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

摘要

The influence of the chain degree of ionization on the adsorption of weakpolyelectrolytes on neutral and on oppositely and likely charged surfaces isinvestigated for the first time, by means of Monte Carlo simulations with themesoscopic interaction model known as dissipative particle dynamics. Theelectrostatic interactions are calculated using the three-dimensional Ewald summethod, with an appropriate modification for confined systems. Effective wallforces confine the linear polyelectrolytes, and electric charges on thesurfaces are included. The solvent is included explicitly also and it ismodeled as an athermal solvent for the polyelectrolytes. The number of solventparticles is allowed to fluctuate. The results show that the polyelectrolytesadsorb both onto neutral and charged surfaces, with the adsorption regulated bythe chain degree of ionization, being larger at lower ionization degrees, wherepolyelectrolytes are less charged. Furthermore, polyelectrolyte adsorption isstrongly modulated by the counterions screening of surface charge. Thesefindings are supported with predictions of adsorption isotherms with varyingionization degree. We obtain also the surface force mediated by adsorbedpolyelectrolytes, which is calculated for the first time as a function ofionization degree. The adsorption and surface force isotherms obtained for weakpolyelectrolytes are found to reproduce main trends in experiments, wheneverthose results are available, and provide additional insight into the roleplayed by the competitive adsorption of the counterions and polyelectrolytes onthe surfaces.