Controlled Synthesis of Silica Capsules: Taming the Reactivity of SiCl4 Using Flow and Chemistry

Abstract

Monodisperse silica microcapsules are typically fabricated using hard templating methods. Though soft templating methods are known, none yet provides a fast and easy method to produce monodisperse capsules. Herein, we describe a mesofluidic strategy whereby monodisperse droplets of reactive silica precursors are formed using a snap-off mechanism via a T junction. Both the mesofluidic system and the composition of the reactive silica formulation are critical features. Using solid-and solution-state 29 Si nuclear magnetic resonance, scanning electron microscopy, and optical microscopy, we have developed models for why some formulations form exploding capsules, why some capsules contain crystalline materials, and why some capsules have thin or thick walls.

Flow-Based Surface Decoration of Microparticles with Titania and Other Transition Metal Oxide Nanoparticles

“…Indeed, solution-phase 29 Si nuclear magnetic resonance (NMR) spectroscopy confirmed that rapid exchange of chloride and ethoxy groups occurred between TEOS and SiCl 4 within 10 min after the preparation of the disperse-phase solution ( Figure S1). This is even faster than in our previous report of purely silica microparticles that did not use titanium alkoxides [26].…”

“…Synthesis of Mixed Silica-Titania Shells via Interfacial Condensation. Previous work in our laboratory demonstrated that fast-reacting precursors such as SiCl 4 could be used to create microcapsules by tuning the condensation rate using alcohol additives [26]. Formation of HCl gas upon fast hydrolysis of the Si-Cl bonds served to create the void around which the interfacial polymerization proceeded, leaving behind the inorganic shell.…”

“…We sought to apply this approach to prepare silicatitania composite materials. Using our previously described simple droplet maker [26], we began to study the condensation of mixed silica and titania precursors.…”

“…We and others have demonstrated the utility of simple devices for the formation of droplets and microcapsules from reactive precursors [25][26][27][28]. While using tubing and T-junctions provides an uncomplicated alternative to chip-based devices, the approach also enables rapid device reconfiguration that can offer new capabilities.…”

“…While using tubing and T-junctions provides an uncomplicated alternative to chip-based devices, the approach also enables rapid device reconfiguration that can offer new capabilities. For example, we have demonstrated that monodisperse SiO 2 capsules were readily formed using a flowbased droplet system via tuned interfacial condensation [26]. The key in our prior system was that we used alcohol additives to tune the interfacial condensation rate.…”