Nanoscopic Hybrid Materials: The Synthesis, Structure and Properties of Peapods, Cats and Kin

Summary

The mechanism for the formation of encapsulated C₆₀ chains is now apparent, and we have successfully synthesized them in large fractions of the tubes that comprise our samples. In contrast to prior studies showing the uptake of liquid into large diameter MWNTs, the mechanism involves transport in the vapor phase or the surface diffusion of individual molecules. SWNTs with small interior diameters are completely filled over long lengths. The extent of filling argues for the entrance of C₆₀ through sidewall defects as well as open ends. A minimum temperature must be achieved in order to promote exterior C₆₀ to enter the tubes. Annealing at too high a temperature will limit the residence time of C₆₀ on the SWNT as well as cause the healing of the nanotubes walls, thereby eliminating access to the nanotube interiors. There is thus a critical temperature window required for the formation of bucky-peapods. The ability to synthesize these unique hybrid materials in bulk will now permit scaled-up empirical study. Interestingly, there is no obvious physical reason why SWNTs could not be filled with any appropriately-sized molecule with an affinity for nanotubes, and present in the gas phase or highly mobile at temperatures within the critical temperature window. Thus, the present work opens the possibility for the general functionalizing of the particular diameter SWNTs produced at highest concentration by PLV and CA methods.