Probing deformation of double-walled carbon nanotube (DWNT)/epoxy composites using FTIR and Raman techniques

Two of the limitations of carbon nanotube (CNT) polymer composites have been the low volume fraction of nanotubes and inadequate load transfer from the polymer to the stiff CNT. Here, we have utilized functionalized mats of double-walled nanotubes (DWNT) to obtain 10 wt.% DWNT in an epoxy matrix, with strength approaching those of quasi-isotropic carbon fiber composites. We used the transmission FTIR technique with in situ loaded specimens to monitor spectral shift per unit applied stress for understanding load transfer behavior at the nanotube–epoxy interface. Tests show that in most cases a tensile stress causes negative FTIR peak shift in the neat epoxy, but this behavior is not always observed for the epoxy matrix in the composite. The FTIR data can be used successfully to estimate the average matrix stress in the composite and thereby the average stress in the nanotubes. In situ Raman studies using the G′ peak are also conducted to obtain complementary information on average tensile stress in the DWNT in the loading direction. The shift response is found to be ∼37 cm−1/GPa.