T-junction Microfluidic Device Research Articles

Extraction-Derived Self-Organization of Colloidal Photonic Crystal Particles within Confining Aqueous Droplets

In this work, we developed a novel and simple microfluidic method for the fabrication of self-assembled monodispersed photonic crystal microbeads with core–shell structures using solvent extraction. Monodispersed aqueous droplets encapsulating colloidal photonic crystal particles were produced in a T-junction microfluidic device, and the controlled transport of water from the aqueous droplets to the oil phase created spherical colloidal crystal microbeads with controlled shell–core structures by extraction-derived self-organization of the colloidal nanoparticles. While the solidification of colloidal particles from emulsion droplets in an oven took tens of hours, the present extraction-derived method reduces the time required for solidification to several minutes. Compared with recent microwave-assisted consolidation methods which showed a particle material dependency, our new method exhibited no such limitation. The results showed that the packing quality of colloidal crystals, which can be precisely controlled by adjusting the extraction rate and surfactant, was high enough to show photonic band-gap characteristics. The reflectance of our photonic microbeads responded precisely to any change in physical properties including the size of colloidal particles and refractive index. A mechanism of the extraction-derived self-assembly of colloidal particles was developed and then supposed by theoretical derivations and experimental results. Finally, the universality of the method was demonstrated by fabricating SiO2 photonic crystal microbeads.

Fabrication of Polyacrylonitrile Microcapsules for ICF Targets

Polyacrylonitrile (PAN) microcapsules for inertial confinement fusion targets were fabricated. First, density-matched double emulsions were generated with a double T-junction microfluidic device. Second, the solvents in the middle phase of the double emulsions were driven off with a rotary evaporator. The radii of the obtained PAN microcapsules with smooth surfaces were in the region of 50 to 500 μm, with shell thickness from 30 to 300 μm. Influences of solvents, flow speeds, and solidification conditions on the microcapsules were studied.

Tunable spatial heterogeneity in structure and composition within aqueous microfluidic droplets

In this paper, we demonstrate biphasic microfluidic droplets with broadly tunable internal structures, from simple near-equilibrium drop-in-drop morphologies to complex yet uniform non-equilibrium steady-state structures. The droplets contain an aqueous mixture of poly(ethylene glycol) (PEG) and dextran and are dispensed into an immiscible oil in a microfluidic T-junction device. Above a certain well-defined threshold droplet speed, the inner dextran-rich phase is "stirred" within the outer PEG-rich phase. The stirred polymer mixture is observed to exhibit a near continuum of speed and composition-dependent phase morphologies. There is increasing interest in the use of such aqueous two-phase systems in microfluidic devices for biomolecular applications in a variety of contexts. Our work presents a method to go beyond equilibrium phase morphologies in generating microfluidic "multiple" emulsions and at the same time raises the possibility of biochemical experimentation in benign yet complex biomimetic milieus.

A novel hybrid system for the fabrication of a fibrous mesh with micro-inclusions

A novel hybrid system combining microfluidic and co-axial electrospinning techniques has been used to generate different types of fibre structures with varied desirable inclusions using food grade polymers, ethyl cellulose and sodium alginate. The processing conditions in the microfluidic T-junction device, i.e. gas pressure and liquid flow rate were adjusted in order to generate near-monodisperse microbubbles which subsequently serve as a platform for particle generation. These particles exhibit micro-scale diameters and different shapes and some bubbles were incorporated into the fibrous mesh prepared by concurrent electrospinning. The fibre/particle structures obtained with different polymers via this novel method could potentially have many applications in various engineering and biological sectors.

Experimental study of microbubble coalescence in a T-junction microfluidic device

This study presents the microbubble coalescence process in a confined microchannel. Triple T-junction microfluidic devices with different main channel size were designed to generate monodispersed microbubble pairs with air/n-butyl alcohol–glycerol solution as the working system. The head-on collision of microbubble pair was realized in the microfluidic devices. Three collision results including absolute coalescence, probabilistic coalescence, and non-coalescence were distinguished. The effects of liquid viscosities and two-phase superficial velocities on the coalescence behavior were determined. The results showed that microbubble coalescence process in the confined space was slightly faster than in the free space. Increasing liquid viscosity apparently prevents coalescence. In the probabilistic coalescence region, higher two-phase superficial velocity could reduce the percentage of coalescence events. Two characteristic parameters representing the bubble contact time and film drainage time have been introduced to analyze the microbubble coalescence behaviors and a linear correlation could clearly distinguish the coalescence and non-coalescence region.

Calcium Alginate Foams Prepared by a Microfluidic T-Junction System: Stability and Food Applications

Highly porous alginate foams were prepared via a novel route in which highly viscous alginate solutions were bubbled using a microfluidic T-junction device. The relationship between bubble size and bubbling conditions such as air pressure and solution flow rate was studied, and the ability of the T-junction setup to generate monodisperse microbubbles (mean diameter, ∼154 μm) and produce porous foams was systematically investigated. The foams were characterised by optical and scanning electron microscopy. Foams of varying lengths (12–45 mm) were successfully prepared using this technique, with an average density of ∼235 kg/m3. The pore diameter within the foams was determined by microscopy to be in the range of 600 nm–200 μm with a mean diameter of ∼31 μm. It was concluded that porosity in the foam (>90%) can be varied depending on the initial bubble size. Thus, a possible production method of stable highly porous solid foams for exploitation in food and bioprocess technologies is presented by which products can be made to different sizes.

The effects of hydrophilic surfactant concentration and flow ratio on dynamic wetting in a T-junction microfluidic device

An initial study was conducted on the influence of the hydrophilic surfactant concentration and two-phase flow-rate ratio on the aqueous-phase wetting ability (dynamic contact angle) in a T-junction PMMA microfluidic device. Cetyltrimethyl ammonium bromide (CTAB) was used as the hydrophilic surfactant for the deionized water aqueous phase while the organic phase was corn oil. Static contact angles and interfacial tensions were measured for systems with surfactant concentrations ranging from 0% to 5.0 × 10 −1% (w/w). Static contacts angles for an oil drop on PMMA in water show a transition from <90° to >90° at CTAB concentrations near 1.0 × 10 −2% (w/w), suggesting a change in the surface energy and a transition from a slightly hydrophobic to hydrophilic PMMA surface for the given systems. Microchannel flow experiments were conducted to study dynamic wetting character, and special attention was paid to the CTAB concentration range between 3.0 × 10 −3% (w/w) and 3.0 × 10 −2% (w/w) to focus on the region in which a wetting transition was observed in the static case. Dynamic contact angles and wetting responded more to changes in the aqueous phase flow rate than to changes in the organic (continuous) phase flow rate, and receding contact angles (plug tails) changed from >90° to <90° at a W:O flow ratio near unity. Different dynamic wetting patterns were produced at different CTAB surfactant concentrations because of the dynamic adsorption of hydrophilic surfactant at the channel wall interface. At concentrations below the critical micelle concentration, CTAB can be used to dynamically alter the surface energy of a PMMA microchannel and change its wetting state allowing for the production of both O/W and W/O type flows. The wetting state (i.e. the extent to which each phase wets the channel wall) is crucial for numerous lab on a chip applications.

Microfluidic Mass‐Transfer Control for the Simple Formation of Complex Multiple Emulsions

Transforming emulsions: A straightforward method for turning a single emulsion into multiple emulsions in a common T-junction microfluidic device has been achieved. Water is introduced into oil using a cosolvent; a single emulsion then forms at a T junction, which is followed by the autocatalytic formation of a multiple emulsion by cosolvent shifting into the continuous phase.

Screening of Biomineralization Using Microfluidics

Biomineralization is the process where biological systems produce well-defined composite structures such as shell, teeth, and bones. Currently, there is substantial momentum to investigate the processes implicated in biomineralization and to unravel the complex roles of proteins in the control of polymorph switching. An understanding of these processes may have wide-ranging significance in health care applications and in the development of advanced materials. We have demonstrated a microfluidic approach toward these challenges. A reversibly sealed T-junction microfluidic device was fabricated to investigate the influence of extrapallial (EP) fluid proteins in polymorph control of crystal formation in mollusk shells. A range of conditions were investigated on chip, allowing fast screening of various combinations of ion, pH, and protein concentrations. The dynamic formation of crystals was monitored on chip and combined with in situ Raman to reveal the polymorph in real time. To this end, we have demonstrated the unique advantages of this integrated approach in understanding the processes involved in biomineralization and revealing information that is impossible to obtain using traditional methods.

Gas–liquid flow in T-junction microfluidic devices with a new perpendicular rupturing flow route

In this paper a series of perpendicular rupturing flow routes with differing angles ranging from 30° to 150° between the entrance channels were used to control the gas–liquid phase dispersed flow in T-junction microfluidic devices. Uniform gas bubble plugs were produced in consistent, two-phase flows within the channels of the microfluidic devices. Both the gas–liquid flow and the size of the gas bubbles, which ranged from 800 to 3100 μm in length, depended on several influential factors including the flow rates, the physical properties of the liquid phase, and the angle between entrance channels. Considering these factors and the equilibrium between the shear force and interfacial tension within the microfluidic channels, an equation was derived in the form of L / w = 1/2( Q G / Q L sin θ + 2/5 cot θ ) 1/2 Ca −1/5 relating the angle between the entrance channels of the two phases to the gas bubble plug length within the microfluidic device. The relationship allows for the prediction of gas bubble plug length in T-junction microfluidic devices employing intersection angles ranging from 30° to 150° and is thus potentially useful for the controllable preparation of monodisperse gas bubbles.

Correlations of droplet formation in T-junction microfluidic devices: from squeezing to dripping

In this work, we have systematically analyzed the scaling law of droplet formation by cross-flow shear method in T-junction microfluidic devices. The droplet formation mechanisms can be distinguished by the capillary number for the continuous phase (Cac), which are the squeezing regime (Cac < 0.002), dripping regime (0.01 < Cac < 0.3), and the transient regime (0.002 < Cac< 0.01). Three corresponding correlations have been suggested in the different range of Cac. In the dripping regime, we developed a modified capillary number for the continuous phase (Cac′) by considering the influence of growing droplet size on the continuous phase flow rate. And the modified model could predict droplet diameter more accurately. In the squeezing regime, the final plug length was contributed by the growth and ‘squeeze’ stages based on the observation of dynamic break-up process. In the transient regime, we firstly suggested a mathematical model by considering the influences of the above two mechanisms. The correlations should be very useful for the application of controlling droplet size in T-junction microfluidic devices.

Controllable Preparation of Monodisperse O/W and W/O Emulsions in the Same Microfluidic Device

This letter presents a simple way to prepare monodisperse O/W and W/O emulsions in the same T-junction microfluidic device just by changing the wetting properties of the microchannel wall with different surfactants. Highly uniform droplets ranging from 50 to 400 mum with a polydispersity index (sigma) value of less than 2% were successfully prepared. With the change in surfactants and surfactant concentrations, the interfacial tension and the wetting properties varied, and disordered or ordered two-phase flow patterns could be controllable. Monodisperse O/W and W/O emulsions were prepared under the action of a cross-flowing shear force or a perpendicular shear force by using an oil solution with 0.1-2.0 wt % Span 80 and an aqueous solution with 0.1-2.0 wt % Tween 20 as a continuous-phase flow, respectively. It gives a controllable method of preparing O/W and W/O emulsions in the same microfluidic device.

Controllable gas-liquid phase flow patterns and monodisperse microbubbles in a microfluidic T-junction device

This letter describes the gas-liquid phase flow patterns and the mechanism of generation of monodisperse microbubbles in a T-junction microfluidic device using the crossflowing shear-rupturing technique. The bubble size is ranged from 100 to 500μm. The air phase states as isolate air slugs, “pearl necklaces,” periodic isolate bubbles, zig-zag bubble patterns, and multiple-bubble layer can be observed in the wider measured channel. The bubble size relates with the continuous phase flow velocity and viscosity as Vb∝1∕(μcuc), while being almost independent of surface tension γ and air phase flow rate Qg, for the conditions used in this work. The bubble formation mechanism by using the crossflowing shear-rupturing technique is different from the hydrodynamic flow focusing and both geometry-dominated breakup techniques. Our system provides independent control of both the size and volume fraction of dispersed bubbles.