Transport-induced inversion of screening ionic charges in nanochannels

TL;DR

This paper uncovers a counter-intuitive ionic screening phenomenon in nanochannels where ionic charges invert under certain conditions, affecting fluid dynamics and electrical properties, with implications for nano-fluidic device design.

Contribution

It introduces a novel charge inversion mechanism caused by ionic transport and electrostatics coupling, expanding understanding of ionic screening in nanochannels.

Findings

Ionic charge inversion occurs under significant ionic transport.

Charge inversion influences fluid flow and current-voltage behavior.

The process is explained by coupling electro-diffusion and electrostatics.

Abstract

This work reveals a counter-intuitive but basic process of ionic screening in nano-fluidic channels. Steady-state numerical simulations and mathematical analysis show that, under significant longitudinal ionic transport, the screening ionic charges can be locally inverted in the channels: their charge sign becomes the same as that of the channel surface charges. The process is identified to originate from the coupling of ionic electro-diffusion transport and junction 2-D electrostatics. This finding may expand our understanding on ionic screening and electrical double layers in nano-channels. Furthermore, the charge inversion process results in a body-force torque on channel fluids, which is a possible mechanism for vortex generation in the channels and their nonlinear current-voltage characteristics.