  A simple model for the friction experienced by the one dimensional water
chains that flow through subnanometer diameter carbon nanotubes is studied. The
model is based on a lowest order perturbation theory treatment of the friction
experienced by the water chains due to the excitation of phonon and electron
excitations in both the nanotube and the water chain, as a result of the motion
of the chain. On the basis of this model, we are able to demonstrate that the
observed flow velocities of water chains through carbon nanotubes of the order
of cm/s can be accounted for, if the nanotube is metallic. If it is insulating,
however, our calculations imply that the flow velocity of the water could be
much larger for the pressure gradient in experimental studies of water flow
through subnanometer diameter nanotubes.
