Transport of ions in hydrophobic nanotubes

TL;DR

This paper develops a theoretical framework for ion transport in hydrophobic nanotubes, explaining enhanced electrokinetic mobility and conductivity through electrostatic and hydrodynamic effects, and offers new insights into zeta potentials.

Contribution

It introduces generalized Onsager relations and exact expressions for electro-osmotic mobility and conductivity in cylindrical channels, emphasizing hydrophobic slip and surface charge mobility.

Findings

Giant enhancement of electrokinetic mobility in hydrophobic nanotubes

Exact formulas for electro-osmotic mobility and conductivity

New interpretation of zeta potentials in cylindrical channels

Abstract

The theory of electrokinetic ion transport in cylindrical channels of a fixed surface charge density is revisited. Attention is focused on impact of the hydrophobic slippage and mobility of adsorbed surface charges. We formulate generalised Onsager relations for a cylinder of an arbitrary radius and then derive exact expressions for the mean electro-osmotic mobility and conductivity. To employ these expressions we perform additional electrostatic calculations, with the special focus on the non-linear electrostatic effects. Our theory provides a simple explanation of a giant enhancement of the electrokinetic mobility and conductivity of hydrophobic nanotubes by highlighting the role of appropriate electrostatic and hydrodynamic length scales and their ratios. We also propose a novel interpretation of zeta potentials of cylindrical channels.