Characterization of the epoxy-metal interphase: FTIR-ERAS and spectra calculation for ultra-thin films

The interphase between polymers and metal substrates can be elucidated by studying ultra-thin films. In this paper, spin coating films (20 nm - 2 μm) are prepared from a two-part epoxy adhesive on Au, Al and Cu. After room temperature cure, the chemical structure of the epoxy films is studied by FTIR external reflection absorption spectroscopy (FTIR-ERAS) and the results are compared with the state in the polymer bulk as measured by attenuated total reflection (FTIR-ATR). Inevitably, this evaluation of the thin film spectra has to account for the optical situation which is significantly different from bulk measurements. Spectra calculation provides the essential tool for a reasonable comparison between bulk and thin film spectra, thus allowing for a detailed quantitative analysis. Thickness and substrate effects on the interphase can then be separated from the optical situation of the measurement. The results reveal very specific features caused by adhesive interactions and different cure behaviour in the interphase on different metal surfaces.