The Effect of Explicit Polar Species on Conformational Behavior of a Single Polyelectrolyte Chain

TL;DR

This study uses dissipative particle dynamics simulations to explore how explicit polar species and dielectric mismatch influence the collapse behavior of polyelectrolyte chains, revealing that polar beads facilitate collapse and that dielectric response is a collective, non-universal effect.

Contribution

It demonstrates that explicit treatment of polar media alters collapse behavior and highlights the non-universality of dielectric effects due to small-scale polar interactions.

Findings

Explicit polar beads promote earlier chain collapse.

Dielectric mismatch affects chain conformation, with polar chains collapsing more easily.

Dielectric response is a collective effect, not solely determined by bulk properties.

Abstract

In this work we investigated the question of how the molecular nature of the dielectric media and the polymer-solvent dielectric mismatch affect the collapse of a polyelectrolyte chain in solution by means of dissipative particle dynamics simulations. First, we studied whether the explicit treatment of dielectric media as polar beads instead of homogeneous dielectric background results in a different system behavior. We showed that the explicit treatment of polar beads facilitates the chain collapse, i.e. it occurs at smaller values of the electrostatic strength parameter values ${\lambda}^2 \sim Q^2/({\epsilon}kT)$. We believe that the main reason for such behavior is that the dielectric response is in fact a collective effect, and the "effective" dielectric permittivity is different from the bulk value when the charges are close to each other and/or the density of the charges is high enough. This implies that the value of ${\lambda}$ does not have a universal meaning due to the small-scale effects related to the presence of polar species; therefore, changing the total unit charge $Q$ or the temperature $kT$ is not equivalent to changing ${\epsilon}$. Next, we investigated how the difference of the dielectric permittivities of the polymer chain and solvent affects the collapse. We showed the polar chain adapts less swollen conformations in the polyelectrolyte regime and collapses easier compared to the case of non-polar chain; the possible reasons for such behavior are discussed.