SWCNT as Cure-Induced Stress Sensors in Epoxy Nanocomposites

Given their unique set of properties, carbon nanotubes are rapidly gaining importance as stress/damage sensors in addition to as mere reinforcing elements in polymer composites. In this work, single-walled carbon nanotubes (SWCNT) are used to monitor internal stresses developing during the curing process of thermoset materials. SWCNT-epoxy composites with high dispersion quality were obtained via calandering. In situ Raman spectroscopy was used to identify chemical and thermal induced stresses by following the changes in the G’-band versus time and temperature. Thermal shrinkage prompts a pronounced effect on the spectral shifts of the composite, pointing at its dominant role (over chemical shrinkage) on the development of the internal stress field. Above Tg, Raman shifts due to temperature increase are found to be negligible, confirming the existence of a stress releasing mechanism. Shift rate of the composites cooling from their processing temperatures depended on the combination of matrix/SWCNT type, pointing at the role of interfacial strength on the load transfer efficiency.