Dispersion of Functionalized Multiwalled Carbon Nanotubes

Abstract

The dispersion of functionalized multiwalled carbon nanotubes (MWNTs) in various solvents is characterized. The nanotubes were functionalized using a Birch alkylation method that afforded a 50−100% increase in <i>o</i>-dichlorobenzene solubility while rendering measurable solubility in otherwise insoluble chloroform and decreasing solubility in <i>N</i>,<i>N</i>-dimethylformamide and <i>N</i>-methyl-2-pyrrolidinone. Dispersibility was contingent on fostering polar interactions between the functionalized nanotubes and solvent despite the purely dispersive nature of the aliphatic chains. Interpretation of these results was performed using the Hansen solubility parameters and the three component surface energy analysis pioneered by van Oss and co-workers. It was found that the simplest interpretation of the Hansen solubility parameter scheme was unable to explain the data. In contrast, the surface energy analysis provides a robust interpretation of the solubility and yields values of 45.6 ± 1.2, 0.78 ± 0.04, and 2.4 ± 0.9 mJ/m² for the Lifshitz−van der Waals (γ^LW), electron acceptor (γ⁺), and electron donor (γ⁻) surface energy components respectively.