Self-organization of PEO-graft-single-walled carbon nanotubes in solutionsand Langmuir-Blodgett films

Poly(ethylene oxide) (PEO), soluble in both water and many organic solvents , is grafted onto single-walled carbon nanotubes (SWNTs), and aggregation b ehaviors of the resulting PEO-graft-SWNT in solutions and in Langmuir-Blodg ett (LB) films are investigated. SWNTs, cleaved by acid, are dispersed rela tively well in DMF and water, but poorly in chloroform and THF. PEO-graft-S WNT was synthesized by treating acid-cut SWNTs with SOCl2, followed by a re action with monoamine-terminated PEO in a DMF and water medium. Atomic forc e microscopy reveals that PEO and SWNT segments take expanded and extended conformations when freshly prepared PEO-graft-SWNTs are cast from water. Wh en PEO-graft-SWNTs are dispersed in chloroform, each SWNT segment collapses into a globular aggregate. Aging the chloroform dispersion produces self-o rganized structures detectable by light scattering. Langmuir-Blodgett films made from this aged solution afford a surface-micelle structure in which t he coagulated collapsed SWNT core is surrounded by extended PEO patches. Ad dition of DMF to this chloroform solution re-expands the SWNT segments, alt hough not completely. These results demonstrate that the conformation of SW NTs can be controlled by solvent quality as if they are ordinary hydrocarbo n-based block copolymers. Yet, the conformational change is not completely reversible, and coagulation, rather than entanglement, becomes the major ev ent even at locally concentrated regions.