Dispersed Flux Research Articles

High-Throughput Microfluidic Production of Droplets and Hydrogel Microspheres through Monolithically Integrated Microchannel Plates.

In this paper, we present a highly effective microfluidic emulsion system using an integrated microchannel plate (MCP), a porous glass membrane that is readily available and densely packs millions of through-microchannels, for high-throughput production of monodisperse droplets. The physical controls of droplet formation, including viscosity, flow rate, and pore size, have been extensively explored for optimum emulsification conditions. The performance of the device has been validated where monodisperse droplets with a narrow coefficient of variance (<5%) can be achieved at a dispersed phase flux of 3 mL h-1 from a piece of 4 × 4 mm2 MCP. The average droplet size is two times the nominal membrane pore diameter and thus can be easily controlled by choosing the appropriate membrane type. The preparation of hydrogel microspheres has also been demonstrated with a high throughput of 1.5 × 106 particles min-1. These microspheres with a uniform size range and rough surface morphology provide suitable bioenvironments and serve as ideal carriers for cell culture. Mouse fibroblasts are shown to be cultured on these 3D scaffolds with an average cell viability of over 96%. The cell attachment rate can reach up to 112 ± 7% in 24 h and the proliferation ability increases with the number of culture days. Furthermore, the device has been applied in the droplet digital polymerase chain reaction for absolute quantification of lung cancer-related PLAU genes. The detection limit achieved was noted to be 0.5 copies/μL with a dynamic range of 105 ranging from 1 × 102 to 1 × 106 copies/μL. Given the easy fabrication, robust performance, and simple operation, the emulsion system sets the stage for the laboratory's droplet-based assays and applications in tissue engineering.

Effect of parameters on ME process by near-field electrospun PTFE membrane

BackgroundMembrane emulsification (ME) is an attractive membrane process to produce various kind of simple or multiple emulsions. The membrane utilized in ME process should have high dispersed phase flux, narrow pore size distribution and excellent antifouling property. MethodsThis work proposed a novel near-field electrospun (NFES) poly(tetrafluoroethylene) (PTFE) membranes with ordered rectangular pore geometry. Compared with other membranes, the order pore geometry of NFES PTFE membrane was helpful to obtain a more homogeneous and more stable water-in-oil (W/O) emulsion. Significant findingsThe droplet size was simply controlled by the NFES PTFE membrane pore size. And NFES PTFE membrane was more conducive to the formation of droplets with narrow droplet size distribution because of its unique straight rectangular membrane pore geometry. In addition, W/O emulsion droplet size be regulated in coordination with operating parameters and phase parameters. Results indicated that a smaller rectangular pore area of PTFE membrane would lead to a smaller droplet size. Introducing of shear stress in the continuous phase was contributed to the generation of monodisperse droplets. When the emulsifier (Span 80) content was 1wt%, the smallest droplet size (∼103.6 nm) was obtained.

A novel membrane emulsification technique for microencapsulation in self-healing concrete: development and proof of concept

Membrane emulsification is a promising new technique that can be deployed as a scalable modular conduit for the consistent and continuous production of single and complex emulsions. This work reports on the development of a manufacturing platform based on membrane emulsification for the first time for microcapsule-based self-healing cementitious materials. The feasibility of single and double emulsion production with wall formation as a secondary step through UV radical polymerisation was explored using a discrete membrane emulsification dispersion cell. The operational parameters (pressure, dispersed phase flux, temperature, shear rate) were established for the specific phase characteristics (viscosity, density, interfacial tension) to achieve control of emulsion droplets and maintain a high encapsulation of core content (high payload). Microcapsules with sodium silicate core and an average diameter of ∼130 μm were produced. Microcapsules were shown to achieve high payload (∼89%). Moreover their thermal stability was characterised and their release performance in the cementitious matrix established. The results demonstrated the capability of membrane emulsification to produce microcapsules with an aqueous core for use in self-healing of cementitious materials.

Encapsulation of resveratrol using Maillard conjugates and membrane emulsification

Resveratrol is a stilbene phenolic associated with health-promoting properties such as antioxidant, anti-inflammatory and chemoprevention. Due to its chemical instability and low water solubility, microencapsulation represents a good alternative to provide better results when employing resveratrol as a nutraceutical ingredient. The main purpose of our work was to use low shear membrane emulsification to produce resveratrol-loaded emulsions of low polydispersity and integrate this process to spray drying to produce a powdered product. Resveratrol was dispersed with palm oil in a continuous phase obtained via Maillard reaction. We evaluated the influence of process conditions and phases composition on emulsions properties and performed the characterization of the spray-dried powder. Emulsions droplet size and span decreased as shear stress was increased. Higher dispersed phase fluxes provided increased droplet size polydispersity. Process conditions were set on 60.0 Pa shear stress and 70 L m-2h−1 of dispersed phase flux, obtaining emulsions with mean diameter around 30 μm and span of 0.76. Despite this relatively high droplet size of the infeed emulsions, the spray drying process resulted in particles with high encapsulation efficiency (97.97 ± 0.01%), and water content (~3.6%) and diameter (~10.2 μm) similar to particles obtained from fine emulsions in previously reported works.

The role of dispersed ash in orbital-scale time-series studies of explosive arc volcanism: insights from IODP Hole U1437B, Northwest Pacific Ocean

ABSTRACTTephra fallout beds in marine sediments provide chronologically precise and highly resolved records of volcanism at time scales relevant to Quaternary climate cycles. While the record of discrete (visible) thin tephra beds is readily accessible, the significance of the dispersed (invisible) tephra record remains unclear. Here we evaluate the role of dispersed tephra for orbital-scale volcanic time variations in the Quaternary (<1.2 Ma) carbonate mud of IODP Hole U1437B (Northwest Pacific). The carbonate mud contains cyclic series of discrete fallout tephra beds from the oceanic Izu Bonin (~85% of tephra beds) and the continental Japan (~15%) volcanic arcs, respectively. Our results show the inorganic aluminosilicate (lithogenic) fraction is a mixture of dispersed Izu Bonin and Japan ash, and Asian dust. The time distribution of the Izu Bonin ash with its distinct composition appears to confirm and enhance the cyclic time variation of the discrete ash beds at Hole U1437B. Dispersed Japan ash resembles Asian dust in trace elements and is only distinguishable in Sr-Nd isotope space. Collectively, our results confirm the existence of periodic, orbital-scale fluctuations of arc volcanic frequency. Orbital-scale time variations of marine ash may be best established by series of discrete marine ash beds, yet the concomitant dispersed ash flux must also be recorded in order to understand the total flux of arc volcanic ash into the ocean basins and thus the role of the volcanism-climate link.

Sustainable Production of Drug-Loaded Particles by Membrane Emulsification

As the field of drug delivery is expanding into consumer products, it is essential to advance in the development of efficient synthesis technologies while preserving, at the same time, human health and the environment for future generations. Here, the sustainable development of polymeric particles for drug delivery is described. Poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) based particles containing dexamethasone were produced by membrane emulsification-solvent diffusion methods. The ability of the synthesis process to control particle-size distribution and morphology and its green impactful (energy consumption, simple (sEF) and complete (cEF) E factor) were evaluated. Particles with sufficiently narrow distribution in their droplet size and mean diameter similar to the membrane pore diameter were produced by increasing the dispersed phase flux to 12.84 L h–1 m–2, minimizing the maximum shear stress to 1.12 Pa and the energy consumption to 3.96 × 105 J m–3. The impact of the solvent...

Microparticles for cell encapsulation and colonic delivery produced by membrane emulsification

Membrane Emulsification was used to encapsulate yeast cells and form microparticles. W/O emulsions were produced using a Dispersion Cell; the aqueous phase consisted of gelatin/chitosan, or pure gelatin solution, containing yeast cells, the continuous phase was 2wt% of SPAN 80 in kerosene. Varying the dispersed phase flux (from 70 to 350Lh-m-2) and the shear stress (from 17 to 1Pa) applied on the membrane surface droplet sizes of between 60 and 340µm were produced, with a coefficient of variation of 17% under the best operating conditions. The liquid drops were loaded with increasing amount of yeast (3.14×107 to 3.14×108 cells/mL). The stability and uniformity of the emulsions was independent of the cell concentration. PTFE coated hydrophobic membrane produced smaller W/O drops compared to FAS coated membranes. The liquid polymeric droplets were solidified in solid particles using thermal gelation and/or ionic crosslinking, obtaining yeast encapsulated particles sized ~100µm. The pH sensitive polymer, Eudragit S100, was used as a coating to create gastro resistant particles suitable for intestinal-colonic targeted release. Viability of the released yeast cells was demonstrated using fluorescence probes and checking cell glucose metabolism with time.

Energy-saving potential of cross-flow membrane emulsification by ceramic tube membrane with inserted cross-section reducers

In this work, oil-in-water emulsions (O/W) were prepared successfully by membrane emulsification with 0.5 μm pore size membrane. Sunflower oil was emulsified in aqueous Tween80 solution with a simple crossflow apparatus equipped with ceramic tube membrane. In order to increase the shear-stress near the membrane wall, a helical-shaped reducer was installed within the lumen side of the tube membrane. This method allows the reduction of continuous phase flow and the increase of dispersed phase flux, for cost effective production. Results were compared with the conventional cross-flow membrane emulsification method. Monodisperse O/W emulsions were obtained using tubular membrane with droplet size in the range 3.3-4.6 μm corresponded to the membrane pore diameter of 0.5 μm. The final aim of this study is to obtain O/W emulsions by simple membrane emulsification method without reducer and compare the results obtained by membrane equipped with helix shaped reducer. To indicate the results statistical methods, 3p type full factorial experimental designs were evaluated, using software called STATISTICA. For prediction of the flux, droplet size and PDI a mathematical model was set up which can describe well the dependent variables in the studied range, namely the run of the flux and the mean droplet diameter and the effects of operating parameters. The results suggested that polynomial model is adequate for representation of selected responses.

Microchannel emulsification study on formulation and stability characterization of monodisperse oil-in-water emulsions encapsulating quercetin

The study used microchannel emulsification (MCE) to encapsulate quercetin in food grade oil-in-water (O/W) emulsions. A silicon microchannel plate (Model WMS 1-2) comprised of 10,300 discrete 10×104μm microslots was connected to a circular microhole with an inner diameter of 10μm. 1% (w/w) Tween 20 was used as optimized emulsifier in Milli-Q water, while 0.4mgml−1 quercetin in different oils served as a dispersed phase. The MCE was carried by injecting the dispersed phase at 2mlh−1. Successful emulsification was conducted below the critical dispersed phase flux, with a Sauter mean diameter of 29μm and relative span factor below 0.25. The O/W emulsions remained stable in terms of droplet coalescence at 4 and 25°C for 30days. The encapsulation efficiency of quercetin in the O/W emulsions was 80% at 4°C and 70% at 25°C during the evaluated storage period.

MAVEN observations of energy‐time dispersed electron signatures in Martian crustal magnetic fields

AbstractEnergy‐time dispersed electron signatures are observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission in the vicinity of strong Martian crustal magnetic fields. Analysis of pitch angle distributions indicates that these dispersed electrons are typically trapped on closed field lines formed above strong crustal magnetic sources. Most of the dispersed electron signatures are characterized by peak energies decreasing with time rather than increasing peak energies. These properties can be explained by impulsive and local injection of hot electrons into closed field lines and subsequent dispersion by magnetic drift of the trapped electrons. In addition, the dispersed flux enhancements are often bursty and sometimes exhibit clear periodicity, suggesting that the injection and trapping processes are intrinsically time dependent and dynamic. These MAVEN observations demonstrate that common physical processes can operate in both global intrinsic magnetospheres and local crustal magnetic fields.

Chitosan and Poly (Vinyl Alcohol) microparticles produced by membrane emulsification for encapsulation and pH controlled release

The Dispersion Cell membrane emulsification technique was used for the production of w/o emulsions with controlled droplet size and narrow size distribution. The influence of the operating parameters of the process was investigated. Varying the dispersed phase flux (10–1250Lh−1m−2) and the shear stress (2–59Pa), droplets between 30 and 280μm were produced with CV’s as low as 18%. Nickel and stainless steel membranes were used for the membrane emulsification. Pore geometry influenced the droplet size as well as uniformity and a normally hydrophilic stainless steel membrane with sharp pore openings produced more uniform and smaller drops compared to a PTFE coated hydrophobic nickel membrane with a conical pore surface. For the dispersed phase 15wt.% PVA or 1–3wt.% chitosan as well as their blends in water were used. Surfactants PGPR and ABIL EM90 were tested to determine their capability to form stable emulsions in Miglyol 840. PGPR could not be used to stabilize the emulsion with chitosan as the dispersed phase, probably due to the chemical interference between the carboxyl group present in the PGPR and chitosan. Solid microparticles were obtained by chemical crosslinking with glutaraldehyde (GA) at different concentrations (1–50vol.%). Particles crosslinked using less than 10vol.% GA were able to swell and release encapsulated compounds. Acid sensitive particles were produced by blending the PVA and chitosan. Up to 80% of Cu2+ and 20% of sodium salicylate was released from the particles under acidic conditions. No significant release was determined under neutral conditions.

Effect of Process Variables on the Production of Flaxseed Oil Emulsions by Cross-Flow Membrane Emulsification

The aim of this work was to study the effect of process variables on the production of flaxseed oil emulsions by cross-flow membrane emulsification. The process was carried out using an ultrafiltration α-alumina membrane with mean pore size of 0.2 µm, and Tween 20 was used as surfactant. The effect of transmembrane pressure (1.5–4.5 bar), cross-flow velocity (3–8 m/s) and surfactant concentration (1–3 %) on the dispersed phase flux, emulsion stability and droplet size distribution and uniformity was evaluated according to a 23 central composite experimental design. Results showed that all the emulsions presented unimodal droplets distribution, and the average droplet diameter was 1.50 μm. Among all the variables studied, only transmembrane pressure had significant influence on the dispersed phase flux—the increase in transmembrane pressure resulted in higher dispersed phase flux. The other variables did not affect any of the analyzed responses within the studied ranges.

Processing effects during rotating membrane emulsification

In this study, a rotating membrane emulsification setup incorporating a 6.1μm pore diameter SPG membrane was used to produce O/W emulsions of average droplet sizes between 23.4 and 216.6μm. All emulsions consisted of 10vol% of sunflower oil or silicone oil stabilised by 1wt% Tween 20. The transmembrane pressure (0.1–1.8bar), rotational speeds (100–2000RPM) annular gap width (5–45mm), dispersed and continuous phase viscosity were all investigated as to their effect on emulsion droplet size and dispersed phase flux. Modification of the dispersed phase flow properties alters the droplet size with four regions being suggested; a decrease in size (as droplet coalescence is minimised), a plateau (size-stable zone), a gradual increase in size (due to transfer of mass via droplet neck) and then a rapid increase (due to jetting). The importance of Taylor vortices development was seen with larger droplets formed in their absence; typically at low rotational speeds, narrow vessel diameters and more viscous continuous phases. It was concluded that the flow behaviour of each phase requires careful consideration to understand the likely formation mechanism(s) during operation. Across the pressure and viscosity ranges investigated, the dispersed phase flux ranged between 50 and 12,500Lm−2h−1 and pore activity was within the range of 0.5–2.7%.

Membranes with tailored wettability properties for the generation of uniform emulsion droplets with high efficiency

Membrane emulsification is a promising technology for the production of micro–nano particles, which is able to compete with the conventional mechanical emulsification processes. The production of emulsions with narrow droplet size distribution at dispersed phase fluxes (productivity) sufficiently high to make the process suitable for industrial application is still a considerable challenge. The interfacial tension between the dispersed phase and the membrane pore wall is a crucial parameter to maintain droplets shape while enhancing productivity. In the present paper, a membrane thickness with asymmetric properties in terms of wettability between external and internal sides has been tested in the preparation of W/O emulsions. The membrane surface wettability modification was obtained by adsorption of hydrophobic macromolecules on the lumen side of hydrophilic membrane. Lipase was used as a model macromolecule. W/O emulsion droplets with smaller droplets size have been produced with lipase-loaded membrane compared with the unmodified hydrophilic membrane. High dispersed phase flux of 30Lh−1m−2 was also obtained with a significant increase of process productivity compared to the use of hydrophobic membranes. These results show that membrane–protein interaction can be used to functionalize opportunely the membrane for membrane emulsification application reducing emulsification time and increasing dispersed phase flux without modifying the control on droplets properties in terms of size and size distribution.

Numerical Analysis on Two-phase Flow Characteristics at Convection Microfluidic Y-junctions

Numerical simulation on two-phase flow characteristics at convection microfluidic Y-junctions based on the two-phase flow interface tracking method. It is found that the Y-angle of the microfluidic Y-junctions, capillary number of continuous phase, and the flux of two phases have a great influence on droplet generation time, rate and size. The decreasing of continuous phase capillary number and Y-angle results in the increasing of the droplet volume. At the same time, with the increasing of flux ratio of the dispersed phase and continuous phase, the influence on the droplet volume is becoming smaller. But the flow flux ratio cannot infinite increase or decrease. Because the dispersed phase can only takes the form of liquid column or silk and it unable to generate the droplet when the ratio is greater than 0.5 or no more than 0.05. When the dispersed phase flux is increasing, the corresponding droplet formation rate is almost proportional increasing; the influence of the dispersed phase flow on the length of the droplets evolution is greater than the continuous phase. In addition, in the formation process of droplet, the filling time becomes longer and the necking time becomes shorter with the increasing of the Y-angle. The droplet detachment mechanism is mainly under the effect of normal stress of the continuous phase.

Polymeric microspheres preparation by membrane emulsification-phase separation induced process

Uniform Polyethersulfone (PES) microspheres of target size in the range of 30–60µm were successfully prepared by combining membrane emulsification technology and phase separation induced process in one step. An emulsion is generated by injecting the polymeric solution through a microporous membrane into the continuous phase which allows also the phase separation induced process and precipitation of the polymer (coagulation bath). Therefore, the droplets formation and solidification occur in a single step. Furthermore, the preparation of non-aqueous (O/O) emulsions by membrane emulsification as well as the preparation of polymeric microspheres by non-solvent induced phase separation has never been reported previously. The effect of continuous phase-coagulation bath composition, hydrophobic emulsifier, dispersed phase flux and shear stress on size and uniformity of PES microspheres has been investigated. Key factors in microspheres production by membrane emulsification and phase separation induced process mechanism include the solvent/non-solvent system type, non-solvent composition and O/O interface composition. Polymeric microspheres with spherical morphology have been produced by tailoring such key factors.

Intensification of production of O/W emulsions using oscillatory woven metal micro-screen (WMMS)

Using high porosity woven metal micro-screen (WMMS), a novel design oscillatory emulsifier had been used for intensification of production of relatively narrow size distribution oil in water (O/W) emulsions. The average droplet size increased with increasing the dispersed phase flow and decreased with increasing both the oscillation frequency and amplitude. The emulsion polydispersity decreased with increasing both oscillation intensities as well as dispersed phase flux. Although the change in droplet size with oscillation was reasonably predicted using a simple torque balance model based on Stokes oscillatory flow, both the flow patterns and the surface phenomena are more complex, and the final droplet size is affected by interactions between different operating and physical parameters.

Neutral and ionised gas around the post-red supergiant IRC +10 420 at AU size scales

IRC +10420 is one of the few known massive stars in rapid transition from the Red Supergiant phase to the Wolf-Rayet or Luminous Blue Variable phase. The star has an ionised wind and using the Br gamma hydrogen recombination emission we assess the mass-loss on spatial scales of order 1 au. We present new VLT Interferometer AMBER data which are combined with all other AMBER data in the literature. The final dataset covers a position angle range of 180 degrees and baselines up to 110 meters. The spectrally dispersed visibilities, differential phases and line flux are conjointly analyzed and modelled. We also present AMBER/FINITO observations which cover a larger wavelength range and allow us to observe the Na I doublet at 2.2 micron. The data are complemented by X-Shooter data, which provide a higher spectral resolution view. The Brackett gamma line and the Na I doublet are both spatially resolved. After correcting the AMBER data for the fact that the lines are not spectrally resolved, we find that Br gamma traces a ring with a diameter of 4.18 milli-arcseconds. We consider a geometric model in which the Br gamma emission emerges from the top and bottom rings of an hour-glass shaped structure, viewed almost pole-on. It provides satisfactory fits to most visibilities and differential phases. The fact that we detect line emission from a neutral metal like Na I within the ionized region, a very unusual occurrence, suggests the presence of a dense pseudo-photosphere. The ionized wind can be reproduced with a polar wind, which could well have the shape of an hour-glass. The resolved Na I emission is found to occur on scales barely larger than the continuum. This fact and that many Yellow Hypergiants exhibit this comparatively rare emission hints at the presence of a "Yellow" or even "White Wall" in the Hertzsprung-Russell diagram, preventing them from visibly evolving to the blue.

Stirred tank membrane emulsification using flat metallic membranes: A dimensional analysis

The performance of a membrane emulsification unit, using flat membranes in a stirred tank, has been examined by dimensional analysis. The dimensionless numbers were defined in terms of shear and membrane pore size. Dimensionless droplet size prediction models based on simple force balances were used to select the most representative dimensionless numbers including operating parameters. Oil-in-water emulsions were produced with tailor-made metallic membranes with pore sizes of 30 and 50μm. Results showed that monodisperse emulsions were produced with span values around 0.5, significantly lower than when a rotor-stator homogenizer is used. The influence of the selected operating parameters (impeller rotational speed, continuous phase viscosity and dispersed phase flux) on droplet size distribution was studied and experimental results were compared with droplet size prediction models. Impeller rotational speed and membrane pore size were the key parameters influencing emulsion droplet size and monodispersity. A correlation based on the Euler dimensionless number, including all the operating parameters is proposed.

Stirred cell membrane emulsification for multiple emulsions containing unrefined pumpkin seed oil with uniform droplet size

Stirred cell membrane emulsification was used to create double water-in-oil-in-water emulsions at the dispersed phase flux of up to 3200 L m −2 h −1. The oil phase was unrefined pumpkin seed oil or sunflower oil containing 30% by volume of internal water phase and the external water phase was 2% Tween 20 (polyoxyethylene sorbitan monolaurate) or 2% Pluronic F-68 (polyoxyethylene-polyoxypropylen copolymer). Using microengineered nickel membranes with pore sizes between 15 and 40 μm, median drop sizes of double emulsion droplets were in the range between 100 and 430 μm, depending mainly on the shear at the membrane surface and dispersed phase injection rate. In most cases the drops were very uniform, with span (i.e. 90% drop size minus 10% drop size divided by median size) values of around 0.5. This data is similar to what was obtained previously for simple O/W emulsions of the same materials. Hence, the internal water phase, and internal surfactant, 5% PGPR (polyglycerol polyricinoleate), did not adversely influence the emulsification process. A marker material, copper sulfate, was added to the internal water phase and the release of copper was monitored with respect to time. For both lipid systems, at the larger droplet size, there was a significant period of no copper release, followed by almost linear release with time. This initial period was absent when the drop size was close to 100 μm. The initial entrapment efficiency of the copper, in all experiments, was higher than 94%.