Our carbon nanotube activities are presently focused on single-walled (SWNT) tubes which can be regarded to first order as rolled-up graphene sheets. Present production methods generate a wide distribution of diameters and "roll-up" types (which can be expressed in terms of a so-called chiral index). For example, the laser ablation method as used by us can generate ca. 50 different tube types simultaneously.
These have strongly chiral-index dependent electronic and optical properties. Consequently there is presently great interest in developing scaleable separation methods. We are pursuing a variety of different approaches (both individually and in combination) towards this goal. These include size exclusion chromatography, density gradient ultracentrifugation and selective solubilization by means of polymer wrapping.
"Near Monochiral Single-Walled Carbon Nanotube Dispersions in Organic Solvents", Ninette Stürzl,Frank Hennrich, Sergei Lebedkin and Manfred M. Kappes, J. Phys. Chem. C, 2009, 113, 14628–14632 .