Unique identification of single-walled carbon nanotubes in composites

The physical properties of single-walled carbon nanotubes (SWNTs) depend strongly upon their structure and so a reliable method to determine this structure is essential to their future applications. Resonant Raman spectroscopy has proven to be a powerful tool to characterize SWNTs, and also to monitor their deformation. The radial breathing modes (RBMs) are commonly used to identify SWNTs, since their position is inversely proportional to the nanotube diameter. In this present study, the RBM intensity variations in epoxy- and poly(vinyl alcohol) (PVA)-SWNTs composites were measured under uniaxial strain using lasers of three wavelengths 632, 785 and 830 nm. These structure-dependent intensity variations are attributed to the effect of strain upon the energy of the SWNT electronic transitions, moving SWNTs closer to or further away from the resonance conditions that enhance the Raman signal. Combining the RBM position, resonance theory and this additional information about the behaviour under strain, a unique nanotube structure can be assigned to each RBM observed in the composites.