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PUBLISHED ONLINE: 1 NOVEMBER 2009 | http://www.nature.com/doifinder/10.1038/nnano.2009.302
Web End =DOI: 10.1038/NNANO.2009.302
Virginia A. Davis1,2, A. Nicholas G. Parra-Vasquez1,2, Micah J. Green1,2, Pradeep K. Rai1,2, Natnael Behabtu1,2, Valentin Prieto1,2, Richard D. Booker1, Judith Schmidt4, Ellina Kesselman4, Wei Zhou5, Hua Fan1, W. Wade Adams1, Robert H. Hauge1,3, John E. Fischer5, Yachin Cohen4, Yeshayahu Talmon4, Richard E. Smalley1,3 and Matteo Pasquali1,2,3*
Translating the unique characteristics of individual single-walled carbon nanotubes into macroscopic materials such as bres and sheets has been hindered by ineffective assembly. Fluid-phase assembly is particularly attractive, but the ability to dissolve nanotubes in solvents has eluded researchers for over a decade. Here, we show that single-walled nanotubes form true thermodynamic solutions in superacids, and report the full phase diagram, allowing the rational design of uid-phase assembly processes. Single-walled nanotubes dissolve spontaneously in chlorosulphonic acid at weight concentrations of up to 0.5wt%, 1,000 times higher than previously reported in other acids. At higher concentrations, they form liquid-crystal phases that can be readily processed into bres and sheets of controlled morphology. These results lay the foundation for bottom-up assembly of nanotubes and nanorods into functional materials.
The lack of scalable assembly methods has been a key block in the manufacture of functional nanomaterials. Fluid-phase assembly is the most promising method for producing large, ordered structures of nano-objects1,2. Single-walled carbon nanotubes (SWNTs) are a particularly important and challenging case, and are a model system for nanorods. Based on single-object data, the thermal, electrical and mechanical properties of SWNTs are unique3 and could be of use in numerous breakthrough applications such as multifunctional high-strength bres, coatings and transparent conducting lms. However, macroscopic SWNT materials demonstrate only a small fraction of the possible single-object properties, largely because of their ineffective assembly, for example, into bres and sheets411. Successful assembly begins with control of dispersion and phase behaviour and requires a scientic understanding of ow, colloidal interactions and solvent removal. (Note that an SWNT dispersion comprises a homogeneous suspension or dissolution of SWNTs and/or small SWNT aggregates, and SWNT phase behaviour refers to the various liquid microstructures that can form as a function of SWNT and solvent parameters.) The dispersion and phase behaviour properties of SWNTs in liquids are particularly complex compared with those of other anisotropic nanomaterials and rod-like...