Surface and zeta potentials of charged permeable nanocoatings

TL;DR

This paper develops a theoretical framework to understand the difference between surface and zeta potentials in charged permeable nanocoatings, especially when the coating thickness is comparable to the diffuse layer, accounting for high potentials and permeability.

Contribution

It introduces a new theory for thin porous coatings that explains the relationship between surface and zeta potentials, including high potential effects and permeability considerations.

Findings

Provides analytic approximations for zeta potential in relevant limits.

Explains transitions between different electro-osmotic flow regimes.

Suggests strategies for tuning electro-osmotic flows in microfluidics.

Abstract

An electrokinetic (zeta) potential of charged permeable porous films on solid supports generally exceeds their surface potential, which often builds up to a quite high value itself. Recent work provided a quantitative understanding of zeta potentials of thick, compared to the extension of an inner electrostatic diffuse layer, porous films. Here, we consider porous coatings of a thickness comparable or smaller than that of the inner diffuse layer. Our theory, which is valid even when electrostatic potentials become quite high and accounts for a finite hydrodynamic permeability of the porous materials, provides a framework for interpreting the difference between values of surface and zeta potentials in various situations. Analytic approximations for the zeta potential in the experimentally relevant limits provide a simple explanation of transitions between different regimes of electro-osmotic flows, and also suggest strategies for its tuning in microfluidic applications.