Evaluation of multi-walled carbon nanotube concentrations in polymer nanocomposites by Raman spectroscopy

A new Raman spectroscopic methodology is proposed to monitor the weight fraction of Multi-Walled Carbon Nanotubes (MWCNTs) in polymeric nanocomposites. In order to disentangle the parameters affecting the frequency of the Raman bands and their intensity, this methodology involves the acquisition of sets of Raman spectra as a function of MWCNTs loading, excitation laser power and temperature. In the specific case of isotactic polypropylene (iPP), any interaction of the carbon nanotubes with the polymeric host has minimal effect on the frequency of the MWCNTs G band (∼1584 cm−1); the same holds for the influence of residual stresses acting on the MWCNTs. The parameter that primarily alters the CNTs Raman bands frequency is temperature, determined by the excitation laser intensity, the MWCNTs concentration and the thermal properties of the polymer matrix. This is demonstrated by confocal micro-Raman spectra collected from agglomerates and from micro-Raman spectra of samples containing either poorly or well dispersed MWCNTs. A direct correlation of the G band frequency with the effective MWCNT wt% loading in the nanocomposites is confirmed after careful and systematic experiments performed on prototype well-dispersed samples.