Coating Analysis via FTIR Spectroscopy

Importance of Coating Analysis

Coatings play a critical role in protecting surfaces from mechanical damage, corrosion, and contamination while enhancing appearance and functional properties such as insulation or wettability. Reliable analytical methods are essential for quality control, ensuring correct coating application, material identification, layer uniformity, and surface cleanliness to prevent product failures.

Objectives and Study Overview

The note illustrates how FTIR spectroscopy can be employed to detect and identify polymer coatings on various substrates, determine layer thickness and assess homogeneity. Two case studies are presented: analysis of coated costume jewelry using the ALPHA II FTIR spectrometer and characterization of enamel coatings on copper wire with the LUMOS II FTIR microscope.

Methodology and Instrumentation Used

• FTIR spectroscopy (ALPHA II) with upward DRIFT sampling for non-destructive surface analysis.
• FTIR microscopy (LUMOS II) for microscopic and map-based reflection or ATR measurements.
• Software: OPUS for spectral acquisition, library search, and thickness calculations using an ATR-COMPLETE library.

Main Results and Discussion

• Costume Jewelry: Reflection spectra revealed the presence of acrylic resin and polyurethane coatings, and confirmed clean metal surfaces. Library search matched unknown spectra to PMMA.
• Enamelled Wire: ATR measurements identified thermoplastic polyurethane with high confidence. Reflection mapping across 15 positions quantified a uniform ~25 µm coating, with optical interference fringes enabling thickness determination despite layer thinness.

Benefits and Practical Applications

FTIR analysis offers a non-destructive, rapid, and precise approach for verifying coating presence, composition, and thickness. It supports quality assurance in manufacturing, failure analysis, reverse engineering, and contamination source identification. The ALPHA II system provides a user-friendly solution for routine checks on larger samples, while LUMOS II enables high-resolution inspection of micro-sized or irregularly shaped parts.

Future Trends and Potential Applications

Continued development of spectral libraries and software algorithms will enhance automated identification and quantification of complex coatings. Integration with imaging techniques, coupling with other spectroscopic methods, and expansion to novel materials such as DLC or nanocomposite films will broaden the applicability of FTIR-based coating analysis.

Conclusion

FTIR spectroscopy, implemented via Bruker’s ALPHA II and LUMOS II platforms, provides a versatile toolkit for comprehensive coating characterization. Its speed, non-destructiveness, and sensitivity make it indispensable for ensuring product performance and reliability across diverse industrial and research settings.