Combined Raman and dielectric spectroscopy on the curing behaviour and stress build up of carbon nanotube–epoxy composites

Single-walled carbon nanotubes (SWCNT) were incorporated into different epoxy matrices to monitor the internal stresses arising from the curing process. The curing reaction of the neat and SWCNT-modified epoxies was investigated by differential scanning calorimetry and parallel-plate rheometry. In situ Raman spectroscopy and electrical conductivity measurements were performed in parallel and the ongoing changes at both spectra were interpreted in terms of evolving stresses. Preliminary investigations were necessary to analyse the temperature dependence of the SWCNT Raman spectra, and its contribution to the overall shifts observed at the curing experiments. Thermal compressive strains were found to develop in the samples only below their glass transition temperature, pointing at a stress releasing effect above it. Chemical shrinkage effects were found to be negligible, or at least undetectable with our technique, in comparison to the temperature-induced Raman shifts.