Correlation between flexibility of chain-like polyelectrolyte and thermodynamic properties of its solution

TL;DR

This study uses Monte Carlo simulations to explore how the flexibility of chain-like polyelectrolytes influences their thermodynamic properties, revealing that flexibility slightly enhances counterion binding but does not fully explain experimental discrepancies.

Contribution

It provides a comparative analysis of flexible versus rigid polyelectrolyte models and their thermodynamic behaviors, highlighting the limited impact of chain flexibility on certain properties.

Findings

Flexible chains show slightly stronger counterion binding.

Thermodynamic differences between models are minimal.

Flexibility does not fully account for experimental deviations.

Abstract

Structural and thermodynamic properties of the model solution containing charged oligomers and the equivalent number of counterions were studied by means of the canonical Monte Carlo simulation technique. The oligomers are represented as (flexible) freely jointed chains or as a linear (rigid) array of charged hard spheres. In accordance with the primitive model of electrolyte solutions, the counterions are modeled as charged hard spheres and the solvent as dielectric continuum. Significant differences in the pair distribution functions, obtained for the rigid (rod-like) and flexible model are found but the differences in thermodynamic properties, such as, enthalpy of dilution and excess chemical potential, are less significant. The results are discussed in light of the experimental data an aqueous polyelectrolyte solutions. The simulations suggest that deviations from the fully extended (rod-like) conformation yield slightly stronger binding of counterions. On the other hand, the flexibility of polyions, even when coupled with the ion-size effects, cannot be blamed for qualitative differences between the theoretical results and experimental data for enthalpy of dilution.