Effect of residual stresses upon the Raman radial breathing modes of nanotubes in epoxy composites

The relative intensity variations of the Raman radial breathing modes (RBMs) are reported for single-walled carbon nanotubes embedded in epoxy composites cured at different temperatures. The magnitude of these intensity variations depends on the RBM being considered. These variations are attributed to the residual strains inside the hot-cured samples, modifying the nanotube electronic density of states. The nanotubes are moved closer or further away from the resonance conditions, which enhance the RBM intensity. The G′ band position shifts to higher wave numbers with rising curing temperature. By comparing this shift to the one from compressive four-point bending tests, the residual strains due to hot curing of the epoxy resin are estimated to be less than 0.5%.