Silica Nanoparticle Crystals and Ordered Coatings Using Lys-Sil and a Novel Coating Device

Silica nanoparticles with a narrow particle size distribution and controlled diameters of 10?20 nm are synthesized via hydrolysis and hydrothermal aging of tetraethylorthosilicate in an aqueous l-lysine solution. Cryo-transmission electron microscopy (cryo-TEM) reveals that the silica nanoparticles assemble to form close-packed nanoparticle crystals over short length scales on carbon-coated grids. Evaporative drying of the same sols results in nanoparticle stability and remarkable long-range facile ordering of the silica nanoparticles over scales greater than 10 ?m. Whereas small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) discount the possibility of a core (silica)?shell (lysine) structure, the possibility remains for lysine occlusion within the silica nanoparticles and concomitant hydrogen bonding effects driving self-assembly. Facile ordering of the silica nanoparticles into multilayer and monolayer coatings over square-centimeter areas by evaporation-induced self-assembly is demonstrated using a novel dip-coating device.