Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session A24: Interfacial flowsLive
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Sponsoring Units: DFD Chair: Yuan-nan Young, New Jersey Inst of Tech |
Monday, March 15, 2021 8:00AM - 8:12AM Live |
A24.00001: A Star is Born: Distinct Marangoni Particulate Patterns Emerging in Confined Spaces Nikolaj Kofoed Mandsberg, Anja Boisen A gradient in surface tension can induce the Marangoni effect. To visualize it, tracker particles (such as pepper flakes) can be distributed over the surface and local introduction of surfactants will result in a particle-free region due to the Marangoni effect. Typically, this region is perfectly circular as a result of rotational symmetry in stresses. However, if the number of tracker particles per surface area is too large, the assumption of negligible interaction breaks down. In this case, the particulate layer can fracture [1]. The densification can be a shock driven jamming and subsequent fracture [2], but it can also be induced alone by the reservoir’s finite size. It is due to the surfactants clearing an area for particles that in turn increases particle density in the rest of the reservoir. We investigated this alternative route to fracture. In particular, we studied the (dynamic) transition from circle to star shape as a function of both initial particle density and added soap volume. |
Monday, March 15, 2021 8:12AM - 8:24AM Live |
A24.00002: Shape transitions of red blood cells in time-dependent microfluidic flows Steffen Michael Recktenwald, Christian Wagner The cardiovascular system is a complex network of branching vessels that transport and distribute blood through our bodies. Blood is mainly comprised of highly deformable red blood cells (RBCs) suspended in plasma that determine the unique flow properties of blood in the pulsatile flow of the circulation. In microfluidic experiments under stationary flow conditions, RBCs exhibit characteristic cell shapes, such as parachutes and slippers, depending on the flow rate and the channel confinement. However, knowledge about the cell shape transitions in unsteady flows, as it is in the circulation, is still lacking. Therefore, we probe the flow behavior of RBCs in time-dependent flow fields using microfluidic experiments in combination with optical microscopy. Employing a customized feedback-control mechanism allows us to track and follow single RBCs along the channel flow direction during the flow modulation. We analyze the time-dependent shapes and dynamics of the cells as a function of the pressure waveform, amplitude, and frequency to understand how the time scale of the flow couples with the characteristic time scale of single RBCs in capillaries. |
Monday, March 15, 2021 8:24AM - 8:36AM Live |
A24.00003: Surface Tension and Surface Excess Analysis of Binary Mixtures of Pentane and 2-Methylpentane for Use in Wickless Heat Pipes Angelo Visco, Elizabeth K Mann, J. Adin Mann, Alexander I Belgovskiy, William Vernon Meyer, Anthony E Smart, Nabin K Thapa Binary mixtures have been shown to improve the function of wickless heat pipes, which offer greater longevity over conventional heat pipes [1]. Fabrication of such wickless heat pipes rely on surface tension effects, such as Marangoni forces, making it essential to understand the interface properties of the liquid and its vapor. Recent improvements in Surface Light Scattering Spectroscopy instrumentation and its software, have not only improved its ease of use but have made possible a substantial improvement in the accuracy of surface tension measurements. With these improvements, we present surface tension and viscosity measurements of a binary mixture system of pentane and 2-methylpentane. The data are fit to an extended Langmuir isotherm model, giving insight into the relative concentration of the various components near the interface, quantified by the surface excess. |
Monday, March 15, 2021 8:36AM - 8:48AM Live |
A24.00004: Nonlinear traveling waves on the interface of a ferrofluid droplet subjected to magnetic field Zongxin Yu, Ivan Christov In this talk, we demonstrate that the combination of a radial and azimuthal external magnetic field can manipulate the interfacial shape of a linearly unstable ferrofluid droplet in a confined Hele-Shaw configuration. We show that weakly nonlinear modal theory can be used to tune the initial unstable growth. Then, nonlinearity arrests the instability, and leads to a permanently deformed droplet shape. Specifically, we show that the deformed droplet can be set into motion with a predictable rotation speed, demonstrating potentially novel nonlinear traveling waves on a fluid-fluid interface. We determine the phase diagram for perturbations that will "grow" into stable spinning gear-shaped droplets. The most linearly unstable wavenumber and the combined strength of the applied external magnetic fields determine the traveling wave shape, which can be asymmetric. Beyond a certain rotation speed, "wave breaking" can occur on this confined interface, much like surface water waves. |
Monday, March 15, 2021 8:48AM - 9:00AM Live |
A24.00005: Marangoni flows and deposits in colloidal binary droplets GUN OH, Woojun Jeong, Byung Weon Droplet evaporation is a versatile process to deposit solute materials on a substrate unless it induces solute accumulation at the contact line because of outward capillary flows. Generating inward Marangoni flows by surface tension gradients is a good candidate to suppress outward capillary flows. Controlling Marangoni flows would be available by adopting binary solvents but actually difficult in colloidal binary droplets, which have been recently studied to uniformly deposit colloidal particles. To understand and manipulate Marangoni flows in colloidal binary droplets, we investigate droplet evaporation and deposition dynamics by changing relative mass ratio of binary solvents. Particularly, we demonstrate that island deposits are created when Marangoni flows overwhelm capillary flows during most of evaporation times. Formation of island deposits in colloidal binary droplets would be a helpful route to achieve uniform deposits of colloidal particles or nanoparticles. |
Monday, March 15, 2021 9:00AM - 9:12AM Live |
A24.00006: Naturally-Occurring Surface-Shock Starburst Instabilities Harrison Toll, Charlotte Jones, Mira Schoeberlein, Katharine Jensen For decades, a curious fluid dynamic instability at the Matanuska Glacier in Alaska has puzzled local glaciologists and tourists alike. Throughout the ablation season, the meltwater that flows from the toe of the glacier is in large parts covered by a thin, black, particulate layer that bursts apart in a distinctive, radially symmetric starburst pattern when touched by hand. In this work, we analyze field videos of these naturally-occurring starbursts that we collected over two summer seasons at Matanuska, as well as a related cracking instability that occurs in particularly dense, muddy areas. We find that these phenomena only occur in response to surfactant perturbations to the surface, such as from introducing skin oil or soap. We further analyze meltwater samples collected from the glacier using contact angle measurements and SEM of extracted particles. Our data indicate that the glacier starbursts are a naturally-occurring example of surfactant shock-driven jamming and fracture. We further discuss other starburst instabilities that we believe may be driven by closely related physics. |
Monday, March 15, 2021 9:12AM - 9:24AM Live |
A24.00007: Eigenmode analysis of membrane stability in inviscid flow Christiana Mavroyiakoumou, Silas Alben We study the stability of a thin membrane with a vortex sheet as a nonlinear eigenvalue problem in the parameter space of membrane mass and pretension. When both membrane ends are fixed, the stability boundary is fairly simple: light membranes become unstable by a divergence instability and heavy membranes appear to lose stability by flutter and divergence, which occurs for a pretension value that increases with the membrane mass. With the leading edge fixed and trailing edge free, or both edges free, the membrane eigenmode shapes become more complicated and eigenmodes transition in shape across the stability boundary. We compare the eigenvalue analysis with simulations of the corresponding initial value problem in the small-amplitude (growth) regime. |
Monday, March 15, 2021 9:24AM - 9:36AM Live |
A24.00008: Oily jets by bubble bursting at an air/water/oil interface Bingqiang Ji, Zhengyu Yang, Jie Feng Bursting of bubbles at a fluid-fluid interface is ubiquitous in nature and many industrial processes, relevant to foam stability, cell cultures in bioreactors as well as ocean spray generation. In particular, bubble bursting plays a key role in mediating the mass transport across the interface and has consequently received significant attention. Here, we report the dynamics of an oily jet produced by bubble bursting at an aqueous surface covered by a layer of oil, which finally ejects oily aerosols into the air. With high-speed imaging, we document the dynamics of the cavity collapse and jet formation with different oil viscosities and layer thicknesses. We observe that the oil layer damps the capillary waves during cavity collapse, hence decreasing the jet radius and increasing the jet velocity. We further propose an effective Ohnesorge number to quantify the jet radius and velocity by taking into account the viscous dissipation from the oil layer. Our study not only advances the fundamental understandings of bubble bursting at a compound interface, but may also shed light on the formation of oily aerosols in the ocean regarding pollutant transport. |
Monday, March 15, 2021 9:36AM - 9:48AM Live |
A24.00009: Particle driven in a crystalline colloidal monolayer Jiayi Deng, Mehdi Molaei, Nicholas G Chisholm, Ravi Radhakrishnan, Kathleen Joan Stebe Probes driven in interfaces displace passive colloidal tracers to generate displacement fields which bear the signature of the degree of organization of the colloidal tracer monolayer. We study the displacement fields around driven ferromagnetic probes particles in monolayers of PS colloidal particles at oil-water interfaces in gaseous, liquid, and crystalline states, increasing the importance of many body effects as order in the monolayer increases. Using correlated displacement velocimetry, we measure the flow field owing to thermal motion of the PS particles absent the driven particles. In the gaseous state, the flow field agrees with the form expected for a Stokeslet in an incompressible interface. In more organized states, the flow field reveals signatures of the coupling between the hydrodynamic and electrostatic interactions. We also characterize the motion around the driven magnetic probe in the ordered colloidal monolayer. Long range motion of the monolayer is observed; this manifestation of many-body electrostatic interactions is discussed in terms of spatial order and vibrational modes. Understanding the coupling between the hydrodynamic and electrostatic interactions allow us design active interfaces that fulfill different needs on interfacial functionality. |
Monday, March 15, 2021 9:48AM - 10:00AM On Demand |
A24.00010: Interfacial properties of poly- and perfluoroalkyl substances at the air-water interface Zahra Abbasian Chaleshtari, Reza Foudazi Poly- and perfluoroalkyl substances (PFAS) are a group of manmade chemicals with each or more than one hydrogen atom on the alkyl chain replaced by a fluorine atom. PFAS have been recognized as contaminants of emerging concern (CECs) duo to toxicity, bioaccumulation, and environmental persistence. Therefore, PFAS properties and remediation methods are being widely investigated in recent studies. Study of interfacial properties of PFAS is of great importance as the air-water interface is a retention source for PFAS transport in atmosphere, soil, and groundwater. In the present study, PFAS adsorption kinetics and equilibrium at the air-water interface are studied by measuring the dynamic surface tension. PFAS interfacial rheological properties are also determined by oscillatory shear flow. We evaluate the effect of perfluoroalkyl chain length, concentration, and composition on the adsorption and viscoelastic behavior of PFAS at the interface. |
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