Variation of single wall carbon nanotube dispersion properties with alkyl amide and halogenated aromatic solvents

Organic solvents from the alkyl amide and halogenated aromatic classes have been analyzed as dispersion agents for high purity single wall carbon nanotubes (SWCNTs). The resulting dispersions from two novel SWCNT solvents, N,N,N′,N′-tetramethylmalonamide (TMMA) and 1-chloronaphthalene (1-CLN), have been compared to the well-established solvents, N,N-dimethylacetamide (DMA) and 1,2-dichlorobenzene (DCB). Optical absorption spectroscopy on a series of high purity SWCNT concentrations was used to obtain solvent-dependent dispersion limits, extinction coefficients, and dispersion stability. The variation in SWCNT optoelectronic properties was measured for each solvent dispersion as a function of ultrasonication time and the results demonstrate that under conventional ultrasonication times the halogenated aromatic solvents (DCB and 1-CLN) can significantly affect the SWCNT optical absorption. A post-dispersion analysis was performed on samples, after removal of the solvents, by Raman spectroscopy to monitor structural changes in the SWCNTs. The spectroscopy results for the halogenated aromatic solvents are consistent with formation of a sonopolymer and subsequent interaction with the SWCNTs. In comparison, the alkyl amide solvents (DMA and TMMA) show similar dispersion limits with no significant change in absorbance as a function of ultrasonication, and can easily be removed without affecting the SWCNTs.