Length Fractionation of Carbon Nanotubes Using Centrifugation

Scalable manufacturing of single wall carbon nanotube (SWCNT) devices, sensors, and therapeutic agents will require precursors possessing well-defined length, chirality, and dispersion characteristics. However, existing synthetic and dispersion methods for SWCNTs produce heterogeneous mixtures of tube diameters, lengths and chiralities. As the unique optical, physical, thermal and electronic properties arise from the specific chiral wrapping vector of the graphene sheet, the necessity for separation of SWCNT materials by chirality is obvious. However, the strength and usability of these chirality specific properties also depends strongly on the length of the nanotube, and thus length fractionation is also desirable or required for many applications. The costeffectiveness of performing both of these separations will determine the future utility of SWCNT based advanced technologies. Recently, several methods have been described to enhance SWCNT population purity of individual SWCNT species. These include electrophoresis, dielectrophoresis, and ion exchange chromatography, which have all been demonstrated to separate tubes by diameter and electronic structure, although with limited throughput. Most recently, an article by Arnold et al. demonstrated the use of ultracentrifugation on single wall carbon nanotubes (SWCNTs) within a density gradient to produce a more facile and scalable, chirality separation. This significant advance works by driving the SWNCTs to their individual equilibrium locations within the density gradient. Length separation has also been carried out using various chromatographic techniques, including gel electrophoresis and size exclusion chromatography (SEC), which yield populations possessing well-defined lengths and length distributions. While SEC methods are scalable in principle, lengths have