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 A06: Colloids and Granular MaterialsLive
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Sponsoring Units: DSOFT Chair: Luis Pugnaloni Room: 06 |
Monday, March 15, 2021 8:00AM - 8:12AM Live |
A06.00001: Critical Scaling of Compression-Driven Jamming of Frictionless Spheres Stephen Teitel, Anton Peshkov We numericaly study the jamming transition of athermal, overdamped, frictionless spheres in two and three dimensions, compressed isotropically at a fixed rate γ. The finite compression rate introduces a control time scale, which allows one to probe the critical time scale associated with jamming. As was found previously for steady-state shear-driven jamming, we find for compression-driven jamming that pressure obeys a critical scaling relation as a function of packing fraction φ and compression rate γ, and that the bulk viscosity p/γ diverges upon jamming. A scaling analysis determines the critical exponents associated with the compression-driven jamming transition. Our results suggest that stress-isotropic, compression-driven, jamming may be in the same universality class as stress-anisotropic, shear-driven, jamming. |
Monday, March 15, 2021 8:12AM - 8:24AM Live |
A06.00002: Packings of superellipse sector particles Sykes Cargile, Kellianne Kornick, Scott V Franklin, Ted Brzinski Non-convex particles are able to mutually entangle, and, for example, produce packings with finite tensile strength even for particles that only interact via repulsive forces. While prior work has focused on the effects of shape parameters such as angularity, aspect ratio, and non-convexity, there has not been a framework that generalizes these results to all particle shapes. Superellipse sector particles (SeSPs) comprise a generalized class of two-dimensional particles defined as sections of superelliptical arcs with finite thickness. Thus, SeSPs form a versatile model system for non-convex particles. SeSP geometry is parameterized by aspect ratio, thickness, subtended arc length, and the powers of the superelliptical curve. The large parameter space allows for independent control of generalizable shape parameters such as aspect ratio, angularity, and non-convexity. We use molecular dynamics simulations to characterize the internal structure and mechanical response of stable packings of SeSPs, as a function of particle geometry. |
Monday, March 15, 2021 8:24AM - 8:36AM Live |
A06.00003: Excluded area, entanglement, and packing of superellipse sector particles Kellianne Kornick, Ted Brzinski, Scott V Franklin Superellipse sector particles (SeSPs) are segments of superelliptical curves and form a tunable set of hard-particle shapes for granular and colloidal systems. SeSPs allow for continuous parameterization of corner sharpness, aspect ratio, and particle curvature; rods, circles, rectangles, and staples are examples of specific SeSPs. We measure the excluded area of SeSPs as a function of opening aperture size, starting with the special case of annular particles before generalizing to more angular shapes. The excluded area of annuli decreases sigmoidally with increasing opening aperture; for SeSPs with sharper corners the curve becomes more step-shaped. Whether two particles can be placed without overlap depends on both radial separation and relative orientation. Mapping allowed two-particle configurations reveals circular regions centered at each of a particle's two endpoints that indicate configurations of mutually-entangled particle interactions. Simultaneous mutual entanglement with both endpoints is geometrically impossible: the overlap of these two regions represents an excluded area in which no particles can be placed regardless of orientation. The regions' distinct boundaries reflects translational frustration with implications for the dynamics of particle rearrangements. |
Monday, March 15, 2021 8:36AM - 8:48AM Live |
A06.00004: Dynamics of an intruder moving through a confined granular medium: Rescaled packing fraction yields data collapse for different intruder and system sizes. C. Manuel Carlevaro, Ryan Kozlowski, Luis Pugnaloni, Hu Zheng, Joshua Socolar, Rituparna Basak, Chao Cheng, Lou Kondic We consider an intruder dragged by a spring though a layer of bidisperse disks constrained in a fixed volume Couette cell in both discrete element simulations and experiments. The spring is loaded slowly, leading to stick-slip dynamics of the intruder. As the intruder advances, the medium develops large density heterogeneities, with a region in front of the intruder more densely packed and a region behind the intruder depleted of particles. We explore a range of annulus widths W, intruder sizes D, and global packing fractions Φ and measure the fluctuating force on the intruder. We find that an effective packing fraction, defined as Φeff = Φ W / (W - D), can account for the combined effect of the three variables, collapsing the data to a single curve. When Φeff is equal to the steady-state packing fraction of quasi-statically sheared packings under fixed confining pressure, the disks pack after some time into annular regions outside the intruder's path, leaving a channel that allows for unimpeded motion of the intruder. Increasing values of Φeff lead to increasing average forces and longer sticking periods as the intruder finds difficult to clear an open channel through which to move. |
Monday, March 15, 2021 8:48AM - 9:00AM Live |
A06.00005: Adjusting Images of a Conical Bead Pile through Linear Transformations Melita F Wiles, Susan Y Lehman A conical bead pile is a used to model a system to learn about the behavior of granular systems. The pile is a critical system of roughly 20,000 steel beads atop a circular base; each bead is 3 mm in diameter. The pile is driven by adding one bead at a time to the pile apex. Any bead drop could trigger an avalanche, which we define as any number of beads leaving the pile. In order to analyze the dynamic behavior of individual avalanches, an aerial view camera records each avalanche at least 50 beads in size. We feed these images into a MATLAB program that analyzes the movement or velocity of sections of the pile. Since the camera cannot be directly above the apex of the pile, but is somewhat offset, the images produced are slightly distorted, leading to relative shifts in the velocity data for different locations on the pile. We reprocess the images taken by the camera using linear transformations through a homography matrix. This process is applied to batches of distorted images through a Mathematica program that produces the ideal viewpoint images. The technique will allow us to accurately analyze the pile behavior and movement of the beads on the pile, regardless of where the beads are located. |
Monday, March 15, 2021 9:00AM - 9:12AM Live |
A06.00006: Physical mechanism of erythrocytes sedimentation rate Alexis Darras, Anil Kumar Dasanna, Semen Buvalyyy, Thomas John, Christian Wagner, Dmitry A. Fedosov, Lars Kaestner Red blood cells (or erythrocytes) sedimentation rate (ESR) is a physical parameter of blood which is often checked in medical diagnosis. It is indeed well known that in case of inflammation, the increase in fibrinogen and other proteins induces a higher ESR. |
Monday, March 15, 2021 9:12AM - 9:24AM Live |
A06.00007: Diffusiophoresis in drying colloidal blends: A powerful tool to control film architecture Ignacio Martin-Fabiani, Yichen Dong, James Tinkler, Radmila Tomovska, Maialen Argaiz, Alberto Scacchi, Andrew Archer, Tao Sun Gradients in particle concentration promote size segregation in drying colloidal blends. As the solvent evaporates, colloids accumulate near the top interface as it moves down. This results in a larger particle concentration close to the air/solvent interface and smaller near the substrate. Such gradient pushes down larger particles at a faster speed than small particles, yielding a stratified colloidal film with the majority of small particles at the top and the majority of large particles at the bottom.1 |
Monday, March 15, 2021 9:24AM - 9:36AM Live |
A06.00008: Particle-resolved topological defects of smectic colloidal liquid crystals in extreme confinement Rene Wittmann, Louis Cortes, Hartmut Löwen, Dirk Aarts Hard particles are a standard model for colloidal systems and can be effectively studied within classical density functional theory (DFT). Fundamental mixed measure theory (FMMT) allows to predict the phase behavior of a hard-body fluid solely from the shape of individual particles. |
Monday, March 15, 2021 9:36AM - 9:48AM Live |
A06.00009: The ciliated structure as a particle detector Jean-Baptiste Thomazo, Benjamin Le Reverrend, Léa-Laetitia Pontani, Alexis Michel Prevost, Elie Wandersman To mimic the mechanical response of passive biological cilia in complex fluids, we study the bending dynamics of an anchored elastic fiber submitted to a dilute granular suspension under shear. We show that the bending fluctuations of the fiber accurately encode minute variations of the granular suspension concentration. Indeed, besides the stationary bending induced by the continuous phase flow, the passage of each single particle induces an additional deflection. We demonstrate that the dominant particle/fiber interaction arises from direct contacts of the particles with the fiber and we propose a simple elastohydrodynamics model to predict their amplitude. Our results shed light on the extreme mechanical sensitivity of biological cilia to detect the presence of solid particles in their vicinity and bring a physical framework to describe their dynamics in particulate flows. |
Monday, March 15, 2021 9:48AM - 10:00AM Live |
A06.00010: The Hydra String Method: A Novel Means to Explore Potential Energy Surfaces and its Application to Granular Materials Christopher Moakler, Katherine A Newhall I will discuss an entirely different approach to understanding the complex behavior of granular materials, built on a novel method to find ensembles of pathways between stable packings of the system. This Hydra String Method is an efficient and autonomous way to trawl any potential energy surface to enumerate the saddles, minima, and form a network representation of the connections between them. I apply the Hydra String Method to bi-disperse configurations of frictionless soft spheres, with the future aim to use the ensembles of pathways to statistically predict the dynamics of a sheared system. |
Monday, March 15, 2021 10:00AM - 10:12AM Live |
A06.00011: Application of computational topology to analysis of granular material force networks in the stick-slip regime. Rituparna Basak, Chao Cheng, Ryan Kozlowski, C. Manuel Carlevaro, Luis A. Pugnaloni, Hu Zheng, Joshua Socolar, Lou Kondic We discuss the properties of force networks in a two-dimensional annular Couette geometry for both experiments and simulations in which a small intruder is pulled by a spring. In particular, the connection between topological features of the force network and fluctuations of the intruder velocity is studied in the stick-slip regime. The force networks are analyzed using persistent homology methods, focusing on the statistics of clusters and loops composed of particles experiencing strong forces. We find that the networks evolve in a nontrivial manner as the system approaches a slip event. The presentation will discuss this evolution for systems of disks and pentagonal particles at several different packing fractions. |
Monday, March 15, 2021 10:12AM - 10:24AM Live |
A06.00012: Capture of particles by a flexible, granular envelope Ted Brzinski, Colby Ferrigno, Katharine D Bancroft A passive, flexible envelope can irreversibly capture comparatively small objects. As a familiar example, objects like fitted sheets and duvet covers in consumer laundry dryers often capture smaller items, like socks. The same mechanics may improve the efficiency of active processes, like the capture of prey by lunge feeding or by the extension of pseudopodia. We have developed a quasi-2D system that models this behavior: a granular chain in a dispersion of smaller, approximately circular particles. The link-scale geometry of the granular chain determines the accessible conformations, leading to a biased non-convexity. We show how the dynamics of particle capture and release depend on the chain geometry, the details of driving, and the system's boundary conditions. |
Monday, March 15, 2021 10:24AM - 10:36AM Live |
A06.00013: Traction Rheoscopy of Colloidal Glass Zsolt Terdik, David Weitz, Frans A Spaepen Micron-sized hard-sphere colloidal particles can be used to form dense amorphous packings. Due to the large size and slow dynamics of colloidal particles, confocal microscopy can be used to investigate the 3D structure and dynamics of these glasses at the particle level. Measuring the stress in colloidal glasses during deformation, however, is a significant challenge; due to the large particle size and thermal interaction energies, colloidal solids have small elastic moduli. We introduce a new technique, traction rheoscopy, to directly measure the mechanical response of colloidal glasses while simultaneously visualizing microstructure. The method consists of a bilayer of colloidal glass atop a calibrated polymer gel of comparable elastic modulus. The bilayer is sheared at constant strain rate. Using a confocal microscope, shear stresses are inferred from the displacement of embedded tracer particles in the polymer gel and both the local strains and the applied strain on the sample are measured. Using these mechanical measurements, we show that under applied shear strains of less than 1%, the colloidal glass exhibits non-monotonic mechanical response. We will share results relating this mechanical response to the locally heterogenous response of the colloidal glass. |
Monday, March 15, 2021 10:36AM - 10:48AM Live |
A06.00014: Spherically confined Brownian suspensions: influence of locally heterogenous structure on diffusion and rheology Alp M Sunol, Roseanna Zia Spherically confined, hydrodynamically interacting colloids provide a framework for understanding biological cells over length and time scales where interparticle interactions and particle motion play central and nontrivial roles in whole-cell behavior. Under different biological conditions, a cell’s overall size, crowding level, and the strength of electrostatic interactions of its constituent molecules can change. Therefore, it is important to understand how each of these changes alters the physics of biological processes that take place inside cells. In this work, we perform dynamic simulations with both Confined Stokesian Dynamics and Confined Brownian Dynamics algorithms. We disentangle the role of entropic and hydrodynamic effects on short- and long-time transport properties of particles under spherical confinement to better understand differences between real life systems under conditions of weak and strong hydrodynamics. Additionally, we find relationships between rheological properties, such as osmotic pressure and viscosity, and the variables volume fraction and particle size within the confinement. |
Monday, March 15, 2021 10:48AM - 11:00AM Not Participating |
A06.00015: Flash NanoPrecipitation of Ionomers for the Scalable Production of Pickering Emulsifiers Douglas Scott, Robert K Prud'homme, Rodney Priestley Pickering emulsifiers have been demonstrated as advantageous alternatives to traditional surfactants, owing to their high interfacial adsorption energy and mechanical functionality. However, translating these benefits on an industrial scale requires continuous fabrication processes with high yield. One potential solution is flash nanoprecipitation (FNP), a scalable process for the production of polymeric colloids. |
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