Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S08: Network Physics of Particulate Systems IIFocus Recordings Available
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Sponsoring Units: GSNP DSOFT DFD Chair: Jeffrey Morris, City College of New York city Room: McCormick Place W-179B |
Thursday, March 17, 2022 8:00AM - 8:36AM |
S08.00001: Effects of particle roughness on the rheology and structure of capillary suspensions Invited Speaker: Erin C Koos Capillary suspensions are three-phase mixtures consisting of particles in a bulk liquid, that are connected by liquid menisci of a secondary liquid. These capillary suspensions have promising applications as precursors for ceramic materials or in the development of new low-fat foods [1]. |
Thursday, March 17, 2022 8:36AM - 8:48AM |
S08.00002: Properties of Amorphous Materials Under Periodic Boundary Conditions Robert C Dennis, Eric I Corwin, Varda F Hagh A packing with periodic boundary conditions requires that all of the particles' images move in concert. An infinitely repeated structure, on the other hand, has no such constraint. As a consequence, a jammed packing under periodic boundary conditions may have a corresponding infinitely repeated lattice representation that is not jammed, or indeed may not even be at a local minimum. In this manuscript we prove this claim and discuss the ways in which periodic boundary conditions succeed to capture the physics of repeated structures and where they fall short. |
Thursday, March 17, 2022 8:48AM - 9:00AM |
S08.00003: The origin of hierarchical viscoelastic response in soft particulate gels. Emanuela Del Gado, Minaspi Bantawa, Bavand Keshavarz, Gareth H McKinley, Michela Geri, Mehdi Bouzid, Thibaut Divoux Soft particulate gels consist of a small amount of solid material (colloidal particles or small aggregates) embedded in a fluid. Due to attractive inter-particle interactions, the solid component self-assembles into an open, porous network which controls the overall mechanical response of the material. We have used large scale simulations with Optimally Windowed Chirp (OWCh) signals in a 3D gel model to investigate the microscopic origin of the linear viscoelastic response of soft particulate gels. The main ingredients of the model are short-ranged attractive interactions and bending stiffness for the inter-particle bonds. Using the OWCh protocol we have analyzed the key features of the frequency-dependent dynamic modulus G*(ω) and their dependence on the gel connectivity and on the preparation protocol. Our analysis indicates that the viscoelastic spectrum of a wide range of gels, with different microstructures, is controlled by an underlying fractal characteristic of the gel network, i.e., its initial rigid backbone, and by the associated hierarchy of time scales. We discuss the microscopic structural and dynamical origin of these hierarchical processes and the emerging scaling behaviors. |
Thursday, March 17, 2022 9:00AM - 9:12AM |
S08.00004: Microscopic interactions and emerging elasticity in model soft particulate gels Minaspi Bantawa, Wayan A Fontaine-Seiler, Peter D Olmsted, Emanuela Del Gado We discuss a class of models for particulate gels in which the particle contacts are described by an effective interaction combining a two-body attraction and a three-body angular repulsion. Using molecular dynamics, we show how varying the model parameters allows us to sample, for a given gelation protocol, a variety of gel morphologies. For a specific set of the model parameters, we identify the local elastic structures that get interlocked in the gel network. Using the analytical expression of their elastic energy from the microscopic interactions, we can estimate their contribution to the emergent elasticity of the gel and gain new insight into its origin. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S08.00005: Yield precursor in primary creep of colloidal gels Jae Hyung Cho, Irmgard Bischofberger Predicting the time-dependent yielding of colloidal gels under constant stress enables control of their mechanical stability and transport. Using rotational rheometry, we show that the shear rate of colloidal gels during an early stage of deformation known as primary creep can forecast an eventual yielding. Irrespective of whether the gel strain-softens or strain-hardens, the shear rate before failure exhibits a characteristic power-law decrease as a function of time, distinct from the linear viscoelastic response. We model this early-stage behavior as a series of uncorrelated local plastic events that are thermally activated, which illuminates the exponential dependence of the yield time on the applied stress. This precursor to yield in the macroscopic shear rate provides a convenient tool to identify the fate of a gel well in advance of the actual yielding. |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S08.00006: Time-resolved structure-property relations in model soft gel networks under large amplitude oscillatory shear Gavin J Donley, Minaspi Bantawa, Emanuela del Gado Soft particulate gels are incredibly useful due to their ability to reversibly yield, i.e. transition between solid-like and fluid-like behavior, when sufficient deformation is applied. While the microscopic dynamics and constitutive flow behavior of these systems have been studied separately in detail, the development of direct connections between the two has been difficult, particularly with regard to the non-linear rheology. To bridge this gap, we use molecular dynamics simulations to perform a series of numerical large amplitude oscillatory shear (LAOS) measurements on a model soft particulate gel. Our system consists of particles that interact with a combination of a two-body short-range attraction and a three-body bending stiffness term, which spontaneously self-assemble into disordered network of soft gels at relatively low volume fractions (Φ < 20%). We track the nonlinear constitutive physics of the gels using the analytical sequence of physical processes (SPP) framework to define time-resolved dynamic moduli within a period of oscillation, and compare their changes to the evolving orientation and deformation of the gel network microstructure to develop structure property relations. |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S08.00007: Orthogonal superposition rheometry of carbon black suspensions - anisotropic thixotropy and anti-thixotropy Yilin Wang, Randy H Ewoldt We report a detailed experimental study of peculiar thixotropic dynamics of carbon black (CB, Vulcan XC-72) suspensions in mineral oil, specifically the observation of sequential thixotropic stress increase then decrease at a fixed shear rate in a step-down test. We reveal how this long-time stress decay is associated with anti-thixotropy, also called rheopexy, rather than viscoelastic relaxation, by using orthogonal superposition (OSP) rheometry, where an oscillatory flow orthogonal to the shear flow is superposed on a rotational rheometer, to probe viscoelastic moduli during the thixotropic dynamics. The orthogonal elastic modulus is present, showing this two-timescale response, which demonstrates that this response involves shear-induced structuring that stores elastic energy. We further show a mechanical anisotropy in the CB suspension under shear using OSP. Therefore, a microstructural schematic is proposed, considering qualitatively thixotropic structure build-up, anti-thixotropic densification, and anisotropic log-rolling. Our observation for these CB suspensions is outside the standard paradigm of thixotropic structure-parameter models, and the elastic response provides us with new insight into this two-timescale thixotropy of CB suspensions. |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S08.00008: Grain-resolving simulations of cohesive granular collapse Eckart H Meiburg, Rui Zhu, Zhiguo He, Kunpeng Zhao, Bernhard Vowinckel We investigate the submerged collapse of weakly polydisperse, loosely packed cohesive granular columns, as a function of aspect ratio and cohesive force strength, via grain-resolving direct numerical simulations. The cohesive force acts to prevent the detachment of individual particles from the main body of the collapsing column, reduce its front velocity, and yield a shorter and thicker final deposit. All of these effects can be accurately captured across a broad range of parameters by piecewise power-law relationships. The cohesive force significantly reduces the amount of available potential energy released by the particles. For shallow columns, the particle and fluid kinetic energy decreases for stronger cohesion. For tall columns, on the other hand, moderate cohesive forces increase the maximum particle kinetic energy, since they accelerate the initial free-fall of the upper column section. Only for larger cohesive forces does the peak kinetic energy of the particles decrease. Computational particle tracking indicates that the cohesive force reduces the mixing of particles within the collapsing column, and it identifies the regions of origin of those particles that travel the farthest. The simulations demonstrate that cohesion promotes aggregation and the formation of flocs. They furthermore provide complete information on the temporally and spatially evolving network of cohesive and direct contact force bonds. While the normal contact forces are primarily aligned in the vertical direction, the cohesive bonds adjust their preferred spatial orientation throughout the collapse. They result in a net compressional stress that slows the spreading of the advancing particle front. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S08.00009: Network physics of shear jamming in dense suspensions Mohammad Nabizadeh, Abhinendra Singh, Safa Jamali Dense suspensions exhibit a range of exotic rheological behavior from shear thickening to shear jamming under large deformation rates. While a more clear picture has emerged over the past few years on the mechanism behind these behavior, collective motion of particles and characteristics of the force and contact networks formed under large deformations is still poorly understood. These inter-particle force chains can be used as a proxy to describe the collective dynamic of the system and the routes for transmission of stresses from particle to global scales in dense suspensions. In this work, two, and three dimensional simulations of shear thickening dense suspensions, their frictional and frictionless force chains are studied under shear. We apply network science tools on the force and contact networks in the shear thickened and jammed states to reveal the fundamental differences between the continuous and discontinuous shear thickening behavior. We show that the network analysis of the inter-connectivity among the particulate network through their corresponding stresses can explain the the origins of shear jamming in dense suspensions. |
Thursday, March 17, 2022 10:12AM - 10:24AM |
S08.00010: Jamming distance, contact networks, and shear thickening of frictional colloids Lilian C Hsiao, Shravan Pradeep, Safa Jamali, Mohammad Nabizadeh We report a series of experimental studies on the rheology and contact network of dense suspensions containing model colloids with tunable surface roughness. Our results suggest that the jamming distance is a universal parameter that normalizes the shear thickening and linear viscoelasticity of frictional and frictionless colloids. To obtain these results, sterically stabilized poly(methyl methacrylate) (PMMA) colloids are suspended in the solvent squalene to provide hard sphere interactions and refractive index matching. A customized confocal rheometer setup is used to generate 3D images of contact networks in shear thickening dense suspensions. Computational results from dissipative dynamics simulations, where rough colloids are modeled as small asperities integrated with a core particle, are in excellent agreement with experimental data. Structural analysis performed on quiescent and sheared suspensions show that for all surface roughness parameters, the shear thickening strength quantified by the slope of the viscosity-stress flow curves shows a universal scaling with jamming distance and the dynamic contact number for a broad class of dense colloidal suspensions. This statement is supported not only by PMMA colloids with hard and charged interactions, but also by other types of colloidal suspensions from the literature, as well as multiple computer simulations on shear thickening. |
Thursday, March 17, 2022 10:24AM - 10:36AM |
S08.00011: Networks of forces in pinned, frictionless jammed systems Amy L Graves, Andy L Zhang, Sean A Ridout, Aarushi Sachdeva, Cacey S Bester, Katharina Vollmayr-Lee, Brian Utter, Theodore Brzinski Square, triangular, honeycomb and random lattices of fixed pins are shown to systematically modify the force network in a jammed solid of bidisperse, frictionless discs. Point J remains isostatic, yet the number of contacts is reduced, which lowers the elastic moduli. Weak contacts become more common, both supporting “buckler” particles and involving “enabler” pins. Further, pins fatten the tail of the normalized force distribution from a gaussian to a power law relationship. Heatmaps of the geometrical and dynamical network reveal a rich local structure. Finally, we examine the stress state via persistent homology – how structure in the contact network changes with increasing contact force filtration. We report the zeroth and first Betti numbers as a function of the threshold force. These quantify the connectedness and circuit rank of the filtered contact network as it varies with pin density and arrangement. |
Thursday, March 17, 2022 10:36AM - 10:48AM |
S08.00012: Interpreting force chain evolution giving rise to granular failure using network science Farnaz Fazelpour, Vrinda Desai, Karen E Daniels When a granular material fails under shear, it can be understood as a loss of stability of the force chain network that supports it. The direct observation of grain kinematics and force chain networks allows us to examine how pre-event observations could forecast the location or timing of a future slip event. However, mining consistent patterns from the complex force networks can be challenging. Recently, network science techniques have been used to characterize networks and understand interactions in complex networks. We perform experiments on sheared quasi-2D granular packing undergoing stick-slip failure. The granular packing is made of photoelastic disks, allowing us to measure interparticle forces using photoelastic force measurements and quantify the evolution of the force network during failure. We create a network corresponding to the granular material, with nodes representing the particles and edges representing the contacts between particles, weighted by force magnitude between corresponding pairs of particles. Force networks at consecutive time steps form a multi-layer network. We utilize community detection techniques which identify strongly-correlated clusters of nodes to find patterns of causality. Temporal and spatial community structure are examined to identify patterns as the loading on granular packing accumulates to surpass a failure criterion. Our preliminary results show that there are promising signals in community structures highlighting the area of high risk and time of failure. |
Thursday, March 17, 2022 10:48AM - 11:00AM |
S08.00013: Dynamics and rheology of periodically driven suspensions Zhouyang Ge, Gwynn J Elfring Suspensions of hydrodynamically interacting particles are important model systems for understanding the dynamics of diverse natural and industrial processes, such as the collective motion of bacterial swarms and the potential fabrication of hyperuniform metamaterials. In many cases, the particle motions are externally controlled by a time-dependent flow, so a basic understanding of their dynamics subject to periodic deformations, e.g. an oscillatory shear flow, will have particular reference values. Recent work in the literature have identified two mechanisms for suspensions of spherical particles in oscillatory shear to undergo a dynamical phase transition from being reversible to diffusive, due to either interparticle collision or attraction [1,2]. However, none of the studies has included long-range hydrodynamic interactions, which are always present regardless of the packing density, and may be especially important for the structure relaxation of concentrated suspensions. Here, we numerically examine the suspension network evolution with full hydrodynamic interactions using a newly developed fast Stokesian dynamics method [3]. Rigorous simulations will be used to illustrate the effects of oscillation amplitude and frequency on the stress distribution and microscopic dynamics, highlighting the connection between suspension rheology and self-organization. |
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