Helical Superstructures of Fullerene Peapods and Empty Single-Walled Carbon Nanotubes\nFormed in Water

Abstract

Aqueous dispersions of fullerene C₇₀-filled carbon nanotubes (C₇₀@SWNTs or peapods) and empty single-walled carbon nanotubes (empty SWNTs) were prepared with the aid of trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (<b>1</b>), which is a carbon nanotube solubilizer. This is the first report describing the\npreparation and characterization of the transparent dispersion/dissolution of the peapods. The UV−vis−near-IR spectra of C₇₀@SWNTs−<b>1</b> and empty SWNTs−<b>1</b> were almost identical. We found by means of transmission\nelectron microscopy and atomic force microscopy that the empty SWNTs and C₇₀-peapods form helical\nnanostructures in the shapes of rings, irregular rings, lassos, handcuffs, catenanes, pseudorotaxanes, and figure-eight structures. The mechanism of the superstructure formation has been discussed in relation to the unique\ncharacteristics of stiff polymer chains with the aid of an off-lattice Monte Carlo simulation.