title: Determination of carbon nanotube density by gradient sedimentation.
abstract: Density gradient centrifugation is a high-resolution technique for the separation and characterization of large molecules and stable complexes. We have analyzed various nanotube structures by preparative centrifugation in sodium metatungstate-water solutions. Bundled, isolated and acid-treated single-walled nanotubes (SWNTs) and multiwall nanotubes (MWNTs) formed sharp bands at well-defined densities. The structure of the material in each band was confirmed by transmission electron microscopy and Raman spectroscopy. Our data suggest respective densities of 1.87, 2.13, 1.74, and 2.1 g/cm(3) for bundled, isolated, and acid-treated SWNTs and MWNTs. These measured results compare well with their calculated densities.
authors.affiliation: Department of Physics and Astronomy, Department of Materials Science and Engineering, Clemson University, Clemson, South Carolina 29634, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Lu
authors.forename: Gayatri
authors.initials: G
authors.lastname: Keskar
authors.forename: Razvan
authors.initials: R
authors.lastname: Ciocan
authors.forename: Rahul
authors.initials: R
authors.lastname: Rao
authors.forename: Rakesh B
authors.initials: RB
authors.lastname: Mathur
authors.forename: Apparao M
authors.initials: AM
authors.lastname: Rao
authors.forename: Lyndon L
authors.initials: LL
authors.lastname: Larcom