Calculating potential of mean force between like-charged nanoparticles: a comprehensive study on salt effects

TL;DR

This study uses Monte Carlo simulations to analyze how salt concentration affects the potential of mean force between like-charged nanoparticles, revealing ion-bridging as a key factor in attraction.

Contribution

It introduces a systematic comparison of pseudo-spring and inverse-Boltzmann methods for calculating potentials of mean force in salt solutions.

Findings

Effective attraction occurs in divalent/trivalent salt solutions.

High salt concentration weakens the nanoparticle attraction.

Ion-bridging configuration is responsible for the attraction.

Abstract

Ions are critical to the structure and stability of polyelectrolytes such as nucleic acids. In this work, we systematically calculated the potentials of mean force between two like-charged nanoparticles in salt solutions by Monte Carlo simulations. The pseudo-spring method is employed to calculate the potential of mean force and compared systematically with the inversed-Boltzmann method. An effective attraction is predicted between two like-charged nanoparticles in divalent/trivalent salt solution and such attraction becomes weakened at very high salt concentration. Our analysis reveals that for the system, the configuration of ion-bridging nanoparticles is responsible for the attraction, and the invasion of anions into the inter-nanoparticles region at high salt concentration would induce attraction weakening rather than the charge inversion effect. The present method would be useful for calculating effective interactions during nucleic acid folding.