A Reactive Molecular Dynamics Simulation of the Flame Synthesis of Silica Nanoparticles

Reactive molecular dynamics simulations (RMDS) with the ReaxFF force field are used to study nucleation and growth of silica nanoparticles during flame synthesis from tetramethoxysilane (TMOS). Two reactive systems (A & B) are considered and formation and/or consumption of various reactants, intermediates and products are followed. In the RMDSs of system A (TMOS, O2, SiO2, and Ar), the temperature-dependence of the formation of initial SimOn seeds show that formation of transient SiO3C3H9 intermediate is an important stage in the conversion of TMOS to the initial SimOn seeds, which then aggregate to produce silica nanoparticles. Increasing temperature speeds up this conversion. Results of the RMDSs on system B (TMOS, O2, Ar, and {SimOn}; the SimOn seeds play the role of initial silica nanoparticles) show that at 2100 K, weak EFs (~1 V/A) narrows the size distribution of the silica nanoparticles compared to that in the absence of EF while by application of stronger EFs (4-8 V/A), the initial SimOn nanoparticles split into smaller species. In the absence of EF, increasing temperature from 1500 K to 3000 K increases sizes of the nanoparticles. The radial distribution functions, coordination numbers, and atomic compositions are used to characterize nanoparticles and evolution of the reaction.