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 A25: Focus Session: Hydrodynamics of Particles and Macromolecules at Fluid Interfaces I |
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Chair: Yuan-nan Young, New Jersey Institute of Technology Room: Georgia World Congress Center B313 |
Sunday, November 18, 2018 8:00AM - 8:13AM |
A25.00001: Electrokinetics of particles on a fluid-fluid interface Petia Vlahovska, Yi Hu, Michael John Miksis Colloidal particles trapped at the interface of a drop assemble in various dynamic patterns, e.g., vortices, when an electric field is applied. In this talk I will overview our experiments exploring the various particle structures, and the theoretical analysis of particle motion along the fluid interface. As a first step, we study the force of the applied electric field on a spherical particle adsorbed at a planar interface. The electric potential is found by using the Mehler-Fock integral transform, which reduces the problem to a system of Fredholm integral equations. The force on an isolated particle is identified numerically, while the far-field interaction force between two particles is identified asymptotically. We find that, at leading order, the interaction between perfect dielectric particles is dominated by the induced dipoles and hence it is repulsive. For leaky dielectric particles the induced quadrupole can become significant and the interaction force can be either attractive on repulsive depending on material parameters.
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Sunday, November 18, 2018 8:13AM - 8:26AM |
A25.00002: From Electrodiffusion Theory to the Electrohydrodynamics of Leaky Dielectrics through the Weak Electrolyte Limit Yoichiro Mori, Yuan-nan Young The Taylor-Melcher (TM) model is the standard model for describing the dynamics of poorly conducting leaky dielectric fluids under an electric field. The TM model treats the fluids as Ohmic conductors, without modeling ionic electrodiffusion. Mathematical reconciliation of the electrodiffusion picture and the TM model has been a major issue for electrohydrodynamic theory. Here, we derive the TM model from an electrodiffusion model the electrochemistry of ion dissociation is modeled explicitly. We introduce salt dissociation reaction terms in the bulk electrodiffusion equations and take the limit in which the salt dissociation is weak (i.e., poorly conducting media). Together with the assumption of small Debye length, we derive the TM model with the surface charge convection term. An important quantity that emerges is the Galvani potential (GP), the jump in voltage across the liquid-liquid interface between the two leaky dielectric media. When the GP is absent, we recover the TM model. In the presence of a non-zero GP, our model predicts that the liquid droplet will drift under an imposed electric field, the velocity of which is computed explicitly to leading order. |
Sunday, November 18, 2018 8:26AM - 8:39AM |
A25.00003: Colloidal stability dictates drop breakup under electric fields Rajarshi Sengupta, Javier A Lanauze, Lynn M Walker, Aditya S Khair The electric field induced breakup of a squalane drop containing a colloidal suspension of carbon black particles with polyisobutylene succinimide (OLOA 11000) surfactant is studied. The drop is suspended in silicone oil. The breakup mode of the drop depends strongly on the suspension stability. A drop of a stable suspension has the same breakup mode as a drop with surfactant alone, i.e., without added carbon black. At lower electric fields, the drop breaks by the formation of lobes at the two ends of the drop; and at higher fields the homogeneous lobes break in a non-axisymmetric manner. However, a drop of an unstable suspension shows a drastically different breakup mode. These drops elongate and form asymmetric lobes that develop fingers and eventually disintegrate in an inhomogeneous fashion. As a basis for comparison, the breakup of a pure squalane drop, and a squalane drop with equivalent surfactant concentrations but no carbon black particles is examined. Axisymmetric boundary integral computations are used to elucidate the mechanism of breakup. Our work demonstrates that colloidal instability on the time scale of drop deformation leads to rich and unexplored breakup phenomena. |
Sunday, November 18, 2018 8:39AM - 8:52AM |
A25.00004: Catching particles on the moving fluid-fluid interface Sungyon Lee, Jenna Brown, Benjamin Druecke, Alireza Hooshanginejad We investigate the drainage of a suspension of non-colloidal particles from an immiscible fluid inside a Hele-Shaw cell. Only for relatively large particles, we observe that particles move slower than the draining mixture and eventually accumulate on the receding interface. The particle accumulation can cause an interfacial instability and lead to particle deposition, if the interface velocity is sufficiently large. This is distinct from the Landau-Levich type coating flows with suspensions, in which only smaller particles are shown to get trapped into the meniscus and are deposited onto the solid substrates. We present experimental results and discuss the physical mechanism of particle accumulation and the resultant instability at the fluid-fluid interface. |
Sunday, November 18, 2018 8:52AM - 9:05AM |
A25.00005: Motion of gold nanorods on the fluid lipid bilayer and cell plasma membranes: Interfacial Nanorheology Mehdi Molaei, John C Crocker We measure the thermal motion of single gold nanorods (GNR) at plasma membranes and on Giant Unilamellar Vesicles (GUV). The goal of this study is to develop a high throughput assay to utilize the 3-d orientation and trajectory of a GNR adhered to the cell plasma membrane to probe its mechanical state. It has been hypothesized that change in surface tension and curvature distribution of the cell membrane affects the liver cancer behavior such as proliferation and matrix production. We bind the GNR to the plasma membrane and model lipid bilayers by functionalizing its surface by magainin peptides. Laser-illuminated dark-field microscope and polarimetric analysis are developed to track the GNR’s 3-d orientation to a precision better than one degree. In plane angular and translational motion of the nanorods are measured to determine the interfacial viscoelasticity of the membrane by incorporating the hydrodynamic drag force on the GNR. Out of plane reorientation of the GNR are analyzed to study the membrane undulation dynamics and to deduce membrane modulus and the surface tension. |
Sunday, November 18, 2018 9:05AM - 9:18AM |
A25.00006: Capillary-Induced Assembly of Janus Particles in Drying Films Xin Yong, Shiyi Qin We perform mesoscale simulations to study the self-assembly and deposition of amphiphilic Janus particles in a drying thin film. Many-body dissipative particle dynamics is applied to model the evaporation of particle-laden films. For charged particles, electrostatic interactions are calculated using a finite-difference Poisson solver, which takes account for the dielectric contrast across the liquid-vapor interface. Given the unique anisotropy of Janus particles, we probe their translational and rotational dynamics in a thin film and subsequent assembly after adsorption to the interface. The simulation provides quantitative insight into the interplay between the electrostatic interactions with substrate, image force due to dielectric discontinuity, and interparticle electrostatic and capillary interactions. Janus particles assemble into a large-scale open fractal structure with identical orientation. In contrast, homogeneous particles form only isolated small aggregates having random orientation. These structures agree well with the deposits observed in experiments. Simulation further indicates the dominant force is capillary attraction due to the interface pinning at rough Janus boundaries. |
Sunday, November 18, 2018 9:18AM - 9:31AM |
A25.00007: Colloidal assembly on the surface of drying sessile droplets Mingfei Zhao, Xin Yong The self-assembly of nano or microparticles on evaporating liquid droplets is an important transport process underpinning various applications, such as printing and surface patterning. By applying a recently developed lattice Boltzmann-Brownian Dynamics (LB-BD) method, we observe the aggregation of colloidal particles on the droplet surface for strong particle-fluid interactions. The effective attraction between particles is probed in detail and shows long-range nature. By simulating drying droplets with different geometries, we find that the aggregation spots relate to the local curvature. This indicates that the effective attraction in the simulation resembles the capillary interaction, which is induced by the disturbance of the fluid interface. In addition, we model the particle assembly under evaporation to reveal the interplay of the long-range particle attraction and the evaporation-induced flow field. Our study aims to provide greater insight into the capillary-like assembly of particles in evaporating liquid masses and its relationship to the final deposit. |
Sunday, November 18, 2018 9:31AM - 9:44AM |
A25.00008: Kinetics of insulin fibril formation in an interfacial shearing flow Hannah Middlestead, Nicholas Debonno, Aditya Raghunandan, Amir Hirsa Studying the formation of amyloid fibril plaques has garnered significant attention as the accumulation of such structures in vivo is the hallmark of disorders such as Alzheimer’s and type-II diabetes. Fibril formation can be accelerated by several factors including changes to pH and temperature conditions. However, the role of the dominant and most varying in vivo factors of fluid flow and shear at hydrophobic interfaces in protein aggregation pathways remain poorly understood. Proteins adsorbed at the air/fluid interface are also subjected to significant hydrodynamic stresses during bioprocessing and drug handling, which leads to unwarranted denaturation/aggregation and subsequent loss in drug efficacy. Here, we study the kinetics of fibril formation for human recombinant insulin solutions in an interfacial shearing flow using fibrillization assays across a wide range of shear rates. We identify differences in the morphology of the fibril structures formed at the air/fluid interface and in bulk solution at different stages of fibril seeding and growth. This is key to elucidating the aggregation pathway and toxicity of shear-induced denaturation and protein fibril formation. |
Sunday, November 18, 2018 9:44AM - 9:57AM |
A25.00009: Abstract Withdrawn |
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