[Show abstract][Hide abstract] ABSTRACT: Poor solubility of single-walled and multiwalled carbon nanotubes (NTs) in water and organic solvents presents a considerable challenge for their purification and applications. Macromolecules can be convenient solubilizing agents for NTs and a structural element of composite materials for them. Several block copolymers with different chemical functionalities of the side groups were tested for the preparation of aqueous NT dispersions. Poly(N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co-4-vinylpyridine) was found to form exceptionally stable NT dispersions. It is suggested that the efficiency of macromolecular dispersion agents for NT solubilization correlates with the topological and electronic similarity of polymer-NT and NT-NT interactions in the nanotube bundles. Raman spectroscopy and atomic force and transmission electron microcopies data indicate that the polycations are wrapped around NTs forming a uniform coating 1.0-1.5 nm thick. The ability to wind around the NT originates in the hydrophobic attraction of the polymer backbone to the graphene surface and topological matching. Tetraalkylammonium functional groups in the side chains of the macromolecule create a cloud of positive charge around NTs, which makes them hydrophilic. The prepared dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for electronic materials and sensing. Positive charge on their surface is particularly important for biological and biomedical applications because it strengthens interactions with negatively charged cell membranes. A high degree of spontaneous bundle separation afforded by the polymer coating can also be beneficial for NT sorting.
Journal of the American Chemical Society 04/2005; 127(10):3463-72. · 10.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A convenient procedure for forming stable suspensions of SWNT's in water and water/DMF solutions is reported. The dispersion process is effective, simple, and universal. It can be applied to different types of single-walled carbon nanotubes (SWNT's) as well as multi walled carbon nanotubes (MWNT's). The stability of SWNT suspensions was achieved by adsorbing an amphiphilic cationic [poly (N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co- 4-vinylpyridine) (16/75/9)] polymer to carbon surface. The amphiphilic nature of the polymer plays a dual action in the functionalization and solubilization of the nanotubes. The hydrophobic alkyl pendent groups of the polymer bind strongly to the surface of the nanotubes, whereas the hydrophilic groups exposes the nanotubes to the solvent medium rendering them soluble in water. The frequency of the Raman radial breathing modes (RBM) and the carbon-carbon stretching mode (known as the G-band) of the nanotubes were seen to increase in the presence of the polymer. Some increase in the intensity of the Raman disorder band (the D-band) was also observed. Raman spectral observations indicate the strong binding of the copolymer to the nanotubes (wrapping) which causes the unbundling of the nanotubes, making them easier to disperse in aqueous solvents.