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Debundling, Dispersion, and Stability of Multiwalled Carbon Nanotubes Driven by Molecularly Designed Electron Acceptors

Gharib, Desi H., Malherbe, Francois, Moulton, Simon E.
Langmuir 2018 v.34 no.40 pp. 12137-12144
carbon nanotubes, dispersions, energy, physicochemical properties, solvents, sonication, stabilizers, toxicity
Carbon nanotubes (CNTs) have attracted significant attention because of their outstanding physical and chemical properties, and yet, their high natural tendency to form bundles, ropes, or aggregates, as a consequence of their strong π–π interactions, limits their solvent processing and further applications. Efficient processing solvents, mostly amide-based, that partially compensate for these strong inter-CNT π–π interactions have been widely reported. However, the yield of debundled/dispersed CNTs and the stability of subsequent dispersions in these solvents remain key challenges. Moreover, there are major concerns related to the large-scale use of conventional solvents, as they are fossil fuel based and intrinsically highly toxic, hence the need to identify environmentally friendly and safer alternatives. Herein, we address these challenges by using a ternary system composed of multiwalled CNTs (MWCNTs), tailored electron-deficient acceptors, and an organic solvent. Not only do the electron-deficient acceptors interrupt the inter-CNTs π–π interactions, thereby enabling the subsequent debundling and dispersion of MWCNTs aggregates in the solvent, they also act as stabilizers, after dispersion, by inhibiting inter-CNT π–π interactions and re-agglomeration. The use of electron acceptors increases the yield by a factor of 165 in N-methyl 2-pyrrolidone, improves the long-term stability of the debundled and dispersed MWCNTs, and reduces the energy input to only 30 min of mild bath sonication, compared with prolonged high-energy sonication reported in the literature. We also report for the first time, the use in MWCNT processing of a “green” biosolvent, dihydrolevoglucosenone, as an environmentally friendly and nontoxic alternative to the more conventional amide-based solvents.