Composites and Noncovalent Interactions with Nanodiamond

Owing to its remarkable properties nanodiamond suits very well to being part of composite materials. In particular it is the small particle size, the hardness, the large chemical inertness, its nontoxicity and the high refractive index that may beneficially complement the properties of the polymer matrix. The latter may be connected to the diamond particles either by covalent bonding or by noncovalent interaction. Numerous examples of noncovalently bound composites have been reported in the literature (Section 5.6.1). StiU the interaction with the matrix is by far more complex than discussed for the nanotubes and fullerenes. This is due to the more variable surface structure that features not only graphitized domains, but also a variety of polar and nonpolar functional groups. 

Oxidized samples of nanodiamond carry many polar functional groups leading to a preferred interaction with polar compounds. The bonding is achieved via 

As a consequence, such composites can easily be dispersed in non- or moderately polar organic media (e.g., 1,2-dichloroethane, THF). 

From the hydrogenation or fluorination of a diamond material, a very hydro-phobic surface results that may then enter into an exchange with rather nonpolar compounds. A connection via Jt-stadting, however, plays just a minor role because graphitic fragments are only found in small domains on the particle surface. In the case of thermally graphitized nanodiamond particles, on the other hand, the conditions largely resemble those observed for multiwalled nanotubes. The interaction of the 7t-electrons with the polymer molecule causes a stable noncovalent incorporation into the composite. 

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