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.