Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session P06: Emergent Mechanics of Active, Robotic, and Living Materials IFocus Live
|
Hide Abstracts |
Sponsoring Units: DSOFT GSNP Chair: Anton Souslov, Univ ot Bath; Jayson Paulose, University of Oregon Room: 06 |
Wednesday, March 17, 2021 3:00PM - 3:36PM Live |
P06.00001: Rectification and transport in non-equilibrium parity violating metamaterials and liquids. Invited Speaker: Suriyanarayanan Vaikuntanathan Understanding transport properties and uncovering new mechanisms for rectification of stochastic fluctuations has been a longstanding problem in non-equilibrium statistical mechanics. First, using a model parity violating metamaterial that is allowed to interact with a bath of active energy consuming particles, we uncover new mechanisms for rectification of energy and motion. Our model active metamaterial can generate energy flows through an object in the absence of any temperature gradient. The nonreciprocal microscopic fluctuations responsible for generating the energy flows can further be used to power locomotion in, or exert forces on, a viscous fluid. Taken together, our analytical and numerical results elucidate how the geometry and inter-particle interactions of the parity violating material can couple with the non-equilibrium fluctuations of an active bath and enable rectification of energy and motion. We will also disucss a microscopic mechanism for how anomalous transport properties can emerge in systems with activty and chirality. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P06.00002: Self-organised polar and nematic structures at the gas-liquid interface of motility-induced phase separation Chiu Fan Lee In a collection of active polar particles with purely steric interactions, a condensed (liquid) phase of active particles can co-exist with a dilute (gas) phase of active particles, in a phenomenon known as motility-induced phase separation (MIPS). Although both the liquid and gas phases are apolar, the interface is simultaneously polar and nematic, leading to interesting properties such as having a negative surface tension. By using a mean-field analysis of a system of active particles with discretized orientations in two dimensions, I obtain the interfacial profiles and elucidate various interfacial properties of the system under MIPS. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P06.00003: Spontaneous oscillations driven by nonreciprocal cross-diffusion Somaiyeh Shokri-Kalan, Zhihong You, M Cristina Marchetti Systems with purely diffusive dynamics are commonly dissipative and evolve to homogeneous steady states. Here, by studying a binary mixture of diffusive particles, we demonstrate that nonreciprocal cross-diffusivities can give rise to a counter-intuitive oscillatory state, in addition to the recently discovered traveling state. Using the Fourier-Galerkin method, we obtain a one-mode approximation that highlights the underlying physics of this nonreciprocity-driven oscillation. We construct a phase diagram which agrees well with the numerical simulations. The model equations we study provide a simplified description of the dynamics of a mixture of purely repulsive active and passive Brownian colloids. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P06.00004: The deformation and flow of a levitated granular membrane Melody Lim, Bryan VanSaders, Anton Souslov, Vincenzo Vitelli, Heinrich Jaeger Many phenomena in nature can be modeled by condensed phases of hard spheres held together by cohesive forces. However, there has been a lack of experimental systems to systematically probe the self-assembly and mechanics of these systems on the mesoscale, particularly in the presence of nonequilibrium driving. Here, we investigate one such model system: sub-millimetre objects acoustically levitated in air. Driven by scattered sound, levitated grains self-assemble into a monolayer of particles, forming mesoscopic granular membranes, with a surface tension and bending rigidity that emerge from long-range interactions. Detuning the acoustic trap can give rise to stochastic active forces and torques that impart angular momentum to levitated objects. As the angular momentum of a quasi-two-dimensional granular membrane is increased, it deforms from a circle to an ellipse, eventually pinching off into multiple smaller clusters. We use hydrodynamic models for rotating liquid drops to describe the granular dynamics and extract the droplet surface tension, and show that long-range acoustic forces and the anisotropy of the droplet give rise to a surface tension that scales with the droplet size. We show how this surface tension is modified by active fluctuations. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P06.00005: Complex Acoustic Fields for Driving Levitated Granular Media Bryan VanSaders, Melody Lim, Vincenzo Vitelli, Heinrich Jaeger Granular systems are inherently nonequilibrium due to strong dissipative effects. When granular systems are driven by external forces which compensate for this dissipation, the behavior of the grains can resemble equilibrium atomic or molecular systems. However, these driven granular materials also exhibit behaviors that are uniquely nonequilibrium. Here, we investigate a model system for driven granular media with attractive forces: sub-millimeter objects acoustically levitated in air. For unsteady acoustic fields with nontrivial mode shapes, levitated objects experience complex driving forces and torques. Furthermore, multiple levitated objects have secondary scattering interactions, driving aggregation into a membrane-like monolayer of close-packed grains. We apply the Lattice Boltzmann Method (LBM) to conduct direct numerical simulations of levitated objects, which permits investigation of fluid-structure interactions, including momentum transfer by acoustic wave scattering and viscous dissipation. Acoustic fields which carry angular momentum, as well as non-spherical levitated objects are investigated. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P06.00006: Controlling elasticity in levitated active hinges Anne Xia, Melody Lim, Bryan VanSaders, Heinrich Jaeger The assembly of millimeter-sized structures remains an outstanding difficulty, particularly those which can be programmed for precise actuation. We use acoustic levitation to address this issue, by which we can assemble sub-millimeter granular clusters with tunable interactions. Acoustic scattering between levitated particles generates attractive forces which are strongly shape-dependent. In particular, cube-shaped particles preferentially come into contact by sharing a single edge and exhibit a hinge-like motion around this connection. We inject energy into the elastic modes of this granular hinge by rapidly switching the acoustic field off and on, tuning the amplitude of these modes. We measure how the elasticity of this nonequilibrium hinge depends on the initial injection of energy and show that acoustic forces act to drive the soft modes into synchronization with the translational motion of the cluster. Our work opens the door to robust, controllable elasticity in a self-assembled, active granular system. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P06.00007: Sculpting Crystals One Burgers Vector at a Time: Towards Colloidal Lattice Robot Swarms Bryan VanSaders, Sharon C Glotzer Plastic deformation of crystalline materials with isotropic particle attractions proceeds by the creation and migration of dislocations under the influence of external forces. If dislocations are produced and migrated under the action of local forces, then material shape change can occur without the application of surface forces. We investigate how particles with variable diameters can be embedded in colloidal monolayers to produce dislocations on demand. We find in simulation that when embedded clusters of variable diameter particles are taken through multiple cycles of swelling and shrinking, large cumulative plastic slip is produced by the creation and biased motion of dislocation pairs in the solid for embedded clusters of particular geometries. In this way, dislocations emitted by these clusters (biased `dislocation emitters') can be used to reshape colloidal matter. Our results are also applicable to larger scale swarms of robotic particles that organize into dense ordered 2D arrangements. We conclude with a discussion of how dislocations fulfill for colloids the role sought by `meta modules' in lattice robotics research, and show how successive applications of shear as a unit operation can produce shape change through slicing and swirling. |
Wednesday, March 17, 2021 4:48PM - 5:00PM Live |
P06.00008: Field-Drive Robot Swarm Quasi-Transitions Gao Wang, Trung Phan, Shengkai Li, Michael Wombacher, Guo Chen, Junle Qu, Yan Peng, Daniel I Goldman, Simon Levin, Robert Austin We present an ecology-inspired form of active matter consisting of a field-drive robot swarm. Each robot moves over a planar dynamic resource environment represented by a large light-emitting diode array in search of maximum light intensity, which they deplete (dim) locally by their presence, as living agents would do by seeking maximum resources yet consuming local resources. We show there emerge dynamic phase transitions as a function of robot density, resource consumption and resource recovery rate. Paradoxically the non-gas phases emerge from smooth, flat resource landscapes, not rough ones, and each phase can directly move to the glass state. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P06.00009: Developmentally driven order-disorder transition in chiral living crystals Tzer Han Tan, Hugh Higinbotham, Alexander Mietke, Yuchao Chen, Peter Foster, Shreyas Gokhale, Jorn Dunkel, Nikta Fakhri Living matter exhibits complex non-equilibrium behavior. Here, we report on the formation of chiral crystals of starfish embryos which undergo autonomous order-disorder transitions. Embryos form a stable bound state at the water-air interface and hydrodynamically self-assemble into 2D crystals with hexagonal order. Time reversal asymmetry leads to emergence of chiral waves and dissipationless mechanical response. Remarkably, as a function of developmental time, these 2D crystals undergo an order-disorder transition characterized by progressive loss of translational and orientational order. Our hydrodynamic model elucidates how near field interactions can lead to the experimentally observed emergent dynamics. |
Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P06.00010: Physical gliders produced from smarticle clouds Akash Vardhan, Ram Avinery, Hridesh Kedia, Kurt A Wiesenfeld, Daniel I Goldman Active matter studies have mainly considered systems in which agents are individually motile and maintain a fixed shape. In contrast our smarticle robots which are planar 3-link, 2-motor/ revolute joint robots (each link ~3 cm long) are unable to self-propel but can self-deform via motor actuation. Here we show in laboratory experiment and numerical simulation that unconfined “clouds” of smarticles spontaneously generate self-organized bound pairs capable of ballistic motion over multiple body-lengths with lifetimes of hundreds of gait periods. The gliders occur in two main configurations which are described by their relative configurations during the motion. We reproduce these gliders in numerical simulation and study their dynamics in detail. One glider configuration is extremely robust to initial conditions and exhibits a clear basin of attraction, while the other configuration is much more selective. In the absence of added noise, both glider types persist indefinitely in simulations, all the while stochastically shifting between internal modes of joint propulsion. In the context of a confined ensemble, multi-bot chains emerge, consisting of glider-like bonds. |
Wednesday, March 17, 2021 5:24PM - 5:36PM Live |
P06.00011: Contact Sensing Enables Tunable Ratcheting of a Robotic Collective Ram Avinery, Shengkai Li, Daniel I Goldman Robotic collectives provide a convenient testbed for the study of stimuli-responsive self-propelled particles, and the generated knowledge, in turn, enables new control schemes for the collective. Here we study a simulated robotic collective, with individuals performing run-and-tumble behavior. In the presence of an asymmetric barrier, the collective exhibits flow towards a preferred side of the barrier, which is known as a ratchet effect [1]. The robots implement contact sensing modeled after our recently developed physical sensor mechanism [2]. We employ various rules in response to detected contact – either passive dynamics, alignment with the wall, or a 90/180-degree turn. For both 90 and 180 degree turns we observe an inverse ratchet effect, where the robots preferentially flow towards the direction opposite to the passive run-and-tumble behavior. The employed rule is tunable instantaneously, which allows the robots to modulate their behavior in real-time. We demonstrate how a sensing-control feedback loop on the individual leads to synchronized collective fluctuations in the presence of an asymmetric barrier. |
Wednesday, March 17, 2021 5:36PM - 5:48PM Live |
P06.00012: A self-kneading chiral crystal Ephraim Bililign, Florencio Balboa Usabiaga, Yehuda Ganan, Vishal H Soni, Sofia Magkiriadou, Michael Shelley, Denis Bartolo, william Thomas Mark irvine Two-dimensional crystals with simple longitudinal interactions are known to melt through an interplay between configurational entropy and topological defect unbinding. We ask a deceptively simple question: what is the effect of adding transverse interactions on this phase and its transitions? To realize this more general class of matter, we build an active chiral crystal composed of spinning magnetic colloids, revealing a lively self-organized steady-state of crystalline whorls that blurs the line between solid and liquid. By combining experimental measurements with fully-resolved hydrodynamic and minimal model simulations, we find that this phase spontaneously arises from the interplay of odd stresses and conventional elasticity, which conspire to produce self-propelled topological defects. As a result, two-dimensional chiral crystals self-knead into an active dynamical phase which preserves order at small scales while powering macroscopic transport at system-spanning scales. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700