Diameter sorting of carbon nanotubes by gradient centrifugation: role of endohedral water

We demonstrate that water filling has a significant, tube‐diameter dependent effect on the effective mass density of individual single‐walled carbon nanotubes suspended in aqueous suspension. On the basis of extensive molecular dynamics simulations of water‐filled carbon nanotubes we have estimated the number density and properties of water molecules inside different types of nanotubes. As the tube diameter becomes comparable with the size of a water molecule, the number density of water molecules jumps discontinously. For tube diameters just above this threshold the water molecules organize into a single file. Shell‐like arrangements are found for even larger radii. Buoyant densities are predicted to change accordingly. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)