The Role of Molecular Clusters in the Filling of Carbon Nanotubes

We have demonstrated that the ability of fullerenes to form clusters is essential for the filling of single-walled carbon nanotubes in solution. In solutions where C-60 exists in the form of discrete solvated molecules (e.g., in CS2) no fullerene encapsulation in nanotubes takes place, as the large molar excess of solvent compared to solute prohibits C-60 from entering the nanotubes. However, in solutions containing large clusters of C-60 (e.g., in n-hexane) nanotubes become densely filled with fullerene molecules despite the large excess of solvent. The interactions between carbon nanotubes and fullerene clusters provide an efficient transport of C-60 into nanotubes that avoids the detrimental effects of the solvent molecules. This new mechanism provides the first rational explanation of experiments involving nanotube filling with guest-molecules in solution.