The image on the right-hand side represents a single-wall (18,0) carbon nanotube decorated with a few carboxyl O=C–OH groups (O atoms as red balls, H atoms as black dots). In the present representation, the percentage of carboxylic functions is 1.6 %. These functional groups can be covalently bound to an ending cap of a nanotube. The attachment of a carboxyl group on a sidewall atom involves a change of sp² to sp³ hybridization, which requires the presence of a defect. For that reason, a multiwall nanotube lends itself well to this type of modification. Once fixed on a nanotube, a carboxyl group can serve to tether different types of chemical moieties [2]. For instance, decoration with sticky moieties, like hydrogen bonding donor/acceptor groups, and their interaction with complementary photoactive moieties may allow the formation of composite materials with a broad spectrum of photophysical properties.

Unlike the previous example, the image on the left-hand side illustrates a case of functionalized nanotube by non-covalent bonding. Organic molecules and surfactants can stick on the surface of a carbon nanotube by weak links, such as π stacking and hydrophobic interactions. The image schematizes the wrapping of a polymer chain around a (12,7) nanotube. Polyfluorene is an example of polymer that can do that. Among other benefits, the dispersion of nanotubes modified this way may be greatly improved in some organic solvents [3]. In the figure, The C atoms have been drawn with their van der Waals radius of 0.17 nm. The external surface of the nanotube looks like a corrugated cylinder of 0.82 nm radius (refer to the nanotube calculator). The wrapped polymer has been represented by a continuous helical structure (1.13 nm outer radius, 0.50 nm minor radius, and 2.73 nm pitch length).