(44f) Silica Nanoparticles: From Facile Synthesis to Ordered Nanoparticle-Crystals and Coatings

Realization of silica nanoparticle-crystals and controlled assembly of large-area nanoparticle films has implications spanning technologies of coatings and colloidal lithography to chemical sensing and biology (i.e., cell encapsulation and anti-immunorejection coatings of implants). Challenges to device fabrication in each of these areas, however, derive at least in part from the lack of a simple means for synthesizing stable and monodisperse silica nanoparticles, and the limited capabilities for rationally tuning particle size, porosity, order, and monolayer continuity. Here, we report on the facile synthesis of silica nanoparticles with narrow particle size distribution in aqueous L-Lysine solutions.¹ The novelty of this work derives from the simplicity of the synthesis via hydrolysis of tetraethylorthosilicate (TEOS) in an aqueous solution of L-Lysine and the identification of a range of handles (e.g., pH, silica content, hydrolysis and hydrothermal ageing temperature) for tuning particle diameter from less than 5 nm to more than 20 nm. The initial stage of nanoparticle formation mimics that for tetrapropylammonium- and other alkylamonium-silica nanoparticles in that the nanoparticles rapidly form upon exceeding the silica solubility limit.

Beyond the novelty of the nanoparticle synthesis, cryo-TEM reveals in situ assembly of these nanoparticles into close-packed nanoparticle-crystals over short length scales on carbon-coated grids. Even more interesting from an applications standpoint is the stability of these nanoparticles and their remarkable, long-range facile ordering over scales greater than 10 µm, revealed after evaporative drying of the same sols.² While small angle x-ray scattering and small angle neutron scattering discount the existence of a core (silica)-shell (lysine) structure of the nanoparticles, we will discuss the possibility of hydrogen bonding effects resulting from lysine occlusion within the nanoparticles for driving the self-assembly. The facile ordering of the silica nanoparticles for multilayer and monolayer coatings over square centimeter areas using a novel device that combines continuous dip-coating and controlled evaporation-induced self-assembly will also be demonstrated.

References

1. Davis, T. M.; Snyder, M. A.; Krohn, J. E.; Tsapatsis, M., Chemistry of Materials 2006, 18, 5814.

2. Snyder, M. A.; Lee, J. A.; Davis, T. M.; Scriven, L. E.; Tsapatsis, M., 2007, Submitted.