Modelling double emulsion formation in planar flow-focusing microchannels

Wang, Ningning; Semprebon, Ciro; Liu, Haihu; Zhang, Chuhua; Kusumaatmaja, Halim

doi:10.1017/jfm.2020.299

Cited by 61 publications

(51 citation statements)

References 85 publications

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“…3 , two examples for slightly different values of Re and Ca are shown. Note incidentally that, in agreement with previous studies 39 , 40 , 42 , 44 , 52 , 53 , 63 , as long as , the internal core, unlike the interface of the external shell, is only mildly affected by the fluid flow. This is due to its higher surface tension induced by the smaller curvature radius, which prevents relevant shape deformations.…”

Section: Resultssupporting

confidence: 91%

“…Continuum theories, combined with suitable numerical approaches (such as lattice Boltzmann methods 39 – 41 and boundary integral method 38 ) have proven capable to capture characteristic features observed in double emulsion experiments, such as their production within microchannels 40 , the typical shape deformations of the capsule (elliptical and bullet-like) under moderate shear flows 42 – 44 , as well as more complex dynamic behaviors, such as the breakup of the enveloping shell occurring under intense fluid flows 45 . However, much less is known about the dynamics of more sophisticated systems, such as multiple emulsions with distinct inner cores, theoretically investigated only by a few authors to date 38 , 39 .…”

Section: Introductionmentioning

confidence: 99%

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The vortex-driven dynamics of droplets within droplets

et al. 2021

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Understanding the fluid-structure interaction is crucial for an optimal design and manufacturing of soft mesoscale materials. Multi-core emulsions are a class of soft fluids assembled from cluster configurations of deformable oil-water double droplets (cores), often employed as building-blocks for the realisation of devices of interest in bio-technology, such as drug-delivery, tissue engineering and regenerative medicine. Here, we study the physics of multi-core emulsions flowing in microfluidic channels and report numerical evidence of a surprisingly rich variety of driven non-equilibrium states (NES), whose formation is caused by a dipolar fluid vortex triggered by the sheared structure of the flow carrier within the microchannel. The observed dynamic regimes range from long-lived NES at low core-area fraction, characterised by a planetary-like motion of the internal drops, to short-lived ones at high core-area fraction, in which a pre-chaotic motion results from multi-body collisions of inner drops, as combined with self-consistent hydrodynamic interactions. The onset of pre-chaotic behavior is marked by transitions of the cores from one vortex to another, a process that we interpret as manifestations of the system to maximize its entropy by filling voids, as they arise dynamically within the capsule.

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

The vortex-driven dynamics of droplets within droplets

et al. 2021

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“…In this paper, we focus on coated microdroplets which consist of an inner droplet encapsulated by a liquid coating. Trains of coated droplets are typically produced with two successive droplet generation devices (Hennequin et al 2009), which can provide a vast range of dynamics (Anna 2016;Wang et al 2020). The coated droplets may be cured into micro-capsules if the coating phase can be polymerised into an elastic membrane, or combine reagents for chemical reactions (Utada et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Self-assembly of coated microdroplets at the sudden expansion of a microchannel

Schirrmann

Cáceres-Aravena

Juel

2021

Microfluid Nanofluid

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We report observations of the self-assembly of coated droplets into regular clusters at the sudden expansion of a microfluidic channel. A double emulsion consisting of a regular train of coated microdroplets was created upstream of the channel expansion, so that the inter-drop distance, droplet length, velocity and coating thickness could be varied by imposing different inlet pressures, albeit not independently. Provided that the enlarged channel remains sufficiently confined to prohibit propagation in double file, droplets can assemble sequentially into regular linear clusters at the expansion. Droplets join a cluster via the coalescence of their coating film with that of the group ahead. This coalescence occurs when the droplets approach each other to within a critical distance at the expansion, enabled by hydrodynamic interactions within the train. Clusters comprising a finite number of droplets are obtained because reconfiguration of the droplet assembly during coalescence increases the distance to the following droplet. Decreasing the inter-drop distance increases the cluster size up to a maximum value beyond which continuous clusters form. Formalising these observations in a simple model reveals that clusters of any size are possible but that they occur for increasingly narrow ranges of parameter values. Our experimental observations suggests that background experimental fluctuations limit the maximum discrete cluster size in practice. This method of self-assembly offers a robust alternative to flow focusing for encapsulating multiple cores in a single coating film and the potential to build more complex colloidal building blocks by de-confining the clusters.

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“…From a theoretical standpoint, such physics can be almost exclusively investigated by means of numerical simulations built on specific computational models, due to the complicated structure of the equations governing the multiscale dynamics, typically ranging from the size of the interface to that of the microfluidic device [21]. In contrast with the enormous progress achieved in the manufacturing of multiple emulsion [1,3,5,[22][23][24][25], theoretical studies about their red dynamic response under shear have been carried on only more recently (especially for double emulsions [26][27][28][29]) and have very partially covered the physics of concentrated phase emulsions [30][31][32].…”

Section: Introductionmentioning

confidence: 99%

“…When two distinct inner cores are included, an external shear flow can cause the formation of a fluid recirculation which triggers a periodic planetary-like motion of the cores, lasting over long periods of time within the external droplet [34]. Such features have been captured, with a good level of accuracy, by means of a careful combination of continuum models and numerical simulations, such as buondary integral methods [27] and lattice Boltzmann approaches [29,34]. Yet, much less is known about the dynamics of a multiple emulsion under shear when the numer of inner cores augments and their concentration is far from the diluted regime.…”

Section: Introductionmentioning

confidence: 99%

Concentrated phase emulsion with multicore morphology under shear: A numerical study

et al. 2020

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We numerically study the dynamic behavior under a symmetric shear flow of selected examples of concentrated phase emulsions with multi-core morphology confined within a microfluidic channel. A variety of new nonequilibrium steady states is reported. Under low shear rates, the emulsion is found to exhibit a solid-like behavior, in which cores display a periodic planetary-like motion with approximately equal angular velocity. At higher shear rates two steady states emerge, one in which all inner cores align along the flow and become essentially motionless and a further one in which some cores accumulate near the outer interface and produce a dynamical elliptical-shaped ring chain, reminiscent of a treadmilling-like structure, while others occupy the center of the emulsion. A quantitative description in terms of i) motion of the cores, ii) rate of deformation of the emulsion and iii) structure of the fluid flow within the channel is also provided.

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Modelling double emulsion formation in planar flow-focusing microchannels

Cited by 61 publications

References 85 publications

The vortex-driven dynamics of droplets within droplets

The vortex-driven dynamics of droplets within droplets

Self-assembly of coated microdroplets at the sudden expansion of a microchannel

Concentrated phase emulsion with multicore morphology under shear: A numerical study

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