Chromatographic fractionation of SWNT/DNA dispersions with on-line multi-angle light scattering

Single wall carbon nanotubes (SWNTs) dispersed in aqueous medium by the use of DNA are separated by size using a size exclusion chromatographic (SEC) column. On-line measurements are made of SWNT concentration, molar mass, and size using UV-vis absorption detection and multi-angle light scattering (MALS). Molar mass and length distributions are calculated for SWNT dispersions from this data. The SWNTs are shown to separate primarily by a SEC mechanism, but the elution times are affected by a high performance liquid chromatography (HPLC) mechanism in which adsorption on the column delays the elution of the components. This mechanism is most evident by the elution of small quantities of large, polydisperse SWNTs after the SEC column limit. MALS data are fit with a polydisperse anisotropic rod scattering function giving low polydispersity for most of the fractions with higher polydispersities near the large size exclusion limit and beyond the small size exclusion limit of the SEC column. These fits indicate that molar mass is proportional to the rod length over a wide range indicating rigid-rod behavior.