Structural properties of cyclic polyelectrolytes in dilute good solvent

TL;DR

This study explores how cyclic topology influences the structure of polyelectrolytes in dilute good solvents, revealing more compact conformations and non-monotonic shape behaviors compared to linear chains, due to topological effects on electrostatics.

Contribution

It provides new insights into the conformational differences of cyclic versus linear polyelectrolytes, supported by scaling analysis, simulations, and an analytical theory highlighting topological effects.

Findings

Cyclic PEs are more compact at low and intermediate electrostatic strengths.

Shape metrics show non-monotonic behavior in cyclic PEs.

Topological effects influence electrostatic interactions and conformations.

Abstract

Cyclic polymers display unique physical behaviors in comparison to their linear counterparts. Theoretical, computational and experimental studies have revealed that some of their distinctive properties are also observed in charged variants of cyclic polymers, known as cyclic polyelectrolytes (PEs), especially in terms of their structural responses to variations in the strength of electrostatic interactions. In this study, we investigate the impact of cyclic topology on the conformations of PE chains in dilute good solvent using scaling analysis and coarse-grained bead-spring molecular dynamics simulations. Our observations indicate that, in contrast to linear PE chains, cyclic topology results in more compact conformations at low and intermediate Bjerrum lengths. Moreover, two structural metrics, asphericity and prolateness, which quantify deviations from spherical and flat molecular shapes, exhibit non-monotonic behaviors for cyclic PEs. This stands in contrast to linear PEs, where these shape characteristics exhibit a monotonic trend with increasing Bjerrum length. A feasible analytical theory, developed to account for ionic distributions around cyclic PE chains, suggests that the fundamental difference between linear and cyclic chain conformations may be attributed to topological effects influencing long-range electrostatic interactions.