Ion specificity and anomalous electrokinetic effects in hydrophobic nanochannels

TL;DR

This paper uses computer simulations and an analytical model to show that hydrophobic nanochannels exhibit ion-specific electrokinetic effects and anomalous flow behaviors due to ion attraction to interfaces, impacting biological modeling.

Contribution

It introduces a modified Poisson--Boltzmann model incorporating ion size-dependent hydrophobic solvation energy to predict ion-specific electrokinetic effects in hydrophobic nanochannels.

Findings

Anomalous electrokinetic effects are common in hydrophobic nanochannels.

Larger ions are more attracted to the vapor-liquid-like interface.

The analytical model accurately predicts flow profiles based on ion size and surface properties.

Abstract

We demonstrate with computer simulations that anomalous electrokinetic effects, such as ion specificity and non-zero zeta potentials for uncharged surfaces, are generic features of electro-osmotic flow in hydrophobic channels. This behavior is due to the stronger attraction of larger ions to the ``vapour--liquid-like'' interface induced by a hydrophobic surface. An analytical model involving a modified Poisson--Boltzmann description for the ion density distributions is proposed, which allows the anomalous flow profiles to be predicted quantitatively. This description incorporates as a crucial component an ion-size-dependent hydrophobic solvation energy. These results provide an effective framework for predicting specific ion effects, with important implications for the modeling of biological problems.