Modified Poisson-Boltzmann theory for polyelectrolytes in monovalent salt solutions with finite-size ions

TL;DR

This paper introduces an enhanced Poisson-Boltzmann theory that accurately models ion distributions around polyelectrolytes in salt solutions, accounting for ion size and species effects, validated against detailed simulations.

Contribution

The authors develop a modified Poisson-Boltzmann model calibrated with coarse-grained and atomistic simulations, improving predictions of ion distributions around polyelectrolytes in various salt conditions.

Findings

Accurately predicts ion distributions around PEs in monovalent salt solutions.

Effective for a wide range of ion sizes and concentrations up to 1 M.

Validated against molecular dynamics simulations.

Abstract

We present a soft-potential-enhanced Poisson-Boltzmann (SPB) theory to efficiently capture ion distributions and electrostatic potential around rodlike charged macromolecules. The SPB model is calibrated with a coarse-grained particle-based model for polyelectrolytes (PEs) in monovalent salt solutions as well as compared to a full atomistic molecular dynamics simulations with explicit solvent. We demonstrate that our modification enables the SPB theory to accurately predict monovalent ion distributions around a rodlike PE in a wide range of ion and charge distribution conditions in the weak-coupling regime. These include excess salt concentrations up to 1 M, and ion sizes ranging from small ions, such as Na or Cl, to softer and larger ions with size comparable to the PE diameter. The work provides a simple way to implement an enhancement that effectively captures the influence of ion size and species into the PB theory in the context of PEs in aqueous salt solutions.