Molecular dynamics simulation of transport characteristics of water molecules through high aspect ratio hourglass-shaped pore

• The non-equilibrium MD simulations were implemented to mimic osmosis-driven flow inside the hourglass-shaped pores.
• We analyze single file water transport through high aspect ratio hourglass-shaped nanopores.
• We observe that the aspect ratio may significantly influence on energy barrier inside the hourglass-shaped nanopores.
• We show that that diffusion can be shifted from Fickian to single-file mechanism by increasing the length.
• We describe that more of the total length covered by frictionless surface while increasing the length.

This research utilizes molecular dynamics (MD) simulations in order to study the effect of the length on water transport properties through the pore with an hourglass shape structure. While the narrowest section of the pore is kept constant, the length of the pore is increased in the range of 100–200 Å. The narrowest section allows water molecules to cross just in single-file configuration. It observed that flow decreases as the length increases unlike the water flux which increases with length, which attributes to the frictionless surface of the pore. In comparable with flux, the efficiency increases as the length increases. The increase of the diffusion coefficient and permeability together suggest that the entrance effect can be negligible as the length increases. It revealed that the friction force decreases with increasing the length. On the other hand, the displacement of water molecules from wall increases with length. These results together suggest that as the length increases the wall surface becomes frictionless.

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