Separation and Characterization of Double-Wall Carbon Nanotube Subpopulations

Abstract

Surfactant-encapsulated double-wall carbon nanotubes (DWCNTs) synthesized by the high-pressure carbon monoxide decomposition (HiPco) process were separated by length and electronic characteristics using density gradient ultracentrifugation (DGU). To ensure our study focuses only on the behavior of DWCNTs, dispersed DWCNTs were first isolated following the method of Green et al. [Green, A. A.; Hersam, M. C. Nat. Nanotechnol. 2008, 264, 1], utilizing the differences in buoyant density of DWCNTs from that of impurity single-wall carbon nanotubes (SWCNTs) and multiwall carbon nanotubes contained in the parent soot. By increasing the density difference between the nanotubes and the density gradient medium, we exploited the length-dependent translation of the nanotubes in response to applied centrifugation to isolate narrow length distribution DWCNT fractions. The length-dependent intrinsic optical response of DWCNTs is consistent compared with the previously reported values for SWCNTs. The controlled addition of cosurfactants is shown to allow resolution of DWCNTs by electronic structure, as demonstrated through optical absorbance, Raman spectra, and electrical conductivity measurements. Measurements of conducting films prepared from separated fractions exhibit significant property differences in the enriched materials.