Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D18: Fluids III |
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Sponsoring Units: DFD Chair: Thomas Sykes, University of Oxford Room: Room 210 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D18.00001: Three dimensional chiral active fluids at intermediate Reynolds numbers Panyu Chen, Scott Weady, Severine Atis, Michael J Shelley, William T Irvine We present an experimental system consisting of millimeter-size spinning magnetic particles suspended in a fluid that organize into a fluctuating lively three-dimensional steady state. We examine the emergence of this state from the dynamics of individual particles and pair-wise interactions all of which bear unique signatures of inertial dynamics of the background fluid. Combining experiments, numerical simulations and theoretical modeling, we reveal novel mechanisms for self propulsion, flocking and binding which form the dynamical building blocks of their collective behavior. Our research provides insight into how inertial effects can have a profound effect on active matter as well as providing a window into the dynamics of chiral active flows in three dimensions. |
Monday, March 6, 2023 3:12PM - 3:24PM |
D18.00002: Active Colloid Guided Non-Equilibrium Assembly. Pronay Dutta, Manasa Kandula
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Monday, March 6, 2023 3:24PM - 3:36PM |
D18.00003: Motion of active Janus colloids in lyotropic chromonic liquid crystals. Devika Gireesan Sudha, David P Rivas, sambeeta Das, Linda Hirst The emergence of active nematics has gathered a lot of attention. An exciting recent development in this field was the creation of living liquid crystals - that combines rod-shaped bacteria with water based liquid crystal which give arise to active nematic phase. Here I will be talking about building a similar system, based on synthetic spherical Janus colloids moving in lyotropic chromonic liquid crystal disodium cromoglycate (DSCG). We use Pt coated Janus microspheres, that are chemically triggered by the presence of hydrogen peroxide and track their motion in the nematic phase of DSCG using polarized microscopy. Our studies on individual behavior reveal that the local liquid crystal orientation dictates the direction of motion of the Janus colloids. |
Monday, March 6, 2023 3:36PM - 3:48PM Author not Attending |
D18.00004: Dynamics of Active Brownian Particles in 2D: macro and microphase separation, cluster diffusion, particle geometry effects Giuseppe Gonnella, Claudio Caporusso, Pasquale Digregorio, Antonio Suma, Demian Levis, Leticia Cugliandolo Active matter systems are non-equilibrium systems in which individual particles continually consume internal energy at a local scale and in a sustained way. Their non-equilibrium nature allows for a variety of intriguing phenomena as for instance motility induced phase separation (MIPS). Here, we illustrate peculiar features of MIPS in a system of Active Brownian Particles (ABPs) in 2D [1]. We explain the growth exponent z ≈ 1/3 in the L∼tz law, L being the typical size of clusters of the dense phase and t the time, in terms of an aggregation-condensation mechanism, also taking into account the fractal geometry of aggregates and the diffusion properties of single clusters. We find anomalous dependence of the cluster diffusion coefficient, which decreases as the inverse of the square root of mass, yet increasing with the square of the Peclet number as in the case of single particles [2]. Moreover, we found evidence of another ordering mechanism, i.e., the micro-phase separation of the dense phase into hexatic domains and vapour bubbles [3]. The growth rate of hexatic domains differs from that of the whole clusters and behaves as LH≈t0.2. The size of bubbles at steady-state are controlled by the propulsion force and are also quantitatively described. Finally, we show that changing the geometry of active particles from disks to dumbbells has enormous effects on the dynamics of MIPS, both affecting the value of the growth exponent (z ≈ 3/5) and the motion of single clusters that acquire evident ballistic behaviour. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D18.00005: Active depletion forces Ashreya Jayaram When immersed in a dispersion of smaller "depletants", a colloidal particle experiences depletion forces in the presence of another colloidal particle or under confinement. While the nature of these forces is well-established for passive systems, much less is known about the consequence of making the depletants self-propelled or "active". In this work, we consider a large, optically trapped probe under circular confinement surrounded by smaller active Janus particles. We find that the force experienced by the probe varies non-monotonically as the distance between the colloid and the confinement is increased. To rationalize this observation, we relate the measured force to the active stress and, subsequently, to the microstructure of the surrounding active fluid. Going beyond synthetic active matter, our work could shed light on the organization of intracellular entities in biological systems. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D18.00006: Adaptive microswimmer navigation via surface interactions. Stefania Ketzetzi, Laura Alvarez Frances, Vivien Willens, Lucio Isa Colloidal swimmers are prominent candidates for numerous applications, e.g. in biomedicine, where they could deliver drugs at specific locations within complex environments, i.e. in the presence of confining geometries. Microswimmers typically tend to self-propel parallel to surfaces (1), which for the case of 3D-printed microstructures causes swimmer capture along one-dimensional paths. Along those paths, swimmers exhibit a plethora of cooperative behaviors, i.e. enhanced propulsion speed, motion at preferred distances in self-assembled trains and even compact chains with rich dynamics, depending on path morphology and swimmer directionality (2). Those activity-induced interactions have opened the door towards increasing motion efficiency. Yet, most colloidal swimmers still only have limited adaptability to navigate within confinements, which hinders their applicability. To overcome this, we are currently investigating the emergence of adaptive motility in self-assembled binary colloidal swimmer systems that reconfigure upon encountering surfaces under an ac field. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D18.00007: On the mechanics of active interfaces Luke Langford, Ahmad K Omar Active Brownian particles (ABPs), purely repulsive particles that can undergo liquid-gas phase separation, are among the most widely studied systems exhibiting nonequilibrium phase coexistence. The interface between coexisting active phases has been the subject of recent controversy due to measurements of a negative mechanical surface tension despite being manifestly stable. In this talk we outline a generic route to derive an interfacial equation of motion (EOM) beginning from the microscopic particle dynamics. Our explicit coarse-graining allows for the description of interfaces arbitrarily far from equilibrium. In general, the nonequiblrium interfacial EOM is KPZ-like with a non-linearity that vanishes when the fluctuation-dissipation theorem is satisfied (i.e., for systems in equilibrium). We apply this perspective to ABPs, demonstrating that the effective surface tension governing the interfacial EOM is indeed distinct from the mechanical surface tension and strictly positive. In addition, we discuss how the effective surface tension and driving coefficient scale with activity and its implications for the stability of active interfaces. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D18.00008: Spinning active rods Thibault Lefranc, Carla Fernandez-Rico, Roel Dullens, Denis Bartolo From active colloids to active droplets, the elementary units of synthetic active matter are isotropic bodies. This simple morphology contrasts with the exemples found in biological systems, from active polymers to bacteria and living creatures. In this talk I will show how to motorise rod-shaped active particles and will provide a first insight into their phase behavior. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D18.00009: Entropons as collective excitations in active solids Hartmut Löwen, Lorenzo Caprini, Andrea Puglisi, Umberto Marini Bettolo Marconi The vibrational dynamics of solids is described by phonons constituting basic collective excitations in equilibrium crystals. Here we consider an active crystal composed of self-propelled particles which bring the system into a non-equilibrium steady-state governed by entropy production. Calculating the entropy production spectrum, we put forward the picture of "entropons", which are vibrational collective excitations responsible for entropy production. Entropons are purely generated by activity and coexist with phonons but dominate over them for large self-propulsion strength. The existence of entropons can be verified in experiments on dense self-propelled colloidal Janus-particles and granular active matter, as well as in living systems such as dense cell monolayers. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D18.00010: Direct Numerical Simulations of Metallodielectric Janus Particles John J Molina, Takuya Eriguchi, Ryoichi Yamamoto Metallodielectric Janus particles under external electric fields have quickly become one of the canonical experimental realizations of active matter systems. However, given the complexity of the system, which includes the polarizability of the particles, the electro-hydrodynamic phenomena (e.g., induced-charge electrophoresis), and the particle-fluid coupling, many of the observed single and many-particle properties have not been fully explained. To overcome this, we introduce an extension of the Smoothed Profile Method [1], a direct numerical simulation method for hydrodynamically interacting rigid particles in complex fluids, in order to explicitly incorporate the propulsion mechanism of metallodielectric Janus particles fueled by external electric fields. We use this model to perform 2D and 3D simulations of Janus particles under AC/DC electric fields, in order to study their single and many-particle dynamics, and the dependence on the (frequency-dependent) material properties. |
Monday, March 6, 2023 5:00PM - 5:12PM Author not Attending |
D18.00011: Activity-induced interactions and collective response in active colloidal suspensions Ignacio Pagonabarraga Active suspensions can displace in a liquid medium in which they are suspended as a result of nonequilibrium processes, such as chemical reactions, or inhomogeneous thermal heating. These are intrinsically out of equilibrium systems, which makes them very versatile, with a natural tendency to self-assemble. Due to their small size, these out of equilibrium dynamical states generates flows that induce long range hydrodynamic interactions. These interactions have profound effects in the transport and assembly of colloidal suspensions. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D18.00012: Power-law intermittency in the active motion of colloidal swimmers Peter Schall, Daniela J Kraft, Stefania Ketzetzi, Nick Oikonomeas-Koppasis Colloidal microswimmers have received broad interest, serving as archetypical active fluid system, and as models for their biological conterparts. While the principles of their motion has been vastly explored and the velocity dependence on system parameters studied in detail, the nature of their time-dependent motion has been less addressed. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D18.00013: Active motion of Janus particles in thermotropic liquid crystals Antonio Tavera-Vazquez, Sam Rubin, Gustavo Perez, Walter Alvarado, Juan J De Pablo Studies of self-propelled colloids suspended in isotropic liquid mixtures have advanced significantly over the last decade. However, investigations of self-propelled systems in out-of-equilibrium liquid crystal (LC) interfaces have been scarce. In this work, we consider light-activated self-propelled particles in nematic systems. Specifically, we use Janus silica particles half-coated with titanium, immersed in a thermotropic LC, and confined in a slit channel. The Janus particles' mobility is triggered by light. The light-absorbing side of the colloids is heated, thereby inducing a localized LC nematic-isotropic (NI) phase transition. Consequently, the colloids move because of the uneven distribution of the NI interface around them. We use particle tracking analysis to examine the optical response of the LC that underlies the particles' trajectories. We implement machine-learning-based simulations to reproduce the colloids' dynamics, accounting for the elastic, surface, and Landau-de Gennes interactions. This research contributes to a better understanding of micro swimmers' trajectories immersed in highly structured media. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D18.00014: From a microscopic inertial active matter model to the Schrödinger equation Michael te Vrugt, Tobias Frohoff-Hülsmann, Eyal Heifetz, Uwe Thiele, Raphael Wittkowski Field theories for the one-body density of an active fluid, such as the paradigmatic active model B+, are simple yet very powerful tools for describing phenomena such as motility-induced phase separation. No comparable theory has been derived yet for the underdamped case. In our work, we introduce active model I+, an extension of active model B+ to particles with inertia. The governing equations of active model I+ are systematically derived from the microscopic Langevin equations. We show that, for underdamped active particles, thermodynamic and mechanical definitions of the velocity field no longer coincide and that the density-dependent swimming speed plays the role of an effective viscosity. Moreover, active model I+ contains the Schrödinger equation in Madelung form as a limiting case, allowing to find analoga of the quantum-mechanical tunnel effect and of fuzzy dark matter in the active fluid. We investigate the active tunnel effect analytically and via numerical continuation. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D18.00015: Characterization of non-equilibrium melting in a 2D crystal Ankit Vyas, Ashley Z Guo, stefano sacanna, Andrew D Hollingsworth, Paul M Chaikin Here we study how a non-equilibrium 2D crystal undergoes melting as a function of activity. We use a system of charged particles confined to an oil-water interface forming a 2D lattice, a fraction of which have additional magnetic particles that sit directly below them and are rotated by an external magnetic field. This activity allows for the proliferation of topological defects, leading to melting of the 2D crystal. We characterize the nature of this melting transition and determine its order using conventional tools such as g6(r) and the local distribution of Ψ6. In addition, we use information theoretic approaches such as the computable information density (CID) and calculation of entropy production to gain further insight into the behavior of this non-equilibrium melting transition. |
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