Viscoelectric Effects in Nanochannel Electrokinetics

TL;DR

This paper demonstrates that incorporating viscoelectric effects into continuum models accurately explains nanochannel electrokinetic behaviors observed in MD simulations, such as decreased electroosmotic mobility and conductance at high surface charge and salt concentrations.

Contribution

The study introduces a viscoelectric-modified continuum model that quantitatively matches MD simulation results and explains previously observed nanochannel electrokinetic phenomena.

Findings

Viscoelectric effects dominate electroosmotic and ion transport behaviors.

Modified model aligns with MD simulation data.

Viscoelectric effects explain decrease in mobility and conductance.

Abstract

Electrokinetic transport behavior in nanochannels is different to that in larger sized channels. Specifically, molecular dynamics (MD) simulations in nanochannels have demonstrated two little understood phenomena which are not observed in microchannels, being: (i) the decrease of average electroosmotic mobility at high surface charge density, and (ii) the decrease of channel conductance at high salt concentrations, as the surface charge is increased. However, current electric double layer models do not capture these results. In this study we provide evidence that this inconsistency primarily arises from the neglect of the viscoelectric effect (being the increase of local viscosity near charged surfaces due to water molecule orientation) in conventional continuum models. It is shown that predictions of electroosmotic mobility in a slit nanochannel, derived from a viscoelectric-modified continuum model, are in quantitative agreement with previous MD simulation results. Furthermore, viscoelectric effects are found to dominate over ion steric and dielectric saturation effects in both electroosmotic and ion transport processes. Finally, we indicate that mechanisms of the previous MD-observed phenomena can be well-explained by the viscoelectric theory.