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Composites of carbon nanotubes

Tchoul, Maxim N.
Scope and Method of Study: The purpose of this research was to study various methods of incorporation of single-walled carbon nanotubes (SWNT) with polymers for producing electrically conductive polystyrene composites. SWNT of three different types were dispersed in solvents by noncovalent "wrapping" with a semiconjugated copolymer, nitric acid oxidation, and covalent grafting with both polystyrene and poly(vinylbenzyl trimethylammonium chloride). Composites were prepare via solution mixing. Effect of the type of SWNT material and the preparation method on electrical conductivity of the resulting composites was investigated.
Findings and Conclusions: Covalent grafting of SWNT with poly(vinylbenzyl trimethylammonium chloride) gave stable dispersions of carbon nanotubes in water and produced polymeric composites via layer-by-layer deposition. Grafting of polystyrene increased dispersability of SWNT in organic solvents. Mild nitric acid oxidation of carbon nanotubes also resulted in stable dispersions of SWNT in DMF, methanol, and water. Mixing SWNT and polystyrene in DMF or chloroform solutions, followed by rapid removing of solvent via either precipitation in water or evaporation under vacuum, resulted in composites with uniform distribution of carbon nanotube bundles. Electrical conductivity of these composites was dependent on the physical properties of bundles of the SWNT such as aspect ratio, density, fraction of metallic nanotubes, chemical functionalization, and presence of the molecules immobilized at the surface.