Atomic-Scale Mechanisms Controlling the Early Aggregation of Sub 10 nm Amorphous Silica Nanoparticles in Vacuum

Optimizing the performance of sub 10 nm SiO2 nanoparticles (NPs) requires controlling their aggregation, which depends on understanding the underexplored early stages of this process. This study uses reactive molecular dynamics (MD) simulations with the ReaxFF potential to investigate the onset of aggregation in 1–5 nm amorphous SiO2 NPs in a vacuum. Aggregation is thermodynamically favored, with dimerization playing a critical role in initiating and stabilizing aggregates. Smaller nanoparticles aggregate more rapidly due to higher surface energy, but their dimers are less stable, influenced by atomic mobility and energy barriers. The volume–specific surface area (VSSA) model reveals an inverse correlation between VSSA and stability, indicating weak attractive forces from steric effects and electrostatic repulsion in larger pairs, potentially delaying aggregation. These findings offer valuable insights into the interplay of thermodynamic and kinetic factors, providing strategies to control SiO2 NP behavior in diverse nanotechnological applications.