Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T25: Constraintbased Rheology of Sense Suspensions and Granular Materials IFocus Recordings Available

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Sponsoring Units: DSOFT GSNP Chair: Abhinendra Singh, University of Chicago Room: McCormick Place W187A 
Thursday, March 17, 2022 11:30AM  12:06PM 
T25.00001: How nanoscale surface physics affects emergent material properties in colloidal suspensions Invited Speaker: Norman J Wagner Two colloidal suspensions of paucidisperse, spherical silica particles with different surface chemistries leading to extreme limits of surface contact friction are studied to identify experimental differences in shear rheology and microstructure and quantitatively test theory and simulation models. The nonequilibrium microstructure in the plane of shear is measured by flowSmall Angle Neutron Scattering (SANS) for steady shear states spanning the shear thinning and shear thickening regimes. The shear rheology and microstructure are compared against predictions from theory for Brownian hard sphere suspensions and stateoftheart simulation methods that incorporate either contact friction or enhanced lubrication hydrodynamics. The first normal stress differences are confirmed to distinguish between these micromechanical mechanisms. The differences in shearinduced microstructures between suspensions with varying contact friction demonstrate that the nonequilibrium microstructure can distinguish between nanotribological interactions in the shear thickened state. Implications for the development of theories for colloidal suspension rheology are discussed. 
Thursday, March 17, 2022 12:06PM  12:18PM 
T25.00002: Disruption of structural order in sheared dense suspensions due to frictional constraints Abhay Goyal, Emanuela Del Gado, Scott Jones, Nicos Martys Dense suspensions exhibit an array of interesting nonNewtonian rheological properties. For practical applications, it is crucial to understand how those properties arise from the microstructure, which depends on both macroscopic forcing and microscopic constraints. We probe this connection with largescale simulations of 100,000 suspended particles undergoing shear. Using varied particle interactions and flow conditions, we explore both shearthinning and shearthickening regimes, while analyzing the microstructural characteristics of both. We observe shearthinning behavior that is coupled to ordering for lubricated contacts, where hexagonal crystal layers with chainlike defects can slide unhindered with the flow. In contrast, upon introducing frictional constraints to sliding motion between particles, the ordering is disrupted and shear thickening becomes apparent. In both cases, we compute the individual particle contributions to the stress to identify the stresscarrying structures that form under shear. The shear stress is found to be highly localized in the defects for the ordered suspension, whereas the introduction of friction substantially changes the nature of the stress localization. 
Thursday, March 17, 2022 12:18PM  12:30PM 
T25.00003: Scaling in shear thickening suspensions with multidirectional flows Meera Ramaswamy, Itay Griniasty, Danilo B Liarte, Emanuela del Gado, Eleni Katifori, James P Sethna, Bulbul Chakraborty, Itai Cohen Recently, we proposed a universal crossover scaling theory to describe shear thickening suspensions. This scaling formulation suggests that the suspension viscosity can be tuned by changing the particle shape, size, roughness or solvent properties which in turn changes the scaling variables. Here, we show that orthogonal perturbations to the flows, which are an effective method for tuning the thickening of suspensions without altering the properties of the suspension particles, can also be folded into this universal scaling picture. Specifically, we show that the effect of adding in orthogonal shear perturbations (OSP) can be incorporated by simply altering the fraction of frictional contacts to include a term that decreases with the ratio of the OSP flow to primary flow shear rates. In addition, the stress dependent fraction of frictional contacts requires a small but significant modification in order to ensure data collapse. These results demonstrate the power, importance and the generality of such universal scaling formulations, and illustrate how this framework can be modified to incorporate other complex flow fields. 
Thursday, March 17, 2022 12:30PM  12:42PM 
T25.00004: Universal scaling in shear thickening suspensions Meera Ramaswamy, Itay Griniasty, Danilo B Liarte, Abhishek Shetty, Eleni Katifori, Emanuela del Gado, James P Sethna, Bulbul Chakraborty, Itai Cohen Nearly all dense suspensions undergo dramatic thickening transitions in their flow behavior when sheared at high stresses. Such transitions occur when the dominant interactions between the suspended particles shift from hydrodynamic to frictional. Here, we give a complete theory of the shear thickening viscosity in terms of a universal crossover scaling from the frictionless jamming point to a rigidity transition associated with friction, anisotropy, and shear. Strikingly, we find experimentally that for two different systems the viscosity can be collapsed onto a single universal curve over a wide range of stresses and volume fractions. The collapse reveals two separate scaling regimes, due to a crossover between frictionless isotropic jamming and a frictional shear jamming point, with different critical exponents. The materialspecific behavior due to the microscale particle interactions is incorporated into an additive analytic background and a scaling variable governing the proximity to shear jamming that depends on both stress and volume fraction. This reformulation opens the door to importing the vast theoretical machinery developed to understand equilibrium critical phenomena to elucidate fundamental physical aspects of the shear thickening transition. 
Thursday, March 17, 2022 12:42PM  12:54PM 
T25.00005: Leveraging polymer glass transition to access thermallyswitchable shear jamming suspensions Chuqiao Chen, Michael van de Naald, Abhinendra Singh, Neil D Dolinski, Grayson L Jackson, Justin Jureller, Heinrich M Jaeger, Stuart J Rowan, Juan De Pablo Dense suspensions can exhibit discontinuous shear thickening (DST) and shear jamming (SJ) where interparticle frictional interactions play a vital role in constraining the relative particle motions. Recent studies have shown that these constraints as well as the macroscale rheological properties can be tuned by the particle properties, including roughness and surface chemistry. However, most theoretical and experimental studies have considered hard nondeformable particles, and little is known about the role of particle stiffness. In this work, we have developed a strategy for tunning the stiffness in situ by designing and utilizing polymeric particles with accessible glass transition temperatures (T_{g}). Around T_{g}, the elastic modulus of particles depends strongly on temperature and changes by ~3 orders of magnitude. We demonstrate that transitioning through T_{g} of polymer particles has a dramatic and nonmonotonic effect on shear thickening and the shear jamming transition can be turned on or off in situ by varying the temperature relative to T_{g}. This behavior is attributed to the significant change in mechanical stiffness as well as the interparticle surface friction near T_{g}. This study lays the groundwork for switchable jamming systems and motivates further research to investigate how polymer dynamics at the interface can affect the constraints on particle relative motions. 
Thursday, March 17, 2022 12:54PM  1:06PM 
T25.00006: Role of solvent on the rheological properties of nonBrownian suspensions Adrien Izzet, Anh Vu Nguyen Le, Guillaume Ovarlez, Annie Colin The rheology of suspension is characterized by a linear dependence of the shear stress σ on the shear rate (Boyer et al. 2011), as a function of the microscopy friction μ_{p}. The coupling between the flow, the normal forces, and μ_{p}, induces a strong dependence of the rheology on σ. While the theoretical framework is wellestablished, measurements of the microscopic properties are missing. In this study, we use TuningFork Microscopy (TFM) to measure μ_{p} between solid polystyrene (PS) particles immersed in a solvent, and we compare our results to numerical simulations (Chèvremont et al. 2019, Lobry et al. 2019). We show that PEG and NaI lead to a constant μ_{p} (resp. 0 and 0.2) and Silicon (Si) oil leads to a decrease of μ_{p} with increasing load. Our results are consistent with the rheology: for Si oil, μ_{p} depends on contact elasticity, thus on the applied load. PSPEG is Newtonian but exhibits shearthinning when the volume fraction φ gets close to Random Loose Packing: beads swelling induces a repulsive force preventing particle contact (Chatté et al. 2018), except at high φ. PSNaI exhibits shearthickening that is more visible at large φ: even at low σ, the suspension flow is in its inertial regime so the viscosity is dominated by particle contacts and increases with the shear rate. 
Thursday, March 17, 2022 1:06PM  1:18PM Withdrawn 
T25.00007: Intrusion into granularfluid mixtures: testing addedmass and DarcyReynolds theories Abe Clark, Joshua A Dijksman, Marc Brassard, Neil Causley, Joshua Strader, Nasser F Krizou We present experimental and theoretical results for impact into two related but distinct systems: (1) cornstarch and water suspensions and (2) beds of glass beads immersed in glycerolwater mixtures. For (1), we find that the predominant theoretical paradigm, the addedmass model, does not capture several important features of the experimental data. Instead, we show that theories based on large viscous forces operating at the boundary of a growing, jammed region better explains the experimental results. For (2), we find that the predominant theory, DarcyReynolds, performs very well over a wide range of particle sizes. We also find that our experimental results for varied viscosity are consistent with Darcy Reynolds theory, but only for a limited range of the viscosity. For large viscosities, observed forces begin to decrease with increasing viscosity, in contrast with the theoretical prediction. 
Thursday, March 17, 2022 1:18PM  1:30PM 
T25.00008: Microstructure and Rheology of SemiDense and Dense Suspensions in Confined Flows Joao M Maia, Shaghayegh Khani, Erika Barcelos, Monica Naccache, Arman Boromand, Fellipe Carvalho In this work, CoreModified Dissipative Particle Dynamics, CMDPD, is employed to model the flow and microstructure development of semidense and dense suspensions under confinement. The walls as well as the solvent are represented as traditional DPD particles which interact centertocenter by soft potentials. Colloidal particles, on the other hand, are modelled as CMDPD particles, having a rigid core and a soft shell and the interactions are driven by a semihard potential. Colloidal particles interactions take place by means of a core force, responsible to tune the rigidity, and a lubrication force, representative of the shortrange hydrodynamic interactions. In this work, the effect of flow rate, confinement and particle rigidity were systematically studied in semidense and dense suspensions in a pressure driven flow. At stronger confinement ratios, lower rigidity and weaker flow strengths the overall particles velocity tends do decrease. Rigid particle suspensions are more viscous and have a slower motion compared to the soft ones. Additionally, rigidity leads to opposite migration effects. Different microstructures and particles arrangement were observed depending on the values of the parameters adopted, with confinement and particle rigidity being the most important factors driving particle migration and clustering. 
Thursday, March 17, 2022 1:30PM  1:42PM 
T25.00009: The Elastic Response of Wire Frame Glasses. David A King This talk considers the elastic response of concentrated suspensions of rigid wire frame particles to a step strain. These particles are constructed from infinitely thin, rigid rods of length L. We specifically compare straight rodlike particles to bent and branched wire frames. In dense suspensions the wire frames are frozen in a disordered state by the topological entanglements between their arms. We present a simple, geometric method for finding the scaling of the elastic stress with concentration in these glassy systems. The behaviour of wire frames is found to be strikingly different from that of rods. The linear elasticity scales like ρ^{3}L^{6} for wire frames, whereas it scales proportional to ρ for rods, where ρ is the number density. The character of the nonlinear response is also markedly different. Wire frame suspensions shear harden below a critical density dependent on the bending modulus of the particles. Suspensions of rods, on the other hand, always shear thin. The reason for these differences is that wire frames can be forced to bend by the entanglements with their surroundings, whereas rods always remain straight. This is found to be very important even for small strains, with most particles being bent above a critical strain γ_{c }∼(ρL^{3})^{1}. 
Thursday, March 17, 2022 1:42PM  1:54PM 
T25.00010: Granular piles traversing the glass transition: A grainscale characterization via the internal energy Stefan Boettcher, Paula A Gago The transition into a glassy state of a tapped granular pile [1,2] is revisited using extensive molecular dynamics simulations. We supplement the conventional approach  based purely on the properties of the ensemble of mechanically stable, static configurations  with the investigation of the grainscale dynamics of the energy, injected through a tap, as it is transmitted and dissipated throughout the pile [3]. We propose an effective measure of this internal energy to play the role of the longsought "temperaturelike" parameter, allowing us to predict the macroscopic state of the static configurations. We show that different horizontal subregions ("layers") along the height of the pile experience different "temperatures" under a same perturbation, resulting in certain regions of the same pile responding glassy while others remain equilibrated at a given tap intensity. Plotting the macroscopic properties (specifically, density and density fluctuations) of each layers as a function of this local effective energy allows us to quantitatively align the results measured in the different layers. We will show that for this collapse with the effective energy, the peak exhibited for the density fluctuations concurs with the point where the different parts of the pile undergo their respective glass transition. 
Thursday, March 17, 2022 1:54PM  2:06PM 
T25.00011: Compressing and Fracturing 2D Crystals Pablo E Illing, JeanChristophe OnoditBiot, Kari DalnokiVeress, Eric R Weeks In this project we simulate a two dimensional aggregate of slightly adhesive droplets in a viscous environment while compressed between two parallel walls, of which only one moves, mimicking the experiment of OnoditBiot et al. [Soft Matter 17, 11941201 (2021)]. For highly monodisperse samples, we observe the structure undergo a transition in a single catastrophic fracture event. As the wall moves, the sample, arranged like a hexagonal closed packed crystal, rearranges itself via row reduction, and gaining one column. As the speed of the walls increases, viscous effects become more relevant. This results in the force necessary for a fracture to become/be higher, alongside the appearance of defects in the crystals during/by the fracture. On the other hand, increasing polydispersity, towards a glassier aggregate, leads to a breakage in smaller, more localized fractures, where catastrophic global fractures events, no longer occur. 
Thursday, March 17, 2022 2:06PM  2:18PM 
T25.00012: Rheology of dense, bidispersed particles suspended in a perturbed shearflow Alessandro Monti, Marco Edoardo Rosti We have studied the phenomenon of segregation of a nonBrownian dense suspension (volume fraction φ=0.50) of rigid, inertialess bidispersed particles, with a large particlesizeratio a_{2}/a_{1}=3, being a_{1} and a_{2} the radii of the smaller and larger particles in the suspension, respectively. The particles have been immersed in a simple shearflow of a Newtonianfluid at a vanishing Reynolds number. The shearrate was fixed to a value that places the rheological response of the suspension in the postshearthickening plateau. 
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