Packings of monodisperse emulsions in flat microfluidic channels

Claussen, Ohle; Herminghaus, Stephan; Brinkmann, Martin

doi:10.1103/physreve.85.061403

Cited by 8 publications

(7 citation statements)

References 30 publications

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“…As they flowed, the drops arranged into a hexagonally packed crystal (Fig. 1A) (23). Due to the tapered channel geometry, the emulsion experienced gradual, elastic compression in the transverse direction as it moved along the channel, except at specific locations where the number of rows of drops N (counted at 60°relative to the x axis across the width of the channel) decreased by one (Fig.…”

Section: Resultsmentioning

confidence: 99%

Spatiotemporal periodicity of dislocation dynamics in a two-dimensional microfluidic crystal flowing in a tapered channel

Gai

Leong

Cai

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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When a many-body system is driven away from equilibrium, order can spontaneously emerge in places where disorder might be expected. Here we report an unexpected order in the flow of a concentrated emulsion in a tapered microfluidic channel. The velocity profiles of individual drops in the emulsion show periodic patterns in both space and time. Such periodic patterns appear surprising from both a fluid and a solid mechanics point of view. In particular, when the emulsion is considered as a soft crystal under extrusion, a disordered scenario might be expected based on the stochastic nature of dislocation dynamics in microscopic crystals. However, an orchestrated sequence of dislocation nucleation and migration is observed to give rise to a highly ordered deformation mode. This discovery suggests that nanocrystals can be made to deform more controllably than previously thought. It can also lead to novel flow control and mixing strategies in droplet microfluidics.many-body system | order | microfluidic crystal | dislocation dynamics | plasticity T he emergence of order and spontaneous self-organization have been of long-standing interest (1). They are key not only to the understanding of complex phenomena from chemical oscillators to swarming behavior in animals (2, 3), but also to novel engineering solutions if harnessed (4, 5). Two-phase flow in microfluidics offers a simple platform for the study of dissipative nonequilibrium systems, where hydrodynamic interactions have led to the emergence of collective dynamics and order (6-10). Most works thus far have focused on dilute emulsions or foams in simple channel geometries. Whereas rich physics has been revealed, these phenomena have yet to find implications in the broader technological context. Nevertheless, concentrated emulsions, bubble rafts, and colloids have long been used as models of crystals for studying grain boundaries, dislocations, plasticity, and other processes central to materials science and solid mechanics (11-16). Such systems have not been applied to model the deformation modes of nanocrystals, however. Recent work on crystal plasticity in microscopic samples found that in contrast to their macroscopic counterparts, both the external geometry and internal structure of the material determine material strength (17). Furthermore, the size and timing of dislocation-induced strain bursts are found to be intermittent, stochastic, and unpredictable (17-20). The stochastic nature of dislocation dynamics complicates the control of the shape of the materials during deformation, and renders their subsequent manipulation and manufacturing challenging (18). What is unknown, however, is whether plasticity remains stochastic as the sample shrinks to the nanoscale, and whether the dimensionality and loading conditions influence the stochasticity. Given the increasing importance of low-dimensional nanodevices in applications from optoelectronics to energy conversion, it is critical to understand how nanomaterials can be shaped, manipulated, and manufactured.In t...

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Section: Resultsmentioning

confidence: 99%

Spatiotemporal periodicity of dislocation dynamics in a two-dimensional microfluidic crystal flowing in a tapered channel

Gai

Leong

Cai

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…6, we analytically computed the dimensionless elastic force f ¼ F e /s from the interfacial energy of the considered droplet packing as function of the droplet confinement A/W 2 and the area fraction u. The calculated elastic force f(u) is plotted as solid lines in Fig.…”

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confidence: 99%

“…Based on these rules, we analytically constructed the three relevant droplet packing and determined the perimeter ' d of the droplet contour, the area A enclosed by it, and the corresponding area fraction u. 6 This allowed us to compute the interfacial energy E d ¼ s effective line tension of the two dimensional droplet contour in a flat Hele-Shaw geometry. 6,8 The elastic force F e of the droplet packing can be obtained as the derivative of the interfacial energy E ¼ NE d of a train of N droplets with respect to the length L of the droplet train for fixed A…”

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confidence: 99%

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Mechanical stability of ordered droplet packings in microfluidic channels

Fleury

Claussen

Herminghaus

et al. 2011

Applied Physics Letters

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The mechanical response and stability of one and two-row packing of monodisperse emulsion droplets are studied in quasi 2d microchannels under longitudinal compression. Depending on the choice of parameter, a considered droplet arrangement is either transformed continuously into another packing under longitudinal compression or becomes mechanically unstable and segregates into domains of higher and lower packing fraction. Our experimental results are compared to analytical calculations for 2d-droplet arrangements with good quantitative agreement. This study also predicts important consequences for the stability of droplet arrangements in flowing systems.

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“…The reservoir with a wide 2D space was replaced with parallelized microfluidic channels to produce droplet arrays. Droplets formed a hexagonal array without grain boundaries in each channel as the width of the channel was much smaller than crystal domain size. , This enabled patterning on two distinct scales and shapes: the line pattern was a few hundreds of micrometers in scale, whereas the hexagonal dot pattern was a few tens of micrometers in scale. This structure was demonstrated by generating droplets with diameters of 44 μm in the drop makers.…”

Section: Resultsmentioning

confidence: 99%

Ordered Packing of Emulsion Droplets toward the Preparation of Adjustable Photomasks

et al. 2014

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Monodisperse emulsion droplets with a high volume fraction form crystalline phases that can potentially serve as adjustable photomasks in photolithography. Such photomasks were prepared using a microfluidic device in which a flow-focusing junction, side channels, and a reservoir were connected in series. Transparent oil droplets were generated in a dye-containing continuous water phase at the flow-focusing junction. The droplets were then concentrated through the selective removal of the continuous phase using the side channels. This process led to the formation of a regular array of droplets in the reservoir with a configuration that depended on the relative height of the reservoir to the droplet diameter. The configurations could be selected among a single-layered hexagonal array, a bilayered square array, and a bilayered hexagonal array. The droplet arrays were used as a photomask to create hexagonal or square arrays of microdots. The transmittance profile of the ultraviolet (UV) light from each droplet was parabolic, which enabled the dot size to be tuned by controlling the UV irradiation time. This mask effect is otherwise difficult to achieve using conventional photomasks. The dot size and array periodicity could be adjusted by the in-situ control of the droplet size at the flow-focusing droplet maker. The combination of droplet size adjustments and the UV irradiation time provided independent control over the dot size and array periodicity to enable the preparation of a series of hexagonal microarrays with a wide spectrum of array parameters using a single microfluidic device.

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Packings of monodisperse emulsions in flat microfluidic channels

Cited by 8 publications

References 30 publications

Spatiotemporal periodicity of dislocation dynamics in a two-dimensional microfluidic crystal flowing in a tapered channel

Spatiotemporal periodicity of dislocation dynamics in a two-dimensional microfluidic crystal flowing in a tapered channel

Mechanical stability of ordered droplet packings in microfluidic channels

Ordered Packing of Emulsion Droplets toward the Preparation of Adjustable Photomasks

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