Nonlinear electro-osmosis in dilute non-adsorbing polymer solutions with low ionic strength

TL;DR

This paper investigates nonlinear electro-osmosis in dilute polymer solutions with low ionic strength using simulations and kinetic theory, revealing mobility saturation due to polymer migration and depletion layer formation.

Contribution

It combines Brownian dynamics simulations with kinetic theory to quantitatively explain nonlinear electro-osmotic mobility in dilute polymer solutions.

Findings

Electro-osmotic mobility increases nonlinearly with electric field.

Polymer migration causes a depletion layer thicker than equilibrium.

Kinetic theory accurately reproduces simulation results.

Abstract

Nonlinear behavior of electro-osmosis in dilute non-adsorbing polymer solutions with low salinity is investigated with Brownian dynamics simulations and a kinetic theory. In the Brownian simulations, the hydrodynamic interaction between the polymers and a no-slip wall is considered with Rotne-Prager approximation of Blake tensor. In a plug flow under a sufficiently strong applied electric field, the polymer migrates toward the bulk, forming a depletion layer thicker than the equilibrium one. Consequently, the electro-osmotic mobility increases nonlinearly with the electric field and gets saturated. This nonlinear mobility qualitatively does not depend on the details of rheological properties of the polymer solution. Analytical calculation of the kinetic theory for the same system reproduces quantitatively well the results of the Brownian dynamics simulation.