| Abstract
| - Poly(ethylene oxide) (PEO), soluble in both water and many organic solvents, is grafted onto single-walled carbon nanotubes (SWNTs), and aggregation behaviors of the resulting PEO-graft-SWNT in solutionsand in Langmuir−Blodgett (LB) films are investigated. SWNTs, cleaved by acid, are dispersed relativelywell in DMF and water, but poorly in chloroform and THF. PEO-graft-SWNT was synthesized by treatingacid-cut SWNTs with SOCl2, followed by a reaction with monoamine-terminated PEO in a DMF and watermedium. Atomic force microscopy reveals that PEO and SWNT segments take expanded and extendedconformations when freshly prepared PEO-graft-SWNTs are cast from water. When PEO-graft-SWNTsare dispersed in chloroform, each SWNT segment collapses into a globular aggregate. Aging the chloroformdispersion produces self-organized structures detectable by light scattering. Langmuir−Blodgett filmsmade from this aged solution afford a surface-micelle structure in which the coagulated collapsed SWNTcore is surrounded by extended PEO patches. Addition of DMF to this chloroform solution re-expands theSWNT segments, although not completely. These results demonstrate that the conformation of SWNTscan be controlled by solvent quality as if they are ordinary hydrocarbon-based block copolymers. Yet, theconformational change is not completely reversible, and coagulation, rather than entanglement, becomesthe major event even at locally concentrated regions.
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