  Water inside a nanocapillary becomes ordered, resulting in unconventional
behavior. A profound enhancement of water flow inside nanometer thin
capillaries made of graphene has been observed [B. Radha et.al., Nature
(London) 538, 222 (2016)]. Here we explain this enhancement as due to the large
density and the extraordinary viscosity of water inside the graphene
nanocapillaries. Using the Hagen-Poiseuille theory with slippage-boundary
condition and incorporating disjoining pressure term in combination with
results from molecular dynamics (MD) simulations, we present an analytical
theory that elucidates the origin of the enhancement of water flow inside
hydrophobic nanocapillaries.
  Our work reveals a distinctive dependence of water flow in a nanocapillary on
the structural properties of nanoconfined water in agreement with experiment,
which opens a new avenue in nanofluidics.
