Suppression of nano-channel ion conductance by electro-osmotic flow in nano-channels with weakly overlapping electrical double layers

TL;DR

This theoretical study explores how electro-osmotic flow suppresses ion conductance in nano-channels with weakly overlapping electrical double layers, revealing a limiting-conductance behavior due to ion depletion.

Contribution

It introduces a combined numerical and mathematical model to analyze EOF effects on ion conductance, highlighting a novel limiting-conductance phenomenon distinct from classical limiting-current behavior.

Findings

EOF causes ion depletion inside nano-channels.

Conductance suppression is significant at moderate biases.

High biases can restore conductance via recirculating vortices.

Abstract

This theoretical study investigates the nonlinear ionic current-voltage characteristics of nano-channels that have weakly overlapping electrical double layers. Numerical simulations as well as a 1-D mathematical model are developed to reveal that the electro-osmotic flow (EOF) interplays with the concentration-polarization process and depletes the ion concentration inside the channels, thus significantly suppressing the channel conductance. The conductance may be restored at high electrical biases in the presence of recirculating vortices within the channels. As a result of the EOF-driven ion depletion, a limiting-conductance behavior is identified, which is intrinsically different from the classical limiting-current behavior.