Electro-Osmotic Flow of Semidilute Polyelectrolyte Solutions

TL;DR

This paper studies electro-osmosis in polyelectrolyte solutions, revealing how polymer-surface interactions and electrostatic potential profiles influence flow direction and magnitude, with implications for controlling flow in microfluidic systems.

Contribution

It introduces a mean-field model to explain electro-osmotic flow behavior in polyelectrolyte solutions, highlighting flow suppression, enhancement, and inversion mechanisms.

Findings

Strong polymer-surface attraction suppresses electro-osmosis.

Polymer depletion enhances electro-osmotic flow.

Flow inversion occurs when electrostatic potential decays with opposite sign.

Abstract

We investigate electro-osmosis in aqueous solutions of polyelectrolytes using mean-field equations. A solution of positively charged polyelectrolytes is confined between two negatively charged planar surfaces, and an electric field is applied parallel to the surfaces. When electrostatic attraction between the polymer and the surface is strong, the polymers adhere to the surface, forming a highly viscous adsorption layer that greatly suppresses the electro-osmosis. Conversely, electro-osmosis is enhanced by depleting the polymers from the surfaces. We also found that the electro-osmotic flow is invertible when the electrostatic potential decays to its bulk value with the opposite sign. These behaviors are well explained by a simple mathematical form of the electro-osmotic coefficient.