Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E37: Focus Session: Electro-Hydro-Dynamics of Drops, Vesicles and Membranes II |
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Chair: David Saintillan, University of California - San Diego Room: Sheraton Back Bay A |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E37.00001: Ellipsoidal relaxation of electrodeformed vesicles Miao Yu, Hao Lin, Rafael Lira, Rumiana Dimova, Karin Riske Electrodeformation has been extensively applied to investigate the mechanical behavior of vesicles and cells. While the deformation process often exhibits complex behavior and reveals interesting physics, the relaxation process post-pulsation is equally intriguing yet less frequently studied. In this work theoretical analysis and experimental quantification on the ellipsoidal relaxation of vesicles are presented, which reveal the simplicity and universal aspects of this process. The Helfrich formula, which is derived only for equilibrated shapes, is shown to be applicable to dynamic situations such as in relaxation. A closed-form solution is derived which predicts the vesicle aspect ratio as a function of time. Scattered data are unified by a timescale, which leads to a similarity behavior, governed by a distinctive solution for each vesicle type. Two separate regimes in the relaxation are identified, namely, the ``entropic'' and the ``constant-tension'' regime. The bending rigidity and the initial membrane tension can be simultaneously extracted from the data/model analysis, posing the current approach as an effective means for the mechanical analysis of biomembranes. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E37.00002: Computational algorithms for vesicle electrohydrodynamics Shravan Veerapaneni In this talk, we discuss a new integral equation method for simulating the electrohydrodynamics of a suspension of vesicles. The classical Taylor-Melcher leaky-dielectric model is employed for the electric response of each vesicle and the Helfrich energy model combined with local inextensibility is employed for its elastic response. The coupled governing equations for the vesicle position and its transmembrane electric potential are solved using a numerical method that is spectrally accurate in space and first-order in time. The method uses a semi-implicit time-stepping scheme to overcome the numerical stiffness associated with the governing equations. We will present new results on the suspension rheology, two-body interactions and pattern formation. This is joint work with Bowei Wu. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E37.00003: Electrohydrodynamics Of Multicomponent Vesicles Prerna Gera, David Salac The addition of cholesterol into a lipid membrane induces the formation of distinct domains. These domains try to minimize the overall energy of the system by coalescence and migration. The application of electric fields will induce flow of these membrane domains and influence the rate at which they coarsen. In this work the electrohydrodynamics of multicomponent vesicles is numerically modelled. The method uses a Cahn-Hilliard-Cook model of the lipid domains restricted to a deforming three-dimensional vesicle and will be briefly discussed. Sample results will be presented and compared to experimental observations. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E37.00004: Magnetohydrodynamics of Vesicles David Salac Lipid molecules are known to have an anisotropic magnetic susceptibility. When a lipid vesicle is exposed to a magnetic field, this anisotropy induces forces which drag the vesicle and the surrounding fluid into motion. Here a new model of a three-dimensional vesicle in the presence of magnetic fields is presented. The model is based on a novel level-set/projection method which enforces volume and surface area conservation simultaneously. The force on the vesicle membrane due to the applied magnetic field will be shown. The simulated dynamics will be compared to experimental results and future possibilities of combining electric and magnetic fields will be discussed. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E37.00005: Stretching surfactant- or protein-coated droplets in a high frequency electric field Greg Randall Surfactant-stabilized and protein-coated droplets are stretched in a high-frequency AC electric field. This is the first work to study aqueous droplets stretching at a frequency (20 MHz) high enough that water behaves as a pure dielectric. Consequently, the water/oil system is free of steady electrohydrodynamic flow. The absence of a steady flow provides a potential way to measure interfacial rheological properties of water soluble additives with droplet stretching models. Results are presented for both the wide gap and thin gap geometries. Adding dilute protein additives (e.g. bovine serum albumin, switchable peptides, hydrophobins) to form interfacial elastic layers inhibits stretching, which is an important milestone in our efforts to engineer a continuous, uniform wall thickness shell production process. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E37.00006: Electrohydrodynamic Printing on Flat and Uneven Surfaces Sepehr Maktabi, Paul Chiarot In electronics manufacturing, the need for high resolution patterns can be met by generating fine droplets using materials printing techniques. Other desirable features are high print speeds, high frequency droplet generation, and large stand-off distances. In this work, an array of emission modes for a tunable electrohydrodynamic (EHD) printing method is reported. Among these, the promising microdripping mode generated droplets an order of magnitude smaller than the nozzle's inner diameter at a frequency range of 2-8 \textit{kHz}. This method is applied to print organic resistors using the conductive ink poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS). They were printed on flat and uneven substrates at speeds up to 50 \textit{mm/s}. They had a width from 50 to 500 \textit{um} and resistance from 1 to 70 $\Omega $\textit{/um}. The effect of supply flow rate, applied voltage, stand-off distance, and target substrate material properties with respect to droplet generation frequency was investigated. Experimental results reveal that frequency increases nonlinearly with the applied voltage, which is strongly influenced by the non-Newtonian shear thinning effect of PEDOT:PSS. The topology of a 3-dimensional substrate is shown to have a significant effect on the structure and function of a printed resistor. [Preview Abstract] |
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