Pair and many-body interactions between ligated Au nanoparticles

Area of Science:

• Materials Science
• Computational Chemistry
• Nanotechnology

Background:

• Gold nanoparticles (AuNPs) functionalized with ligands are crucial in various applications.
• Understanding ligand behavior and inter-particle forces is key to controlling nanoparticle assembly and function.
• Previous studies have explored nanoparticle interactions, but the role of ligand coverage in complex aggregation states requires further investigation.

Purpose of the Study:

• To investigate the influence of ligand coverage and particle separation on the properties of dodecane thiol-capped gold nanoparticles (AuNPs).
• To analyze the structural changes in ligand shells and inter-particle forces across different aggregation states (isolated, pair, and square lattice).
• To develop an analytical model for the potential of mean force and explore higher-order contributions to inter-particle interactions.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model dodecane thiol-ligated 5-nm AuNPs in a vacuum.
• Simulations were conducted for isolated AuNPs, pairs of AuNPs, and a square lattice of four AuNPs.
• Analysis focused on ligand density distribution, ligand envelope structure, and the potential of mean force (PMF) as a function of ligand coverage and particle separation.

Main Results:

• Ligand density profiles exhibit characteristic oscillations near the AuNP core, decaying at larger distances.
• Interactions between AuNPs significantly alter ligand distributions, with these changes being coverage-dependent.
• The potential of mean force (PMF) between AuNPs systematically depends on ligand coverage, affecting its shape, depth, and position.
• An effective pair potential of mean force for a square lattice, incorporating three- and four-NP contributions, shows an attractive well, contrasting with previous findings of purely repulsive contributions.

Conclusions:

• Ligand coverage is a critical parameter that dictates both the structure of the ligand shell and the inter-particle forces between AuNPs.
• The observed attractive well in the effective pair potential for a square lattice suggests that higher-order (three- and four-particle) interactions are significant and can be attractive, contrary to previous assumptions.
• These findings are crucial for predicting and controlling the self-assembly and bulk behavior of nanoparticle systems.