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 M3: Collective Behavior and MicroswimmersBio Fluids: External
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Chair: Jared Barber Jr., Indiana University-Purdue University Indianapolis Room: 403 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M3.00001: Impact of Motile Bacterial Suspensions on Viscous Fingering and Mixing Jane Chui, Harold Auradou, Pietro de Anna, Karen Fahrner, Howard Berg, Ruben Juanes Viscous fingering is a hydrodynamic instability that occurs when a less viscous fluid displaces a more viscous one. Instead of progressing as a uniform front, the less viscous fluid forms fingers to create complex patterns. Understanding how these patterns and their associated gradients evolve over time is of critical importance in characterizing the mixing of two fluids, which in turn is important to applications such as enhanced oil recovery, bioremediation, and microfluidics. Here, we investigate the impact of replacing the less viscous fluid with an active suspension of motile bacteria. In this series of experiments, a suspension of motile \textit{Escherichia coli} capable of collective swimming is injected into a microfluidic Hele-Shaw cell under viscous fingering conditions. Through videomicroscopy, we obtain high-resolution concentration fields to determine the evolution of the mixing zone (region with concentration gradients). We quantify the impact that active suspensions have on the formation of viscous fingering patterns and mixing efficiency between the two fluids, and---conversely---report details of the collective swimming behavior in the presence of a viscous-gradient front. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M3.00002: Camphor swimmers Laurent Maquet, Dolachai Boniface, Ronan Kervil, C\'ecile Cottin-Bizonne, Christophe Ybert Camphor swimmers have been studied for a long time. Still, not everything has been understood, especially for symmetrical swimmers. Here, we deepen the understanding of this specific type of swimmer. Our swimmers are made of a disc of agarose in which camphor is homogeneously precipitated. These swimmers are able to swim at a air-water interface by releasing camphor in the water, which produces a soluto-capillary Marangoni flow. The configuration of this flow is such that an immobile swimmer is unstable, and swimmers will always tend to swim. We observe that the speed of the swimmers decreases over time. This aging effect is explained through a model for the diffusion of the camphor in the agarose matrix of the disc. We also observe and characterize the effect of the meniscus on the edge of the water surface, and propose solutions to overcome the problem linked to this meniscus (i.e. the capture of the swimmers). [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M3.00003: An improved squirmer model for Volvox locomotion Timothy Pedley We recently used the Lighthill-Blake envelope (or 'squirmer') model for ciliary propulsion to predict the mean swimming speed $U$ and angular velocity $\Omega$ of spherical $Volvox$ colonies [1]. Input was the measured flagellar beating patterns (a symplectic metachronal wave) of $Volvox~carteri$ colonies with different radii $a$ [2]. The predictions were compared with independent measurements of $U$ and $\Omega$ as functions of $a$, and proved to be substantial underestimates of both $U$ and $\Omega$, by about $80\%$, probably because the envelope model ignores the fact that, during the recovery stroke, most of a flagellum is much closer to the no-slip colony surface than during the power stroke. In consequence $U$ and $\Omega$ will be proportional to the beating amplitude $\epsilon$ not to $\epsilon^2$ as in the Lighthill-Blake theory. A new model is proposed, based on a shear-stress (not velocity) distribution (cf [4]) that is applied at a smaller radius in the recovery stroke than in the power stroke. Agreement with experiment is greatly improved\\ \\$[1]$ Pedley et al, JFM 798:165,2016. [2] Brumley et al, PRL 109:268102,2012. [3] Drescher et al,PRL 102:168101,2009. [4]Short et al, PNAS 103:8315,2006. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M3.00004: Decreasing Viscosity within Freely Suspended Liquid Film by Bactria Tayebeh Saghaei, Ali-Reza Moradi, Mehdi Habibi, Sharereh Tavaddod The effect of existent active particles on rheological terms of fluid to introduce a macroscopic parameter for estimating the global motility of a large population of swimming cells have been studied extensively. In this paper, the viscosity are obtained through the measurement of the rotation rate changes of a rotating thin layer of a fluid including E.coli bacteria. A freely suspended film of a fluid is rotated under various tensions as a ``liquid film motor'' (LFM) and the rotation velocity changes are measured. Our experiments have revealed that the viscosity can decrease compared to the viscosity of the same liquid without bacteria or with dead bacteria. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M3.00005: Sedimentation and gravitational instability of Escherichia coli Suspension Dominique Salin, Carine Douarche The successive runs and tumbles of Escherichia coli bacteria provide an active matter suspension of rod-like particles with a large swimming, Brownian like, diffusion. As opposed to inactive elongated particles, this diffusion prevents clustering of the particles and hence instability in the gravity field. We measure the time dependent $E.\; coli$ concentration profile during their sedimentation. After some hours, due to the dioxygen consumption, a motile / non-motile front forms leading to a Rayleigh-Taylor type gravitational instability. Analysing both sedimentation and instability in the framework of active particle suspensions, we can measure the relevant bacteria hydrodynamic characteristics such as its single particle sedimentation velocity and its hindrance volume. Comparing these quantities to the ones of equivalent passive particles (ellipsoid, rod) we tentatively infer the effective shape and size of the bacteria involved in its buoyancy induced advection and diffusion. [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M3.00006: ABSTRACT WITHDRAWN |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M3.00007: Dynamics and structure of an apolar active suspension in annulus Sheng Chen, Peng Gao, Tong Gao We study the complex dynamics of a two-dimensional suspension comprising non-motile active particles confined in an annulus. A coarse-grained liquid crystal model is employed to describe the nematic structure evolution, and hydrodynamically couples with the Stokes equation to solve for the induced active flows in the annulus. For dilute suspensions, coherent structures are captured by varying particle activity and gap width, including unidirectional circulations, traveling waves, and chaotic flows. For concentrated suspensions, the internal collective dynamics are featured by motile disclination defects and flows. In particular, we observe an intriguing quasi-steady state at certain gap widths during which $+1/2$-order defects oscillate around equilibrium positions accompanying traveling-wave flows that switch circulating directions periodically. We perform linear stability analyses to reveal the underlying physical mechanisms of pattern formations during a concatenation of phase transitions. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M3.00008: Magnetic Particle Dynamics in Synthetic Mucus Louis Rogowski, Benjamin Woodruff, Amanda Liew, Richard Burns, Hoyeon Kim, Jamel Ali, MinJun Kim The viscoelastic nature of human mucus is the result of complex fiber networks generated by mucin glycoproteins. Micro- and nanoparticles easily become entangled within these fiber networks, causing reduced particle diffusivity. Actuatable magnetic microparticles entangled within these fibers, in certain cases, have been demonstrated to have novel interactions with surrounding mucus environments. Individual particles have been observed to form mucin fiber tails that allow them to swim freely through the medium. Particles bonded with mucin fibers can also experience new forms of controllable motion, like z-plane shifting and wobble swimming, not previously encountered in past work. In high density fiber networks, microparticles are observed to gradually roll themselves through the networks by simple directional rotation. In lower concentrations of mucus, particles can have sudden and rapid translator properties when encountering dense patches of fibers. Understanding these unique fluidic interactions inside synthetic mucus can greatly contribute to in vivo fluid dynamics, pharmacology, and microrobotics. [Preview Abstract] |
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