Atomistic Hydrodynamics and the Dynamical Hydrophobic Effect in Porous Graphene

TL;DR

This paper develops a multiscale simulation method to study water flow through nanoporous graphene, revealing that permeability is governed by a crossover between two molecular transport mechanisms rather than hydrophobicity.

Contribution

It introduces a constraint dynamics-based nonequilibrium molecular dynamics method for simulating steady-state flow in nanoscale pores, bridging atomistic and hydrodynamic scales.

Findings

Permeability trend is governed by transport mechanism crossover.

Method validated on a model system.

Hydrophobicity does not solely determine permeability.

Abstract

Mirroring their role in electrical and optical physics, two-dimensional crystals are emerging as novel platforms for fluid separations and water desalination, which are hydrodynamic processes that occur in nanoscale environments. For numerical simulation to play a predictive and descriptive role, one must have theoretically sound methods that span orders of magnitude in physical scales, from the atomistic motions of particles inside the channels to the large-scale hydrodynamic gradients that drive transport. Here, we use constraint dynamics to derive a nonequilibrium molecular dynamics method for simulating steady-state mass flow of a fluid moving through the nanoscopic spaces of a porous solid. After validating our method on a model system, we use it to study the hydrophobic effect of water moving through pores of electrically doped single-layer graphene. The trend in permeability that we calculate does not follow the hydrophobicity of the membrane, but is instead governed by a crossover between two competing molecular transport mechanisms.