Supramolecular self-assembly of single walled carbon nanotubes (SWNTs)

Applications of single walled carbon nanotubes (SWNTs) have been limited by their heterogeneity and the lack of selective assembly methodology. A selective SWNT junction formation was achieved by fullerene (C60) end-capped linker connecting SWNTs via their open ends. The SWNT junction was demonstrated in both single solvent (N-methyl pyrrolidone, NMP) and binary solvent mixtures (NMP and toluene). Initially, bis-fullerene linker was prepared following existing literature. However, spectroscopic characterisation revealed that the reaction between azide terminated PEG and C60 yield a novel closed ring structure rather than the linear dumbbell structure. The chain length of the PEG was found to be the key in the resulting structure of the adduct. Alternative synthetic methods were sought and the multifullerene end-capped linkers were synthesised via an one-step catalytic transesterification between polyethylene glycols (PEGs) and phenyl-C61-butyric acid methyl ester (PCBM) with a catalytic amount of dibutyltinoxide. Polydisperse and monodisperse branched PEGs were employed in the synthesis and purification was only achieved in the latter material. Both linear and star shape linkers were employed in the assembly process and the resulting SWNT junctions were characterised by atomic force microscopy (AFM). The SWNT junctions were found to be mainly localised on the body of the SWNT to give a ‘head-to-body’ assembly rather than the desired ‘head-to-head’ assembly, due to SWNT defects. While exploring the SWNT dispersion in organic solvents, a side reaction was observed during the sonication of NMP, causing significant contamination issues in AFM sample and high temperature annealing was found to be useful in improving sample quality. IR and UV-vis absorption spectroscopy revealed that NMP might polymerise during sonication, most likely due to amide bond cleavage. In addition, the resulting polyamide originated from NMP might play an important role in the dissolution of SWNT and other nanomaterials in amide solvents.Open Acces