A theoretical understanding of ionic current through a nanochannel driven by a viscosity gradient

TL;DR

This paper develops a Maxwell-Stefan based model to understand how viscosity gradients drive ionic currents in nanochannels, highlighting the influence of solvent ideality, ionic strength, and pH, and aligning well with experimental data.

Contribution

It introduces a theoretical 1D model using Maxwell-Stefan equations to explain ionic current driven by viscosity gradients in nanochannels, considering solvent ideality and solution properties.

Findings

Ionic current depends on solvent ideality and matches experimental data.

Bulk ionic strength and pH significantly affect ion drift.

Diffusion gradients contribute notably to ionic transport.

Abstract

It has been recently shown that a viscosity gradient could drive electrical current through a negatively charged nanochannel (Wiener and Stein, arXiv: 1807.09106). To understand the physics underlying this phenomenon, we employed the Maxwell-Stefan equation to obtain a relation between the flux of solvent species and the driving forces. Our 1D model, which was derived for both ideal and non-ideal solvents, shows that the ionic current depends on the ideality of the solvent, though both scenarios demonstrated good agreement with experimental data. We employed the model to understand the impact of solution bulk ionic strength and pH on the drift of ionic species with same reservoirs solution properties. Our modeling results unveiled the significant impact of bulk solution properties on the drift of ions which is in agreement with the experiments. Moreover, we have shown that the diffusion gradient along the nanochannel contributes significantly into driving ionic species if we even apply a small ionic concentration gradient to both reservoirs. Our modeling results may pave the way for finding novel applications for drift of ions toward a diffusion gradient.