Effect of dispersed phase viscosity on maximum droplet generation frequency in microchannel emulsification using asymmetric straight-through channels

Effect of dispersed phase viscosity on maximum droplet generation frequency in microchannel emulsification using asymmetric straight-through channel

Rapid generation of highly uniform droplets using asymmetric microchannels fabricated on a single crystal silicon plate

A microfluidic device can be identified by the fact that it has one or more channels with at least one dimension less than 1 mm. The most common types of microfluidic devices are: (i) soft microfluidic devices fabricated in elastomeric materials such as PDMS by soft lithography [1], (ii) glass devices manufactured in quartz glass or glassy polymers such as PMMA by etching or micromachining [2], and (iii) microchannel (MC) array devices fabricated in silicon by photolithography and wet-etching or deep-reactive ion etching processing [3]. Microfluidic devices can be used for capillary electrophoresis [4], liquid-liquid extraction [5], immunoassays [6], cellomics [7], proteomics [8], DNA analysis [9], blood rheology measurements [10], microreactors [11], droplet formation [2], etc. The soft microfluidic devices such as T-junctions and flow focusing devices are suitable for rapid generation of monodispersed droplets with a coefficient of variation (CV) in a dripping regime of generally less than 3 %. Although the frequency of drop production can be as high as 7000 Hz, the overall productivity in terms of volume flow rate of the disperse phase is very low because the droplets are formed from a single channel. Silicon MC array devices are much more suitable for large-scale applications because the total number of microchannels on a chip can be hundreds of thousands. The aim of this work was to investigate the generation of uniform droplets at high production rates using novel asymmetric MC array microfabricated on a silicon plate [12]. Monodispersed emulsion droplets are much more favourable both in fundamental studies and practical applications. Emulsion appearance and rheology, stability against Oswald ripening and creaming, and the suitability of droplets as templates to the production of solid micro- and nano-particles are strongly influenced by their particle size distribution

Microchannel emulsification

Microchannel emulsificatio

Production of uniformly sized emulsion drops at high production rates using asymmetric micro channel plates

The purpose of this work was to investigate maximum disperse phase flux required for production of monodisperse drops in a straight-through microchannel (MC) array device. The experiments have been carried out using single-crystal silicon MC plate consisting of about 23,000 asymmetric MCs fabricated by photolithography and deep reactive ion etching (DRIE). Each MC consisted of a rectangular 50×10 μm slot and a circular 10 μm-diameter hole in the middle of each slot. A depth of the hole was 70 μm and the slot depth was 30 μm. The dispersed phase was soybean oil, MCT (middle-chain fatty acid triglyceride) oil and n-tetradecane with a viscosity at 293 K of 50, 20, and 2.7 mPa·s, respectively. The continuous phase was 2 wt% Tween 20 or SDS. (Continues...)

Generation of highly uniform droplets using asymmetric microchannels fabricated on a single crystal silicon plate: effect of emulsifier and oil types

Uniform droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a mean diameter of 26–29 μm have been generated using asilicon 24 × 24 mm microchip consisting of 23,489 asymmetric microchannels fabricated by photolitography and deep-reactive ion etching. Each microchannel consisted of a circular 10-μm diameter straight hole with a length of 70 μm and a 50 × 10 μm rectangular microslot with a depth of 30 μm. At the constant oil flux of 10 L m− 2 h− 1, the percent of active channels increased with increasing the oil viscosity and ranged from 4% for n-tetradecane to 48% for soybean oil. The size distribution span for SDS (sodium dodecyl sulphate)- and Tween 20 (polyoxyethylene (20) sorbitan monolaurate)-stabilized soybean and MCT oildroplets was 0.21–022. The ability of asymmetricmicrochannels to generate monodisperse soybean oildroplets at the very low SDS concentration of 0.01 wt.% has been demonstrated. At the SDS concentration below the CMC, the generated droplets tend to attach to the plate surface, whereas at the higher SDS concentration they detach from the plate as soon as they are formed. The agreement between the experimental and CFD (Computational Fluid Dynamics) simulation results was excellent for soybean oil and the poorest for n-tetradecane

Manufacture of monodisperse oil-in-water emulsions at high droplet formation rates using novel asymmetric silicon microchannels

Manufacture of monodisperse oil-in-water emulsions at high droplet formation rates using novel asymmetric silicon microchannel

High-performance microchannel emulsification device with microfabricated asymmetric through-holes

High-performance microchannel emulsification device with microfabricated asymmetric through-hole

Production of uniform droplets using membrane, microchannel and microfluidic emulsification devices

This review provides an overview of major microengineering emulsification techniques for production of monodispersed droplets. The main emphasis has been put on membrane emulsification using Shirasu Porous Glass and microsieve membrane, microchannel emulsification using grooved-type and straight-through microchannel plates, microfluidic junctions and flow focusing microfluidic devices. Microfabrication methods for production of planar and 3D poly(dimethylsiloxane) devices, glass capillary microfluidic devices and single-crystal silicon microchannel array devices have been described including soft lithography, glass capillary pulling and microforging, hot embossing, anisotropic wet etching and deep reactive ion etching. In addition, fabrication methods for SPG and microseive membranes have been outlined, such as spinodal decomposition, reactive ion etching and ultraviolet LIGA (Lithography, Electroplating, and Moulding) process. The most widespread application of micromachined emulsification devices is in the synthesis of monodispersed particles and vesicles, such as polymeric particles, microgels, solid lipid particles, Janus particles, and functional vesicles (liposomes, polymersomes and colloidosomes). Glass capillary microfluidic devices are very suitable for production of core/shell drops of controllable shell thickness and multiple emulsions containing a controlled number of inner droplets and/or inner droplets of two or more distinct phases. Microchannel emulsification is a very promising technique for production of monodispersed droplets with droplet throughputs of up to 100 l h−1

CFD analysis of microchannel emulsification: Droplet generation process and size effect of asymmetric straight flow-through microchannels

Asymmetric straight flow-through microchannel (MC) arrays are high-performance MC emulsification devices for stable mass production of uniform droplets. This paper presents computational fluid dynamics (CFD) simulation and analysis of the generation of soybean oil-in-water emulsion droplets via asymmetric straight flow-through MCs, each consisting of a microslot and a narrow MC. We also used CFD to investigate the effects of the channel size and the flow of the dispersed phase on MC emulsification using asymmetric straight flow-through MCs with a characteristic channel size of 5 to 400 μm. The overall shape of an oil-water interface and the time scale during droplet generation via a control asymmetric straight flow-through MC were appropriately simulated. Better insight was obtained on the flow profile of the two phases and the internal pressure balance of the dispersed phase during droplet generation. Comparison of the CFD and experiment results also provided insight into dynamic interfacial tension during droplet generation. Successful droplet generation was observed below a critical dispersed-phase velocity. In this case, the resultant droplet size was proportional to the channel size and was not sensitive to the dispersed-phase velocity applied. The maximum droplet generation rate per channel was inversely proportional to the channel size, unless the buoyancy force did not promote droplet detachment. The maximum droplet productivity per unit area of an asymmetric straight flow-through MC array was estimated to be constant, regardless of channel size

High-performance production of monodisperse emulsions using microfabricated asymmetric through-hole array

This paper reports high-performance production of monodisperse emulsions using numerous asymmetric through holes microfabricated on a silicon chip. Monodisperse oil-in-water (O/W) emulsions with droplet sizes of approximately 30 µm were stably produced via asymmetric through holes at high droplet generation rates up to several hundreds of thousands per second. This paper also reports three-dimensional simulation of emulsion droplet generation via an asymmetric through hole using a computational fluid dynamics (CFD) method. The calculation results showed an excellent agreement with the experimental results and provided a better understanding of the droplet generation process