title: Advanced sorting of single-walled carbon nanotubes by nonlinear density-gradient ultracentrifugation.
abstract: Existing methods for growing single-walled carbon nanotubes produce samples with a range of structures and electronic properties, but many potential applications require pure nanotube samples. Density-gradient ultracentrifugation has recently emerged as a technique for sorting as-grown mixtures of single-walled nanotubes into their distinct (n,m) structural forms, but to date this approach has been limited to samples containing only a small number of nanotube structures, and has often required repeated density-gradient ultracentrifugation processing. Here, we report that the use of tailored nonlinear density gradients can significantly improve density-gradient ultracentrifugation separations. We show that highly polydisperse samples of single-walled nanotubes grown by the HiPco method are readily sorted in a single step to give fractions enriched in any of ten different (n,m) species. Furthermore, minor variants of the method allow separation of the mirror-image isomers (enantiomers) of seven (n,m) species. Optimization of this approach was aided by the development of instrumentation that spectroscopically maps nanotube contents inside undisturbed centrifuge tubes.
authors.affiliation: Department of Chemistry and R.E. Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, Texas 77005, USA.
authors.forename: Saunab
authors.initials: S
authors.lastname: Ghosh
authors.forename: Sergei M
authors.initials: SM
authors.lastname: Bachilo
authors.forename: R Bruce
authors.initials: RB
authors.lastname: Weisman
mesh_terms: D002499:Centrifugation, Density Gradient / Q000379:methods*; D002942:Circular Dichroism; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000145:classification; D017711:Nonlinear Dynamics; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013237:Stereoisomerism; D014461:Ultracentrifugation / Q000379:methods*
chemical_list: D037742:Nanotubes, Carbon
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