Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N11: Active Colloids IIRecordings Available
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Sponsoring Units: DFD Chair: Shih-Yuan Chen, Northwestern University Room: McCormick Place W-181B |
Wednesday, March 16, 2022 11:30AM - 11:42AM |
N11.00001: Colloidal spinners self-organize into an odd crystalline whorl state Ephraim S Bililign, Florencio Balboa Usabiaga, Yehuda A Ganan, Alexis Poncet, Vishal H Soni, Sofia Magkiriadou, Denis Bartolo, Michael J. Shelley, William T Irvine We report the assembly of an odd crystal comprised of thousands of spinning colloidal magnets. By activating the system at the single unit level, we extend the simple longitudinal interactions of typical crystals to incorporate a broader class of transverse interactions. At the system scale, this deceptively simple generalization organizes colloidal spinners into a crystalline whorl state that blurs the line between solid and liquid. The crystal whorl dynamics drive super-diffusive mass transport, which can be controlled over orders of magnitude. We show this state is generically accessible due to an instability driven by odd elastic stresses. |
Wednesday, March 16, 2022 11:42AM - 11:54AM |
N11.00002: Dynamic Simulation of a Population of Quincke Particles Hang Yuan, Monica Olvera De La Cruz Understanding the universal principles hidden behind the diverse collective behaviors exhibited in various active systems is of great interest to the active matter community. The active particles driven by Quincke rotation, which is the spontaneous rotation of dielectric particles immersed in a weakly-conducting liquid under the application of a DC electric field, serves as an ideal synthetic system for studying collective motions of active materials. Quincke particles have been reported to show rich emergent patterns at different conditions such as swarms, clusters, vortexes, bands, amorphous solids and so on. We report here on the development of a particle-based simulation of a population of Quincke particles. The simulation method modifies the Stokesian Dynamics method with the additional Quincke rotation mechanism. With all essential microscopic interactions like electrostatic and hydrodynamic interactions systematically considered, we are possibly to elucidate the physical principles governs the formation of emergent diverse collective behaviors of Quincke particles with large-scale simulations. |
Wednesday, March 16, 2022 11:54AM - 12:06PM |
N11.00003: Instability of dilute suspensions over and through riblets Maryam Bagheri, Vijay M Kumar, Parisa Mirbod Understanding the flow behavior of suspensions has been of great importance due to the potential applications in the environmental, industrial, and pharmaceutical fields. This study is focused on the motion of a dilute, non-Brownian, neutrally-buoyant suspension of rigid spherical particles passing over and through a periodic two-dimensional riblet geometries transverse to the mean flow. We performed both particle image velocimetry and particle tracking velocimetry (PIV/PTV) techniques to examine the velocity, vorticity, and particle concentrations along the streamwise and spanwise directions and pressure drop measurements. We also analyzed in detail the flow and particle dynamics. The results clearly demonstrate that the flow instability in a channel with riblets occurs at much lower flow rates compared to the Newtonian solvent. |
Wednesday, March 16, 2022 12:06PM - 12:18PM |
N11.00004: Quincke oscillations of colloids at planar electrodes Zhengyan Zhang, Hang Yuan, Yong Dou, Monica Olvera De La Cruz, Kyle Bishop Dielectric particles in weakly conducting fluids rotate spontaneously when subject to strong electric fields. Such Quincke rotation near a plane electrode leads to particle translation that enables physical models of active matter. Here, we show that Quincke rollers can also exhibit oscillatory dynamics, whereby particles move back and forth about a fixed location. We explain how oscillations arise for micron-scale particles commensurate with the thickness of a field-induced boundary layer in the nonpolar electrolyte. This work enables the design of colloidal oscillators. |
Wednesday, March 16, 2022 12:18PM - 12:30PM |
N11.00005: Molecular Dynamics Simulations of Diffusiophoretic Motion of Nanoparticles Binghan Liu, Gary S Grest, Shengfeng Cheng Diffusiophoresis refers to the spontaneous motion of particles or polymers in a fluid induced by a concentration gradient of solutes. Large scale molecular dynamics simulations are used to study the diffusiophoretic movement of colloidal particles dispersed in a suspension of nanoparticle solutes that possess a steady-state concentration gradient. This gradient is caused and maintained by a membrane that is transparent to the solvent but allows unidirectional passage of the nanoparticle solutes from one side to the other. By suppressing the overall flow across the system, a concentration gradient of the nanoparticle solutes is established, which leads to a chemical potential gradient for the colloidal particles and drives their diffusiophoretic motion. With this setup, the sign of the diffusiophoretic mobility and its dependence on the size contrast between the diffusiophoretic colloidal particles and the nanoparticle solutes are systematically studied. By elucidating the physics of diffusiophoresis, the results will help reveal the fundamental mechanism underlying the recently observed stratification phenomena in suspensions of colloidal particles with polydisperse size distributions. |
Wednesday, March 16, 2022 12:30PM - 12:42PM |
N11.00006: A thermodynamically compliant model for the dynamics of a swarm of microswimmers Andrés Córdoba, Jay D Schieber The effect of the concentration of swimmers in the dynamics of a swarm of diffusiophoretic microswimmers is analyzed. For that purpose, a Janus dumbbell model inspired by the nonequilibrium thermodynamics of multi-component fluids that undergo chemical reactions is used. One of the beads of the dumbbell is allowed to act as a catalyst for a chemical reaction between the reactants. The entropy balance for the model allows one to check that the entropy production rate stays positive for a given set of parameters [J. Chem. Phys. 152, 194902 (2020)]. The second law of thermodynamics shows that in the typical classification of microswimming mechanisms the Janus dumbbell is a pusher. The flow field produced by a periodic swarm of these pusher dumbbells is found by solving the Stokes equation. A Janus dumbbell in the swarm can swim up to seven times faster than when alone. This occurs in a swarm where the distance between dumbbells is about 3.3 times their length. However, at those higher dumbbell concentrations hydrodynamic interactions produce significant rotational velocities that, after some time of ballistic motion, can cause instabilities in the ordered structure of the swarm. |
Wednesday, March 16, 2022 12:42PM - 12:54PM |
N11.00007: Omnidirectional treadmills on a chip for swimming microorganisms Jeremias M Gonzalez, Ajay Gopinathan, Bin Liu Motilities of swimming microorganisms are typically studied in a close geometry confined by glass substrates or microfluidic boundaries. Here, we introduce a microscope-compatible microfluidic chip that generates three-dimensional flows that serve virtually as omnidirectional treadmills for microorganisms. Such flows are generated by dynamic pressure regulations through six microfluidic channels offset in elevations. We demonstrate the micromanipulation capacity of such a treadmill by drawing flows into desired patterns, e.g., a square pattern with all entrained microparticles following a square-shaped trajectory. We also show that such flows are uniform for the purpose of the microorganisms' treadmill, consistent with a strain-free condition that is preserved by the symmetry incorporated into the chip. We extend the application of such strain-free treadmills to freely swimming bacteria as perturbation-free manipulations. |
Wednesday, March 16, 2022 12:54PM - 1:06PM |
N11.00008: Agilely Reconfigurable Swarms Stimulated by Light in an Electric Field Donglei E Fan Collective behaviors represent a wide range of phenomena that exist both in nature and artificial systems. Simple interactions among many constituting members in a system can result in complex structures and motions. Here, we report an innovative colloidal system made of dense Si nanorods that exhibit agilely reconfigurable swarming behaviors that can be readily switched by visible light in an AC rotating field. We observed two distinct self-organizing phenomena, i.e., nanowires form into interconnected 2D networks and self-assembled multi-droplets. Theoretical modeling considering light-controlled electrostatic interactions well explains the observation. This research presents an emerging swarm system that opens new opportunities for fundamental research and applications. |
Wednesday, March 16, 2022 1:06PM - 1:18PM |
N11.00009: Light-switchable propulsion of active particles with reversible interactions Hanumantha Rao Vutukuri Active or self-propelled colloidal-particle systems are currently a subject of great interest in soft condensed matter science, owing to their ability to mimic the collective behavior of complex living systems, but also to serve as model systems to study intrinsically out-of-equilibrium systems. Self-propelled particles can exhibit rich collective behavior, such as clustering, segregation, and anomalous density fluctuations, by consuming internal energy or extracting energy from their local environment in order to generate their own motion. Control over the propulsion direction and switchability of the interactions between the individual self-propelled units may open new avenues in the designing materials from within. In this talk, we present a unique self-propelled particle system, consisting of half-gold coated Titania particles, in which we can fast and on-demand reverse the propulsion direction, by exploiting the different photocatalytic activities on both sides. We demonstrate that the reversal in propulsion direction changes the nature of the hydrodynamic interaction from attractive to repulsive and can drive the particle assemblies to undergo both fusion and fission transitions. Moreover, we show these active colloids can act as nucleation sites, and switch rapidly the interactions between active and passive particles, leading to reconfigurable assembly and disassembly. Our experiments are qualitatively described by a minimal hydrodynamic model. These results would open new possibilities to drive the arrested systems (e.g. gels, and glasses) by “stirring with light”. |
Wednesday, March 16, 2022 1:18PM - 1:30PM |
N11.00010: Development of all magnetic active matter Gouri Patil, Pranay Mandal, Ambarish Ghosh In the world of low Reynolds number, the role of inertia is entirely negligible, which has resulted in the evolution of novel swimming strategies adopted by the microorganisms to overcome the fluidic drag. Inspired by such techniques, we model magnetically actuated helical swimmers as active particles1. The activity and density of this artificial system can be tuned externally to better understand the evolution of collective behaviour like the swarming/flocking phenomena. In the past, helical swimmers were designed for reciprocal swimming with motility in the form of back-and-forth motion and unspecified directionality. This represents a zero-force, zero-torque active matter system with enhanced diffusion2,3. Here for the first time4, we break the time-reversal symmetry by engineering a suitable magnetic field aided by thermal fluctuations in the surrounding medium. The swimmers can exhibit non-reciprocal swimming with enhanced diffusivities, with activity as a function of the frequency of the external field and a two-parameter space. The experimental results and numerical simulations are in excellent agreement, establishing an all magnetic active matter. |
Wednesday, March 16, 2022 1:30PM - 1:42PM |
N11.00011: Collective dynamics of driven colloids on ordered and disordered magnetic landscapes Pietro Tierno, Ralph L Stoop, Dominik Lips, Philipp Maass In this talk I will discuss recent results obtained in my group by using paramagnetic colloidal particles driven across two dimensional periodic and random magnetic landscapes. These |
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