Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y44: Focus Session: Jamming in Granular Media II |
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Sponsoring Units: GSOFT Room: 214D |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y44.00001: Percolation and jamming transitions in particulate systems with and without cohesion Lou Kondic, Lenka Kovalcinova, Arnaud Goullet We consider percolation and jamming transitions for particulate systems exposed to compression. For dry granular systems, interacting by repulsive forces in addition to friction and viscous damping, it is found that these transitions are influenced by a number of effects, and in particular by the compression rate. In a quasi-static limit, we find that for the considered type of interaction between the particles, percolation and jamming transitions coincide. For cohesive systems, however, we find that the differences between the considered transitions persist in quasi-static limit. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y44.00002: The birth and the growth of Boson peak -- insights from the normal modes analysis of granular experiments? Jie Zhang, Ling Zhang, Jie Zheng The origin of the Boson peak in amorphous materials has been a long-lasting puzzle for more than decades for researchers in the field. In order to understand the physics of the boson peak, we have experimentally measured the density of states (DOS) from the hexagonal lattice to the disordered structures in 2D packing of granular materials, which are made of photo-elastic disks allowing a precise measurement of contact forces between disks to determine the dynamical matrix of the system. These disks are wrapped with Teflon tapes to mimic frictionless particles so that the rotational degree of freedom can be ignored to a good approximation. By varying the pressure of the disordered crystal, we find the strong evidence that the first Van Hove singularity gradually evolves into the Boson peak. In geometrically disordered packing, the position of the Boson peak is influenced by the degree of the geometric disorder. Starting from a geometrically ordered crystal packing, a slight increase of the geometrical disorder will cause the Boson peak to have a sudden discontinues shift to a lower frequency. We find that such a shift might be related to the change of the topology of the strong and weak force networks in the system, which is currently still under investigation. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y44.00003: Shear Modulus Heterogeneities in Disordered Frictionless Particle Packings Leo Silbert, Hideyuki Mizuno, Matthias Sperl It is understood that amorphous solids, ranging from thermal glasses to athermal granular packings, exhibit spatially inhomogeneous mechanical properties. Here, we explore the spatial extent of elastic modulus heterogeneities using computer simulations of a model granular material composed of frictionless, monodisperse spheres, through the implementation of an equilibrium fluctuation formalism. This protocol allows us to decompose the elastic moduli into their affine and nonaffine components. We first validate our numerical scheme by examining how the macroscopic values of the bulk and shear moduli vary as we tune the density of the packing towards its state of marginal stability, that lies at a critical solids packing fraction. Paying particular attention to the shear modulus, we find that it is the fluctuations in the shear modulus that control the mechanical stability of the solid. Furthermore, we are able to associate a characteristic length scale with the relative heterogeneities in the local shear modulus that grows on approach to the critical packing density. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 9:12AM |
Y44.00004: Shear Jamming in Granular Media Invited Speaker: Thibault Bertrand We numerically study two-dimensional packings of bidisperse disks created using isotropic compression and simple shearing protocols. To create jammed packings by compression, we start with $N$ particles with random initial positions and grow their diameters by successive small packing fraction increments each followed by relaxation of particle overlaps using energy minimization until the system cannot be compressed further without particle overlaps in the relaxed state. Jammed packings created via isotropic compression exist over a range of packing fractions $\phi$. Because of the spread of jammed packing fractions, during compression the system may reach a packing fraction above the minimum value before jamming. If an unjammed packing is then sheared by a strain $\gamma$, it can jam. Using a combination of compression and shearing, we can define jamming protocols as trajectories in the $(\phi, \gamma)$ plane that yield jammed packings. In this plane, we can reach a particular point $(\phi_n, \gamma_n)$ in many ways. We will focus on two of these: (1) shearing to $\gamma_n$ at $\phi=0$ followed by compression to $\phi_n$ at $\gamma=\gamma_n$ and (2) compression to $\phi_n$ at $\gamma=0$ followed by shearing to $\gamma_n$ at $\phi=\phi_n$. For protocol 1, we find that the probability of obtaining a jammed packing at $\phi$ and $\gamma$, $P(\phi,\gamma)=Q(\phi)$, is independent of $\gamma$. For protocol 2, we use a simple theory to deduce $P(\phi,\gamma)$ from $Q(\phi)$. Furthermore. we find that frictionless jammed packings form one-dimensional families in the $(\phi, \gamma)$ plane. The one-dimensional families are projections from the $2N$-dimensional configuration space onto the $(\phi, \gamma)$ plane. If the system reaches a given packing fraction by isotropic compression without jamming, the system will eventually ``hit'' one of the families and jam during shear. In packings composed of frictionless particles, the range of accessible jammed packing fractions shrinks with increasing $N$. However, in packings composed of frictional disks, we have shown that the families are no longer one-dimensional, the range of jammed packing fractions is broad even for large $N$ and depends on the number of missing contacts $m$. Therefore, the theoretical predictions used above for packings of frictionless disks must be modified to explain packings formed under shear in frictional systems. We predicted and measured the probability of forming a jammed packing with friction coefficient $\mu$ and $m$ missing contacts, $P_m(\mu)$. Here, we extend these studies to include the dependence of the jamming probability on packing fraction and shear strain, $P_m(\mu,\phi,\gamma)$, and relate this function to shear-jammed packings in frictional systems. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y44.00005: The onset of geometric rigidity in granular systems below jamming Peter Morse, Eric Corwin We report on a new purely geometric phase transition in soft athermal spheres which occurs significantly below the jamming density. This state is characterized by the onset of local rigidity as evidenced by changes in the symmetry of the local Voronoi cell. We relate this local rigidity onset to the eventual mechanical jamming transition through a rigidity percolation picture. We present a functional transformation mapping a minimized packing to a new packing by replacing every particle with the maximum inscribed sphere in its Voronoi cell. We demonstrate that there exists a line of fixed points between the onset of local rigidity and the jamming point under this transformation. Surprisingly, this transformation has a second attractor to systems with mean contact number of $d+1$. We identify these as random loose packings in polydisperse systems. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y44.00006: Jamming Percolation in Three Dimensions Eial Teomy, Antina Ghosh, Yair Shokef We introduce a three-dimensional kinetically-constrained model for jamming and glasses [1], and prove that the fraction of frozen particles is discontinuous at the directed-percolation critical density. In agreement with the accepted scenario for jamming- and glass-transitions, this is a mixed-order transition; the discontinuity is accompanied by diverging length- and time-scales. Because one-dimensional directed-percolation paths comprise the backbone of frozen particles, the unfrozen rattlers may use the third dimension to travel between their cages. Thus the dynamics are diffusive on long-times even above the critical density for jamming. Our new model is a non-trivial extension of the two-dimensional spiral model [2]. \\[4pt] [1] A. Ghosh, E. Teomy, and Y. Shokef, \textit{Europhys. Lett.} \textbf{106}, 16003 (2014).\\[0pt] [2] G. Biroli and C. Toninelli, \textit{Eur. Phys. J. B} \textbf{64}, 567 (2008). [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y44.00007: Renewal Events in Glass-Forming Liquids -- Glass Dynamics with Ideal Age Zero Julian Helfferich, Falko Ziebert, Hendrik Meyer, Stephan Frey, J\"org Baschnagel, Katharina Vollmayr-Lee, Alexander Blumen When a glass-forming liquid is cooled through the glass transition temperature, the system falls out of equilibrium and evolves slowly over time in a process called physical aging. During aging, dynamic observables depend on the history of the process, i.e. the time since vitrification and the quenching procedure, hampering any attempt to directly compare the dynamics of different glass formers. The continuous-time random walk (CTRW) interpretation, however, offers a remedy for the history dependence of the dynamic observables. This interpretation is based on the observation that single-particle trajectories display hopping-like motion, i.e. long periods of localization interrupted by fast ``jumps.'' In the CTRW picture, these jumps are renewal events, i.e. each particle carries its own ``internal clock'' which can be reset on any jump. This ``internal time'' can be treated as the ideal age: All particles display identical (ensemble averaged) dynamics with respect to this time, regardless of their history. In this talk, I will discuss how to decide whether jumps in the single-particle trajectories can be treated as jumps of a CTRW and demonstrate how these events can be utilized to gain history-independent dynamic observables. [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y44.00008: Local structure as a mechanism for dynamical arrest: tackling the lengthscale conundrum Paddy Royall, Andrew Dunleavy, Karoline Wiesner, Ryoichi Yamamoto, Thomas Speck, Stephen Williams Among the key challenges to our understanding of the process by which supercooled liquids transform into solid glasses is that it is accompanied by little apparent change in structure. Recently geometric motifs representing locally favoured structures have been identified in supercooled liquids, but a causal link between these locally favoured structures (LFS) and solidification remains elusive. One ``smoking gun'' for such a link would be coincidence of dynamic lengthscales which reflect solidification and lengthscales associated with structural features. However, this coincidence remains elusive, at least in the dynamical regime accessible to numerical simulations and colloidal experiments. Here we re-evaluate the lack of coincidence of dynamic and static lengthscales in the regime accessible to simulation. We consider the isoconfigurational ensemble, in which any spatial heterogeneity in dynamics is encoded in the structure. Using an information theoretic method we extract a new dynamic lengthscale which is matched very closely by structural length-scales associated with geometric motifs. This provides a possible resolution of the discrepancy in dynamic and structural lengthscales found in conventional studies. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y44.00009: Cluster Analysis of Particle Jumps in SiO2 Glass Jonathan Cookmeyer, Katharina Vollmayr-Lee, Horacio Castillo, Juergen Horbach With a Molecular Dynamics simulation, we study the behavior of 115248 SiO2 particles after a quench from a fully equilibriated configuration at a high temperature to a temperature below the glass transition. By analyzing single particle trajectories, we identified ``jumps'' when particles moved significantly relative to their fluctuations. We consider the collective motion of these jump events by identifying jumps that occur close in space and time. We will show preliminary results of the cluster size distribution for different temperatures (i.e. 2500 K, 2750 K, and 3000 K), as well as the dependence of this distribution on waiting time. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y44.00010: Softness and Kinetic Heterogeneities in Glassy Liquids Samuel Schoenholz, Ekin Cubuk, Efthimios Kaxiras, Andrea Liu One signature feature of glassy liquids is the existence of kinetic heterogeneities. Isoconfigurational approaches show that there is a connection of these kinetic heterogeneities to the underlying structure of the liquid, but do not identify the particular structural features that are important in leading to enhanced mobility. We use machine-learning methods to show that the thermally-induced rearrangements that corresponding to enduring displacements in glassy liquids occur at ``flow defects'' that can be identified from the liquid structure. We will discuss the dynamics and spatial structure of the defect population, as well as the connection between the defect population and kinetic heterogeneities. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y44.00011: Jamming in Quasi-2D Self-Assembled Nanoparticle Monolayers Leandra Boucheron, Jacob Stanley, Yeling Dai, Sean You, Suresh Narayanan, Alec Sandy, Zhang Jiang, Mati Meron, Binhua Lin, Oleg Shpyrko In this work, we experimentally probed the interparticle dynamics of iron oxide nanoparticle thin films self-assembled at the liquid-air interface. Upon deposition on a water surface in a Langmuir-Blodgett trough by the drop-casting technique and subsequent lateral compression, iron oxide nanocrystals coated in oleic acid ligands self-assembled into a relatively uniform quasi-2D monolayer. Utilizing X-Ray Photon Correlation Spectroscopy (XPCS) at beamline 8-ID-I of the Advanced Photon Source at Argonne National Lab, we measured the characteristic timescale of in-plane interparticle dynamics. We quantified the aging behavior of the film utilizing both second-order and two-time autocorrelation analysis. We also determined the degree of jamming in the system by a stretched exponential model, yielding exponents varying between a value of 1.5 and 2. We have concluded that despite the quasi-2D nature of our system, verified by x-ray reflectivity, interparticle diffusion in our nanoparticle monolayers bears the signature of a largely three-dimensional jammed system. [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y44.00012: Universal Aging Dynamics in SiO2 Horacio E. Castillo, Katharina Vollmayr-Lee, Christopher H. Gorman Using molecular dynamics simulations, we study the aging dynamics of amorphous BKS silica. The system is quenched from a high temperature to below the mode coupling critical temperature. We analyze the dynamic susceptibility and the local incoherent intermediate scattering function as a function of the aging time. We find that those quantities display scaling behavior for this strong glass former. Our results show surprising similarities to previous results for fragile glass formers. [Preview Abstract] |
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