Aggregation behavior of chemically attached poly(ethylene glycol) to single-walled carbon nanotubes (SWNTs) ropes

The aggregation behavior of poly(ethylene glycol) (PEG)-grafted single-walled carbon nanotubes (SWNTs) was investigated by Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and high-resolution transmission electron microscopy (HR-TEM). The hybrid functional material was synthesized by producing carboxylic acid groups at nanotube ends and side-wall defect sites, which provide reaction sites for various guest species, followed by a reaction with hydroxyl-terminated PEG in various solvents. FTIR and TGA analyses confirm that the PEG chains were covalently attached to the functionalized SWNTs ropes. Transmission electron microscopy (TEM) images of the PEG-grafted SWNTs revealed two different morphologies, depending on solvent quality: PEG and SWNT segments self-organize into ring-like structure in which the aggregated PEG core is surrounded by SWNT bundles, when freshly prepared PEG-grafted SWNTs are cast from benzene/tetrahydrofuran solvent mixture. Instead, the hybrid polymers form a highly dispersed morphology in selective solvents for SWNTs. The novel aggregation mode originates from strong association of polymer chains with nanotubes, as in the aggregation behavior of micro-phase separated copolymers in dilute solution.