Water transport within carbon nanotubes on a wave.

Water molecules possess discontinuous properties in confined surroundings as compared to the bulk, their transport velocity shows a step change with the increase in the radius of hydrophobic carbon nanotubes (CNTs). Here, we report that the chain of water molecules in CNTs behaves as a "spring" owing to hydrogen bonding. Thus, the transport of water molecules in confined systems proceeds as a wave motion with eigen frequencies in the terahertz region which is determined by the CNT size. Water velocities derived from molecular dynamics (MD) fit well with the ones from finite element methods (FEM) on consideration of both the no-slip and slip boundary conditions for CNT diameters less than 1 nm and more than 1 nm, respectively. The present work helps clarify the features of mass and momentum transfers in confined surroundings, and provides perspectives for mass transfer applications.