Influence of Explicit Ions on Titration Curves and Conformations of Flexible Polyelectrolytes: A Monte Carlo Study

Abstract

Acid/base and conformational properties of a weak polyelectrolyte chain surrounded by explicit ions (counterions and salt particles) are investigated using Monte Carlo simulations. The influence of the pH, monomer size, presence of explicit ions, salt particles, salt size, and valency on the polyelectrolyte titration process is systematically investigated. It is shown that the presence of explicit ions, the increase in pH and monomer sizes, and the decrease in salt radius are parameters that favor the monomer deprotonation processes hence affecting the global acid/base polyelectrolyte chain properties. The competition between attractive and repulsive, long-range and local electrostatic interactions leads to a heterogeneous distribution of charges and ions along the polyelectrolyte backbones. This subtle electrostatic competition leads to equilibrated chain conformations ranging from extended to globular conformations. A simple screening effect is achieved with monovalent salt resulting in a slight limitation of the formation of extended structures at high pH values. Focusing on trivalent salt, the local complexation of several chain monomers around each trivalent cation leads to the formation of collapsed structures. The decrease in the size of trivalent cations promotes the deprotonation process, in particular, when trivalent salt cations are smaller than the monomer size.

Influence of charged intramolecular hydrogen bonds in weak polyelectrolytes: A Monte Carlo study of flexible and extendible polymeric chains in solution and near charged spheres

“…At a chosen α , it would clearly cost more energy to increase ionization of a longer chain due to the higher number of vicinal charges. As for the qualitative behavior of curves, it agrees nicely with what published in the literature so far, albeit the ionization degree tends to be slightly higher at a chosen pH‐p K a due to the extendible bonds.…”

“…In this respect, we opted for using an extension of the titrable linear spring‐charged bead model proposed by Åkesson et al, introducing a short range many‐body interaction between conjugated acid–base pair that limits the number of cH‐Bond per charged group ( vide infra see Polyelectrolyte Models section). To quantitatively gauge the effect of such interaction on polyelectrolyte properties, titration experiments can be simulated as suggested in the literature varying the parameters that define the model. Particularly, we investigated the impact of the many‐body interaction strength and the maximum number of cH‐Bonds allowed.…”

Grand-Reaction Method for Simulations of Ionization Equilibria and Ion Partitioning in a Broad Range of pH and Ionic Strength

“…The variation of polymer ionization was achieved by varying its acidity constant, while the solution pH was a result of the simulation. The constant-pH method has been introduced to enable simulations of acid-base ionization reactions at a given pH 43 It has also been used to simulate various polyelectrolyte systems [44][45][46][47][48][49][50][51][52][53] . However, the simulated systems were not explicitly coupled to a reservoir.…”

Coupling of Charge Regulation and Conformational Equilibria in Linear Weak Polyelectrolytes: Treatment of Long Range Interactions via Effective Short-Ranged and pH-Dependent Interaction Parameters

“…[5,15,[21][22][23][24][25]. For systems with a small number of sites (N ≤ 20), the necessary thermal averages can be performed by direct enumeration, while for a large number of sites Monte Carlo (MC) simulations become necessary [26][27][28][29][30][31][32][33][34][35][36][37].…”