We investigate electro-osmosis in aqueous solutions of polyelectrolytes using mean-field equations [1]. 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. Furthermore, we mention the result is related to the electrophoresis of charged colloids.

[1] Yuki Uematsu and Takeaki Araki, J. Chem. Phys. 139, 094901 (2013).