Micelle-Encapsulated Carbon Nanotubes:  A Route to Nanotube Composites

Abstract

We report a general approach toward dispersing single-walled carbon nanotubes (SWNTs) in solvents and polymer materials, by encapsulating SWNTs within cross-linked micelles. Micelles made from polystyrene-block-poly(acrylic acid) (PS-b-PAA), an amphiphilic block copolymer, are first assembled around SWNTs by gradually adding H2O to a suspension of nanotubes in dimethylformamide. The hydrophilic, outer shells of these micelles are then chemically cross-linked with a difunctional linker molecule. Pure encapsulated SWNTs (e-SWNTs) can then be separated from empty cross-linked micelles by consecutive cycles of centrifugation and redispersion. Atomic force and transmission electron microscopies of the resulting nanostructures demonstrate that individual nanotubes (rather than bundles) have been completely encased in polymer shells whose thickness is slightly larger than that of empty micelles. e-SWNTs encapsulated in PS-b-PAA can be permanently redispersed in H2O, in organic solvents, and in both hydrophobic and hydrophilic polymer matrices with minimal sonication. Micelle encapsulation could improve the compositing of SWNTs in a wide variety of polymer materials for structural, electronic, and thermal applications.

Effect of Water Content on Encapsulation of SWNTs and Hydrophobic Dyes within PS-b-PAA Block Copolymer Micelles

“…R h of pure PS 159 -b-PAA 58 micelle was 20 nm at wc = 90%, which is consistent with the radius of dry spherical micelle previously measured with AFM. 27 These data support that deswollen spherical micelles were formed at high water content (wc = 90%). R h of SWNT@ PS 159 -b-PAA 58 is much larger than that of pure PS 159 -b-PAA 58 , which is possibly because of the limitation of light scattering technique to 1D structure such as SWNT.…”

“…We recently reported single-walled carbon nanotubes (SWNTs) and gold nanoparticles encapsulated within block copolymer micelles in aqueous media. [27][28][29][30] In this method, block copolymers spontaneously formed thick concentric shell structures around nanotube-or nanoparticle core when solvent was gradually exchanged from DMF to water. Unlike other polymer wrapping methods, the shell of the resulting nanostructures was very thick and completely isolated nanomaterials from outer environment.…”

“…27 Since both nanotubes and PS 159 -b-PAA 58 block copolymers were not able to be directly solubilized in aqueous solvent, they were first co-suspended in DMF, and then H 2 O was gradually added under vigorous sonication. As increasing water content (wc), originally insoluble SWNTs/co-polymer mixtures gradually formed homogeneous dispersion, which implies the formation of block copolymer micelles around SWNTs.…”

“…The swollen micelles more effectively solubilize SWNTs because of their larger internal diameter, but obviously their structural integrity is weak when they are swollen. 27 Deswelling decreases the diameter of micelle, and consequently have SWNTs precipitate out of micelle core. …”

Fabrication of biosensors using vinyl polymer-grafted carbon nanotubes

“…Shen et al, 2007;Kitano et al, 2007). Thereafter, small molecules (Kooi et al, 2002;Liu, 2005;Tasis et al, 2003) or polymer chains (Kang & Taton., 2003; O. K. Kim et al, 2003) can be chemically attached to the CNTs by esterification and amidation reactions via the carboxylic acid moieties. The chemical modification is an especially attractive target, as it can improve solubility (Bahr et al, 2001) and processing ability and allows the unique properties of CNTs to be coupled to other types of materials.…”