Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z49: Focus Session: Self-Phoretic Colloids and Active Emulsions II |
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Sponsoring Units: GSOFT Chair: Michelle Driscoll, New York University Room: 217D |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z49.00001: Building a dynamic cell from the bottom up Viva R. Horowitz, Thomas G. Dimiduk, Irep Gozen, Yue N. Ren, Vinothan N. Manoharan We aim to understand cellular processes, particularly intracellular transport, at a physical level by building simple, well-controlled systems that mimic the functions of a cell. We have created a simple artificial cell using a bilayer phospholipid vesicle containing Janus swimmers as microscale motors. These Janus swimmers are propelled by the catalytic breakdown of hydrogen peroxide on their platinum hemispheres. We encapsulate these Janus swimmers in the interior of the artificial cell. We investigate the superdiffusive motion using multimodal imaging tools, including digital holography and fluorescence, to shed light on how the dynamics of Janus swimmers depends on the confinement. These dynamics and transport processes may prove necessary to sustain gene expression, growth, and reproduction in future artificial cells. [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z49.00002: Internally driven solids Ananyo Maitra, Suropriya Saha, Ramin Golestanian, Sriram Ramaswamy What is the long-wavelength, long-time dynamics of an elastic solid composed of motile orientable particles? Can different types of interactions between the motile particles lead to different varieties of active solid? What is the dynamics if the motile particles orient along a spontaneously chosen axis? Is it different from a passive solid which is driven externally? What if the inter-particle interactions instead favour aster-like configurations? I will present an answer to these questions and point out the differences and similarities between internally driven and externally driven solids. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z49.00003: Controlling Compartmentalization Through Active Confinement Matthew Spellings, Michael Engel, Daphne Klotsa, Kyle Bishop, Sharon Glotzer Active matter is an exciting area of study that displays promising new behaviors previously unobtainable in equilibrium systems and could help bridge the gap between equilibrium colloidal- and nanoscale particles and living cells. In this talk, we will discuss novel, emergent behavior observed simulations of confined ``cells'' comprised of active particles. We show how the results of a microscopic model are reproduced in a continuum model. [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z49.00004: Self Propelled nanorods at an interface Jeremie Palacci, Takuji Adachi, Jun Zhang, Leif Ristroph, Mike Shelley Self-propelled colloids are micron-scale particles which can harvest the energy from the surrounding medium and convert it into propulsion and work. Here we study the impact of the interface ---solid. fluid, slipping, non-slipping\textellipsis --- on the dynamics of the self-propulsion for a suspension of active nanorods. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z49.00005: Velocity distributions in self-assembled phases of active magnetic colloids Alexey Snezhko Colloids of strongly interacting particles driven out-of-equilibrium by an external periodic forcing often develop nontrivial collective dynamics and dynamically assembled structures. We use ferromagnetic colloidal micro-particles suspended over a water-air interface. The system is energized by a single-axis alternating magnetic field applied in-pane of the interface. Experiments revealed a rich variety of self-assembled phases (in particular, ``wires,'' ``rotators'') emerging in such systems in a certain range of excitation parameters. Velocity distributions of particles in driven magnetic colloids in ``rotators'' phase were carefully examined. The studies revealed strongly non-Maxwellian nature of velocity statistics for both subsystems: single particles and self-assembled rotators. The high energy tails of velocity distributions are stretched exponential. Dissipations due to inelastic collisions and viscous damping contribute to the form of the high energy tails. When viscous damping dominates over collisional dissipation the distribution is nearly exponential (such behavior is observed for the gas of rotators) while in the opposite case (single particles driven by field) the core of the distribution is Gaussian and only high energy tails are close to exponential. [Preview Abstract] |
Friday, March 6, 2015 12:15PM - 12:27PM |
Z49.00006: Strongly confined active brownian particles Yaouen Fily, Aparna Baskaran, Michael Hagan We explore the effect of boundaries on active suspensions by considering non-aligning self-propelled particles confined by hard frictionless walls. In small boxes, the density and pressure are sensitively controlled by the shape of the box. We show those quantities can be predicted for arbitrary box shapes, and discuss the role of concavity and dimensionality. This in turn provides a tool to design and understand such confining boxes. [Preview Abstract] |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z49.00007: Using light patterns to manipulate self-propelled particles Melissa Ferrari, Michelle Driscoll, Jeremie Palacci, Stefano Sacanna, David Pine, Paul Chaikin Soft active matter systems, characterized by their ability to extract energy from their environment to perform mechanical work, exhibit phenomena far from equilibrium. We study a class of synthetic light activated colloidal swimmers which self-propel osmotically on a surface. Here we propose a method to manipulate the migration of the light activated colloids by carefully tuning their macroscopic environment. Through integration of a modified commercial projector with an optical microscope, we are able to shine static and dynamic light patterns onto the sample plane where the light activated swimmers live. We can use specific light patterns to set up swimmer density gradients in our sample. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 1:15PM |
Z49.00008: Active droplets as biomimetic model swimmers Invited Speaker: Corinna Maass Large ensembles of biological swimmers form one of the biggest ecosystems on earth: marine phytoplankton. Investigating the dynamics of such a system is of prime ecological importance, however, as any modelling would need to include the interplay of turbulence, long-range hydrodynamics, buoyancy, as well as the self-propelled motion of the swimmers, this proves a daunting task both analytically and numerically. A scalable system of artificial swimmers with well understood and tunable interactions should help with decoupling some of these effects and studying them separately. Active emulsions of self-propelled droplets present a suitable experimental model system for the collective behaviour of biological swimmers, as they exhibit both autonomous motion and chemotaxis, move freely in three dimensions, can be produced and stored in large, monodisperse quantities and are stable over time scales comparable to biological systems. We demonstrate some of these features on a system of liquid crystal droplets driven by solubilisation into a micellar aqueous surfactant solution. [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z49.00009: Active Brownian and Run-and-Tumble particles: A comparison of the large scale dynamics Benjamin Hancock, Aparna Baskaran Active Brownian particles, such as self phoretic colloids, are a class of self propelled particles which swim at fixed speed with orientation that gradually changes through rotational diffusion. Some bacteria obey Run-and-Tumble dynamics, in which particles swim along a fixed orientation until a tumble event occurs that randomly selects a new orientation. At long time and length scales the diffusive-drift limit of the above dynamics appear to be identical. In this large scale limit, we study the effects of external fields on the dynamical properties of these two classes of self propelled particles. [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z49.00010: The role of hydrodynamics and confinement on the collective behavior of active emulsions Shashi Thutupalli, Delphine Geyer, Howard Stone Active droplets i.e. emulsion droplets which exhibit self-propelled motion are of tremendous interest in understanding the collective dynamics of systems far from thermal equilibrium. A particularly appealing feature of these active droplet systems is that the coupling between the individuals is well-controlled and mediated by purely physical effects such as steric interactions and hydrodynamics. We create such active droplet systems using liquid crystalline emulsions in aqueous phases stabilized by surfactants. The propulsion of the individual droplets is fully 3 dimensional and occurs via a spontaneously broken symmetry (unlike colloidal swimmers which are often asymmetric by design) which is sustained via dissipation of chemical energy. Here, we show that hydrodynamics and geometry play a crucial role in the emergent self-organization of the active droplets. In particular, we describe the pair-correlations emerging in a population of active droplets confined in Hele-Shaw geometry. We further demonstrate that these interactions result in the formation of stable travelling bands in reduced confinement and self-organize into crystalline vortices at a single interface. [Preview Abstract] |
Friday, March 6, 2015 1:39PM - 1:51PM |
Z49.00011: Glassy dynamics of self-propelled particles: computer simulations and a mode-coupling-like theory Grzegorz Szamel, Elijah Flenner, Ludovic Berthier We use a combination of computer simulations and theory to elucidate glassy dynamics of self-propelled particles. We compare the relationship between the steady state structure of the self-propelled system and its long-time dynamics with that of an equilibrium Brownian system. We find that an athermal self-propelled system can have a more pronounced local structure but faster relaxation than a similar equilibrium system. Interestingly, the dependence of the dynamics on the persistence time of the self-propulsion can be non-monotonic, with the dynamics speeding up and then slowing down with increasing persistence time. We show that these effects are captured by a mode-coupling-like theory. [Preview Abstract] |
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