Raman microscopy of residual strains in carbon nanotube/epoxy composites

Carbon nanotube (CNT) strain variations with temperature, as measured with Raman microscopy, are reported for pristine and functionalized CNT/epoxy composites. The CNT strain is derived from the difference in frequencies of the CNT vibrational G+-mode in the composite and that of a relaxed CNT, and shown to serve as a measure of the local residual strains in the composites. The magnitudes of these strains vary with both CNT functionalization and CNT concentration. At room temperature and with the same local concentration of CNTs in the composite, the strains of oxidized and polyamidoamine-functionalized CNTs are found to be 2.5 times higher than that of the composite containing pristine CNTs. The higher residual strain of the composites loaded with functionalized CNTs reflects their better adhesion and integration in the polymer matrix. These findings are in accordance with the improved tensile properties measured for the functionalized CNT composites.