Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A36: Microscale Flows: Assembly and Fabrication |
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Chair: Boris Stoeber, University of British Columbia Room: 618 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A36.00001: Colloidal particle dynamics during band assembly Andrew Yee, Minami Yoda Evanescent-wave visualizations have shown that colloidal polystyrene particles in a dilute (volume fractions $< 4 \times 10^{-3}$) suspension assemble into structures called ``bands'' that only exist near the walls in combined Poiseuille and electroosmotic ``counterflow'' through silica and polydimethylsiloxane-silica microchannels. These bands have cross-sectional dimensions of a few $\mu$m and a length comparable to that of the channel of a few cm. Two-color experiments, where $\sim$1\% of the $a \approx$ 250~nm particles are tracers labeled with a different fluorophore, are used to investigate particle dynamics over time for a range of flow conditions. In the initial accumulation stage, the near-wall particle concentration increases sharply, and continues to increase after the first band is observed, before decreasing to a roughly constant value with a stable number of ``steady-state'' bands. Although the particles appear to be in a liquid state within these structures, they do not follow the flow, even before the bands form, and have negligible cross-stream motion. The velocities of near-wall particles within the steady-state bands are found to be much less than those between the bands. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A36.00002: Solvent-phase electrodeposition of highly concentrated, vertically aligned carbon nanotubes for scalable fabrication of carbon-nanotube membranes Richard Castellano, Eric Meshot, Francesco Fornasiero, Robert Praino, Jerry Shan Membranes incorporating vertically aligned carbon nanotubes (VA-CNTs) as through-pores have been shown to transport fluids at rates orders-of-magnitude faster than predicted by theory, offering promise as highly permeable membranes for applications as diverse as protective yet breathable garments, and desalination membranes$^{\mathrm{1}}$. There is a need for cost-effective and scalable methods for fabricating VA-CNT membranes. Here, we describe a solution-based fabrication technique for VA-CNT membranes using electric-field alignment and electrophoretic concentration of CNTs initially dispersed in a solvent$^{\mathrm{2}}$. The quality of electrodeposition is described in terms of the resulting CNT number density. Multiple rounds of solvent-phase CNT alignment and deposition are performed, before the solvent is finally replaced with a UV-curable prepolymer, all while an electric field is applied to preserve CNT alignment. The liquid prepolymer is cured to form membranes, which are shown to have open CNT pores with flow enhancement. We compare the solution-fabricated VA-CNT membranes to those fabricated by other, less-scalable means, and discuss the implications for large-scale production of such membranes. \begin{enumerate} \item N. Bui, \textit{et al.}, Adv. Mat. (2016) \item R. J. Castellano, \textit{et al.}, J. Applied Physics. (2015) \end{enumerate} . [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A36.00003: Multiphase modeling of precipitation-induced membrane formation Patrick Eastham, Nick Moore, Nick Cogan, Qingpu Wang, Oliver Steinbock We have formulated a model for the dynamic growth of a membrane developing in a flow as the result of a precipitation reaction, a situation inspired by recent microfluidic experiments. A key challenge is that the location of the immobile membrane is unknown \emph{a priori}. To model this situation,we use a multiphase framework with fluid and membrane phases; the aqueous chemicals exist as scalar fields that react within the fluid to induce phase change. Analysis demonstrates no-slip behavior on the developing membrane without \emph{a priori} assumptions on its location, with additional numerical simulation in 2D microfluidic geometries. The model has applications towards precipitate reactions where the precipitate greatly affects the surrounding flow, a situation appearing in many laboratory and geophysical contexts. More generally, this model can be used to address fluid-structure interaction problems that feature the dynamic generation of structures. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A36.00004: Dynamic elastocapillarity of hairy tubes Jonghyun Ha, Kaiying Jiang, Sameh Tawfick Elastocapillarity, which is the capillary-driven deformation of slender materials, can be mundanely observed in our daily lives, such as painting, washing the hair, wet grass or leaves. Here, we introduce a novel elastocapillary phenomenon in hairs assembled into ring-shaped cross sections thus forming “hairy-tubes” composed of an empty hole surrounded by a hairy wall. The heterogeneous hairy tubes have two distinct spacing length scales: the narrow spacing among the individual hairs and the large inner diameter of the tube which is a few millimeters. The hairy tubes are immersed in a liquid bath, and once they pierce the liquid interface, the fibers self-assemble due to the capillary action. In particular, we observe that the drainage dynamics between the fibers play an important role in the deformation trend, which has two distinct modes. The fibers locally coalesce in the low drainage rate forming tubes having smaller inner and outer diameters than the dry counterparts with denser fiber packing within the walls, while they completely collapse into round bundles and eliminate the internal diameter at the high drainage rate. Based on the physics of elastocapillarity, we theoretically and experimentally explain the shape shifting induced by surface tension, depending on the structure size and the drainage speed. This study provides the model system of capillary induced self-assembly of heterogeneous hairy structures, which have far more applications, such as micro/nanoscale manufacturing and soft actuators. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A36.00005: Electric field driven aggregation of negatively and positively polarized particles in dilute suspensions Boris Khusid, Qian Lei, Ezinwa Elele We will present data on the electric field driven particle aggregation in dilute suspensions of nearly neutrally-buoyant negatively and positively polarized particles. Following the application of a sufficiently strong high-frequency AC field to both suspensions, particles aggregated head-to-tail into chains that bridged the gap between two electrodes. Once a weak DC field was added, negatively polarized particles formed a cellular pattern, in which large-scale particle-free domains were enclosed by particle-rich thin walls. The appearance of such patterns in suspensions of negatively polarized particles in a strong AC field was observed by Kumar, Khusid, Acrivos, PRL95, 2005 and Agarwal, Yethiraj, PRL102, 2009. However, formation of cellular structures is not predicted by current theories for the field induced particle aggregation in polarized suspensions. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A36.00006: Fabrication of water-in-water colloidosomes from aqueous two-phase systems using droplet microfluidics Wei Guo, Yage Zhang, Shipei Zhu, Anderson H. C. Shum We describe the fabrication of stable and monodispersed colloidosomes derived from water-in-water microdroplets using an integrated high-throughput microfluidic system. Liquid-liquid phase separation of aqueous two-phase systems (ATPS) inside the microdroplets is used as the driving force to form the semipermeable shell of colloidosomes. Droplets of water-in-oil are firstly generated in a microfluidic flow-focusing device, where aqueous dextran solutions with the addition of negative-charged nanoparticles are used as dispersed phase. Then we use a pico-injector to introduce another component, aqueous polyethylene glycol (PEG) solutions with the addition of positive-charged polyelectrolytes, into the microdroplets. Phase separation inside the pico-injected droplets happens due to the non-equilibrium osmotic pressure between the two components, triggering the formation of crosslinked shells by complex coacervation. Our confocal images and stiffness test show that these shells have stable morphology and robust structures. Finally, we use a microfluidic sorting module to transfer those droplets containing crosslinked shells from oil phase to aqueous PEG phase, allowing the fabrication of water-in-water colloidosomes in a high-throughput way. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A36.00007: Self-assembling complex and functional structures at the (sub)millimeter scale Vandewalle Nicolas, Ylona Collard, Galien Grosjean When soft ferromagnetic particles are suspended at air-water interfaces in the presence of a vertical magnetic field, dipole-dipole repulsion competes with capillary attraction such that structures self-assemble. The complex arrangements of such floating bodies are emphasized. By adding a horizontal and oscillating magnetic field, periodic deformations of the assembly are induced. We show herein that collective particle motions induce locomotion at low Reynolds number. The physical mechanisms and geometrical ingredients behind this cooperative locomotion are identified. These physical mechanisms can be exploited to much smaller scales, offering the possibility to create artificial and versatile microscopic swimmers. Moreover, we show that it is possible to generate complex structures that are able to capture particles, perform cargo transport, fluid mixing, etc... [Preview Abstract] |
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