Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session M26: Surface Tension Effects: Interfacial Phenomena II |
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Chair: Dinesh Bhagavatula, University of Florida Room: North 226 ABC |
Monday, November 22, 2021 1:10PM - 1:23PM |
M26.00001: Cell mortality associated with acute hydrodynamic stressors from capillary pinch-off Oliver McRae, James C Bird From bubbles bursting in bioreactors to droplets flung off rupturing fluid films, rapidly rearranging fluid interfaces have the potential to generate immense hydrodynamic stressors in the nearby fluid. Biological cells near these interfaces—e.g. bacteria in respiratory droplets—must navigate this stressful environment in order to survive. Past studies have shown that elevated hydrodynamic stressors over longer periods of time can negatively impact cell viability. However, the impact that short timescale hydrodynamic stressors have on cell viability is not well understood. Here we quantify, using numerical simulations, spatiotemporal hydrodynamic stressors for a range of biologically inspired fluid flows. We also experimentally measure the viability of mammalian cells near to bubbles undergoing a short timescale rearrangement. Our results show that short timescale hydrodynamic stressors can predictably lower the viability of biological cells. Furthermore, the above result combined with the stressors from simulations, suggest a hydrodynamical selectivity on the droplet-based transport of certain microorganisms. We anticipate our study to catalyze more refined modelling of the relationship between stressor magnitude and duration, and microorganism viability and proliferation. |
Monday, November 22, 2021 1:23PM - 1:36PM |
M26.00002: Beating surface tension: oxide-skin mediated formation of liquid metal suspensions and emulsions Najam Ul Hassan H Shah, Wilson Kong, Shreyas Kanetkar, Nathan Casey, Robert Y Wang, Konrad Rykaczewski Room temperature gallium-based liquid metals have surface tension that is about ten times higher than that of water. As a result, the direct mixing of a secondary gas, liquid, or solid phase into the liquid metals is challenging. This presentation will discuss how the few nanometer thin gallium oxide skin that forms rapidly upon exposure to trace amounts of oxygen provides a general path for incorporation of any secondary phase into the liquid metal. Using in-situ imaging in an electron microscope, we show that during shear mixing patches of the oxide stick to even highly "liquid-metal-phobic" solid microparticles and provide local wetting spots for the liquid. This microscale wetting mechanism provides a general path for making liquid metal suspensions with various solid additives [1]. Using high-speed microscopic imaging, we will also show that the incorporation of oxide flakes created during rapid shear mixing of the liquid metal in air allows for making stable liquid metal foams [2]. Mixing these foams with a secondary liquid enables the formation of liquid-in-liquid metal emulsions [3]. These complex suspensions, foams, and emulsions have highly tunable properties and thereby numerous potential applications, including thermal interface materials, soft robotics, and biomedical devices. |
Monday, November 22, 2021 1:36PM - 1:49PM |
M26.00003: Axisymmetric membranes with edges under external force: buckling, minimal surfaces, and tethers Leroy Jia, Steven Pei, Robert A Pelcovits, Thomas R Powers We use theory and numerical computation to determine the shape of an axisymmetric fluid membrane with a resistance to bending and constant area. The membrane connects two rings in the classic geometry that produces a catenoidal shape in a soap film. In our problem, we find infinitely many branches of solutions for the shape and external force as functions of the separation of the rings, analogous to the infinite family of eigenmodes for the Euler buckling of a slender rod. Special attention is paid to the catenoid, which emerges as the shape of maximal allowable separation when the area is less than a critical area equal to the planar area enclosed by the two rings. A perturbation theory argument directly relates the tension of catenoidal membranes to the stability of catenoidal soap films in this regime. When the membrane area is larger than the critical area, we find additional cylindrical tether solutions to the shape equations at large ring separation, and that arbitrarily large ring separations are possible. These results apply for the case of vanishing Gaussian curvature modulus; when the Gaussian curvature modulus is nonzero and the area is below the critical area, the force and the membrane tension diverge as the ring separation approaches its maximum value. |
Monday, November 22, 2021 1:49PM - 2:02PM |
M26.00004: Pinch-off dynamics of oil column determines the oil fraction of compound bubble Amrit Singh, Bingqiang Ji, Jie Feng Compound multiphase bubbles are widely present in nature and industrial processes, such as gas releases from natural seeps and oily bubbles used in froth flotation. In these scenarios, the effect of the outer coating phase on bubble formation and the coating fraction remains unknown. Here, we use a customized co-axial orifice system to investigate the formation mechanism of millimeter-sized compound multiphase bubbles. We experimentally study how the orifice geometry and liquid properties control the oil fraction of the formed oil-coated bubbles. After the gas bubble detaches from the inner orifice, it rises under buoyancy, and stretches the oil column to cause pinch-off, forming an oil-coated bubble. The pinch-off location of the oil column sets the oil fraction of the oil-coated bubble. We show that the oil column pinch-off location is mainly determined by the size ratio of the gas bubble/oil tail to the outer orifice. A theoretical model is proposed to predict the oil fraction, which agrees well with the experimental results. Our findings provide potential guidelines for the controllable generation of compound bubbles using co-axial orifices. |
Monday, November 22, 2021 2:02PM - 2:15PM |
M26.00005: Passive devices for high throughput liquid handling Samira Shiri, Mohsin J Qazi, Mark Menesses, Nate J Cira Handling precise volumes of liquid is essential in myriad experiments, from chemistry to thelife sciences. Traditional methods to transfer liquids include manual and automated pipetting.When running many experiments, manual pipetting is time consuming and tedious. Using robotscan reduce labor and speed up procedures, but leads to high capital costs that concentrate thenecessary devices to a small number of specialized laboratories. In the Cira lab, we have developeda platform for high throughput liquid handling that enables parallel manipulation of thousands ofindependent liquid mixtures in a few minutes at volumes down to nanoliters, without the need for aunique pipette tip for each reaction. The platform works passively based on capillarity for both lowand high surface tension liquids. Furthermore, a straightforward fabrication protocol, not relying oncomplex micro/nano fabrication or challenging molecular syntheses, should help enable widespreadutility. |
Monday, November 22, 2021 2:15PM - 2:28PM |
M26.00006: Effects of oil properties on the aerosolization of crude oil-dispersant slicks during bubble bursting Diego F Muriel, Subhamoy Gupta, Joseph Katz This study examines the effect of dispersant and oil properties on the aerosolization of fresh and weathered crude oil slicks by bursting of a plume of ~0.7 mm bubbles. A Scanning Mobility Particle Sizer measures the size distribution of aerosols in the 20-400 nm range in a clean air chamber. The 500 μm thick slicks contain oils of varying origin, viscosity, interfacial tension, and weathering state. Test are performed with and without pre-mixed dispersant (Corexit 9500A), which reduces the oil-seawater interfacial tension by two orders of magnitude at a dispersant-to-oil ratio of 1:25. The nano-aerosol concentration decreases for slicks without dispersant, but increases upon introduction of dispersant. For most cases, the concentration increases with decreasing Capillary or Morton numbers. To explain the origin of nano-droplets, we show that prior to bubble injection, even mild agitation of the oil-dispersant interface generates a subsurface cloud of nano-droplets that diffuses away from the interface. This process appears to be caused by thermal capillary instability when the interfacial tension is low enough to increase the thermal length scale to a few nm. Only bubbles larger than 0.5 mm, which form film droplets upon bursting, contribute to the increase in nano-aerosols. |
Monday, November 22, 2021 2:28PM - 2:41PM |
M26.00007: Theoretical model for breakup of a liquid filament on a solid surface Hyejun Jeon, Hyoungsoo Kim We theoretically studied how a liquid filament on a substrate breaks down. This instability problem has been broadly explored due to several applications particularly for surface patterning, e.g., metal nanoparticle patterning, multiple-droplet coating, and liquid metal wires for flexible devices. Previous studies are mostly studied by experiments and numerical simulations. Thus, we developed a theoretical model for the instability of a liquid filament on a substrate where the solid-liquid interaction is crucial. Based on the extended lubrication theory, linear perturbation approximations, and additional no-slip boundary condition, finally, we obtained simplified non-linear governing equations, which are only function of the axial direction and time. We found that the theoretical model can predict a breakup of the filament and the satellite droplet formation, which show that the boundary condition on a stationary surface plays an important role to make satellite droplets. In addition, we presented that radii of the satellite droplets have a linear relation with the aspect ratio of the wavelength and the mean radius of a liquid filament. |
Monday, November 22, 2021 2:41PM - 2:54PM |
M26.00008: Flow Control by Electrohydrodynamic or Thermocapillary Actuation for Enhancing Pattern Fidelity in Nanofilms Yi Hua Chang, Sandra M Troian During the past decade, the pursuit of large area, contact-free and relatively low cost film patterning techniques has introduced several novel methods ideally suited to fabrication of optical micro-components. Especially noteworthy are those methods that rely on the projection of very large electric or thermal gradient field distributions onto the surface of molten nanofilms. These projected fields deform a slender featureless liquid film into 3D shapes which are then rapidly solidified in situ. Approaches described in the literature have exclusively relied on the “forward problem”, whereby intuition of the desired final shape helps guide application of suitable electric or thermal boundary conditions used to solve the highly nonlinear film evolution equation. For optical applications, however, such 3D patterning requires highly accurate solution of the “inverse problem” to elicit those optimal boundary conditions which yield the desired shape within a given time interval. We have tackled the inverse problem by formulation of an optimization routine incorporating external field distributions arising from variations in topography, temperature or voltage applied to the confining or supporting substrates. Using target shapes representative of microlens arrays or other optical components, we demonstrate numerically different strategies available for pattern optimization subject to spatiotemporal actuation. |
Monday, November 22, 2021 2:54PM - 3:07PM Not Participating |
M26.00009: Dewetting of thin nematic films in the presence of spatially-varying substrate anchoring Lou Kondic, Linda J Cummings, Michael A Lam Partially wetting nematic liquid crystal (NLC) films on substrates are unstable to dewetting-type instabilities due to destabilizing solid/NLC interaction forces. These instabilities are modified by the nematic nature of the films, which influences the effective solid/NLC interaction. In the present contribution, we focus on the influence of imposed substrate anchoring on the instability development. The analysis is carried out within a long-wave formulation based on the Leslie–Ericksen description of NLC films. Linear stability analysis of the resulting equations shows that some features of the instability, such as emerging wavelengths, may not be influenced by the imposed substrate anchoring. Going further into the nonlinear regime, considered via large-scale GPU-based simulations, shows however that nonlinear effects may play an important role, in particular in the case of strong substrate anchoring anisotropy. |
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