MWNTs homogeneous dispersion

FIGURE 6.10 Scheme of a PU-MWNT nanocomposite foam showing the formation of an effective electrical pathway by physical contact between MWNTs homogeneously dispersed throughout the foam cell walls and struts. 

The core-shell structure of PU-functionalized MWNTs was found via transmission electron microscopy (TEM) by Chen et al. (47). Ultra-high resolution TEM indicated that a layer of an amorphous structure with a thickness in the range of 2 to 5 nm was formed on the surface of the MWNT-PU. Functionalized MWNT samples could be dispersed very well in highly polar solvents and formed a homogenous solution, which was stable even after 10 days. Neither sedimentation nor aggregation of the MWNT bundles was observed. 

Nanotube functionalization is performed in other examples listed in Table 11.1. In 1999, Shaffer et al. used carboxylated MWNTs. By contrast to studies described in the followings, this allows to the achievement of homogeneous composites with a large nanotube fraction of about 50 wt%. However, the improvement of the Young s modulus is still weak, particularly if we consider the large amount of CNTs included in the matrix. Liu et al. (47) reported an improvement of mechanical properties with SWNTs which are covalently functionalized by OH groups, compared to the same neat nanotubes simply dispersed with SDS. 

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