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Evanescent wave spectroscopy for in-situ cure monitoring

The curing of epoxy adjacent an embedded silica fiber has been monitored in situ by evanescent wave spectroscopy. The epoxy studied is partially fluorinated and has a lower refractive index than the silica optical fiber. This lower refractive index allows the silica optical fiber to be used as a waveguide for the internal reflection of near-infrared light. The curing agent was polyoxypropylenediamine. The epoxy curing was monitored as a function of time by analysis of the near-infrared spectra of the epoxy/curing agent adjacent the fiber. The results obtained from the examination of the near-infrared spectra, particularly the disappearance of the primary N-H stretching/bending combination band at approximately 4935 cm-1 and the accompanying increase of the C-N overtone band at approximately 4650 cm-1, showed that the epoxy curing reaction could be followed in real time using an 85 micron diameter silica optical fiber bundle. It was found that the primary amine groups are essentially completely reacted after 60 minutes.