Non-monotonic behavior of weak-polyelectrolytes adsorption on a cationic surface: A Monte Carlo simulation study

In this work, the weak polyelectrolyte (PE) adsorption on a strong cationic surface is studied with constant pH Monte Carlo simulations using a coarse-grained model. When a large number of PE chains is added to the system, the PE adsorbed amount vs pH curve exhibits a non-monotonic behavior, with the appearance of a maximum close to the intrinsic pK-value of the PE titratable groups. The apparent pK(a)(0)-value of the PE chains shows a nontrivial tendency depending on the pH-value and the surface coverage degree. In increasing the pH-value, the small anions that accompany the cationic surface are replaced by PE chains and small cations. For pH > pK(a)(0 )+ 1, an evident charge reversion of surface is observed. These results are explained analyzing the interplay between the attractive and repulsion electrostatic interactions between the different components of the system (inter- and intra-charged monomers of PE chains, the strong cationic surface and small ions) and their effects on the PE chain ionization.

Automated summary

In this study, weak polyelectrolyte adsorption on a strong cationic surface was investigated using constant pH Monte Carlo simulations. The results showed a non-monotonic behavior of PE adsorbed amount with pH, and the apparent pKa(0) value of PE chains varied with pH and surface coverage. Additionally, the replacement of small anions with PE chains and small cations at higher pH values led to a significant charge reversion on the surface when pH was greater than pKa(0) + 1.