Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E18: Biofluids: Vesicles |
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Chair: Michael Miksis, Northwestern University Room: 28D |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E18.00001: Lipid Bilayer Vesicle Dynamics in DC Electric Fields Lane McConnell, Petia Vlahovska, Michael Miksis Vesicles, which are closed lipid bilayers, provide a valuable model to study the dynamics of the biomembranes that surround cells. Recent small deformation analysis of vesicles exposed to a DC electric field has revealed several interesting phenomena, including transitions from oblate to prolate ellipsoidal shapes and damped tumbling in the case of combined electric field and shear flow. Here we investigate the behavior and stability of a vesicle in a uniform DC electric field numerically using the boundary integral method. The vesicle membrane is modeled as an infinitely thin, capacitive, area-incompressible interface, with the surrounding fluids presumed to act as leaky dielectrics. Vesicle dynamics are determined by balancing the hydrodynamic, bending, tension, and electric stresses on the membrane. Our investigation compares the full nonlinear numerical results to the small deformation theory and to recent experimental data, and presents a thorough analysis of the relevant parameter space. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E18.00002: Asymmetric Vesicle Instability in Extensional Flow Andrew Spann, Hong Zhao, Eric Shaqfeh Previous researchers have chronicled the breakup of drops in an extensional flow as they stretch into a dumbbell shape with a long thin neck. Motivated by recent experimental observations, we study an apparently similar problem with vesicles, which are deformable but incompressible membranes that conserve area and volume. First, we simulate vesicles in an unbounded uniaxial extensional flow which are given general radial perturbations from an initially stable symmetric equilibrium state. For sufficiently low reduced volume ($<$ 0.74 at matched inner/outer viscosity) there exists a capillary number at which an asymmetric perturbation mode will grow, resulting in the formation of an asymmetric dumbbell shape with a thin connecting cylindrical bridge analogous to the shapes associated with drop breakup. Our simulations help elucidate a mechanism for this instability based on a competition between internal pressure differentials in the vesicle resulting from the membrane bending force and ambient flow. We compare and contrast this transition to the ``standard'' drop breakup transition. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E18.00003: A transient solution and scaling laws for vesicle electrodeformation and relaxation Hao Lin, Jia Zhang, Jefferey Zahn A transient analysis for vesicle deformation and relaxation under DC electric fields is presented. The theory extends from a droplet model developed by us, with the additional consideration of a lipid membrane separating two fluids of arbitrary properties. For the latter, both a membrane-charging and a membrane-mechanical model are supplied. The main result is an ODE governing the evolution of the vesicle aspect ratio. The model prediction is extensively compared with experimental data, and is shown to accurately capture the system behavior. More importantly, the comparison reveals that vesicle relaxation obeys a universal behavior regardless of the means of deformation. The process is governed by a single timescale that is a function of the vesicle initial radius, the fluid viscosity, and the initial membrane tension. This universal scaling law can be used to calculate membrane properties from experimental data. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E18.00004: The dynamics of a vesicle during adhesion processes Maurice Blount, Michael Miksis, Stephen Davis We analyze the adhesion of a two-dimensional vesicle to a flat substrate by a long-range attractive, short-range repulsive force, in the asymptotic limit that the length scale on which this force acts is much smaller than the vesicle's perimeter. As the vesicle is pulled down towards the substrate, a thin wetting layer is trapped underneath it whose thickness is determined by the adhesive force. At the edges of this wetting layer are boundary layers whose evolution is governed by adhesive, bending and viscous stresses. We use a lubrication approximation to describe the fluid flow inside these boundary-layer regions, and we show how these regions control the dynamics of the remainder of the vesicle. We obtain traveling-wave solutions for the lubrication flow and discuss their relevance during the adhesive process. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E18.00005: The dynamics of adhesion of a pair of vesicles Johann Walter, L. Gary Leal Adhesive interactions within a suspension of vesicles, such as many personal care products, vectors for drug delivery or artificial blood, can lead to aggregation of the vesicles and dramatic changes to the properties of the suspension. We study the adhesion of a pair of unilamellar, charged vesicles under flow, in the presence of a non-adsorbing polymer or micelle creating a depletion attraction force between the vesicles. Simulations are conducted using a numerical model coupling the boundary integral method for the motion of the fluids and a finite element method for the membrane mechanics (resistance to bending and area increase are both taken into account). The dynamics of the drainage process are studied. At steady state, the adhesion energy is found to depend greatly on the ability of the vesicles to increase their surface area. Finally, when the vesicles are separated in an elongational flow, different behaviors are observed depending on the deformability of the vesicles: an increase of the film thickness with a constant contact area, or peeling-off phenomenon where the contact area decreases at constant film thickness. [Preview Abstract] |
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