Functionalization and alignment of carbon nanotubes

Covalent functionalization of nanotubes can improve nanotube dispersion in solvents and polymers significantly. Various strategies for chemical functionalization of CNTs have been 

Other functionalization methods of CNTs, such as by atomic irradiation, ion deposition, plasma irradiation and proton bombardment, are also frequently used to fabricate CNT based nanocomposites [39-41]. Although functionalization of CNTs can aid to promote interaction between CNTs and the polymer matrix, the main disadvantage of covalent functionalization is that it introduces defects and disrupts the perfect structure of CNTs walls which is detrimental to the desirable mechanical properties of CNTs. 

Unlike the covalent functionalization approach, noncovalent functionalization provides an alternative method to modify and tailor the surface properties of CNTs in order to increase their solubility in solvents or compatibility with polymer matrix. In this method, the tubular surface of a CNT is noncovalently wrapped with polymer chains due to van der Waals attractive forces or through tt-tt interactions. This noncovalent wrapping approach has also been widely used and is particularly attractive because it offers the possibility of attaching chemical handles without affecting the electronic network of the nanotubes [42-45]. Coleman et al [46-49] illustrated an example of noncovalent wrapping by tt-tt interaction between CNTs and poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylene vinylene) (PmPV), a conjugated luminescent polymer, to obtain a CNT-PmPV composite. 

For bulk materials, Jin et al fabricated poly (methylmethacrylate) (PMMA)/MWNT nanocomposites by melt mixing. MWNTs were well dispersed in the matrix [90]. Melt compounding is also widely used for the fabrication of composite fibers. Sandler et al mixed polyamide-12 pellets and CNTs in a twin-screw micro-extruder and then the extrudate was chopped and fed into a capillary rheometer with 1 mm die. The CNTs in the spun fibers were uniformly dispersed [91]. Not only can thermoplastic polymers be melt-compounded, polyimide, a thermoset plastic, can be also prepared by mixing the imide oligomer at 320 °C on a steel plate and then cured at 370°C. It was found that the dispersion of CNTs in 

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