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We present and validate simple mesofluidic devices for producing monodisperse droplets and materials. The significance of this work is a demonstration that simple and complex droplet formulations can be prepared uniformly using off-the-shelf small-diameter tubing, barbed tubing adapters, and needles. With these simple tools, multiple droplet-forming devices and a new particle concentrator were produced and validated. We demonstrate that the droplet-forming devices could produce low-dispersity particles from 25 to 1200 Km and that these results are similar to results from more complicated devices. Through a study of the fluid dynamics and a dimensional analysis of the data, we have correlated droplet size with two dimensionless groups, capillary number and viscosity ratio. The flowfocusing device is more sensitive to both parameters than the T-junction geometry. The modular character of our mesofluidic devices allowed us to rapidly assemble compound devices that use flow-focusing and T-junction devices in series to create complex droplet-in-microcapsule materials. This work demonstrates that flow chemistry does not require complicated tools, and an inexpensive tool-kit can allow anyone with interest to enter the field.

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Journal of Flow Chemistry
Authors: L. Zane Miller, Jeremy L. Steinbacher, Tania I. Houjeiry, Ashley R. Longstreet, Kendra L. Woodberry, B. Frank Gupton, Banghao Chen, Ron Clark and D. Tyler McQuade

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 29Si 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.

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The Sandmeyer reaction of anilines to generate aryl azides, followed by the Ru(porphyrin)CO-catalyzed addition to styrenes affording N-aryl aziridines was successfully performed for the first time in mesoreactors, under continuousflow conditions. Mesofluidic technology allowed for a rapid screening of different parameters and a quick identification of the optimized reaction conditions for the two separate steps. The two optimized reactions were then combined in a single continuous process that allowed a safe and efficient synthesis of N-arylaziridines from convenient commercially available starting materials.

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Journal of Flow Chemistry
Authors: Druval S. De Sá, Bojan A. Marinkovic, Eric C. Romani, Tommaso Del Rosso, Rodrigo O. M. A. de Souza, Alessandro Massi and Omar Pandoli

We present prototyping of meso- and microfluidic photocatalytic devices, functionalized through incorporation of TiO2 nanoparticles in polydimethylsiloxane (PDMS), and comparison of their efficiencies for the degradation of rhodamine B (10−5 mol/L). The prototyping of the photocatalytic devices involves simple and low-cost procedures, which includes microchannels fabrication on PDMS, deposition and impregnation of TiO2 on PDMS, and, finally, plugging on the individual parts. For the microfluidic device with 13 μL internal volume, photocatalytic TiO2–PDMS composite was sealed by another PDMS component activated by O2 plasma (PDMS–TiO2–PDMS). For the mesofluidic device, a homemade polyetheretherketone (PEEK) flow cell with 800 μL internal volume was screwed on a steel support with a glass slide and the photocatalytic composite. The photocatalytic activities of the devices were evaluated using two different pumping flow systems: a peristaltic pump and a syringe pump, both at 0.05 mL/min under the action of 365 nm ultraviolet (UV) light. The characterization of TiO2–PDMS composite was performed by confocal Raman microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The photocatalytic microreactor was the most efficient, showing high organic dye photodegradation (88.4% at 12.5 mW/cm2).

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Journal of Flow Chemistry
Authors: L. Zane Miller, James J. Rutowski, Jonathan A. Binns, Guillermo Orts-Gil, D. Tyler McQuade and Jeremy L. Steinbacher

We present a rapid approach for forming monodisperse silica microcapsules decorated with metal oxide nanoparticles; the silica–metal oxide composites have a hierarchical architecture and a range of compositions. The details of the method were defined using titania precursors. Silica capsules containing low concentrations of titania (<1 wt. %) were produced via an interfacial reaction using a simple mesofluidic T-junction droplet generator. Increasing the titania content of the capsules was achieved using two related, flow-based postsynthetic approaches. In the first approach, a precursor solution containing titanium alkoxides was flowed through a packed-bed of capsules. The second approach provided the highest concentration of titania (3.5 wt. %) and was achieved by evaporating titanium precursor solutions onto a capsule packed-bed using air flow to accelerate evaporation. Decorated capsules, regardless of the method, were annealed to improve the titania crystallinity and analyzed by optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), and Fourier transform infrared (FT-IR) spectroscopy. The photocatalytic properties were then compared to a commercial nanoparticulate titania, which the microcapsule-supported titania outperformed in terms of rate of degradation of an organic dye and recyclability. Finally, the generality of the flow-based surface decoration procedures was demonstrated by synthesizing several composite transition metal oxide–silica microparticle materials.

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. “ Simplified mesofluidic systems for the formation of micron to millimeter droplets and the synthesis of materials ” J. L. Steinbacher , Y. Lui , B. P. Mason , W. L. Olbricht , D. T. McQuade Journal of Flow Chemistry 2012 , 2 , 56 – 62

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chemistry is suitable for space applications (Table 1 ). Most importantly, there is no headspace in micro- and mesofluidic flow reactors in which chemicals can float to make results irreproducible. In addition to that, the flow rate and the pressure can be

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