Non-covalent and reversible functionalization of carbon nanotubes.

Antonello Di Crescenzo,Antonella Fontana,Valeria Ettorre

doi:10.3762/bjnano.5.178

Abstract

Carbon nanotubes (CNTs) have been proposed and actively explored as multipurpose innovative nanoscaffolds for applications in fields such as material science, drug delivery and diagnostic applications. Their versatile physicochemical features are nonetheless limited by their scarce solubilization in both aqueous and organic solvents. In order to overcome this drawback CNTs can be easily non-covalently functionalized with different dispersants. In the present review we focus on the peculiar hydrophobic character of pristine CNTs that prevent them to easily disperse in organic solvents. We report some interesting examples of CNTs dispersants with the aim to highlight the essential features a molecule should possess in order to act as a good carbon nanotube dispersant both in water and in organic solvents. The review pinpoints also a few examples of dispersant design. The last section is devoted to the exploitation of the major quality of non-covalent functionalization that is its reversibility and the possibility to obtain stimuli-responsive precipitation or dispersion of CNTs.

Highlights

Carbon nanotubes (CNTs) are hollow cylindrical tubes with nanometer scale diameters and lengths up to a few micrometers
Zhong and Claverie demonstrated from adsorption isotherm measurements [68] that MWCNTs form stable aqueous dispersions when 90% of their surface is covered by the dispersant, while for SWCNTs, 45% of the surface has to be covered in order for the dispersion to be stable
Once CNTs are properly disentangled by overcoming the strong van der Waals interactions among the tubes via sonication, it is essential to disfavor the approach of CNTs to each other

Summary

Introduction

Carbon nanotubes (CNTs) are hollow cylindrical tubes with nanometer scale diameters and lengths up to a few micrometers. Typical dispersants are polymers formed by repetitive units of alkyl chains and aromatic moieties which exploit both π-stacking to the CNT surface and van der Waals interactions between the hydrophobic nanotube surface and alkyl tails It has been demonstrated [49] that poly(m-phenylene vinylene-co-2,5dioctyloxy-p-phenylene vinylene) (PmPV, see Table 1) effectively adsorbs onto the nanotube surface allowing to obtain a good dispersion of MWCNTs produced by arc discharge in toluene. In the case of polymers and to what has already been underlined for classical surfactant molecules, we have demonstrated [70] that polymeric micelles concentration is not related to the formation of stable SWCNT dispersions, the outmost requirement in order to obtain a stable CNTs dispersion being the adsorption degree, up to an almost complete saturation, of the nanotube surface with proper dispersant molecules. In these carbon scaffolds the nucleobases directly interact with SWCNT sidewalls, while the hydrophilic sugar-phosphate backbone is oriented towards the solvent [5]

Design of novel dispersant

Findings

Conclusion