Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M07: Microscale Flows: Emulsions |
Hide Abstracts |
Chair: Myeongsub Kim, Florida Atlantic University Room: Georgia World Congress Center B212 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M07.00001: Microscopic Rearrangements in the Flow of Highly Polydisperse Dense Emulsions Yonglun Jiang, Eric R Weeks We study the flow of dense polydisperse quasi-two-dimensional emulsions. In particular, we are interested in highly polydisperse samples with the largest droplets as much as ten times the size of the smallest. The droplets are confined between two parallel glass plates so that the system is quasi-2D and driven by a syringe pump. We use video microscopy to examine local rearrangements as the sample flows and we study how rearrangements differ for large and small droplets. In particular, we find the large droplets generally follow the mean flow, while the small droplets have significant nonaffine motions and move more erratically. We quantify these results using nearest neighbor changes as well as D2min (Falk & Langer, PRE 1998). |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M07.00002: Flow of a highly-concentrated emulsion through a narrow constriction Alexander Zinchenko, Robert Davis Multipole-accelerated boundary-integral algorithm is developed to study creeping flow of an emulsion of many (N>100) deformable 3D drops with high volume fraction (80-90%) though a microchannel with tight constriction. The simulation setup is designed to resemble the experiments [1]; the channel depth and throat width are comparable to the drop non-deformed size and are an order of magnitude smaller than the entrance width, so that the emulsion flow away from the throat is rearranged into a single file motion in the constriction. Periodic inlet/outlet boundaries with prescribed pressure drop are used to formulate boundary-integral equations based on the 1-periodic Green function. Multipole acceleration tools [2] allow for necessary ultra-high resolution on the drop surfaces and channel walls to study the statistics of drop rearrangement/breakup at the constriction, critical breakup conditions and the dependence of flow rate on the capillary number and channel geometry. [1] L. Rosenfeld et. al. Break-up of droplets in a concentrated emulsion flowing through a narrow constriction. Soft Matter, 2014, 10, 421-430. [2] A.Z. Zinchenko & R.H. Davis. Emulsion flow through a packed bed with multiple drop breakup. J. Fluid Mech., 2013, 725, 611-663. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M07.00003: Oil-Free Passive Generation of Aqueous Two-Phase System Micro Droplets Mohammad Mastiani, Seokju Seo, Babak Mosavati, Myeongsub Kim The high efficacy of aqueous two-phase system (ATPS) droplets has been proven in a wide variety of biological and medical applications over the last decade due to its excellent biocompatibility. However, due to ultra-low interfacial tension, droplet generation in ATPS is extremely difficult when compared with the conventional water-in-oil (W/O) system. Consequently, without involvement of any external means, current manufacturing methods are either unable to produce droplets or limited to generate them in an extremely narrow range of flow conditions. In this work, we passively produced ATPS droplets with a wide range of droplet size at high generation frequency without employing an oil phase or external forces. We successfully generated ATPS droplets with a radius as small as 7 μm at the maximum frequency up to 300 Hz, which has not been achieved in previous studies. We found that the droplet size is correlated to the pressure and flow rate ratios with the power-law exponents of 0.8 and 0.2, respectively. In addition, this study is the first to report the information of flow rate and Capillary (Ca) number. It was found that the range of Ca in ATPS is 0.3–1.7, as compared to less than 0.1 in the W/O system, indicating the nature of ultra-low interfacial tension in ATPS. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M07.00004: Synthesizing Pickering Nanoemulsions via condensation on oils Hassan Bararnia, Dongjin Kang, Sushant Anand In this work a novel method is presented to synthesize Pickering emulsions. Unlike the typical two-step techniques which are widely being used to make emulsions herein we propose a single process which leads to small size (Micro-Nano) water droplets dispersion in oil phase possessing hydrophobic silica nanoparticles . The predominant advantage stems from the heterogenous nucleation of water vapor nuclei on the sub-cooled oil-air interface associated with spontaneously submergence within the oil. The positive spreading coefficient of oil prevents droplet growth induced by vapor diffusion via cloaking, while irreversible particle adsorption suppresses the merging event occurring between the adjacent droplets. We discuss how particles properties such as hydrophobicity, size, concentration as well as condensation time affect the emulsion size. The competition between particle adsorption rate, condensation rate can be finely adjusted using above-mentioned parameters to obtain stable nano-emulsions at even low nanoparticle loadings. We discuss the energetics of emulsion formation by condensation, and show the vapor-condensation process can be easily scaled to produce larger quantities of emulsions in energy-efficient manner. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M07.00005: Nano Ping Pong Ball Kwangseok Park, Hyoungsoo Kim Micro-and nanocapsules are widely utilized in various industries such as pesticides, cosmetics, medicines, and foods to protect and deliver internal substances as effective carriers. Typically, polymers are used to make the shell of capsules, which is fabricated by using complicated demands, e.g. temperature control, pH control, and chemical processes. In this study, we show a fabrication method for a self-encapsulated nanoshell carrier without the skilled expertise or the high-priced technical equipment. A water droplet containing high concentration of salt in an oil phase. As the water diffuses into the oil, the salt concentration at the water-oil interface increases and the salt crystal grows in time. Eventually, a completely encapsulated shell structure is created. Using this one-step method, we produced nanocapsules with several hundred nanometers in size. In this talk, we show how the perfect shell structure in nanometer-sized using the crystallization process which has no grain boundary. We expect that this method will bring about remarkable cost saving and process simplification in the nanocapsule production technology. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M07.00006: Abstract Withdrawn
|
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M07.00007: Probing the interfacial rheology of complex emulsions using microfluidic droplet deformation dynamics Shweta Narayan, Davis B Moravec, Brad G. Hauser, Andrew J. Dallas, Cari Dutcher Chemically stabilized emulsions can often be difficult to separate, since diffusion of surfactant molecules from the bulk and their subsequent adsorption at the liquid-liquid interface reduces the interfacial tension between the two phases, leading to increased emulsion stability. Additionally, surfactant molecules can render the interface viscoelastic, posing a challenge for coalescence of droplets. Here we present a microfluidic platform for investigating the fundamental physical properties affecting coalescence of surfactant-stabilized liquid-liquid interfaces. In previous work, a dynamic microfluidic tensiometer was used to measure the time-dependent interfacial tension from deformation of droplets traveling through a contraction geometry. To further investigate the interfacial rheology of surfactant-stabilized emulsions, a microfluidic platform is used to perturb droplet shape. The shape relaxation dynamics can be correlated with interfacial moduli on length and time scales relevant to emulsion separation applications. The results of this work will be used to infer properties of complex emulsions which can impact the coalescence behavior of micron-scale droplets and the subsequent separation of these emulsions. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M07.00008: Strategic obstacle placement reduces drop breakup probability in emulsion flow Jian Wei Khor, Alison Dana Bick, Ya Gai, Sindy Tang Droplet microfluidics has enabled a wide range of high throughput applications such as digital polymerase chain reaction (dPCR) and antibiotic screening. However, few studies have attempted to increase the throughput of the drop interrogation process. Here we investigate the effect of an obstacle on the throughput of drops flowing as a 2D monolayer concentrated emulsion flowing in a linearly converging channel into a constriction, a common geometry for drop content interrogation. Drop-drop interactions near the constriction entrance can lead to breakup of these drops at high flow rates, setting an upper limit for drop interrogation throughput. Previously, strategic placement of a circular post near a narrow exit can reduce conflict between interactions among living organisms or particles. Inspired by such works, we placed a circular post near the constriction entrance in order to reduce catastrophic drop-drop interactions that lead to drop breakup. Notably, when placed at appropriate location, the obstacle reduced the drop breakup fraction by up to 90%, thereby enabling a 12-fold increase in drop interrogation rate. Strategic obstacle placement is therefore an attractive strategy for increasing droplet microfluidic application throughput. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M07.00009: Timescale and Spatial Distribution of Local Plastic Events in a Two-Dimensional Microfluidic Crystal Ya Gai, Alison Dana Bick, Sindy K.Y. Tang When a microfluidic crystal consisting of a concentrated emulsion flows in a convergent channel, the boundary conditions enforce a sequence of droplet rearrangements (T1 events). At low flow rates, these T1 events are periodic in space and time, giving rise to a surprisingly ordered flow pattern. At high flow rates, this order was lost. To understand the transition from order to disorder, we examined the timescale and spatial distribution of T1 events during the flow of a monolayer of monodisperse droplets within a concentrated emulsion confined in a convergent tapered microchannel. We show that the duration of a single T1 event consists of three distinct regimes, with two transitions upon an increase in applied strain rate. The first transition involves a change in the dynamics of the thin film formed between the emulsion drops, the second transition entails the emulsion transitioning from a solid to liquid-like state. Our results are used to understand the relationship between macroscopic properties and microscopic flow structures of the emulsion, as well as guiding the design of flow control elements in microfluidic devices. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700