Composites and composite components, finally, make an important part of the topic, mostly in relation with aeronautics issues and challenges (within Aerospace Valley-labelled projects). Now that the CNT growth is reasonably well controlled, nanocomposites (here standing for "composites whose at least one component is nanosized") give a tremendous perspective in improving the properties of structural materials. One of the main challenges in nanocomposites is achieving a good dispersion of the nanoparticles in the matrix. Hence, we investigate the dispersion mechanisms of MWCNTs in the polymer (PEEK, a high performance thermoplastic polymer) as a function of processing parameters. Starting with DWCNTs as model materials, MET and Raman G-band mapping allowed discriminating between regions with DWCNT concentrations varying from agglomerated to dispersed through the specific spectral line shapes of the G band sensitive to inner and outer tubes.
Detailed wettability studies showed that CNTs spontaneously self-disperse in PEEK thin films upon annealing. This can be explained by the drastically different absorption properties of the CNTs and polymer matrix in the near IR spectral region, which induces the preferential heating of CNTs and the surrounding and therefore enhances molecular diffusion along the CNTs. As a result, electrical transport measurements carried out at CEMES showed that the electrical conductivity in thin PEEK polymer films with highly and uniformly dispersed CNTs is one to two orders of magnitude higher than in conventional thermoplastic polymers in which the dispersion was poorly achieved by stirring or shear-mixing.
Nanocomposite with 0.8w% of DWCNTs in a PEEK matrix. The shape and wavenumber position of the G band (From Raman spectroscopy) is different for areas with individualized DWCNTs and areas where DWCNTs are not well dispersed (bundled).
Other works on epoxy matrix nanocomposites aimed at obtaining the coefficient of thermal expansion of SWCNTs, peapod-derived DWCNTs, and the epoxy matrix respectively, thanks to the dependence on the Raman band frequency shifts, and demonstrated the poor stress transfer from the outer to the inner tubes in DWCNTs when the composite is subjected to mechanical stress. A consequence of the latter is that poor stress transfer in MWCNTs is anticipated.
Similar studies on other kinds of matrices (i.e., metal such as Cu, prepared under partnership) are carried out, in addition including the study of tribological effects. Again, Raman spectroscopy is helpful showing the increase of DWCNT concentration in the wear area along with their partial damaging.
DWCNTs/Cu nanocomposite subjected to friction stresses. Outside the wear area, the Raman spectrum is dominated by the background generated by the Cu matrix. In the wear area, the signal from the DWCNTs prevails (revealing the preferred removal of the Cu matrix) yet exhibiting an intense D band revealing the occurrence of some damaging brought to the DWCNTs.