Nanofluidic Diode for Simple Fluids without Moving Parts.

The fabrication of small scale, fixed structure fluidic diodes for simple fluids is quite challenging and has not yet been achieved. Here, we fabricate a moving part-free nanofluidic diode for simple fluids using heterogeneous nanochannels, half of which is hydrophilic and the other half is hydrophobic. It accepts water flows in the forward (from hydrophilic to hydrophobic) direction, while the flows in the backward direction are blocked for pressure drop range 0<ΔP<0.63 MPa. The diode is ensured by a potential energy barrier at the channel entrance on the hydrophobic side due to the molecular interactions between the water and channel surface. As the upstream pressure becomes higher than 0.63 MPa, the fluidic diode turns to be a rectifier, which allows flows in both the forward and backward directions but with different flow rates. At sufficiently high driving pressures, the fluidic system fails in flow rectification, analogous to the breakdown of electronic diodes. The three different flow modes (diode, rectifier, and breakdown) of the fluidic chip and the underlying rectification mechanisms are confirmed by molecular dynamics simulations.