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Journal of Flow Chemistry
Authors: Piotr M. Korczyk, Monika E. Dolega, Slawomir Jakiela, Pawel Jankowski, Sylwia Makulska, and Piotr Garstecki

Conducting reactions in droplets in microfluidic chips offers several highly attractive characteristics, among others, increased yield and selectivity of chemical syntheses. The use of droplet microfluidic systems in synthetic chemistry is, however, hampered by the intrinsically small throughput of micrometric channels. Here, we verify experimentally the potential to increase throughput via an increase of the scale of the channels.We use the results of these experiments characterizing the processes of (1) generation of droplets, (2) mixing in droplets, (3) inter-phase extraction, and (4) the yield of synthesis of pyrrole, to postulate a number of guidelines for scaling up the throughput of microfluidic droplet systems. In particular, we suggest the rules for maximizing the throughput via an increase of the size of the channels and via parallelization to optimize the throughput of synthesis against the cost of fabrication of the chips and against the kinetic requirements of specific reactions.

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processes. In order to generate large surface areas for fast drying, the slurry is disintegrated in very small droplets which are sprayed into a hot gas stream using nozzles. During the free falling period of the droplets there is a heat and mass exchange

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31 744 Fónagy, A., Yokoyama, N., Matsumoto, S. (2001) Physiological status and change of cytoplasmic lipid droplets in the pheromone-producing cells of the silkmoth, Bombyx

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A new way to perform reactions in core—shell double emulsions is reported herein. The phase boundaries of the threephase droplet flow were used to pressurize the reactants in the shell liquid, enhancing the reaction rate of a cycloaddition greatly in comparison to known methods. As key parameters, solvophobic effects and precise control over the droplet sizes were used to exploit a reaction with a negative volume of activation. The internal pressure of the reaction solution was regulated purely by the thickness of the shell liquid without adding additional reagents. Additionally, the reaction performed better when the core droplet was used to stir the shell droplet, considerably improving the mass transfer inside the otherwise diffusion-limited process.

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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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Abstract  

This article is dedicated to develop an experimental approach for directly visualizing the global freezing phase change behavior of micro liquid droplets. The infrared (IR) thermograph was proposed to image the basic solidification phenomena of droplet and to acquire its temperature variations during the transient process. In particular, the volumetric recalescence event, regarded as initiation of freezing, was revealed by IR images for the first time. Preliminary results demonstrated that the involved temperature transition due to release of the latent heat can be accurately characterized by evident color break in IR images. Further, experiments were also performed simultaneously on three kinds of droplets made of pure water, dimethylsulfoxide (DMSO) and nano liquid to grasp more precise temporal and spatial temperature distribution. Types of the occurring solidification and the initial frozen volume produced from the recalescence were generally discussed. The IR monitoring method suggests a straightforward way for detecting the freezing phase change activity and its temperature evolution at micro scale.

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Abstract  

We studied thermal transitions and physical stability of oil-in-water emulsions containing different milk fat compositions, arising from anhydrous milk fat alone (AMF) or in mixture (2:1 mass ratio) with a high melting temperature (AMF–HMT) or a low melting temperature (AMF–LMT) fraction. Changes in thermal transitions in bulk fat and emulsion samples were monitored by differential scanning calorimetry (DSC) under controlled cooling and reheating cycles performed between 50 and –45C (5C min–1). Comparison between bulk fat samples and emulsions indicated similar values of melting completion temperature, whereas initial temperature of fat crystallization (T onset) seemed to be differently affected by storage temperature depending on triacylglycerols (TAG) composition. After storage at 4C, T onset values were very similar for emulsified and non-emulsified AMF–HMT blend, whereas they were lower (by approx. 6C) for emulsions containing AMF or mixture of AMF–LMT fraction. After storage at –30C, T onset values of re-crystallization were higher in emulsion samples than in bulk fat blends, whatever the TAG fat composition. Light scattering measurements and fluorescence microscopic observations indicated differences in fat droplet aggregation-coalescence under freeze-thaw procedure, depending on emulsion fat composition. It appeared that under quiescent freezing, emulsion containing AMF–LMT fraction was much less resistant to fat droplet aggregation-coalescence than emulsions containing AMF or AMF–HMT fraction. Our results indicated the role of fat droplet liquid-solid content on emulsion stability.

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Abstract  

It is shown that for porous systems filled with a solvent, if the temperature domains of crystallization and melting of the solvent are well separated, DSC technique, combined with suitably chosen thermal cycles, provides crystallization and melting curves which are independent of a) the mass of the material, b) the thermal contact between DSC pan and material and c) the thermal conductivity of the material. This method called DSC fractionation is applied to butyl rubber containing small water nodules. Thermoporosimetry is then applied to get the size distribution of mesoscopic solvent droplets.

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Abstract  

An experimental method was conducted to evaluate the minimum bubble nucleation energy of freon-12 for application in the superheated-liquid-droplet (SLD) technique. The minimum energy needed for an incident particle to cause the bubble nucleation is based on the theoretical calculation ofW min/ηkr c value. The calculated value may mislead the result of measured intensity due to its under/overestimation ofW min/ηkr c values at various temperatures. Nevertheless, the experimental evaluation ofW min/ηkr c of freon-12 for causing the bubble nucleation is barely touched because the proper methodology has not developed fully. The minimum energy needed to produce the bubble nucleation, can be evaluated by mixing the alpha-emitting nuclides with the SLD. By direct hitting the SLD with alpha-particle, the energy deposited inside the SLD may cause the bubble nucleation if the deposited energy is larger than theW min/ηkr c of freon-12 droplet at that specific temperature. The experimental evaluated values in this study agree with the theoretical estimation in 78% for SLD emulsion temperature within 22–34°C. Tests suggest that to apply the SLD in measuring the alpha-emitting nuclides, the emulsion temperature should be maintained below 30°C to get a maximum efficiency and to avoid interference from beta or gamma event.

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The infection-induced overproduction of reactive oxygen species (ROS) in resistant plants is usually ascribed to the host. Here we tested the possible contribution of the parasite, the rice blast fungus to ROS production. Droplets of spore suspensions or water were kept on rice leaves or on a plastic. After one day, superoxide radical and hydrogen peroxide were chemically assayed in drop diffusates. Similar measurements were done on diffusates of rice calli submerged in spore suspension or water. Negligible amounts of ROS were found in diffusates of plant tissues treated with water. In contrast, diffusates from tissues treated with spore suspensions had appreciable levels of ROS, usually higher in incompatible combinations than in compatible ones. However, diffusates of spores incubated on plastic produced ROS to an extent comparable to those of infected tissues. In diffusates of spores, O 2 was found after their germination, and H 2 O 2 was found after appressorium formation. Various fungal strains differed in ROS production. The results suggest that spores of the blast inoculum may contribute significantly to ROS production on rice leaves, at least, at early stages of the disease. This might be a factor of incompatibility suppressing a parasite and/or inducing defense responses of a host.

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