Scalable and Stable Manufacture of Molecular-Sized Silica Nanoparticles by Evaporation-Induced Self-Assembly

Silica nanoparticles on the single-nanometerscale are promisingbuilding blocks for the construction of functional nanomaterials.Generally, silica nanoparticles are formed via controlled nucleationand growth in dilute aqueous solutions to avoid aggregation, whichhampers their large-scale production and surface modification withorganochlorosilanes. Herein, we report a simple and scalable processto prepare uniform and unprecedentedly small silica nanoparticles(& SIM;2 nm in size) via the evaporation-induced self-assembly ofsilicate species and surfactants in a rotary evaporator. The as-synthesizedreverse-type silica-surfactant mesostructured composite wasdisassembled in tetrahydrofuran to obtain a clear colloidal dispersion.Surface modification was achieved by direct silylation of the mesostructuredcomposite with organochlorosilanes. Small-angle X-ray scattering analysisof the nanoparticle dispersion after surface trimethylsilylation indicatedthe absence of larger nanoparticles. The trimethylsilylated nanoparticleswere assembled by solvent evaporation to form a transparent film.Nanoindentation tests revealed that this nanoparticle film exhibitedplasticity and softness similar to organic polymers. Additionally,the thermal stability became significantly higher (10% weight lossat & SIM;500 & DEG;C in the air) when the surface was modified withdimethylsilyl (Me2Si(OSi)(2)) groups. These featuresof the silica nanoparticles prepared using our method have promisingapplications in emerging fields.