The influence of oxygen-containing functional groups on the dispersion of single-walledcarbon nanotubes in amide solvents

Abstract

Surface composition plays an important role in carbon nanotube dispersibility in differentenvironments. Indeed, it determines the choice of dispersion medium. In this paper theeffect of oxidation on the dispersion of HiPCO single-walled carbon nanotubes (SWNTs) inN-methyl-pyrrolidinone (NMP),N, N-dimethylformamide (DMF),N, N-dimethylacetamide(DMA), N-dodecyl-pyrrolidinone (N12P) and cyclohexyl-pyrrolidinone (CHP) was systematicallystudied. During the oxidation process, similar amounts of carboxylic acid and phenolicgroups were introduced to mostly already existing defects. For each solvent thedispersion limits and the absorption coefficients were estimated by optical absorptionanalysis over a range of SWNT concentrations. The presence of acid oxygenatedgroups increased SWNT dispersibility in NMP, DMF and DMA, but decreased inN12P and CHP. The absorption coefficients, however, decreased for all solventsafter oxidation, reflecting the weakening of the effective transition dipole of theπ–π transition with even limited extension functionalization and solvent interaction. Theanalysis of the results in terms of Hansen and Flory–Huggins solubility parametersevidenced the influence of dipolar interactions and hydrogen bonding on the dispersibilityof oxidized SWNTs.