Molecular Dynamics Simulations of Evaporation-Induced Nanoparticle Assembly

TL;DR

This study uses large-scale molecular dynamics simulations to investigate how evaporation rates influence the quality of nanoparticle assemblies, revealing that slower evaporation yields fewer defects.

Contribution

The paper provides new insights into the physical factors affecting nanoparticle assembly during evaporation, emphasizing the role of evaporation rate in defect formation.

Findings

Slower evaporation improves nanoparticle crystal quality.

Fast evaporation leads to more defects and grain boundaries.

Diffusion time competes with accumulation rate at the interface.

Abstract

While evaporating solvent is a widely used technique to assemble nano-sized objects into desired superstructures, there has been limited work on how the assembled structures are affected by the physical aspects of the process. We present large scale molecular dynamics simulations of the evaporation-induced assembly of nanoparticles suspended in a liquid that evaporates in a controlled fashion. The quality of the nanoparticle crystal formed just below the liquid/vapor interface is found to be better at relatively slower evaporation rates, as less defects and grain boundaries appear. This trend is understood as the result of the competition between the accumulation and diffusion times of nanoparticles at the liquid/vapor interface. When the former is smaller, nanoparticles are deposited so fast at the interface that they do not have sufficient time to arrange through diffusion, which leads to the prevalence of defects and grain boundaries. Our results have important implications in understanding assembly of nanoparticles and colloids in non-equilibrium liquid environments.