Nanofluidic charge transport under strong electrostatic coupling conditions

TL;DR

This paper explores how strong electrostatic interactions and multivalent ions influence charge transport in nanofluidic systems, revealing mechanisms for current reversal and ion separation that could enhance device performance.

Contribution

It introduces a self-consistent model incorporating multivalent charges into electrostatic equations, uncovering new charge transport phenomena in nanofluidic channels under strong-coupling conditions.

Findings

Negative streaming currents caused by multivalent cation attraction.

Reversal of average potential within the no-slip zone.

Charge separation driven by attractive polarization forces in nanoslits.

Abstract

The comprehensive depiction of the many-body effects governing nanoconfined electrolytes is an essential step for the conception of nanofluidic devices with optimized performance. By incorporating self-consistently multivalent charges into the Poisson-Boltzmann equation dressed by a background monovalent salt, we investigate the impact of strong-coupling electrostatics on the nanofluidic transport of electrolyte mixtures. We find that the experimentally observed negative streaming currents in anionic nanochannels originate from the collective effect of the Cl attraction by the interfacially adsorbed multivalent cations, and the no-slip layer reducing the hydrodynamic contribution of these cations to the net current. The like-charge current condition emerging from this collective mechanism is shown to be the reversal of the average potential within the no-slip zone. Applying the formalism to surface-coated membrane nanoslits located in the giant dielectric permittivity regime, we reveal a new type of streaming current activated by attractive polarization forces. Under the effect of these forces, the addition of multivalent ions into the KCl solution sets a charge separation and generates a counterion current between the neutral slit walls. The adjustability of the current characteristics solely via the valency and amount of the added multivalent ions identifies the underlying process as a promising mechanism for nanofluidic ion separation purposes.