Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session M13: Microswimmers IIIBio Fluids: External
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Chair: Giacomo Gallino, Ecole Polytechnique Federale de Lausanne Room: 506 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M13.00001: Bimetallic Microswimmers Speed Up in Confining Channels Chang Liu, Chao Zhou, Wei Wang, H.P. Zhang Synthetic microswimmers are envisioned to be useful in numerous applications, many of which occur in tightly confined spaces. It is therefore important to understand how confinement influences swimmer dynamics. Here we study the motility of bimetallic microswimmers in linear and curved channels. Our experiments show swimmer velocities increase, up to 5 times, with the degree of confinement, and the relative velocity increase depends weakly on the fuel concentration and ionic strength in solution. Experimental results are reproduced in a numerical model which attributes the swimmer velocity increase to electrostatic and electrohydrodynamic boundary effects. Our work not only helps to elucidate the confinement effect of phoretic swimmers, but also suggests that spatial confinement may be used as an effective control method for them. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M13.00002: Dynamic Equilibrium of Microswimmers Mehdi Mirzakhanloo, Mir Abbas Jalali, M.-Reza Alam Here we show that two propelling microswimmers may fall into an equilibrium state at which they both remain stagnant indefinitely. This so-called ``Dynamic Equilibrium" is a result of hydrodynamic interactions between the two swimmers, and is obtained through the formation of a nested saddle-shaped flow field near swimmers. We use, as a benchmark, a newly proposed artificial microswimmer named Quadroar which consists of two axles (with rotating disks at each end) connected by a reciprocating linear actuator. Quadroar induces an oscillatory flow field which closely resembles that of Chlamydomonas Reinhardtii (a single-cell green alga). Dynamic equilibrium has not been observed at large Reynolds number regimes, and therefore this finding may have unique and important implications in the collective behavior at low Reynolds numbers. Specifically, if our finding can be generalized to many microswimmers, that is, if a dynamic equilibrium can be found between multiple microswimmers, then it means that a flock of microswimmers may come to an absolute halt in which they will be trapped forever. [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M13.00003: Self-Propulsion Of Catalytic Conical Micro-Swimmer Giacomo Gallino, Francois Gallaire, Eric Lauga, Sebastien Michelin Self-propelled artificial micro-motors have attracted much attention both as fundamental examples of active matter and for their potential biomedical applications (e.g. drug delivery, cell sorting). A popular design exploits the catalytic decomposition of a fuel (e.g. hydrogen peroxide) on the active surface of the motor to produce oxygen bubbles that propel the swimmer, effectively converting chemical energy into swimming motion. We focus here on a conical shape swimmer with chemically-active inner surfaces. Using numerical simulations of the chemical problem and viscous hydrodynamics, we analyze the formation, growth and motion of the bubbles inside the micro-motor and the resulting swimming motion. Our results shed light on the fundamental hydrodynamics of the propulsion of conical swimmers and may help to improve the efficiency of these machines. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M13.00004: Rheotaxis of elongated platinum-gold nanoswimmers Quentin Brosseau, Yang Wu, Leif Ristroph, Jun Zhang, Michael Ward, Michael Shelley Directed motion of self-propelled colloids has attracted much attention~as a possible means~to transport microscopic cargo to desired locations.~However, active~colloids, such as our~gold--platinum~(Au-Pt) bi-metallic~motors (\textasciitilde 2~micrometers) that~are~powered by hydrogen peroxide~(H2O2),~are subjected to Brownian motion and~move diffusively.~ These~swimmers~can be directed~via interactions~with structured substrates, e.g. within~an array of asymmetric pillars.~ Our current study~focuses on realizing the directed motion in an imposed open flow, of these active nanorods.~This dynamic response, often referred to as ``rheotaxis'', is found in many marine~organisms. The effect of flow geometry and flow~characteristics~will be discussed in more details. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M13.00005: Net motion of acoustically levitating nano-particles: A theoretical analysis Kevin Lippera, Olivier Dauchot, Michael Benzaquen A particle 2D-trapped in the nodal planed of a standing acoustic wave is prone to acoustic-phoretic motion as soon as its shape breaks polar or chiral symmetry. such a setup constitues an ideal system to study boundaryless 2D collective behavior with purely hydrodynamic long range interactions. \\ Recent studies [1] have indeed shown that quasi-spherical particles may undergo net propulsion, a feature partially understood theoretically in the particular case of infinite viscous boundary layers [2]. \\ We here extend the theoretical results of [2] to any boundary layer thickness, by that meeting typical experimental conditions. In addition, we propose an explanation for the net spinning of the trapped particles, as observed in experiments [1]. \\ \\ $[1]$ Wang, Castro, Hoyos, and Mallouk, ACS nano {\bf 6}(7) 2012 \\ $[2]$ Nadal and Lauga, Phys. Fluids {\bf 26}, 2014 [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M13.00006: Simulation of arbitrarily shaped colloids with active boundary layers Florencio Balboa Usabiaga, Bakytzhan Kallemov, Blaise Delmotte, Aleksandar Donev In this work, we will explore the simulation of active particles of arbitrary shape in Stokes flow. We will discuss how to represent rigid bodies with a multiblob model and how to model the active boundary layers created by phoretic particles with an active velocity slip. In our framework, the simulation of active or passive colloids only requires one mobility solve per time step and the activity effects do not increase the computational cost respect the simulation of passive colloids. We will validate our method against the classical squirmer model and show results for active micro-rods that assemble under their self-induced extensile flows. [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M13.00007: Autophoresis in three dimensions Maciej Lisicki, Shang-Yik Reigh, Eric Lauga Janus particles with the ability to move phoretically in self-generated chemical concentration gradients are model systems for active matter. Their motion typically consists of straight paths, with rotational diffusion being the dominant reorientation mechanism. We show theoretically that by a suitable surface coverage by activity and mobility, both translational and rotational motion can be induced in three dimensions. Resulting trajectories are generally helical, and their pitch and radius can be controlled by adjusting the angle between the translational and angular velocity. We construct a theoretical framework to calculate the resulting motion for an arbitrary coverage and introduce a simple intuitive patch model, which serves as a guide for designing arbitrary phoretic spheres. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M13.00008: Metachronal Motion of Artificial Cilia Srinivas Hanasoge, Peter Hesketh, Alexander Alexeev, Matthew S. Ballard Most microorganisms use asymmetrically oscillating hair like cilia on their surface to achieve fluid transport. These cilia are often seen to beat in a metachronal fashion with a constant phase difference with the neighbors which generates a travelling wave. Although the origin of metachronal waves in such cilia is not well understood, mimicking such behavior in synthetic systems could prove useful in achieving similar advantages. In this work, we demonstrate metachronal waves in synthetic magnetic ciliary systems. The soft magnetic cilia are forced by a uniform rotating magnetic field. The cilia bend as the field rotates and tend to align along the direction of field to minimize the potential energy. Longer cilia bend to a larger degree, while the shorter cilia show less bending. This difference in the bending of cilia based on their length leads to a phase difference in their oscillation cycle. We exploit this phase differences to metachronally oscillate the synthetic cilia. We fabricate an array consisting of cilia with increasing lengths, in which the cilia beat with a constant phase difference with the neighboring cilia, producing a travelling wave. Such behavior could potentially be useful in enhanced fluid and particle transport as seen in natural systems. [Preview Abstract] |
Tuesday, November 21, 2017 9:44AM - 9:57AM |
M13.00009: Levitation and locomotion on an air-table of plates with herringbone grooves John Hinch, Helene de Maleprade Recent experiments in ESPCI in Paris and numerical simulations in Nano- and Microfluidics in Darmstadt have shown that plates with herringbone grooves in their base are accelerated on an air-table in the direction that the chevron grooves point. A simple two-dimensional model is constructed of the air flow down a channel with pressure controlled influx across the lower boundary. Limiting cases are considered of low and high Reynolds numbers, and of small and large pressure drop down the channel compared with the pressure drop across the porous plate. The levitation and locomotion forces are calculated. A prediction is made for the locomotive acceleration which avoids the complications of the shorter grooves which exit the front and back edges. [Preview Abstract] |
Tuesday, November 21, 2017 9:57AM - 10:10AM |
M13.00010: Viscous streaming for locomotion and transport Mattia Gazzola, Tejaswin Parthasarathy Rectified and oscillatory flows associated with vibrating boundaries have been employed in a variety of tasks, especially in microfluidics. The associated fluid mechanics is well known in the case of simple geometries, cylinders in particular, yet little is known in the case of active, complex systems. Motivated by potential applications in swimming mini-bots, we established an accurate and robust computational framework to investigate the flow behavior associated with oscillations of multiple and deforming shapes with an emphasis on streaming assisted locomotion and transport systems. [Preview Abstract] |
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