Electrokinetic Effects on Flow and Ion Transport in Charge-Patterned Corrugated Nanochannels

TL;DR

This study demonstrates how charge patterning and geometric undulations in nanochannels can be used to control ion transport directionality and selectivity under pressure, revealing two distinct flow regimes and their effects.

Contribution

It introduces a novel mechanism for rectified ion transport in charge-patterned nanochannels, combining simulations and particle tracking to analyze flow regimes and ion selectivity.

Findings

Reversing pressure gradient switches ionic species transport.

Two flow regimes identified with different velocity behaviors.

Peak charge selectivity occurs near double layer overlap and transition point.

Abstract

The phase offset between surface charge modulation and geometric undulations in a corrugated nanochannel provides a tunable mechanism for rectified, diode-like ion transport under purely pressure-driven conditions: reversing the applied pressure gradient selectively activates transport of opposite ionic species, generating a net ionic current whose sign and magnitude are set by the charge-geometry alignment. Fully coupled Poisson-Nernst-Planck-Stokes simulations reveal the underlying two-regime structure: at low driving force (Regime I), throughput is suppressed below the Poiseuille limit by a localized streaming potential that pins counterions within the electric double layer; above a threshold pressure (Regime II), the mechanical force overcomes electrostatic resistance, producing an abrupt, orders-of-magnitude rise in mean velocity. Electroosmotically driven flow undergoes a qualitatively similar but smoother transition. Peak charge selectivity is achieved at near-complete electric double layer overlap and driving forces just below the Regime I-Regime II transition. Random walk particle tracking confirms selective rectification and quantifies the dependence of ion dispersion on surface charge placement across both regimes.