  Nano-scale fluid transport has vast applications spanning from water
desalination to biotechnology [1,2]. It is possible to pump fluids in
nano-conduits using pressure gradients [3], thermal methods [4], electric [5,6]
and magnetic fields [7], and with manipulations of surface chemistry and
electric fields [8-10]. Inspired by the capillary-driven phase change heat
transfer devices, we present a phase-change driven nanopump operating almost
isothermally. Meticulous computational experiments on different sized nanopumps
revealed efficient operation of the pump despite the reduction in system size
that extinguishes capillary pumping by annihilating the liquid meniscus
structures. Measuring the density distribution of liquid in cross sections near
to the evaporating and condensing liquid-vapor interfaces, we discovered that
phase change induced molecular scale mass diffusion mechanism replaces the
capillary pumping in the absence of meniscus structures. Therefore, proposed
pumps can serve as a part of both nanoelectromechanical (NEMS) and
microelectromechanical systems (MEMS) with similar working efficiencies, and
can be used for continuous gas separation applications.
