Spectroscopic insights into adhesion failure at the buried epoxy-metal interphase using AFM-IR

Local AFM-IR analysis is performed on the organic coating residues remaining on carbon steel substrates after pull-off adhesion tests. This approach provides unique spectral information, because scattering from these rough substrates has previously prohibited transflectance FTIR analysis of such regions. The AFM-IR spectra of epoxy-amine residues display characteristic oxidation bands, which can only be detected by ATR-FTIR spectroscopy of intact coatings after thermal aging. These oxidation bands are shown to be more intense for thinner coating remnants and dominate the spectra of residue left by coatings removed after thermal aging at 70 degrees C for 4 weeks. This, alongside distinctive changes in the macroscopic adhesion behavior after thermal aging, provides direct evidence that rapid oxidation occurs in the buried polymer-metal interphase during thermal aging.