The influence of charged-induced variations in the local permittivity on the static and dynamic properties of polyelectrolyte solutions

Abstract

There is a large body of literature investigating the static and dynamic properties of polyelectrolytes due both to their widespread application in industrial processes and their ubiquitous presence in biology. Because of their highly charged nature, polyelectrolytes tend to alter the local dielectric permittivity of the solution within a few nanometers of their backbone. This effect has, however, been almost entirely ignored in both simulations and theoretical work. In this article, we apply our recently developed electrostatic solver based on Maxwell's equations to examine the effects of the permittivity reduction in the vicinity of the polyelectrolyte. We first verify our new approach by calculating and comparing ion distributions around a linear fixed polyelectrolyte and find both quantitative and qualitative changes in the ion distribution. Further simulations with an applied electric field show that the reduction in the local dielectric constant increases the mobility of the chains by approximately ten percent. More importantly, variations in the local dielectric constant lead to qualitatively different behavior of the conductivity.

Theoretical and Computational Insight into Solvent and Specific Ion Effects for Polyelectrolytes: The Importance of Local Molecular Interactions

“…Corresponding simulation findings for water molecules around charged and uncharged objects as well as around polyelectrolytes were observed in Refs. [26,[63][64][65][66]. All studies reveal significant ordering effects when compared to bulk phase due to the polarity of water molecules.…”

“…Interestingly, although the corresponding expressions (Equation 18) can be used for further evaluation in mean field PB approaches, their occurrence can be solely attributed to specific molecular representations which are usually ignored. Recent experimental and simulation outcomes suggested that comparable effects also rationalize the dynamic properties of polyelectrolytes in presence of high salt concentrations [26,65,69]. Specifically the dielectric decrement effect and its influence on the polyelectrolyte in terms of dynamic properties like ionic conductivities attracted recent experimental and theoretical attention [26,65].…”

“…Recent experimental and simulation outcomes suggested that comparable effects also rationalize the dynamic properties of polyelectrolytes in presence of high salt concentrations [26,65,69]. Specifically the dielectric decrement effect and its influence on the polyelectrolyte in terms of dynamic properties like ionic conductivities attracted recent experimental and theoretical attention [26,65]. In these publications, the authors used coarse-grained Lattice-Boltzmann/MD simulations in combination with advanced electrostatic solvers to study the influence of polyelectrolytes and ions on the dielectric constant of the solution.…”

“…For instance, previous atomistic MD simulations revealed that the molecular solvation behavior influences significantly the amount of dissociated counterions, and thus the corresponding conformational behavior with regard to repulsive electrostatic interactions or charge screening effects along the polyelectrolyte backbone [18,24,25]. The molecular arrangement of the solvent molecules is influenced by the presence of the polyelectrolyte as manifested by local variations of the dielectric constant, charge hydration asymmetry effects or modified charge transport mechanisms [26][27][28]. Comparable molecular interactions also dominate the occurrence of various polyelectrolyte structures in bulk phase, as can be seen by the formation of polyelectrolyte micelles, pearl-necklace structures, the onset of microphase separation processes between polar and apolar regions as well as the formation of polyelectrolyte complexes [29][30][31][32][33][34] and coacervates [35].…”

Properties of Ion Complexes and Their Impact on Charge Transport in Organic Solvent-Based Electrolyte Solutions for Lithium Batteries: Insights from a Theoretical Perspective

“…Despite this simple view, it has to be mentioned that the value of the dielectric constant also depends on the chosen position, as it can locally change in close vicinity to ions, uncharged solutes, interfaces, and due to inhomogeneities in the solution [64,[110][111][112][113]. Moreover, it is also affected by solvent-solvent, solvent-ion, and ion-ion interactions, which contribute significantly to the net value of the dielectric constant.…”