(615i) Advanced Double Emulsion Templating of Silica Microreactors

Emulsion droplets are commonly used as templates for the formation of hollow solid microspheres, which can be composed of different materials and serve a wide range of purposes. Here we study the scalable, double emulsion-based production of microreactors for synthesis processes with gas phase reactants. Hollow silica microspheres with porous walls decorated on the inside by gold catalyst nanoparticles are especially useful for the synthesis of semiconductor nanowires; they are poised for an enabling role in the scalable production of “designer nanowires”, such as nanowires with a chosen sequence of functional blocks encoded along their length. We will show that the requisite microreactor capsules can be prepared from an aqueous gold dispersion, a nonaqueous dispersion of modified silica particles, and an aqueous emulsifier solution, by applying a scalable process involving (a) the batch production of a w/o/w double emulsion, (b) osmotic swelling, (c) particle cross-linking, (d) solvent extraction, and (e) drying. The influence of individual steps, materials and process parameters on the capsule morphology and stability upon drying will be discussed in some detail.