Hydrodynamic flow in the vicinity of a nanopore induced by an applied voltage

TL;DR

This study uses continuum simulations to analyze ion transport and fluid flow near a nanopore under voltage, revealing concentration polarization, vortex formation, and nonlinear current-voltage behavior with potential applications in separation technologies.

Contribution

It provides a detailed continuum model of electrohydrodynamics in nanopores, highlighting the role of surface charge and nonlinear flow effects, extending previous molecular dynamic findings.

Findings

Concentration polarization layers form on membrane surfaces.

Electric pressure induces vortical fluid motion.

Flow strength depends nonlinearly on applied voltage.

Abstract

Continuum simulation is employed to study ion transport and fluid flow through a nanopore in a solid-state membrane under an applied potential drop. Results show the existence of concentration polarization layers on the surfaces of the membrane. The nonuniformity of the ionic distribution gives rise to an electric pressure that drives vortical motion in the fluid. There is also a net hydrodynamic flow through the nanopore due to an asymmetry induced by the membrane surface charge. The qualitative behavior is similar to that observed in a previous study using molecular dynamic simulations. The current--voltage characteristics show some nonlinear features but are not greatly affected by the hydrodynamic flow in the parameter regime studied. In the limit of thin Debye layers, the electric resistance of the system can be characterized using an equivalent circuit with lumped parameters. Generation of vorticity can be understood qualitatively from elementary considerations of the Maxwell stresses. However, the flow strength is a strongly nonlinear function of the applied field. Combination of electrophoretic and hydrodynamic effects can lead to ion selectivity in terms of valences and this could have some practical applications in separations.