Materials science is testing the boundaries of what is possible with chemistry and physics. Some of the most important scientific breakthroughs are being made in the field of materials science, particularly in fields working towards meeting demands for energy and consumer electronics.

Materials scientists use FTIR spectroscopy to identify unknown materials, to determine the composition and purity of materials, and to study the chemical structure of materials. FTIR spectroscopy can also be used to detect chemical changes in materials due to changes in temperature, pressure, or other environmental factors.

Separator materials for lithium-ion batteries

Examples include separator materials for fuel cells and lithium-ion batteries, where FTIR can be used to check for structural changes imparted by processes designed to improve the performance of the membranes. For these thin film materials, transmission FTIR may be the most convenient method, but ATR-FTIR has its uses too.

Tkarcher, CC BY-SA 3.0, via Wikimedia Commons

In particular, because ATR is a surface technique, it can be useful for analysing treated films and coatings, where one side has a modification and the other is left untreated. Spectra recorded on each side will reveal the differences. For example, one group looked at a poly(ethylene oxide) coating imparted onto a commercial polypropylene separator for a lithium-sulfur battery [1]. They were able to observe C-O-C stretching bands on the coated side of the material which were absent on the uncoated side through ATR-FTIR spectroscopy, demonstrating that the coating had not migrated through the material and that the membrane was truly asymmetrical.

Functional materials

Materials with intrinsically useful properties, such as magnetism, pyroelectricity, piezoelectricity, energy storage, are termed ‘functional’ materials [2]. They are commonly used as sensors, luminescent emitters, and similar applications involving electromagnetic interaction. Detectors used for spectroscopy, such as DTGS or MCT are functional materials. So are materials such as zinc oxide (ZnO), a type of transparent conductive oxide used in touchscreens and liquid crystal displays, and bismuth oxide (Bi2O3), which has various applications in electronics and photocatalysis.  

One class of materials that has been extensively studied using spectroscopic methods such as FTIR are Metal Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs). These are three-dimensional compounds containing voids, or pores, which can potentially be used for storage of gases or operate as catalysts [3]. Because they consist of organic building blocks linked by metallic or covalent linkages, FTIR can easily be used to check for bands associated with the formation of bonds, and also to look for depletion of bands associated with the precursor molecules used in their synthesis [4].

ATR-FTIR is one of the most convenient methods for characterising such materials, since the final product is usually a fine powdered solid that can be analysed very simply.

General advantages and limitations of ATR-FTIR

Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy is a powerful technique used in the field of materials analysis. Some of the advantages and limitations of ATR-FTIR spectroscopy are as follows:

Advantages of ATR-FTIR:

  1. Non-destructive: ATR-FTIR spectroscopy is a non-destructive technique that allows for the analysis of solid and liquid samples without altering their properties or structure.
  2. Rapid analysis: The technique is relatively fast and requires minimal sample preparation, making it suitable for high-throughput analyses.
  3. High sensitivity: ATR-FTIR spectroscopy is a highly sensitive technique that can detect trace amounts of materials.
  4. Versatility: ATR-FTIR spectroscopy can be used to analyze a wide range of materials, including polymers, minerals, fibers, and biological materials.

Limitations of ATR-FTIR:

  1. Surface analysis: ATR-FTIR spectroscopy is limited to the analysis of the surface of a sample, typically to a depth of a few microns.
  2. Sample requirements: The technique requires a flat surface on which to perform the analysis, and the sample must be compatible with the ATR crystal used in the analysis.
  3. Spectral artifacts: ATR-FTIR spectra can be affected by factors such as crystal temperature, pressure, and contact force, which can cause spectral artifacts and affect the accuracy of the analysis.
High Temperature Golden Gate diamond ATR accessory
Golden Gate diamond ATR with high-temperature top-plate.

In summary, ATR-FTIR spectroscopy is a versatile and sensitive technique that offers numerous advantages for materials analysis. However, it is also subject to certain limitations, and careful consideration must be given to sample preparation and analysis conditions to ensure accurate and reliable results.

References

  1. Poly(ethylene oxide)-coated double-layer separator for lithium-sulfur battery, J.M. Conder, C.Hänsel, S.Trabesigner, P. Novák, L. Gubler. PSI Electrochemistry Laboratory – Annual Report 2015, Paul Scherrer Institut (available at https://www.psi.ch/lec)
  2. https://www.imperial.ac.uk/materials/research/functional/
  3. Metal—organic framework, Wikipedia. https://en.wikipedia.org/wiki/Metal%E2%80%93organic_framework
  4. Acridine-Functionalized Covalent Organic Frameworks (COFs) as Photocatalysts for Metallaphotocatalytic C-N Cross-Coupling, M. Traxler, S. Gisbertz, P. Pachfule, J. Schmidt, J. Roeser, S. Reischauer, B. Pieber, A. Thomas, Angew. Chem. Int. Ed. 2022, 61, e202117738 (DOI: https://doi.org/10.1002/anie.202117738)