Thermoset composites with improved mechanical properties can be obtained with the addition of homogenously dispersed, well adhered to the matrix carbon nanotubes. Under these constraints, the existence of an effective load transfer mechanism in combination with the electronic and vibrational properties of CNT enables their utilisation as stress sensors in addition to reinforcing elements in the polymeric matrix. In the present work, well dispersed single-walled carbon nanotubes (SWCNT) at concentrations slightly above the percolation threshold (~0.1 wt%) were incorporated to different epoxy resins and utilised to characterise 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 plates rheometry. The effect of the nanotubes on the cure parameters (i.e. gelation and vitrification times) and glass transition temperature of the neat resins were found to be negligible at this concentration. In-situ Raman and dielectric spectroscopy were performed in parallel on the SWCNT-modified resins, and the ongoing changes at both spectra yield information of the chemical or thermal induced stresses arising at the cure cycle, and which can be responsible for a) the detriment of the mechanical performance of the composite or b) the disruption of the growing SWCNT conductive network. It was found that chemical shrinkage effects are almost negligible in contrast to thermal stresses induced by cooling of the sample below its glass transition temperature (T_g). No stresses were detected for temperatures above T_g of the fully cured composites, pointing at a relaxation effect. Additionally, Raman shift rates of the composites cooling from their ultimate processing temperature were found to be strongly dependent on the chemistry of the epoxy system, pointing at the role of the interfacial interactions of the SWCNT with the matrix upon their shrinkage behaviour.

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