Ji Yeon Huh 1 Angela R. Hight Walker 2, Hyun Wook Ro 1, Jan Obrzut 1, and Jeffrey A. Fagan

Polymers Division 1 and Physics Laboratory 2, NIST, Gaithersburg, Maryland 20899.

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, utilizing the differences in buoyant density of DWCNTs from impurity single wall carbon nanotubes (SWCNTs) and multi wall carbon nanotubes (MWCNTs) 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 co-surfactants 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.