Theory and simulations of water flow through carbon nanotubes: prospects and pitfalls.

We study water flow through carbon nanotubes using continuum theory and molecular dynamics simulations. The large slip length in carbon nanotubes greatly enhances the pumping and electrokinetic energy conversion efficiency. In the absence of mobile charges, however, the electro-osmotic flow vanishes. Uncharged nanotubes filled with pure water can therefore not be used as electric field-driven pumps, contrary to some recently ventured ideas. This is in agreement with results from a generalized hydrodynamic theory that includes the angular momentum of rotating dipolar molecules. The electro-osmotic flow observed in simulations of such carbon nanotubes is caused by an imprudent implementation of the Lennard-Jones cutoff. We also discuss the influence of other simulation parameters on the spurious electro-osmotic flow.