Formation of self-assembled nanostructures from polymer-grafted single-wall carbon nanotubes

Abstract

Since their discovery in 1991, carbon nanotubes have intensively been investigated because of their potential applications in opto-electronics, membranes and storaging materials. Recently most of the reported functionalizations of single walled carbon nanotubes (SWNTs) have been base on the use of nanotubes having carboxylic acid groups in their side-wall and end-parts. While previous studies of chemical modifications of SWNTs emphasized the solubility and functionality of them, our research is being progressed in the direction of creating new class of self-assembling nano-structured material from SWNT-polymer building block. The Polymer-grafted SWNTs was synthesized by treating shortened SWNTs with $SOCl_2$, followed by reaction with various polymers. Transmission electron microscopy (TEM) reveals that poly(butadiene) (PB)-grafted SWNTs self-organize in a selective solvent to form a micelle-like core-shell morphology. In this self-assembled nanostructure, a PB core is surrounded by SWNT bundles. A similar core-shell morphology is observed in poly(ethylene glycol) (PEG)-grafted SWNT systems. The tendency of these systems to form micelles originates from the strong association between polymer chains covalently linked to the side-walls of SWNTs. The polymer attachment at the side-walls of the nanotubes was verified by direct visualization of Au (gold) grafting sites on functionalized SWNT in Au-grafted SWNT system. This aggregation behavior resembles the self-assembly of graft copolymers in dilute solution. Our findings open up exciting possibilities for the fabrication of novel self-assembling structures based on nanotubes, and provide a new approach for building a variety of superstructures. Unlike the previous self-assembling materials, this new materials will give high stable and ordered nanostructures, since the mechanical and electronic property of the carbon nanotubes are already well known, based on the previous theoretical and experimental results on t...