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.