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 L05: Active Matter in Complex Environments IIILive
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Sponsoring Units: DSOFT DBIO GSNP DFD Chair: Sujit Datta, Princeton University; Tapomoy Bhattacharjee, Princeton University Room: 05 |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L05.00001: Crowding-Enhanced Diffusion: An Exact Theory for Highly Entangled Self-Propelled Stiff Filaments Suvendu Mandal, Christina Kurzthaler, Thomas Franosch, Hartmut Löwen We study a strongly interacting crowded system of self-propelled stiff filaments by event-driven Brownian dynamics simulations and an analytical theory to elucidate the intricate interplay of crowding and self-propulsion. We find a remarkable increase of the effective diffusivity upon increasing the filament number density by more than one order of magnitude. This counterintuitive “crowded is faster” behavior can be rationalized by extending the concept of a confining tube pioneered by Doi and Edwards for highly entangled, crowded, passive to active systems. We predict a scaling theory for the effective diffusivity as a function of the Peclet number and the filament number density. Subsequently, we show that an exact expression derived for a single self-propelled filament with motility parameters as input can predict the nontrivial spatiotemporal dynamics over the entire range of length and timescales. In particular, our theory captures short-time diffusion, directed swimming motion at intermediate times, and the transition to complete orientational relaxation at long times. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L05.00002: Dynamics of entangled active polymers Andrés R Tejedor, Jorge Ramirez The more accurate theory to describe the dynamical response of entangled linear polymers is the tube theory. In this work, we extend the theory to consider the effect of an active force (drift) that drives the polymer along the tube in a certain direction. We envision a flexible linear polymer which diffuses through a mesh of fixed obstacles under the effect of some internal activity, which results in a constant drift velocity pointing always in the same direction along the tube but slow enough to keep the isotropy of the reptation theory. The combination of reptation and activity results in new physical behavior not previously reported. In particular, the transport properties are significantly enhanced: the dependence of the viscosity with the molecular weight becomes linear whereas the diffusion coefficient of the center of mass becomes independent of the molecular weight. In addition, a superdiffusive regime in the mean squared displacement of the center of mass emerges at intermediate distances. We hypothesize that the model can be experimentally accessible employing the tools of active matter and it will be useful in the design of superfluid materials. All our results have been derived by means of analytical theory and verified by Brownian dynamics simulations. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Not Participating |
L05.00003: Can activity in a suspension cause thickening or dethickening? Edward Ong, Danilo Liarte, Itay Griniasty, Meera Ramaswamy, Christopher Ness, James Patarasp Sethna, Itai Cohen We describe our investigations into the ability of active matter to tune shear thickening and jamming in colloidal suspensions. Active colloidal suspensions exhibit many interesting features including swarming, motility-induced phase separation and disordered hyperuniformity. Such features arise microscopically from various self-propulsion and self-organization mechanisms and can lead to rheological signatures such as shear thinning and super fluidity. Here, by altering the density and activity of the microparticles, we propose to tune the shear thickening, jamming and yielding behavior of an active colloidal suspension. We carry out our investigations on an active optorheological medium consisting of titanium dioxide particles which self-propel upon activation by ultraviolet light, allowing the activity and thus the shear thickening rheology of the suspension to be tuned via the light intensity and particle concentrations. The addition of activity to the parameter space governing the transition between the thickened, jammed and yielding state would provide an extremely powerful and convenient tuning mechanism to rapidly modify the shear behavior of the suspension on the go. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L05.00004: Active colloidal gel Mengshi Wei, Matan Yah Ben Zion, Olivier Dauchot One of the distinctive properties of living systems is to be self-driven. They thereby access emergent properties. Molecular motors, which stiffen and contract cytoskeletal networks, make a good example in nature. Here, we designed an artificial self-driven active gel which combines elastic architectures and activity by embedding active particles inside colloidal networks. By triggering the activity of a small fraction of active particles, the colloidal networks re-organize due to the internal driving. At the microscopic level, we look into the short time vibrational dynamics and long-time dynamical correlations and analyze how they depend on the local structure of the gel. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L05.00005: What can kinetic Monte Carlo do for active Matter? Juliane Klamser, Olivier Dauchot, Julien Tailleur As an efficient numerical method, discrete-time, continuous-space Monte Carlo (MC) is wildly used in physics. While constructing an active matter version is straightforward, the question remains to what extent it faithfully captures real-world active systems. We focus on a kinetic MC version for the simplest kind of active matter: persistently moving, non-polar, interacting particles. On the multi-particle level, the MC dynamics captures not only Motility-induced phase separation (a characteristic active matter phenomenon) but also features a non-equilibrium extension of the celebrated two-dimensional melting. An attempt to characterize these phases and their transitions traditionally relies on the existence of a thermodynamic pressure, which is not guaranteed outside equilibrium. In fact, small modifications of the MC rules have existential consequences for thermodynamic pressure. For a soundly chosen version of the MC dynamics, we show that pressure is a thermodynamic state variable over a robust parameter range. This is demonstrated by deriving the corresponding Langevin description and the associated expression for pressure, which is confirmed by large scale many-particle simulations. This work, therefore, contributes to equipping a MC toolbox for active Matter. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L05.00006: A reinforcement learning approach to optical control of active matter Martin Falk, Arvind Murugan Even in bulk, uniform systems, active matter has already shown exciting new physics and potential for materials development. Additionally, spatio-temporal control of active systems is becoming experimentally possible in a variety of ways. Activity itself is an appealing control knob that is qualitatively similar across active matter systems; while active systems can differ in their details, they generally contain a scalar field associated with local microscopic energy dissipation. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L05.00007: Energetics of critical oscillators in active bacterial baths Edgar Roldan, Ashwin Gopal, Stefano Ruffo We investigate the nonequilibrium energetics near a critical point of a non-linear driven oscillator immersed in an active bacterial bath. At the critical point, we reveal a novel scaling exponent of the average power in terms of the effective diffusivity and the correlation time of the bacterial bath. We also investigate the mean stationary power and the variance of the work both below and above the saddle-node bifurcation. Above the bifurcation, the average power attains an optimal, minimum value for finite correlation time that is below its zero-temperature limit. We also reveal a finite-time uncertainty relation for active matter which leads to values of the Fano factor of the work that can be below 2k_B T_eff, with T_eff the effective temperature of the oscillator in the bacterial bath. We analyze different Markovian approximations to describe the nonequilibrium stationary state of the system. Finally, we illustrate our results in the experimental context considering driven colloidal particles in periodic optical potentials within an E. Coli bacterial bath. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L05.00008: Swimming behavior of Paramecium in crowded environments Nicolas Escoubet, Romain Brette, Alexis Michel Prevost, Léa-Laetitia Pontani Paramecium is a large unicellular ciliate (100-300 µm long) that swims in fresh water environments. Its swimming behavior is classically described as alternations between “straight” paths and abrupt changes in direction, known as the avoiding reaction (AR). This AR can either be spontaneous or induced by mechanosensitive contacts with obstacles. No quantitative measurements of this swimming behavior at both local length scales and large times have been provided so far. Here, we report on extensive measurements of the trajectories of Paramecium tetraurelia in engineered environments with and without obstacles. At large times, we find that Paramecium’s motion is diffusive-like and our preliminary results suggest that the diffusion constant decreases with the obstacles density. We are currently investigating the local details of the mechanosensitive AR in order to understand how this diffusive regime depends on the mechanosensitivity of Paramecium. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L05.00009: Using unsupervised machine learning to detect depinning and clustering transitions in active matter driven across quenched disorder Danielle McDermott, Cynthia Reichhardt, Charles Reichhardt Using large-scale numerical simulations of active disks, we demonstrate that a machine learning order parameter can detect depinning transitions and different dynamic flow phases in systems driven far from equilibrium. We model active agents as monodisperse disks executing run-and-tumble motion subject to an external driving force in an environment of quenched disorder. The machine learning order parameter identifies a variety of transitions including the formation of clogged states at low applied drive, the depinning transition and onset of clustering states at intermediate drives and laned states at high drives. These phase transitions are not readily distinguished with traditional measurements, such as the average cluster size and giant cluster fluctuations. We develop several order parameters using principal component analysis applied to particle location, local ordering, and local velocity and compare these to traditional measures. Our results should be useful to characterize a broad class of particle-based systems that exhibit depinning and clustering transitions. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L05.00010: Modeling collective cell migration on substrates with topological defects Kurmanbek Kaiyrbekov, Kyle T Sullivan, Brian Camley Collective migration of cell monolayers is important for both wound healing and development, and an example of active matter physics in biology. Recent experiments have highlighted the importance of liquid crystal order and topological defects within these layers, in particular suggesting that +1 defects have a role in organizing tissue morphogenesis. In this work we perform 2D active Monte Carlo simulations to investigate cell arrangements and motion on a substrate patterned with ridges that induce a +1 defect. We model different cell types as self-propelled deformable ellipses that interact via Gay-Berne potential. We find that, consistent with experiments from the Serra group, cells are denser and more isotropic toward the center of the defect. This density change is controlled by the stiffness of the cells and their preferred aspect ratio. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L05.00011: Extracted Active Fluctuations from an Active-Passive Mixture Reveal the Dynamic Class of Active Materials Chong Shen, H Daniel Ou-Yang Dynamic class of active materials, i.e., run-and-tumble, active Brownian, etc., can be characterized by the histograms of their active fluctuations. However, active fluctuations cannot be directly measured because they are always mixed with thermal fluctuations in experiments. Extracting the active fluctuations from that of a mixture is nontrivial because the histogram is not a linear superposition of the histograms of the active and passive fluctuations. We developed a deconvolution method to extract the active fluctuations from that of a mixture. Our deconvolution method is verified by Langevin-based numerical simulation of an active Brownian particle (ABP) in quadratic confinement. Using our method, we have extracted active fluctuations from an ICEP-driven particle in an optical trap, which reveals expected ABP dynamics. We have also extracted active fluctuations from a probe particle embedded in a suspension of E. coli, which reveals an unexpected run-and-tumble dynamic of the probe particle. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L05.00012: Inverse Solidification Induced by Active Janus Particles Vyacheslav Misko V. R. Misko, T. Huang, S. Gobeil, X. Wang, F. Nori, J. Schütt, J. Fassbender, G. Cuniberti, D. Makarov, L. Baraban (RIKEN; TU, HZDR-Dresden; VU-Brussels; U-Michigan). Crystals melt and the crystalline long-range order vanishes when thermal excitations or defect concentration in the lattice is sufficiently high. In contrast to this classical scenario, we demonstrate [1] a counter-intuitive occurrence of crystalline long-range order in an initially disordered matrix of passive colloidal particles accommodating chemically active defects - photocatalytic Janus particles (JP). The observed crystallization occurs when the amount of active-defect-induced fluctuations reaches critical value. The driving mechanism behind this unusual behavior resembles a blast-induced solidification. Here the role of "internal micro-blasts" is played by the active defects. The defect-induced solidification occurs under non-equilibrium conditions: the resulting solid exists as long as a constant supply of energy is provided by the catalytic photochemical reaction at the surface of active JP. Our findings could be useful for understanding of the phase transitions of matter under extreme conditions far from thermodynamic equilibrium. [1] T. Huang et al., Adv. Funct. Mater. 2003851 (2020). |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L05.00013: Slow Diffusion in Active Bath: Theoretical Description of the Activity-induced Energy Landscape Subhasish Chaki, Rajarshi Chakrabarti Active motions giving rise to non-equilibrium fluctuations are ubiquitous in biological cells. In the dilute active systems, the dynamics of the active system can be mapped to an effective equilibrium by defining an active temperature. This active temperature is usually higher than the ambient temperature and hence, the mean escape of time of the active particle decreases with increasing the activity. However, in dense active environment like biological cells, the scenario will be completely different. In this context, we have studied a prototype model for diffusion in an activity-induced rugged energy landscape to describe the dynamics of a tagged particle in a dense active environment. In the low activity limit, we have found that the mean escape time increases with increasing the activity. Hence, the dynamics of the tagged particle will be slowed down with increasing the activity and this is completely different than what we have seen in the effective equilibrium approach. The activity-induced rugged energy landscape approach to describe the slow dynamics is valid for small activity and high persistence time limit.<gdiv></gdiv><gdiv></gdiv> |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L05.00014: First passage of an active particle in the presence of
passive crowders Animesh Biswas, J. M. Cruz, Punit Parmananda, Dibyendu Das
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