Stable Dispersions of Nitrogen Containing Multi-Walled Carbon Nanotubes

Stable dispersions of pure and nitrogen containing multi-walled carbon nanotubes (MWCNTs and N-MWCNTs respectively) were prepared using a variety of solvents (such as N-methyl-2-pyrrolidone (NMP), benzyl alcohol, acetophenone, N-dimethylacetamide (DMA), etc. with surface energies ranging between 45.8 mJ/m(2) (diethyl ether) and 102.3 mJ/m(2) (water). Sedimentation measurements were employed to confirm the stability of the dispersions over time. Amongst the solvents employed DMA proved to be particularly efficient, i.e., up to 82% of the nanotubes initially dispersed remained in solution. Moreover, we showed that the surface chemistry of carbon nanotubes (CNTs) governs their dispersibility. For instance, the higher the N content is within the N-MWCNTs, the lower the surface energy of the solvent must be to successfully disperse the nanotubes. These findings not only play an important role in overcoming current obstacles commonly encountered in existing CNT processing procedures but also provide a technique for processing CNTs efficiently without altering their properties. Ultimately, it may be possible to manipulate the surface chemistry of CNTs in-situ, e.g., by inserting heteroatoms, to such extend that they may disperse spontaneously in aqueous solutions, hence paving the way for biomedical applications etc.