Separation of mixed SWNTs and MWNTs by centrifugal force - an experimental study

For eventual commercial applications of carbon nanotubes (CNTs) in nanoscale devices, it will be very important to realize effective separation of mixed single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). We have developed a new method to separate a mixture of SWNTs and MWNTs by centrifugal force in an aqueous solution of glycerol. The method proposed in this paper takes advantage in the difference of the density and diameter of the SWNTs and MWNTs, which effectively produce a difference of sedimentation velocity between them along the direction of spinning radius when centrifugal force is exerted. The inert gradient agent acts to both stabilize the fluid environment of the centrifuge tube and facilitate sharp resolution of zones of the centrifuge fluid in the tubes after the centrifugation. Experiments show that SWNTs and MWNTs subside at different speeds during the procedure of centrifugation and suspend at different levels in the centrifugal tube, due to difference in their buoyant densities, at the end of centrifugation. Our results indicate that the centrifugal technique can provide a rapid and repeatable separation of mixtures of SWNTs and MWNTs.