Fabrication and Characterization of "Nano-Beakers" for the Synthesis of Ceramic Colloids



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Microreactors are devices containing microscale channel networks, called microfluidics, in which a variety of reactions and analysis schemes can be performed. They allow for precisely controlled reaction times and mixing rates, higher yields, smaller waste production, reproducible multi-phase flow patterns, and an ability to scale-up the method to produce larger volumes of product. Ceramic microspheres, such as those made of silica or titania, show promise for improving current methods and materials of many applications, ranging from medical imaging and drug delivery, renewable energy, and chromatography, to name a few. The microspheres can be easily synthesized by sol-gel chemistry using batch methods, however, the products are often polydisperse and their sizes irreproducible. Segmented flow microreactors offer a solution to these problems with their highly controllable reaction times, enhanced mixing capabilities, and reproducible reaction conditions that are made possible by isolating the reaction in a series of periodically spaced “nanobeakers”. In this project, silica and titania microspheres were synthesized in three different reactors: a batch reactor (essentially a beaker), a single phase microreactor, and a segmented flow microreactor. It was hypothesized that the microspheres with the narrowest size distribution would be produced by the segmented flow microreactor involving nano-beakers, followed by the batch reactor, and finally the single phase microreactor. The microreactors were not microfabricated, as is the usual method of device production, but were constructed from commercially available T-junctions, capillaries, and pumps. This project represents the first time that a microreactor built with commercially available capillary fluidics has been used to synthesize microparticles using segmented flows. First, the segmented flow microreactor was characterized to understand the effect that reagent flow rates have on the volume and periodicity of the nanobeakers. Then, the average diameter and size distribution of microspheres produced by each reactor were measured after several different reaction times by dynamic light scattering as well as from images taken on a scanning electron microscope. Microspheres were successfully produced in the single phase microreactor, demonstrating that capillary-based microreactors are a viable alternative to microfabricated devices. Contrary to expectations, the segmented flow microreactor produced microspheres with the widest size distribution. SEM images suggest that the problem lies in the distribution of reagents into the nanobeakers upon segmentation, disrupting the development of microspheres with a defined morphology. Further investigation into how the reagents are distributed and how flow rates and capillary dimensions affect this would help to improve the segmented flow microreactor and achieve better results.



microfluidics, microspheres, chemistry, silica