TMA | DMA |
|---|---|---|---|---|---|
| Physical properties | Specific heat capacity | ■ | – | – | – |
| Expansion coefficient | – | – | ■ | ■ | |
| Young’s modulus | – | – | – | ■ | |
| Physical transitions | Melting and crystallisation | ■ | – | – | ■ |
| Evaporation, softening, drying | ■ | ■ | ■ | ■ | |
| Glass transition, softening | ■ | – | – | ■ | |
| Polymorphism (solid-solid transitions) | ■ | – | – | ■ | |
| Liquid crystals | ■ | – | – | – | |
| Purity analysis | ■ | – | – | – | |
| Chemical properties | Decomposition, degradation, pyrolysis, oxidation, stability | – | ■ | – | – |
| Composition, content (moisture, fillers, ash) | – | ■ | – | – | |
| Kinetics, reaction enthalpies | ■ | ■ | – | – | |
| Crosslinking, vulcanization (process parameters) | ■ | ■ | – | ■ |
Figure 1 Thermal Analysis in Practice Tips and Hints. Mettler Toledo.
We have differential scanning calorimetry (DSC) and thermogravimetric analysers (TGA) techniques in CAF. A DSC analyser measures the energy changes (specifically the heat flow) that occur as a sample is heated, cooled or held isothermally, together with the temperature at which these changes occur. Thermogravimetric analysis (TGA) is an experimental technique that measures the amount and rate of change in the weight of a material as a function of temperature or time in a controlled atmosphere.
Instruments.
- DSC Q2000 (TA): A research grade instrument with a cooling system and an autosampler allowing scanning at rates up to 200 ºC/min and a broad range of temperatures (-90 ºC to 400ºC). Fast and easy to use with modulation capability ideal for characterisation of melting, glass transition and crystallisation properties.
- DISCOVERY X3 DSC (TA): An advanced version of the Q2000 that can test three materials at once, increasing the confidence on real-time comparisons and improving productivity and data precision within a broad range of temperatures (-90 ºC to 400ºC).
- Simultaneous TGA-DSC Q600SDT (TA) is a thermal instrument capable of differential scanning calorimetry and thermogravimetric experiments at the same time from room temperature up to 1500 ºC, making it ideal for inorganic samples.
- TGA Q50 (TA): This thermogravimetric analyser is mainly used to study the thermal stability of materials for a material characterisation or as a pre-study of the usable temperature range on a DSC. it could also give composition information with adequate additions. It is used to characterize materials in various environmental, food, pharmaceutical, and petrochemical applications. It is a technique in which the mass of a substance is monitored as a function of temperature or time as the sample specimen is subjected to a controlled temperature program in a controlled atmosphere. It has a temperature working range from room temperature to 1000ºC.
- Discovery SA Dynamic Vapour Sorption analyser (DVS) (TA): This thermogravimetric technique is used to determine the amount of moisture a material can adsorb or desorb as a function of its mass, temperature, time, and relative humidity. This instrument is primarily concerned with applications where changing levels of humidity can influence or significantly alter important properties or uses of a material (for example, physical properties (Tg), stability, shelf life, bioavailability). This instrument has high-end specs, with a modern autosampler allowing analysis of reactive samples thanks to immediate piercing of pre-encapsuled pans, it has a working range of 5° C to 85 °C, a baseline drift of less than 1ug and a relative humidity working range from 0% to 98%.
- Hot Stage Microscopy FP90 (Metler Toledo): The hot/cold stage with a camera enables video imaging of thermal events of a variety of samples at different magnifications thanks to the attached Leica optical microscope with 5x, 10x and 20x objectives. It is a useful complement to the previous techniques. In addition to thermal events, the microscope can also capture images, allows sizing of micro-objects and can record videos to observe kinetics of a variety of physical processes; for example, to investigate swelling kinetics of polymeric samples.
Application notes.
- In Food Science: DSC to analyse the effects different sugars have on the starch gelatinisation or DVS to assess Shelf Life and Storage Stability.
- In Pharmacy: to evaluate the impact of processing methods and polymeric carrier on the physiochemical properties (miscibility) of solid dispersions of different drugs with DSC. Assessing Amorphous – Crystalline Phase Changes of new polymers and drugs with DVS.
- In Chemistry: Characterisation of new solid-state materials for energy applications and electronic properties or new polymers. Carbon nanotubes characterization: determination of the weight remaining as a function of temperature.
*Hibbard, Thomas, Mitchell, Hannah, Kim, Yoonha, Shankland, Kenneth and Al-Obaidi, Hisham (2023) Spray dried progesterone formulations for carrier free dry powder inhalation. European Journal of Pharmaceutics and Biopharmaceutics, 189. pp. 264-275.
*Mukherjee, Shriparna, Powell, Anthony V., Voneshen, David J. and Vaqueiro, Paz ORCID logo (2022) Talnakhite: a potential n-type thermoelectric sulphide with low thermal conductivity. Journal of Solid State Chemistry, 314. 123425.
*Bolger, Alexandra May, Rastall, Robert A., Oruna-Concha, Maria Jose ORCID logo and Rodriguez-Garcia, Julia ORCID logo (2021) Effect of D-allulose, in comparison to sucrose and D-fructose, on the physical properties of cupcakes. LWT-Food Science and Technology, 150.