Molecular Spectroscopy Application eHandbook

Significance of Coatings Analysis

Coatings play a critical role across industries—from aerospace, automotive and marine applications to protective architectural finishes. Their chemical composition, curing state and uniformity directly influence performance factors such as corrosion resistance, UV stability, adhesion and aesthetic qualities.

Study Objectives and Overview

This body of work demonstrates advanced spectroscopic methods for non‐destructive, rapid and on‐site evaluation of a wide range of coatings. Key aims include:

• Quantifying component mix ratios in two‐component (2K) systems to ensure proper cure and avoid costly rework.
• Distinguishing coatings with similar formulations via multivariate classification.
• Monitoring real‐time weathering effects on industrial epoxy finishes under accelerated conditions.
• Profiling film thickness, optical properties and spatial uniformity of thin and multilayer coatings.

Methodology and Instrumentation

Agilent FTIR and UV‐Vis‐NIR platforms are employed, featuring:

• Agilent 4300 Handheld FTIR: Lightweight (2.2 kg), ergonomic, field‐deployable mid‐IR spectrometer with interchangeable interfaces (diffuse reflectance, external specular reflectance, ATR, grazing angle).
• Agilent Cary 7000 Universal Measurement Spectrophotometer (UMS): High‐throughput UV‐Vis‐NIR analysis of thin films and optical components up to 200 mm diameter.

Measurement modes include:

• Diffuse Reflectance FTIR for non‐destructive bulk and surface‐sensitive analysis.
• External Specular Reflectance FTIR for thin‐film and metal‐coated surfaces.
• ATR FTIR for smooth, intimate‐contact surfaces (limited penetration).
• UV‐Vis‐NIR reflectance/transmission mapping for angular dependence and thickness profiling.

Multivariate tools:

• Partial Least Squares (PLS) for quantitative mix‐ratio calibration.
• PLS Discriminant Analysis (PLS‐DA) for classification of closely related acrylic formulations.
• Automated Component Reporting in Agilent MicroLab PC for multi‐model decision logic and pass/fail flagging.

Main Results and Discussion

• 2K PU mix ratio: A PLS model (R²>0.99, SEP~0.04) enabled
  in-situ quantification of A:B component ratios within 40 s, color-coded in‐spec vs. out‐of‐spec on‐screen.
• 2K epoxy mix ratio: Similar results achieved for marine epoxy primer systems (average mix‐ratio error <3 %).
• Acrylic coating identification: Library similarity matches (hit quality >0.998) provided an initial screening, but PLS‐DA (R²>0.99) delivered positive discrimination of 14 coatings using a single handheld method.
• Accelerated weathering: Non‐destructive FTIR diffuse spectra detected chemical changes in a 2K epoxy over 56 days (ASTM G155), yielding two PLS models (0–28 d, 28–56 d) with prediction error <1.25 d.
• Thin‐film optical profiling: UV‐Vis‐NIR mapping characterized angular reflectance of displays and optical wafers, measured thickness of epoxy primers and anodization layers via FTIR, and extracted optical constants of multi‐layer dielectric stacks.

Practical Benefits

• Real‐time on‐site decisions: Avoid sample removal or lab turnaround delays.
• Non‐destructive testing (NDT): Preserve high‐value parts and coatings for continued service.
• Method consistency: Predefined workflows and software logic reduce operator dependency.
• Broad applicability: From field‐level QA/QC to R&D formulation screening and failure analysis.
• Enhanced reliability: Chemometric calibration and classification ensure high confidence in results.

Future Trends and Applications

• Integration with AI/ML: Automated anomaly detection and predictive maintenance based on spectral time‐series data.
• In-line monitoring: Real‐time quality control during spray, cure and finishing operations.
• Expanded reflectance interfaces: Micro‐spot, imaging FTIR for sub‐mm spatial mapping.
• Cloud‐based spectral libraries: Centralized reference databases for global fleet management.
• Extended spectral ranges: Combined mid-IR, far-IR and Raman for deeper molecular insights.

Conclusion

Agilent’s portable FTIR and UV‐Vis‐NIR solutions empower researchers and manufacturers to perform rapid, non‐destructive, and highly reliable coatings analysis. By leveraging advanced sampling interfaces and chemometric models, users can optimize formulation, assure quality, troubleshoot defects, and extend coating lifetimes—all at the point of need.

References

• [1] Identification of Acrylic Coatings Using Handheld FTIR, Agilent Publication 5991-5965EN.
• [2] Rapid Quantification of 2K PU Mix Ratios via Portable FTIR, Agilent Publication 5991-6976EN.
• [3] Non-Destructive FTIR Weathering Study on 2K Epoxy Coatings, Agilent Publication 5991-6976EN.
• [4] Handheld FTIR Chemometric Classification for Coating Discrimination, Applied Spectroscopy, 2018, 72(4), 639-648.
• [5] UV-Vis-NIR Mapping Techniques for Thin-Film Profiling, J. Spectrosc. Imaging, 2019, 8, 12-25.