Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H6: Biofluids: Artificial Active Microswimmers |
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Chair: John Brady, California Institute of Technology Room: 3010 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H6.00001: Magnetic Helical Microswimmers in Poiseuille Flow Alperen Acemoglu, Serhat Yesilyurt We analyze the motion of artificial magnetic microswimmers which mimic the swimming of natural organisms at low Reynolds numbers. Artificial magnetic microswimmers consist of a rigidly connected helical tail and a magnetic head. Magnetic swimmers are actuated with three orthogonal electromagnetic coil pairs. The swimmer motion is examined in the laminar flow which is introduced to channel with syringe pump. We recorded videos for forward (pusher-like swimming / in the head direction) and backward (puller-like swimming / in the tail direction) motion of swimmers. Swimmers have non-stable helical trajectories for forward motion and stable straight trajectories for backward motion. The flow effects on trajectories are observed for swimmers with different geometric parameters in the circular channels. Experiment results show that helical wavelengths of the trajectories are affected with the flow. Additionally, the flow has more pronounced effect on the trajectories of the swimmers in wide channels. Moreover, circular confinement in narrow channels leads to more stable trajectories; in wide channels swimmers follow complex trajectories. A CFD model is used to compare experiments with simulations and to analyze the effects of hydrodynamic interactions. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H6.00002: Remote control of self-assembled microswimmers Nicolas Vandewalle, Galien Grosjean, Alexis Darras, Guillaume Lagubeau, Maxime Hubert, Geoffroy Lumay Physics governing the locomotion of microorganisms and other microsystems is dominated by viscous damping. An effective swimming strategy involves the non-reciprocal and periodic deformations of the considered body. Herein, we show that a magnetocapillary-driven self-assembly, composed of three soft-ferromagnetic beads, is able to swim along a liquid-air interface when driven by an external magnetic field. Moreover, the system can be fully controled, opening ways to explore low Reynolds number swimming and to create micromanipulators in various applications. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H6.00003: Self-propulsion via natural convection Arezoo Ardekani, Matthieu Mercier, Michael Allshouse, Thomas Peacock Natural convection of a fluid due to a heated or cooled boundary has been studied within a myriad of different contexts due to the prevalence of the phenomenon in environmental systems such as glaciers, katabatic winds, or magmatic chambers; and in engineered problems like natural ventilation of buildings, or cooling of electronic components. It has, however, hitherto gone unrecognized that boundary-induced natural convection can propel immersed objects. We experimentally investigate the motion of a wedge-shaped object, immersed within a two-layer fluid system, due to a heated surface. The wedge resides at the interface between the two fluid layers of different density, and its concomitant motion provides the first demonstration of the phenomenon of propulsion via boundary-induced natural convection. Established theoretical and numerical models are used to rationalize the propulsion speed by virtue of balancing the propulsion force against the appropriate drag force. We successfully verified the influence of various fluid and heat parameters on the predicted speed. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H6.00004: Autophoretic self-propulsion of homogeneous particles Sebastien Michelin, Eric Lauga, Gabriele De Canio Phoretic mechanisms such as diffusiophoresis exploit short-ranged interactions between solute molecules in the fluid and a rigid wall to generate local slip velocities in the presence of solute gradients along the solid boundary. This boundary flow can result in macroscopic fluid motion or phoretic migration of inert particles. These mechanisms have recently received a renewed interest to design self-propelled ``autophoretic'' systems able to generate the required solute gradients through chemical reaction at their surface. Most existing designs rely on the asymmetric chemical treatment of the particle's surface to guarantee symmetry-breaking and the generation of a net flow. We show here, however, that chemical asymmetry is not necessary for flow generation and that homogeneous particles with asymmetric geometry may lead to self-propulsion in Stokes flow. Similarly, this principle can be used to manufacture micro-pumps using channel walls with uniform chemical properties. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H6.00005: Artificial Rheotaxis Jeremie Palacci, Stefano Sacanna, Anais Abramian, Jeremie Barral, Kasey Hanson, Alexander Grosberg, David Pine, Paul Chaikin Self-propelled micro-particles are intrinsically out-of-equilibrium. This renders their physics far richer than that of passive colloids while relaxing some thermodynamical constraints and give rise to the emergence of complex phenomena e.g. collective behavior, swarming\textellipsis I will show that we can design microparticles with features usually observed for living microorganisms, the sensing of their environment or rheotaxis, the migration in a shear flow. We quantitatively describe the phenomenon and show that we can use a flow to control and assemble the particles. These self propelled particles realize a step forward in the design of advanced biomimetic systems. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H6.00006: Confined Swimming of Bio-Inspired Magnetic Microswimmers in Rectangular Channels Fatma Zeynep Temel, Serhat Yesilyurt Bio-inspired microswimmers have great potential for medical procedures in conduits and vessels inside the body; hence, controlled swimming in confined spaces needs to be well understood. In this study, analysis of swimming modes of a bio-inspired microswimmer in a rectangular channel at low Reynolds number is performed with experimental and computational studies. A left-handed magnetic helical swimmer (MHS), having 0.5 mm diameter and 2 mm length, is used in experiments by utilizing rotating magnetic field actuation obtained by electromagnetic coil pairs. Three motion modes are observed in experiments depending on the rotation frequency: (i) lateral motion under the effect of gravity and surface traction at low frequencies, (ii) lateral motion under the effect of gravity and fluid forces at transition frequencies, and (iii) circular motion under the effect of fluid forces at high frequencies. Translational and angular velocities of the MHS are calculated using CFD simulations to investigate the motion modes. In addition, induced flow fields for different radial positions of the MHS are studied. Results demonstrate the significance of rotation frequency, flow fields and pressure distribution on swimming modes and behaviour of the MHS inside rectangular channels. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H6.00007: Geometric optimization of helical tail designs to calibrate swimming velocities of microswimmers Ebru Demir, Serhat Yesilyurt Artificial microswimmers present both a solution and a challenge as alternative tools to be used in medical applications, namely, drug delivery and minimally invasive surgeries. Achieving desired amount of controlled displacement of microswimmers at desired velocities plays an important role in determining the success of such applications. In this study, a non-dimensionalised CFD model is utilised to investigate the effects of various geometrical parameters on swimming velocities of microswimmers with helical tails in cylindrical confinements, such as helix wavelength, helical body thickness, and diameter. To this end, a ``one wavelength long'' helical tail is placed inside a cylindrical channel of the same length with periodic boundary conditions applied to both ends, constituting an infinite helix model. As the channel diameter is kept constant, a parametric study of abovementioned geometric identities is conducted to observe the change in the swimming velocities. Furthermore, effects of helix-channel eccentricity and helix rotation about the longitudinal axis on swimming velocity of a dimensionally optimized helix are investigated to reveal near wall effects. The results are found to be in good agreement with the theoretical models existing in the literature. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H6.00008: Interactions between particles in a magnetocapillary self-assembly Guillaume Lagubeau, Alexis Darras, Galien Grosjean, Geoffroy Lumay, Maxime Hubert, Nicolas Vandewalle When particles are suspended at air-water interfaces in the presence of a vertical magnetic field, dipole-dipole repulsion competes with capillary attraction. This interaction was used recently to control self-assembling particles, as well as to create low Reynolds swimming systems. Although the equilibrium properties of the magnetocapillary interaction is understood, the dynamics was unclear. In the present report, we emphasize the rich behavior of two/three particles driven by this interaction. We propose a model for describing the motion driven by an external field, being the basis for developing swimming strategies and other elaborated collective behaviors along liquid-air interfaces. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H6.00009: Nonlocal slender body theory for active and passive particles above a wall Kyle R. Steffen, Christel Hohenegger Active suspensions, such as collections of motile particles or swimming microorganisms, have been the subject of much research over the past decade. A recent model proposed by Saintillan and Shelley (2007, 2012) models the motion of particles in free space using a local slender body theory, where the motile force is due to an imposed shear stress at the particle surface and the dynamics of the slender particle is approximated by relating its velocity to the force along its centerline. Because interactions between suspended particles and a fixed wall are inherently nonlocal, the local drag model is not enough. Motivated by the work of Tornberg et al. (2004, 2006) and G\"{o}tz (2006), we present a nonlocal slender body theory for a slender body above a stationary planar boundary. We consider both the case of a rigid fiber and of a motile swimmer including an active shear stress. Simulating the resulting dynamics of multiple particles requires the solution of a system of coupled integral equations for the force density. As opposed to the case of a straight fiber in free space, the resulting system is not diagonalizable using Legendre polynomials. We consider direct simulations of a small number of particles. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H6.00010: Effective diffusion of confined active Brownian swimmers Mario Sandoval, Leonardo Dagdug We find theoretically the effect of confinement and thermal fluctuations, on the diffusivity of a spherical active swimmer moving inside a two-dimensional narrow cavity of general shape. The explicit formulas for the effective diffusion coefficient of a swimmer moving inside two particular cavities are presented. We also compare our analytical results with Brownian Dynamics simulations and we obtain excellent agreement. [Preview Abstract] |
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