Dissipative particle dynamics simulations of weak polyelectrolyte adsorption on charged and neutral surfaces as a function of the degree of ionization

TL;DR

This study uses dissipative particle dynamics simulations to explore how the degree of ionization affects weak polyelectrolyte adsorption on various surfaces, revealing that lower ionization enhances adsorption and that counterion screening significantly influences surface interactions.

Contribution

First simulation study to analyze the effect of ionization degree on weak polyelectrolyte adsorption and surface forces using dissipative particle dynamics with explicit solvent and electrostatics.

Findings

Adsorption increases at lower ionization degrees.

Counterion screening significantly modulates adsorption.

Surface force profiles depend on ionization degree.

Abstract

The influence of the chain degree of ionization on the adsorption of weak polyelectrolytes on neutral and on oppositely and likely charged surfaces is investigated for the first time, by means of Monte Carlo simulations with the mesoscopic interaction model known as dissipative particle dynamics. The electrostatic interactions are calculated using the three-dimensional Ewald sum method, with an appropriate modification for confined systems. Effective wall forces confine the linear polyelectrolytes, and electric charges on the surfaces are included. The solvent is included explicitly also and it is modeled as an athermal solvent for the polyelectrolytes. The number of solvent particles is allowed to fluctuate. The results show that the polyelectrolytes adsorb both onto neutral and charged surfaces, with the adsorption regulated by the chain degree of ionization, being larger at lower ionization degrees, where polyelectrolytes are less charged. Furthermore, polyelectrolyte adsorption is strongly modulated by the counterions screening of surface charge. These findings are supported with predictions of adsorption isotherms with varying ionization degree. We obtain also the surface force mediated by adsorbed polyelectrolytes, which is calculated for the first time as a function of ionization degree. The adsorption and surface force isotherms obtained for weak polyelectrolytes are found to reproduce main trends in experiments, whenever those results are available, and provide additional insight into the role played by the competitive adsorption of the counterions and polyelectrolytes on the surfaces.