Large permeabilities of hourglass nanopores: From hydrodynamics to single file transport

TL;DR

This study demonstrates that hourglass-shaped nanopores exhibit significantly higher hydrodynamic permeability than straight nanotubes, with optimal geometry enhancing transport efficiency, as shown by molecular dynamics simulations aligned with continuum predictions.

Contribution

The paper introduces the concept that hourglass nanopore geometry can greatly enhance permeability, validated by molecular dynamics and continuum hydrodynamics, revealing optimal angles for maximum transport.

Findings

Permeability peaks at an opening angle around 5 degrees.

Hourglass nanopores have five times higher permeability than straight nanotubes.

Permeability exceeds that of nanopores in graphene sheets.

Abstract

In fluid transport across nanopores, there is a fundamental dissipation that arises from the connection between the pore and the macroscopic reservoirs. This entrance effect can hinder the whole transport in certain situations, for short pores and/or highly slipping channels. In this paper, we explore the hydrodynamic permeability of hourglass shape nanopores using molecular dynamics (MD) simulations, with the central pore size ranging from several nanometers down to a few Angstr{\"o}ms. Surprisingly, we find a very good agreement between MD results and continuum hydrodynamic predictions, even for the smallest systems undergoing single file transport of water. An optimum of permeability is found for an opening angle around 5 degree, in agreement with continuum predictions, yielding a permeability five times larger than for a straight nanotube. Moreover, we find that the permeability of hourglass shape nanopores is even larger than single nanopores pierced in a molecular thin graphene sheet. This suggests that designing the geometry of nanopores may help considerably increasing the macroscopic permeability of membranes.