On the calculation of potential of mean force between atomistic nanoparticles

TL;DR

This study uses molecular dynamics to calculate the potential of mean force between atomistic silica and gold nanoparticles, revealing how surface coatings and particle size influence their effective interactions.

Contribution

It provides a detailed atomistic analysis of nanoparticle interactions, validating methods against analytical theory and exploring effects of surface grafting.

Findings

Silica nanoparticles show similar interactions across sizes, with surface interaction peaks for larger particles.

Bare gold nanoparticles have weak interactions, increasing with polyethylene coating.

PMF profiles resemble Lennard-Jones potentials, becoming more repulsive with higher grafting density.

Abstract

We study the potential of mean force (PMF) between atomistic silica and gold nanoparticles in the vacuum by using molecular dynamics simulations. Such an investigation is devised in order to fully characterize the effective interactions between atomistic nanoparticles, a crucial step to describe the PMF in high-density coarse-grained polymer nanocomposites. In our study, we first investigate the behavior of silica nanoparticles, considering cases corresponding to different particle sizes and assessing results against an analytic theory developed by Hamaker for a system of Lennard-Jones interacting particles [H. C. Hamaker, Physica A, 1937, 4, 1058]. Once validated the procedure, we calculate effective interactions between gold nanoparticles, which are considered both bare and coated with polyethylene chains, in order to investigate the effects of the grafting density \rho_g on the PMF. Upon performing atomistic molecular dynamics simulations, it turns out that silica nanoparticles experience similar interactions regardless of the particle size, the most remarkable difference being a peak in the PMF due to surface interactions, clearly apparent for the larger size. As for bare gold nanoparticles, they are slightly interacting, the strength of the effective force increasing for the coated cases. The profile of the resulting PMF resembles a Lennard-Jones potentials for intermediate \rho_g , becoming progressively more repulsive for high \rho_g and low interparticle separations.