Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E10: Microscale Flows: Emulsions |
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Chair: Sindy Tang, Stanford University Room: 110 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E10.00001: Rearrangement dynamics of concentrated emulsions in a tapered micro-channel Ya Gai, Claudiu Stan, Sindy Tang We describe the flow of a monolayer of monodisperse droplets within a high-volume-fraction emulsion in a tapered micro-channel. The flow of droplets in micro-channels can be non-trivial, and may lead to unexpected phenomena such as long-period oscillations and chaos. Previously, there have been studies on concentrated emulsions in straight channels and channels with bends. The dynamics of how drops flow and rearrange in a tapered geometry has not yet been characterized. At sufficiently slow flow rates, the drops arrange into a hexagonal lattice. At a given x-position, the time-averaged droplet velocity magnitudes are uniform. The instantaneous drop velocities, however, reveal a different pattern. A wave-like pattern is observed from the kymograph of droplet velocities at a fixed x-position in the channel where the number of rows of drops decreases from N to N-1. Such wave-like pattern arises from the collective slipping motion of the drops in the rearrangement zones along the 60 degrees axes, the easy slip directions of a hexagonal lattice. To our knowledge, such reproducible slipping motion has not been reported. Current work is in progress to identify the physical factors that govern such slipping motion. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E10.00002: A simple and low-cost 3d-printed emulsion generator J. M. Zhang, A. A. Aguirre-Pablo, E. Q. Li, S. T. Thoroddsen The technique traditionally utilized to fabricate microfluidic emulsion generators, i.e. soft-lithography, is complex and expensive for producing three-dimensional (3D) structures. Here we apply 3D printing technology to fabricate a simple and low-cost 3D printed microfluidic device for emulsion generation without the need for surface treatment on the channel walls. This 3D-printed emulsion generator has been successfully tested over a range of conditions. We also formulate and demonstrate uniform scaling laws for emulsion droplets generated in different regimes for the first time, by incorporating the dynamic contact angle effects during the drop formation. Magnetically responsive microspheres are also produced with our emulsion templates, demonstrating the potential applications of this 3D emulsion generator in material and chemical engineering. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E10.00003: Continuous Microfluidic Fabrication of Synthetic Asymmetric Vesicles for Membrane Biology Studies Li Lu, Jeffrey Schertzer, Paul Chiarot Membrane vesicles are spherical structures comprised of a single lipid bilayer enclosing an aqueous lumen. In nature, vesicles carry out many important functions in both eukaryotic and prokaryotic organisms. When preparing vesicles artificially, it is difficult to simultaneously control vesicle membrane asymmetry, size, unilamellarity, throughput, and monodispersity. Membrane asymmetry, where each leaflet of the lipid bilayer consists of a different lipid distribution, is of particular importance as it is a feature of nearly all natural membranes. In this study, we report on a novel microfluidic strategy to build monodisperse asymmetric vesicles with customized membrane composition, size, and luminal content at high-throughput. The microfluidic device consists of a triangular post region and two flow-focusing regions. The major steps of the vesicle fabrication process include: (1) assembly of the inner-leaflet, (2) continuous flow separation - replacing the inner-leaflet-lipid with the outer-leaflet-lipid, (3) assembly of the outer-leaflet, and (4) extraction of the intermediate oil layer. Membrane asymmetry and unilamellarity are confirmed using a fluorescence quenching assay and a membrane protein insertion assay, respectively. Our vesicle fabrication method can yield membrane asymmetries as high as 95{\%}, which is maintained at a high-degree for over 30 hours. In addition, over 80{\%} of the vesicles remain stable for at least 6 weeks. The effect of bilayer composition on the mechanical properties of the membrane and the role of small molecules on membrane architecture will be investigated. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E10.00004: Changing Emulsion Dynamics with Heterogeneous Surface Wettability Peichun Amy Tsai, Qiang Meng, Yali Zhang, Jiang Li, Rob Lammertink, Haosheng Chen We elucidate the effect of heterogeneous surface wettability on the morphology and dynamics of microfluidic emulsions, generated by a co-flowing device. We first design a useful methodology of modifying a micro-capillary with desired heterogeneous wettability, such as alternating hydrophilic and hydrophobic regions. Subsequently, the effects of flow rates and heterogeneous wettability on the emulsion morphology and motion in the micro-capillary are investigated. Our experimental data reveal a universal critical time scale of advective emulsions, above which the microfluidic emulsions remain intact, whereas below this time-scale emulsions become adhesive or inverse. A simple model based on a force balance can be used to explain this critical transition. These results show a control of emulsion dynamics by tuning the droplet size and the Capillary number, the ratio of viscous to surface effects, with heterogeneous surface wettability. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E10.00005: A scalable platform for functional emulsions Jie Feng, Janine K. Nunes, Sangwoo Shin, Jing Yan, Yong Lin Kong, Robert K. Prud'homme, Luben N. Arnaudov, Simeon D. Stoyanov, Howard A. Stone Bubble bursting at interfaces plays an important role in a spectrum of physical and biological phenomena, from foam evolution to mass transport across various interfaces. Recently, bubble bursting at an air/oil/water-with-surfactant compound interface was found to disperse submicrometer oil droplets into the water column (Feng et al. \textit{Nature Phys.}, 2014). Inspired by this observation, we propose a new platform to generate functional oil-in-water nanoemulsions. We place functional materials in the appropriate phase, and document that the bubbling system has the capability to produce nanoemulsions encapsulating quantum dots, silica nanoparticles and lipid molecules. In addition, we demonstrate scaling up of the bubbling system and find that the produced nanoemulsions have good stability for days, which offers the flexibility of further treatments and functionalization. Considering the simplicity and energy efficiency of the new bubbling platform, together with the diversity of products and the potential for mass production, our one-step encapsulation system offers a new toolbox for generating (multi-)functional nanoemulsions and nanoparticles. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E10.00006: Fluid entrainment in confined colloid-polymer mixtures Rodrigo Ledesma Aguilar, Siti Aminah Setu, Roel P.A. Dullens, Aurora Hernandez Machado, Ignacio Pagonabarraga, Dirk G.A.L. Aarts We present experimental results of the flow of two-phase colloid polymer mixtures in microfluidic channels. The weak-length scale separation between the contact-line slip length and the thickness of the channels determines the maximum of speed stable moving fronts, which can be controlled by changing the bounding geometry. Channels beyond a velocity-dependent maximum thickness trigger the formation drop-emitting jets controlled by thermal fluctuations. A hydrodynamic model, supported by numerical simulations, reveals that the fluid dynamics is dominated by viscous and capillary forces at length-scales comparable to a slip-region near the contact line. Our findings show that length-scale overlap can be used as a new fluid-control mechanism in strongly confined systems. [Preview Abstract] |
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