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1.
Scale-up and control of droplet production in coupled microfluidic flow-focusing geometries 总被引:1,自引:1,他引:0
A single microfluidic chip consisting of six microfluidic flow-focusing devices operating in parallel was developed to investigate the feasibility of scaling microfluidic droplet generation up to production rates of hundreds of milliliters per hour. The design utilizes a single inlet channel for both the dispersed aqueous phase and the continuous oil phase from which the fluids were distributed to all six flow-focusing devices. The exit tubing for each of the six flow-focusing devices is separate and individually plumbed to each device. Within each flow-focusing device, the droplet size was monodisperse, but some droplet size variations were observed across devices. We show that by modifying the flow resistance in the outlet channel of an individual flow-focusing device it is possible to control both the droplet size and frequency of droplet production. This can be achieved through the use of valves or, as is done in this study, by changing the length of the exit tubing plumbed to the outlet of the each device. Longer exit tubing and larger flow resistance is found to lead to larger droplets and higher production frequencies. The devices can thus be individually tuned to create a monodisperse emulsion or an emulsion with a specific drop size distribution. 相似文献
2.
Computational fluid dynamics analysis of microbubble formation in microfluidic flow-focusing devices
Bubble formation in a microfluidic flow-focusing device is simulated using the volume-of-fluid approach to achieve a complete
solution of the Navier–Stokes equations for both the gas and liquid phases. The results of the simulation show good agreement
with previous experimental results. A detailed examination of the predicted pressure and velocity profiles from the simulation
also provide further validation for the conclusions drawn previously with experimental results. The simulation results show
the existence of two distinct modes of bubble formation. Simulations of systems an order of magnitude smaller than those investigated
experimentally indicate that such reduced systems sizes are a viable approach that would result in much smaller bubble sizes. 相似文献
3.
Simulations of extensional flow in microrheometric devices 总被引:1,自引:0,他引:1
Mónica S. N. Oliveira Lucy E. Rodd Gareth H. McKinley Manuel A. Alves 《Microfluidics and nanofluidics》2008,5(6):809-826
We present a detailed numerical study of the flow of a Newtonian fluid through microrheometric devices featuring a sudden
contraction–expansion. This flow configuration is typically used to generate extensional deformations and high strain rates.
The excess pressure drop resulting from the converging and diverging flow is an important dynamic measure to quantify if the
device is intended to be used as a microfluidic extensional rheometer. To explore this idea, we examine the effect of the
contraction length, aspect ratio and Reynolds number on the flow kinematics and resulting pressure field. Analysis of the
computed velocity and pressure fields show that, for typical experimental conditions used in microfluidic devices, the steady
flow is highly three-dimensional with open spiraling vortical structures in the stagnant corner regions. The numerical simulations
of the local kinematics and global pressure drop are in good agreement with experimental results. The device aspect ratio
is shown to have a strong impact on the flow and consequently on the excess pressure drop, which is quantified in terms of
the dimensionless Couette and Bagley correction factors. We suggest an approach for calculating the Bagley correction which
may be especially appropriate for planar microchannels.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
An electro-spraying microfluidic chip was integrated with a parallel electrode and flow-focusing device to successfully generate uniform emulsions with an electric field. This approach utilizes a high electric field driven by a direct-current voltage to form a stable Taylor cone in the flow-focusing position. The Taylor cone can then generate stable and uniform emulsions that are less than 5?μm in diameter. The emulsion size is controlled by the surfactant concentration, the ratio of the water and oil phase flow rates and the strength of the electric field. When the strength of the electric field increases at a high surfactant concentration and low ratio of flow rates, the Taylor angle decreases, which causes the emulsion size to decrease. In this study, the water emulsion diameter ranged from 1 to 98?μm, and the poly(lactic-co-glycolic acid) (PLGA) emulsion size ranged from 7 to 70?μm. The microfluidic chip developed in this work has the advantages of actively controlling the emulsion size and generating uniform emulsions (the relative standard deviation was less than 10%) and represents a new emulsion generation process. 相似文献
5.
Irene Arcos-Turmo Miguel Ángel Herrada José María López-Herrera David Fernandez Rivas Alfonso M. Gañán-Calvo Elena Castro-Hernández 《Microfluidics and nanofluidics》2018,22(8):79
A novel swirl flow-focusing microfluidic axisymmetric device for the generation of monodisperse microbubbles at high production rates to be used as in-line contrast agents for medical applications is presented. The swirl effect is induced upstream of the discharge orifice by a circular array of microblades which form a given angle with the radial direction. The induced vortical component on the focusing liquid stabilizes the gas meniscus by the vorticity amplification due to vortex stretching as the liquid is forced through the discharge orifice. The stabilized meniscus tapers into a steady gas ligament that breaks into monodisperse microbubbles. A reduction up to \(57\%\) in the microbubble diameter is accomplished when compared to conventional axisymmetric flow-focusing microdevices. An exhaustive experimental study is performed for various blade angles and numerous gas to liquid flow rate ratios, validating previous VoF numerical simulations. The microbubbles issued from the stabilized menisci verify prior scaling law of flow-focusing. 相似文献
6.
Shin-Hyun Kim Jin Woong Kim Do-Hoon Kim Sang-Hoon Han David A. Weitz 《Microfluidics and nanofluidics》2013,14(3-4):509-514
We report a parallelized capillary microfluidic device for enhanced production rate of monodisperse polymersomes. This device consists of four independent capillary microfluidic devices, operated in parallel; each device produces monodisperse water-in-oil-in-water (W/O/W) double-emulsion drops through a single-step emulsification. During generation of the double-emulsion drops, the innermost water drop is formed first and it triggers a breakup of the middle oil phase over wide range of flow rates; this enables robust and stable formation of the double-emulsion drops in all drop makers of the parallelized device. Double-emulsion drops are transformed to polymersomes through a dewetting of the amphiphile-laden middle oil phase on the surface of the innermost water drop, followed by the subsequent separation of the oil drop. Therefore, we can make polymersomes with a production rate enhanced by a factor given by the number of drop makers in the parallelized device. 相似文献
7.
T. X. Chu A.-V. Salsac D. Barthès-Biesel L. Griscom F. Edwards-Lévy E. Leclerc 《Microfluidics and nanofluidics》2013,14(1-2):309-317
We have designed a microfluidic system that enables both the fabrication of calibrated capsules and the in situ characterization of their mechanical properties. The fabrication setup consists of a double flow-focusing system. A human serum albumin aqueous solution is introduced in the central channel of a first Y-junction. Intercepted by the lateral flows of a hydrophobic phase, it is dispersed into microdroplets. A cross-linking agent is then introduced at a second Y-junction allowing a membrane to form around the droplets. The time of cross-linking is controlled by the length of a wavy channel located downstream of the second junction. A cylindrical microchannel finally enables to deform and characterize the capsules thus formed. The mechanical properties of the capsule membrane are obtained by inverse analysis. The results show that the drop size increases with the flow rate ratio between the central and lateral channels. The mean shear modulus of the capsules fabricated after 23 s of cross-linking is of the order of the surface tension between the two phases indicating that a reaction time of 23 s is too short for an elastic membrane to form around the droplet. When the cross-linking time is increased to 60 s, the microcapsules surface is wrinkled, thus confirming that a solid membrane is formed around the drop. The mean shear modulus of the capsule membrane increases with the cross-linking time, which is in agreement with our previous chemical results and proves that a fine control of the mechanical properties is possible by choosing adequately the control parameters of the system. 相似文献
8.
A combined circuit/device model for the analysis of integrated microfluidic systems is presented. The complete model of an integrated microfluidic device incorporates modeling of fluidic transport, chemical reaction, reagent mixing, and separation. The fluidic flow is generated by an applied electrical field or by a combined electrical field and pressure gradient. In the proposed circuit/device model, the fluidic network has been represented by a circuit model and the functional units of the /spl mu/-TAS (micro Total Analysis System) have been represented by appropriate device models. We demonstrate the integration of the circuit and the device models by using an example, where the output from the fluidic transport module serves as the input for the other modules such as mixing, chemical reaction and separation. The combined circuit/device model can be used for analysis and design of entire microfluidic systems with very little computational expense, while maintaining the desired level of accuracy. 相似文献
9.
Jörg Strutwolf Grégoire Herzog Alexandra Homsy Alfonso Berduque Courtney J. Collins Damien W. M. Arrigan 《Microfluidics and nanofluidics》2009,6(2):231-240
A microfluidic device is presented with off-chip electrodes residing in a reservoir and connected via micro-capillaries to
the Y-shaped microfluidic channel. The device is tested by potentiometric measurements involving dual-stream laminar flow
of two aqueous solutions carrying different electrolytes at various concentrations. Open circuit potentials are measured for
a series of solutions of alkali metal chlorides and tetraalkylammonium chlorides as well as for dilute hydrochloric acid.
The open circuit potential for the microfluidic chip was calculated by taking into account the diffusion potential at finite
ionic strength as well as the potential difference introduced by the reference electrode system. The liquid junction potential
developed at the boundary of the co-flowing aqueous solutions may be manipulated to have greater or lesser relative contributions
to the measured open circuit potential based on use of electrolyte salts having cation and anion pairs of similar or dissimilar
mobilities in solution. A reasonable agreement between theoretical and experimental values of the open circuit potential is
observed for these situations. The results show that simple microfluidic structures possess a rich environment for exploration
and application of the solution chemistry of ions. 相似文献
10.
11.
Taotao Fu Youguang Ma Denis Funfschilling Huai Z. Li 《Microfluidics and nanofluidics》2011,10(5):1135-1140
This communication describes the gas–liquid two-phase flow patterns and the formation of bubbles in non-Newtonian fluids in
microfluidic flow-focusing devices. Experiments were conducted in two different polymethyl methacrylate (PMMA) square microchannels
of, respectively, 600 × 600 and 400 × 400 μm. N2 bubbles were generated in non-Newtonian polyacrylamide (PAAm) solutions of different concentrations. Slug bubble, missile
bubble, annular and intermittent flow patterns were observed at the cross-junction by varying gas and liquid flow rates. Gas
and liquid flow rates, concentration of PAAm solutions, and channel size were varied to investigate their effect on the mechanism
of bubble formation. The bubble size was proportional to the ratio of gas/liquid flow rate for slug bubbles and could be scaled
with the ratio of gas/liquid flow rate as a power–law relationship for missile bubbles under wide experimental conditions. 相似文献
12.
The aim of this study was to investigate the effect of operating parameters such as liquid flow rate, gas inlet pressure, and capillary diameter as well as the influence of the physical properties of the liquid, in particular viscosity, on the generation of monodisperse microbubbles in a circular cross section T-junction device. Aqueous glycerol solutions with viscosities ranging from 1- to 100 mPa s were used in the experiments. The bubble diameter generated was studied for systematically varied combinations of gas inlet pressure, liquid flow rate, and liquid viscosity with a fixed capillary inner diameter of 150 μm for the liquid and gas inlet channels as well as the outlet channel. In addition, the effect of channel geometry on bubble size was studied using capillaries with inner diameters of first 100 and then 200 μm. In all the experiments the distance between the coaxial capillaries at the junction was set to be 200 μm. All the microbubbles produced in this study were highly monodisperse (polydispersity index <1 %) and it was found, as expected, that bubble formation and size were influenced by the ratio of liquid to gas flow rate, capillary size, and liquid viscosity. The experimental data were then compared with empirical scaling laws derived for rectangular cross-section junctions. In contrast with these previous studies, which have found bubble size to be dependent on either the flow rate ratio (the squeezing regime) or capillary number (the dripping regime), in this experimental study bubble size was found to depend on both capillary number and flow ratio. 相似文献
13.
Elena Castro-Hernández Maarten P. Kok Michel Versluis David Fernandez Rivas 《Microfluidics and nanofluidics》2016,20(2):40
We present a numerical and experimental study on a non-planar three-dimensional design of a microfluidic flow-focusing device for the well-controlled generation of monodisperse micron-sized droplets. Three relevant geometric parameters were identified: the distance between the inner inlet channel and the outlet channel, the width of the outlet channel, and its length. Simulation data extracted from a full parameter study and finite element simulations yielded four optimum designs that were then fabricated using soft lithography techniques. Under the predicted operating conditions, micro-droplets of a size of \({\sim}1\,\upmu \text {m}\) in diameter are obtained from a channel \(50\,\upmu \text {m}\) in width. This work represents an important breakthrough in the practical use of flow-focusing devices delivering a ratio of constriction to droplet size of 50 times, with the advantage of reduced clogging of the micro-channel, greatly improving the control and reliability of the device. 相似文献
14.
The heatable microfluidic chip developed herein successfully integrates a microheater and flow-focusing device to generate uniform-sized gelatin emulsions under various flow rate ratios (sample phase/oil phase, Q s/Q o) and driven voltages. The gelatin emulsions can be applied to encapsulate vitamin C for drug release. Our goal is to create the thermal conditions for thermo-sensitive hydrogel materials in the microfluidic chip and generate continuous and uniform emulsions under any external environment. The gelatin emulsion sizes have a coefficient of variation of <5 % and can be precisely controlled by altering the flow rate ratio (Q s/Q o) and driven voltage. The gelatin emulsion diameters range from 45 to 120 μm. Moreover, various sizes of these gelatin microcapsules containing vitamin C were used for drug release. The developed microfluidic chip has the advantages of a heatable platform in the fluid device, active control over the emulsion diameter, the generation of uniform-sized emulsions, and simplicity. This new approach for gelatin microcapsules will provide many potential applications in drug delivery and pharmaceuticals. 相似文献
15.
Tao Wu Zhaofeng Luo Weiping Ding Zhengdong Cheng Liqun He 《Microfluidics and nanofluidics》2017,21(8):129
We proposed a new flow-focusing technique for generation of monodisperse femtoliter droplets, based on the capillary micro-cross. A funnel-shaped interface of two phase system is observed in a capillary cross for mass production of uniform drops, where a tapered exit orifice is extruded into the dispersed feeding capillary. The droplets, down to 2 μm in size at frequency of 20 kHz, are controllable in size when choosing orifice and capillary sizes, as well as flow rates of inner and outer fluids. For a specific diameter of exit orifice, there is a maximal flow rate of outer fluid, beyond which the interface will be penetrated. Until then, the interface is in steady state and all droplets are highly uniform (<3%), implicating an absolute instability in the whole process. 相似文献
16.
Emulsification in a microfluidic flow-focusing device: effect of the viscosities of the liquids 总被引:2,自引:2,他引:0
Zhihong Nie MinsSeok Seo Shengqing Xu Patrick C. Lewis Michelle Mok Eugenia Kumacheva George M. Whitesides Piotr Garstecki Howard A. Stone 《Microfluidics and nanofluidics》2008,5(5):585-594
We report the results of a comparative study of microfluidic emulsification of liquids with different viscosities. Depending
on the properties of the fluids and their rates of flow, emulsification occurred in the dripping and jetting regimes. We studied
the characteristic features and typical dependence of the size and of the size distribution of droplets in each regime. For
each liquid, we identified a range of hydrodynamic conditions promoting generation of highly monodisperse droplets. Viscosity
played an important role in emulsification: highly viscous liquids were emulsified into larger droplets with lower polydispersity.
Although it was not possible to provide a unified scaling for the volumes of the droplets, our results suggest that the break-up
dynamics of the lower viscosity fluids resembles the rate-of-flow-controlled break-up, as reported earlier for the formation
of bubbles in flow-focusing geometries [Garstecki P, Stone HA, Whitesides GM (2005) Phys Rev Lett 94:164501]. The results
of this study can be helpful for a rationalized selection of liquids for the controlled formation of droplets with a predetermined
size and with a narrow distribution of sizes. 相似文献
17.
Robert Gorkin Salar Soroori William Southard Liviu Clime Teodor Veres Horacio Kido Lawrence Kulinsky Marc Madou 《Microfluidics and nanofluidics》2012,12(1-4):345-354
In traditional centrifugal microfluidic platforms pumping is restricted to outward fluid flow, resulting in potential real estate issues for embedding complex microsystems. To overcome the limitation, researchers utilize hydrophilic channels to force liquids short distances back toward the disk center. However, most polymers used for CD fabrication are natively hydrophobic, and creating hydrophilic conditions requires surface treatments/specialized materials that pose unique challenges to manufacturing and use. This work describes a novel technology that enjoys the advantages of hydrophilic fluidics on a hydrophobic disk device constructed from untreated polycarbonate plastic. The method, termed suction-enhanced siphoning, is based on exploiting the non-linear hydrostatic pressure profile and related pressure drop created along the length of a rotating microchannel. Theoretical analysis as well as experimental validation of the system is provided. In addition, we demonstrate the use of the hydrostatic pressure pump as a new method for priming hydrophobic-based siphon structures. The development of such techniques for hydrophobic fluidics advances the capabilities of the centrifugal microfluidic platform while remaining true to the goal of creating disposable polymer devices using feasible manufacturing schemes. 相似文献
18.
On the thin-film-dominated passing pressure of cancer cell squeezing through a microfluidic CTC chip
Detection of circulating tumor cells (CTCs) shows strong promise for early cancer diagnosis, and cell-deformation-based microfluidic CTC chips have been playing an important role. For the design and optimization of high-throughput CTC chips, the dynamic pressure drop in the microfluidic chip during the CTC passing process is a key parameter related to the device sensitivity and filtering performance and has to be given very serious consideration. Although insights have been provided by previous researches, there is still a lack of understanding of the fundamental physics and complex interplay between viscous tumor cell and the flow inside the microfluidic filtering channel. In this paper, the process of the viscous cell squeezing through a microchannel is modeled by solving the governing equations of microscopic multiphase flows, with the tumor cell modeled by a droplet model and the immiscible cell–blood interface tracked by the volume-of-fluid method. Detailed dynamics regarding the filtering process is discussed, including the cell deformation, flow characteristics, passing pressure characteristics as well as the relationship between the pressure drop across the device and the thin film formed in the filtration channel. Current simulation shows a good agreement with analytic results, and an analytical formula is proposed to predict the passing pressure in the microchannel. Our study provides insights into the fluid physics of a viscous cell passing through a constricted microchannel, and the proposed formula can be readily applied to the design and optimization of cell-deformation-based microchannels for CTC detection. 相似文献
19.
Yutao Lu Taotao Fu Chunying Zhu Youguang Ma Huai Z. Li 《Microfluidics and nanofluidics》2014,16(6):1047-1055
The present work aims at studying the nonlinear breakup mechanism for Taylor bubble formation in a microfluidic flow-focusing device by using a high-speed digital camera. Experiments were carried out in a square microchannel with cross section of 600 × 600 μm. During the nonlinear collapse process, the variation of the minimum radius of bubble neck (r 0) with the remaining time until pinch-off (τ) can be scaled by a power–law relationship: \(r_{0} \propto \tau^{\alpha } .\) Due to the interface rearrangement around the neck, the nonlinear collapse process can be divided into two distinct stages: liquid squeezing collapse stage and free pinch-off stage. In the liquid squeezing collapse stage, the neck collapses under the constriction of the liquid flow and the exponent α approaches to 0.33 with the increase in the liquid flow rate Q l. In the free pinch-off stage, the value of α is close to the theoretical value of 0.50 derived from the Rayleigh–Plesset equation and is independent of Q l. 相似文献
20.
Generating gas/liquid/liquid three-phase microdispersed systems in double T-junctions microfluidic device 总被引:1,自引:0,他引:1
This article describes the generation of microdispersed bubbles and droplets in a double T-junctions microfluidic device to
form immiscible gas/liquid/liquid three-phase flowing systems. Segmented gas plugs are controllably prepared in water at the
first T-junction to form gas/liquid two-phase fluid with the perpendicular flow cutting method. Then using this two-phase
fluid as the cross-shearing fluid for the oil phase at the second T-junction, the gas/liquid/liquid three-phase flowing systems
are prepared. Interestingly, it is found that the break-up of the oil droplets is mainly dominated by the cutting effect of
the gas/liquid interface or the pressure drop across the emerging droplet, but independent with the viscous shearing effect
of the continuous phase, even at the capillary number (Ca = u
wμw/γow) higher than 0.01. The size laws and the distributions of the bubbles and droplets are investigated carefully, and a mathematical
model has been developed to relating the operating conditions with the dispersed sizes. 相似文献