Salt-Induced Counterion-Mobility Anomaly in Polyelectrolyte Electrophoresis

TL;DR

This paper investigates how salt concentration affects the movement of polyelectrolytes and counterions, revealing a salt-dependent mobility anomaly explained by electrostatic screening effects.

Contribution

It introduces a hydrodynamic simulation approach to study counterion mobility anomalies in polyelectrolytes, linking electrostatic screening to mobility sign changes.

Findings

Counterion mobility changes sign with salt concentration.

Simulation results align with experimental DNA data.

Electrostatic screening explains the mobility anomaly.

Abstract

We study the electrokinetics of a single polyelectrolyte chain in salt solution using hydrodynamic simulations. The salt-dependent chain mobility compares well with experimental DNA data. The mobility of condensed counterions exhibits a salt-dependent change of sign, an anomaly that is also reflected in the counterion excess conductivity. Using Green's function techniques this anomaly is explained by electrostatic screening of the hydrodynamic interactions between chain and counterions.