Modular Engineering of H-Bonded Supramolecular Polymers for Reversible Functionalization of Carbon Nanotubes

Abstract

A H-bond-driven, noncovalent, reversible solubilization/functionalization of multiwalled carbon nanotubes (MWCNTs) in apolar organic solvents (CHCl(3), CH(2)Cl(2), and toluene) has been accomplished through a dynamic combination of self-assembly and self-organization processes leading to the formation of supramolecular polymers, which enfold around the outer wall of the MWCNTs. To this end, a library of phenylacetylene molecular scaffolds with complementary recognition sites at their extremities has been synthesized. They exhibit triple parallel H-bonds between the NH-N-NH (DAD) functions of 2,6-di(acetylamino)pyridine and the CO-NH-CO (ADA) imidic groups of uracil derivatives. These residues are placed at 180° relative to each other (linear systems) or at 60°/120° (angular modules), in order to tune their ability of wrapping around MWCNTs. Molecular Dynamics (MD) simulations showed that the formation of the hybrid assembly MWCNT•[X•Y](n) (where X = 1a or 1b -DAD- and Y = 2, 3, or 4 -ADA-) is attributed to π-π and CH-π interactions between the graphitic walls of the carbon materials and the oligophenyleneethynylene polymer backbones along with its alkyl groups, respectively. Addition of polar or protic solvents, such as DMSO or MeOH, causes the disruption of the H-bonds with partial detachment of the polymer from the CNTs, followed by precipitation. Taking advantage of the chromophoric and luminescence properties of the molecular subunits, the solubilization/precipitation processes have been monitored by UV-vis absorption and luminescence spectroscopies. All hybrid MWCNTs-polymer materials have been also structurally characterized via thermogravimetric analysis (TGA), transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS).

Non-covalent and reversible functionalization of carbon nanotubes

“…Llanes-Pallas et al have shown that such a non-covalent solubilization can be realized by exploiting the formation of hydrogen bonds between the 2,6-di(acetylamino)pyridine and the imidic groups of uracil derivatives [86]. In apolar organic solvents such hydrogen bonding interactions are effective and keep the nanotube in solution, whereas the addition of polar solvents destroys the H-bonds causing the detachment of the polymer from CNT surface and the precipitation of the nanotubes.…”

Effects of carbon nanotubes on polymer physics

“…A height of 9 nm was found which the authors could not explain. 12 DNA 13 and poly(3-hexylthiophene) 14 have been shown to wrap around single-walled carbon nanotubes. STM allows the determination of the chiral angle and the polymer spacing along the nanotube.…”

Near-Edge X-ray Absorption Fine Structure Studies of Electrospun Poly(dimethylsiloxane)/Poly(methyl methacrylate)/Multiwall Carbon Nanotube Composites

“…14 This property ensemble is of great importance in the study of CNT composites, where sophisticated conformational bonding has been reported by way of “polymer-wrapping”, 8 and supramolecular chemistry provides multiple bonding possibilities at the nanotube-polymer interface. 8, 15 …”