Measurement of composite surface contamination using the Agilent 4100 ExoScan FTIR with diffuse reflectance sampling interface

Significance of the Topic

The integrity of composite materials is critical in aerospace, automotive and industrial applications. Surface contamination by hydrocarbons or silicones can compromise adhesive bonding, repair quality and long‐term performance. Rapid, noninvasive detection methods are therefore essential to maintain manufacturing efficiency and ensure safety.

Objectives and Study Overview

This application note evaluates the capability of a portable FTIR spectrometer to detect and quantify surface contaminants on carbon–epoxy composites. Two common contaminants—silicone and hydraulic fluid—were applied at controlled concentrations. The study compares contaminated samples with blanks and assesses the effectiveness of solvent wiping and plasma cleaning protocols.

Methodology and Instrumentation

Sample Preparation and Measurement Procedure:

• Composite coupons were contaminated with known amounts of silicone in chloroform (0, 40, 78, 300 µg/cm²) and with hydraulic fluid to saturation.
• Each sample was measured directly with the Agilent 4100 ExoScan FTIR by co‐adding 128 scans at 8 cm⁻¹ resolution (~30 s per sample).
• Solvent cleaning (acetone wipe) and three distinct plasma cleaning treatments were applied to halves of the hydraulic‐fluid‐contaminated coupons.

Instrument Details:

• Agilent 4100 ExoScan FTIR Spectrometer
• Diffuse reflectance sampling interface optimized for low‐reflectance carbon composite surfaces
• Portable handheld design delivering full laboratory FTIR performance

Main Results and Discussion

Silicone Detection:

• Characteristic IR bands at 1260, 1095, 1018 and 800 cm⁻¹ were observed with negative absorbance due to strong reflectance absorption.
• A calibration curve based on the 800 cm⁻¹ band area showed a non‐linear second‐order response over the full concentration range, but a linear fit was adequate below ~100 µg/cm².
• Estimated limit of detection for silicone is approximately 10 µg/cm².

Hydraulic Fluid Monitoring and Plasma Cleaning:

• Contaminated composites exhibited CH stretching at 2930 cm⁻¹ and a C=O shoulder at 1730 cm⁻¹, corresponding to hydraulic fluid residue.
• Solvent wiping alone left residual fluid in micro‐cracks; plasma cleaning effectiveness varied with treatment energy.
• One plasma protocol fully removed fluid without damaging the epoxy substrate, while excessive energy led to substrate degradation (loss of epoxy signature).
• Under‐cleaning left detectable fluid bands, highlighting the need to optimize plasma parameters.

Benefits and Practical Applications

Use of the handheld FTIR with diffuse reflectance sampling offers:

• In situ, nondestructive contamination assessment directly on production parts.
• Rapid analysis (<30 s) facilitating real‐time quality control.
• High sensitivity to trace silicone and hydrocarbon films without sample removal.
• Capability to validate surface cleaning procedures, including plasma treatment.

Future Trends and Potential Applications

Advancements in portable FTIR technology may enable:

• Automated on‐line monitoring in manufacturing lines.
• Integration with robotic inspection systems for large structures.
• Development of expanded contaminant libraries (paints, greases, residues) for broader industrial use.
• Enhanced chemometric models for multicomponent quantification and mapping.

Conclusion

The Agilent 4100 ExoScan FTIR with diffuse reflectance interface effectively detects and quantifies silicone and hydraulic‐fluid contamination on carbon–epoxy composites. Its portability and rapid measurement capabilities support improved quality assurance and optimized surface‐preparation workflows in industrial and repair settings.

Reference

• Seelenbinder J. Measurement of composite surface contamination using the Agilent 4100 ExoScan FTIR with diffuse reflectance sampling interface. Agilent Technologies Application Note, publication number 5991-0007EN, March 23, 2015.