Rapid Self-Assembly of Core−Shell Organosilicon Microcapsules within a Microfluidic Device

Abstract

The preparation of hierarchically structured organosilicon microcapsules from commercially available starting materials is described. Using a microfluidic device, an emulsion of dichlorodiphenylsilane is formed in a continuous phase of aqueous glycerol. The silane droplets undergo hydrolysis, condensation, and crystallization within minutes to form self-assembled, core-shell microcapsules. The microparticles have been characterized with light and electron microscopy, nuclear magnetic resonance spectroscopy (NMR), diffusion-ordered NMR spectroscopy (DOSY), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). The characterization data show that the microcapsule walls consist of amorphous, oligomeric poly(diphenylsiloxane) surrounded by a spiny layer of crystalline diphenylsilanediol. Glycerol is occluded within the wall material but is not covalently bound to the silicon components. Glycerol is a crucial element for producing low-dispersity microcapsules with well-ordered surface spines, as the use of methyl cellulose as viscomodifier yields amorphous surfaces.

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

“…Prior work in our group using reactive silicon chlorides revealed that the continuous phase must have a viscosity sufficient to enable droplet production and just enough water to enable condensation. Too much water causes the condensation reaction to occur rapidly and directly at the disperse phase/continuous phase junction, leading to clogging of the device [27]. A continuous phase of 80 % glycerol/water provides the high viscosity (η = 60 mPa s) [27] and at the same time reduces the concentration of water.…”

“…Too much water causes the condensation reaction to occur rapidly and directly at the disperse phase/continuous phase junction, leading to clogging of the device [27]. A continuous phase of 80 % glycerol/water provides the high viscosity (η = 60 mPa s) [27] and at the same time reduces the concentration of water. Though other continuous phases may provide sufficient properties, the low cost of glycerol makes this system attractive.…”

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

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