Poly(ethylene oxide) (PEO), soluble in both water and many organic solvents, is grafted onto singlewalled carbon nanotubes (SWNTs), and aggregation behaviors of the resulting PEO-graft-SWNT in solutions and in Langmuir-Blodgett (LB) films are investigated. SWNTs, cleaved by acid, are dispersed relatively well in DMF and water, but poorly in chloroform and THF. PEO-graft-SWNT was synthesized by treating acid-cut SWNTs with SOCl2, followed by a reaction with monoamine-terminated PEO in a DMF and water medium. Atomic force microscopy reveals that PEO and SWNT segments take expanded and extended conformations when freshly prepared PEO-graft-SWNTs are cast from water. When PEO-graft-SWNTs are dispersed in chloroform, each SWNT segment collapses into a globular aggregate. Aging the chloroform dispersion produces self-organized structures detectable by light scattering. Langmuir-Blodgett films made from this aged solution afford a surface-micelle structure in which the coagulated collapsed SWNT core is surrounded by extended PEO patches. Addition of DMF to this chloroform solution re-expands the SWNT segments, although not completely. These results demonstrate that the conformation of SWNTs can be controlled by solvent quality as if they are ordinary hydrocarbon-based block copolymers. Yet, the conformational change is not completely reversible, and coagulation, rather than entanglement, becomes the major event even at locally concentrated regions.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Surfaces and Interfaces