Molecular simulation of gold nanoparticle dispersion and aggregation in supercritical CO2

Abstract

We report molecular dynamics simulations for multiple passivated gold nanoparticles (NPs) in supercritical CO2 (scCO2). This simulation provides a direct visual observation on dispersion behavior and aggregate morphology for the NPs suspended/blended in the scCO2 fluid. Extensive interfacial structure properties, thermodynamic free energies, and dynamics’ properties were used to characterize the effective particle interactions. The effects of surface ligand length, solvent density, and surface coverage were examined. Our simulation results indicate that the NP dispersion is controlled by both the steric repellence between the capping ligands and the solvation interaction between surface ligands and solvent. Increasing surface coverage or ligand length leads to better dispersion owing to enhancing excluded-volume effect. Meanwhile, increasing solvent density can increase repulsive interaction between the passivated NPs, thereby producing a stable dispersion. In general, the simulation presents a guide in understanding and manipulating NP interactions in supercritical fluids.