Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session E43: Jamming and the Glass Transition I 
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Sponsoring Units: GSNP GSOFT Chair: Ray Orbach Room: 346 

E43.00001: ABSTRACT WITHDRAWN 
Tuesday, March 15, 2016 8:12AM  8:24AM 
E43.00002: Jamming for a system of granular crosses Zegan Shang, Hu Zheng, Dong Wang, Jonathan Bares, Robert Behringer A disordered stressfree granular packing can be turned into a rigid structure, which is called jammed state, by increasing the density of particles per unit volume or by applying shear deformation. The jamming behavior of systems made of of 2D circular discs have been investigated in detail, but very little is known about the special geometry particles, particularly nonconvex particles like crosses. Here, we perform an experimental study on the jamming of a system of quasi2D granular crosses. In the present experiments, we measure the pressure, and coordinate number evolution of a 2D packing of photoelastic cross discs. This talk will present results from a simple shear experiment for stresses and for the order parameter associated with the cross orientation and its correlation. [Preview Abstract] 
Tuesday, March 15, 2016 8:24AM  8:36AM 
E43.00003: Experimental studies of contact networks in jammed colloidal systems Eru KyeyuneNyombi, Lane Gilchrist, Hernán Makse Recent theoretical advances in the statistical mechanics of jamming have provided a new outlook for thermodynamically characterizing packings of granular matter. Packing density, spatial ordering metrics, and the number of interparticle contacts are a few fundamental parameters used in various theoretical models. However, experimental measurements of interparticle forces have been illusive. Here, fluorescent molecular probes are used to identify interparticle contacts in high resolution confocal images of jammed colloidal systems. [Preview Abstract] 
Tuesday, March 15, 2016 8:36AM  8:48AM 
E43.00004: Experimental Study of Athermal Elastic Network Mechanics Jonathan Michel, Peter Yunker Recently, significant theoretical effort has been directed towards understanding the mechanics of networks. Elastic networks are of inherent fundamental interest \footnote{Mao, X., Stenull, O. and Lubensky, T.C., ``Elasticity of a filamentous kagome lattice'', Physical Review E, 87:042604} and serve as useful analogs for describing other physical systems. Recent applications include modeling of collagen \footnote{Licup, J. et al.,``Stress Controls the mechanics of collagen networks'', PNAS, 2015, 112:95739578} and descriptions of jamming in granular media and glass formation \footnote{Liu, A and Nagel, S. R., ``The Jamming Transition and the Marginally Jammed Solid'', Annual Reviews of Condensed Matter Physics, 2010, 1:34769}. I propose to discuss ongoing experimental efforts to study mechanical properties of elastic networks, such as Young’s modulus and ultimate strength, in the athermal limit. I will begin with the simple case of regular, isostatic crystalline lattices and proceed to studies of random, connected elastic networks of varying bond number for a given number of lattice sites, including both isostatic and subisostatic networks. [Preview Abstract] 
Tuesday, March 15, 2016 8:48AM  9:00AM 
E43.00005: Interparticle contact networks of granular packings below jamming Bhaskar Sen Gupta, Thibault Bertrand, Corey S. O'Hern, Mark D. Shattuck We employ computer simulations to investigate the structural properties of interparticle contact networks in granular packings of bidisperse disks below jamming onset at which the system becomes solidlike. We show that the properties of the contact networks are highly sensitive to changes in the packinggeneration protocol and its numerical implementation. Thus, we formulate an analytical method to implement steepest descent of hard, athermal particles undergoing isotropic compression, which allows us to calculate the number of contacts as a function of packing fraction. These results represent an important first step in developing a theoretical description of shear and compressioninduced jamming in frictional granular media. [Preview Abstract] 
Tuesday, March 15, 2016 9:00AM  9:12AM 
E43.00006: Contact breaking in frictionless granular packings Qikai Wu, Thibault Bertrand, Corey O'Hern, Mark Shattuck We numerically study the breaking of interparticle contact networks in static granular packings of frictionless bidisperse disks that are subjected to vibrations. The packings are created using an isotropic compression protocol at different values of the total potential energy per particle $E_p$. We first add displacements along a single vibrational mode $i$ of the dynamical matrix to a given packing and calculate the minimum amplitude $A_i$ of the perturbation at which the first interparticle contact breaks. We then identify the minimum amplitude $A_{\rm min}$ over all perturbations along each mode and study the distribution of $A_{\rm min}$ from an ensemble of packings at each $E_p$. We then study two, three, and multimode excitations and determine the dependence of $A_{\rm min}$ on the number of modes that are included in the perturbation. [Preview Abstract] 
Tuesday, March 15, 2016 9:12AM  9:24AM 
E43.00007: Echoes of the glass transition in athermal soft spheres Peter Morse, Eric Corwin The glass transition and the athermal jamming transition are both transitions from one disordered state to another marked by a sudden increase in rigidity. Before the onset of rigidity, thermal hard spheres and athermal soft spheres both share the same configuration space. Is there a signature of the glass transition in the topology of the allowed configuration space, and is this same signature present for athermal spheres? I will answer these questions by introducing the concept of local rigidity, and in doing so, I will demonstrate the existence of a prejamming phase transition precisely at the glass transition density. [Preview Abstract] 
Tuesday, March 15, 2016 9:24AM  9:36AM 
E43.00008: Structural Signatures of the glass transition Chi Zhang, Nicoletta Gnan, Emanuela Zaccarelli, Frank Scheffold The nature of colloidal glasses and the glass transition remains a topic of scientific interest. Scientists often focus on the study of dynamical properties since major structural changes have not been found to date in the vicinity of the glass transition. In this work we study both structural and dynamic signatures of the glass and jamming transition. Confocal microscopy measurements and molecular dynamic simulations are conducted on buoyancy and index matched microscale emulsion droplets with polydispersity of 12\%, where crystallization is avoided. We find that the glass transition of such system is associated with detailed structural signatures on both global and local scales. At the global level, the peak amplitude of the radial distribution function shows a nonmonotonic evolution around a volume fraction of 59\%. At the individual particle level, some local parameters such as the configuration of the nearest neighbors and the locally favoured structures also evolve differently across a volume fraction of about 59\% whereas the jamming transition if clearly observed at higher densities 64.2\%. Our results reveal clear structural signatures of the glass transition, which could help the further understanding of the underlying physical mechanism leading to dynamical arrest. [Preview Abstract] 
Tuesday, March 15, 2016 9:36AM  9:48AM 
E43.00009: Casimir forces in systems near jamming Justin Burton, JuanJos\'{e} Li\'{e}torSantos Casimir forces arise when longranged fluctuations are geometrically confined between two surfaces. In most cases these fluctuations are quantum or thermal in nature, such as those near a classical critical point, yet this is not a requirement. The $T=0$ jamming transition in frictionless, granular systems shares many properties with classical critical points, such as a diverging correlation length, although it has recently been identified as a unique example of a random firstorder transition (RFOT). Here we show the existence of Casimir forces between two pinned particles immersed in systems near the frictionless jamming transition. We observe two components to the total force: a shortranged, depletion force and a longranged, repulsive Casimir force. The Casimir force dominates when the pinned particles are much larger than the ambient jammed particles. In this case, we find that particles with the largest forces have the least number of contacts, and that these particles are clustered between the pinned particles, giving rise to a repulsive force which is independent of system preparation and interparticle potential. [Preview Abstract] 

E43.00010: ABSTRACT WITHDRAWN 

E43.00011: ABSTRACT WITHDRAWN 
Tuesday, March 15, 2016 10:12AM  10:24AM 
E43.00012: Rheological Transition of Sheared Frictionless Disks with Rotational Motion Peter Olsson, Steve Teitel We consider the massive Durian bubble model for sheared bidisperse disks, but modified so as to include the rotational motion of particles due to dissipative collisional torques. In such a model, particles possess a viscous tangential dissipation, though no elastic tangential friction. As the packing fraction is increased, we find a discontinuous transition from Bagnoldian to Newtonian rheology, at a packing fraction that lies below the jamming transition. At this transition we find a region of coexisting shear bands of Bagnoldian and Newtonian rheology, and suggestions of discontinuous shear thickening upon increasing the shear strain rate. [Preview Abstract] 
Tuesday, March 15, 2016 10:24AM  10:36AM 
E43.00013: Critical Scaling of Bagnold Rheology at the Jamming Transition of Frictionless Disks Stephen Teitel, Daniel V\aa gberg, Peter Olsson We simulate sheardriven, frictionless, bidisperse disks in two dimensions, as a function of applied shear strain rate and packing fraction, for a model with a normal viscous dissipation that results in Bagnoldian rheology for all control parameters. Carrying out a critical scaling analysis of the pressure and shear stress near the jamming transition we find values of the critical exponents that disagree with theoretical predictions of Otsuki and Hayakawa[1] but are closer to more recent theoretical results by DeGiuli et al[2], as well as earlier simulations by Peyneau and Roux[3]. We find that it is essential to include leading correctionstoscaling to arrive at selfconsistent results. \\ \\ {[}1{]} M. Otsuki and H. Hayakawa, Prog. Theor. Phys. 121, 647 (2009) and Phys. Rev. E 80, 011308 (2009) \\ {[}2{]} E. DeGiuli, G. Du\"{r}ing, E. Lerner, and M. Wyart, Phys. Rev. E 91, 062206 (2015) \\ {[}3{]} P.E. Peyneau and J.N. Roux, Phys. Rev. E 78, 011307 (2008) [Preview Abstract] 
Tuesday, March 15, 2016 10:36AM  10:48AM 
E43.00014: Single Particle Jumps in Sheared SiO2 Sean McMahon, Katharina VollmayrLee, Jonathan Cookmeyer, Juergen Horbach We study the dynamics of a sheared glass via molecular dynamics simulations. Using the BKS potential we simulate the strong glass former SiO2. The system is initially well equilibrated at a high temperature, then quenched to a temperature below the glass transition, and, after a waiting time at the desired low temperature, sheared with constant strain rate. We present preliminary results of an analysis of single particle trajectories of the sheared glass. [Preview Abstract] 
Tuesday, March 15, 2016 10:48AM  11:00AM 
E43.00015: Increasing the maximally random jammed density with electric field to reduce the fat level in chocolate R. Tao, H. Tang Chocolate is one of the most popular food types and flavors in the world. Unfortunately, at present, chocolate products contain too much fat, leading to obesity. For example, a typical molding chocolate has various fat up to 40{\%} in total and chocolate for covering ice cream has fat 50 60{\%}. Especially, as children are the leading chocolate consumers, reducing the fat level in chocolate products to make them healthier is important and urgent. While this issue was called into attention and elaborated in articles and books decades ago and led to some patent applications, no actual solution was found unfortunately. Why is reducing fat in chocolate so difficult? What is the underlying physical mechanism? We have found that this issue is deeply related to the basic science of soft matters, especially to their viscosity and maximally random jammed (MRJ) density $\varphi_{x} $. All chocolate productions are handling liquid chocolate, a suspension with cocoa solid particles in melted fat, mainly cocoa butter. The fat level cannot be lower than 1$\varphi_{x} $in order to have liquid chocolate to flow. Here we show that that with application of an electric field to liquid chocolate, we can aggregate the suspended particles into prolate spheroids. This microstructure change reduces liquid chocolate's viscosity along the flow direction and increases its MRJ density significantly. Hence the fat level in chocolate can be effectively reduced. We are looking forward to a new class of healthier and tasteful chocolate coming to the market soon. [Preview Abstract] 
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