Unexpected Two-Stage Swelling of Weak Polyelectrolyte Brushes with Divalent Counterions

22 July 2024, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

We use particle-based, coarse-grained simulations to study the influence of divalent counterions on a weak polyelectrolyte brush. Our simulations show a profound influence of even small concentrations of divalent salt on the titration behavior of the brush, which is shown to be a combined effect of electrostatic interactions and the Donnan effect. Furthermore, we examine the partitioning of mono- and divalent counterions into the brush. We demonstrate the preferred uptake of divalent ions by the brush, which is further enhanced by electrostatic correlation effects. Finally, our simulations reveal a hitherto unobserved two-stage swelling of the brush as a function of the pH in the presence of divalent salt. This phenomenon arises as a consequence of charge regulation and ion partitioning.

Keywords

pH
charge regulation
multivalent
weak polyelectrolyte
brush
Monte Carlo
Molecular Dynamics
Simulation

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