100 research outputs found
Forced generation of simple and double emulsions in all-aqueous system
We report an easy-to-implement method that allows the direct generation of
water-in-water (w/w) single emulsions. The method relies on direct perturbation
of the pressure that drives the flow of the dispersed phase of the emulsions.
The resultant inner jet is induced to break up into droplets due to the growth
of the perturbation through Rayleigh-Plateau instability [L. Rayleigh, Proc. R.
Soc. London 29, 71-97 (1879)]; this leads to the formation of monodisperse
droplets. By implementing this method on a modified microfluidic device, we
directly generate water-in-water-in-water (w/w/w) double emulsions with good
control over the size and the number of encapsulated droplets. Our approach
suggests a new route to apply droplet-based microfluidics to completely
water-based systems
Fluctuation-induced dynamics of multiphase liquid jets with ultra-low interfacial tension
Control of fluid dynamics at the micrometer scale is essential to emulsion
science and materials design, which is ubiquitous in everyday life and is
frequently encountered in industrial applications. Most studies on multiphase
flow focus on oil-water systems with substantial interfacial tension. Advances
in microfluidics have enabled the study of multiphase flow with more complex
dynamics. Here, we show that the evolution of the interface in a jet surrounded
by a co-flowing continuous phase with an ultra-low interfacial tension presents
new opportunities to the control of flow morphologies. The introduction of a
harmonic perturbation to the dispersed phase leads to the formation of
interfaces with unique shapes. The periodic structures can be tuned by
controlling the fluid flow rates and the input perturbation; this demonstrates
the importance of the inertial effects in flow control at ultra-low interfacial
tension. Our work provides new insights into microfluidic flows at ultra-low
interfacial tension and their potential applications
Mechanical compression to characterize the robustness of liquid marbles
In this work, we have devised a new approach to measure the critical pressure that a liquid marble can withstand. A liquid marble is gradually squeezed under a mechanical compression applied by two parallel plates. It ruptures at a sufficiently large applied pressure. Combining the force measurement and the high-speed imaging, we can determine the critical pressure that ruptures the liquid marble. This critical pressure, which reflects the mechanical robustness of liquid marbles, depends on the type and size of the stabilizing particles as well as the chemical nature of the liquid droplet. By investigating the surface of the liquid marble, we attribute its rupture under the critical pressure to the low surface coverage of particles when highly stretched. Moreover, the applied pressure can be reflected by the inner Laplace pressure of the liquid marble considering the squeezing test is a quasi-static process. By analyzing the Laplace pressure upon rupture of the liquid marble, we predict the dependence of the critical pressure on the size of the liquid marble, which agrees well with experimental results
Coalescence of electrically charged liquid marbles
© The Royal Society of Chemistry. In this work, we investigated the coalescence of liquid water marbles driven by a DC electric field. We have found that two contacting liquid marbles can be forced to coalesce when they are charged by a sufficiently high voltage. The threshold voltage leading to the electro-coalescence sensitively depends on the stabilizing particles as well as the surface tension of the aqueous phase. By evaluating the electric stress and surface tension effect, we attribute such coalescence to the formation of a connecting bridge driven by the electric stress. This liquid bridge subsequently grows and leads to the merging of the marbles. Our interpretation is confirmed by the scaling relation between the electric stress and the restoring capillary pressure. In addition, multiple marbles in a chain can be driven to coalesce by a sufficiently high threshold voltage that increases linearly with the number of the marbles. We have further proposed a simple model to predict the relationship between the threshold voltage and the number of liquid marbles, which agrees well with the experimental results. The concept of electro-coalescence of liquid marbles can be potentially useful in their use as containers for chemical and biomedical reactions involving multiple reagents
Corrugated interfaces in multiphase core-annular flow
Microfluidic devices can be used to produce highly controlled and
monodisperse double or multiple emulsions. The presence of inner drops inside a
jet of the middle phase introduces deformations in the jet, which leads to
breakup into monodisperse double emulsions. However, the ability to generate
double emulsions can be compromised when the interfacial tension between the
middle and outer phases is low, leading to flow with high capillary and Weber
numbers. In this case, the interface between the fluids is initially deformed
by the inner drops but the jet does not break into drops. Instead, the jet
becomes highly corrugated, which prevents formation of controlled double
emulsions. We show using numerical calculations that the corrugations are
caused by the inner drops perturbing the interface and the perturbations are
then advected by the flow into complex shapes
Controlled actuation of liquid marbles on a dielectric
Motivated by the great potential of droplet microreactors for chemical and biological applications, a general and robust method utilizing an electric field is developed for sustained, directional and two-dimensional manipulation of nonwetting droplets (termed “liquid marbles”). With the understanding of the mechanism of actuation, this method allows individual liquid marbles to be actuated and coalesced on demand by fine-tuning the driving voltage. Moreover, in our system, cross-contamination between marbles during manipulation is avoided as confirmed by the absence of any trace DNA after amplification using a loop-mediated isothermal amplification reaction
Corrugated interfaces in multiphase core-annular flow
International audienceMicrofluidic devices can be used to produce highly controlled and monodisperse double or multiple emulsions. The presence of inner drops inside a jet of the middle phase introduces deformations in the jet, which leads to breakup into monodisperse double emulsions. However, the ability to generate double emulsions can be compromised when the interfacial tension between the middle and outer phases is low, leading to flow with high capillary and Weber numbers. In this case, the interface between the fluids is initially deformed by the inner drops but the jet does not break into drops. Instead, the jet becomes highly corrugated, which prevents formation of controlled double emulsions. We show using numerical calculations that the corrugations are caused by the inner drops perturbing the interface and the perturbations are then advected by the flow into complex shapes
Electrocoalescence of liquid marbles driven by embedded electrodes for triggering bioreactions
Liquid marbles need to be controlled precisely to benefit applications, for instance, as microreactors on digital microfluidic platforms for chemical and biological assays. In this work, a strategy is introduced to coalesce liquid marbles via electrostatics, where two liquid marbles in contact can coalesce when a sufficiently high voltage is applied to embedded electrodes. With the understanding of the mechanism of coalescence through relating the electric stress and the restoring capillary pressure at the contact interface, this method coalesces liquid marbles efficiently. When compared with the existing electrocoalescence method, our approach does not require immersion of electrodes to trigger coalescence. We demonstrate this to exchange the medium for the culture of cell spheroids and to measure the cell metabolic activity through a CCK-8 assay. The manipulation of liquid marbles driven by electrostatics creates new opportunities to conduct chemical reactions and biomedical assays in these novel microreactors
Fabrication of monodisperse poly(dl- lactic acid) microparticles using drop microfluidics
Monodisperse poly(dl-lactic acid) particles with a diameter between 11 and 121 μm were fabricated by drop microfluidics/solvent evaporation method using flow focusing glass capillary device. In the dripping regime, the ratio of droplet diameter to orifice diameter was in the range of 0.37−1.34 and was inversely proportional to the 0.39 power of the ratio of the continuous phase flow rate to dispersed phase flow rate
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