Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W17: Jamming and the Glass Transition |
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Chair: Kai Zhang, Yale University Room: 402 |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W17.00001: Evolution of force networks in dense particulate matter Lou Kondic, Miro Kramar, Arnaud Goullet, Konstantin Mischaikow We present novel methods used to describe temporal evolution of force networks in dense particulate matter. The methods, based on algebraic topology, allow to quantify the evolution of these networks in precise terms. Different measures that we have developed allow to distinguish between local and global changes of the networks and furthermore illustrate strong dependence of the evolution itself on the state of the system. We will focus in particular on discussing the crucial factors that determine the time scales on which the networks evolve. [Preview Abstract] |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W17.00002: Characterizing dense granular systems by percolation and statistical properties of force networks Lenka Kovalcinova, Arnaud Goullet, Lou Kondic We consider a two dimensional granular systems compressed isotropically within a square box, We study the force networks, including evoltion of their statistical and percolation properties. Using the information about the total forces between the particles, the number of contacts and forming clusters, we identify the phase transition in granular systems, as well as distinguish between the system that do and do not crystallize. We discuss the influence of various physical parameters inlcuding the speed of compression on jamming and percolation transitions, and on force statistics. For systems without cohesion, we find that the jamming and percolation transitions coincide in the quisistatic limit. In the last part of the talk, we will present preliminary results discussing the degree to which out finding extend to cohesive systems. [Preview Abstract] |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W17.00003: New order metric for 3D packings Zhusong Li, Corey S. O'Hern, Mark D. Shattuck Characterization of the structure of static granular packings is important in both theory and applications. For example, it is often useful to assign a value to the degree of structural order in a system. However, most current order metrics assume a particular symmetry for the ordered structure. For systems composed of monodisperse spheres, it is known that the face-centered cubic (FCC) structure is the most ordered. Thus, order metrics that quantify icosahedral order are often selected for studies of monodisperse spheres. However, what order metrics should be used for bi-disperse system with arbitrary size ratio and mixture fraction that do not possess strong icosahedral order? We propose using the Shannon entropy that counts the number of distinct local geometric structures (e.g Voronoi polyhedra) as a measure of generic order. Using this new order metric, we find that we can distinguish order in systems where other metrics fail. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W17.00004: Ioffe-Regel limits of marginally jammed solids Xipeng Wang, Ning Xu We measure both the transverse and longitudinal dynamical structure factors from the normal modes of vibration of marginally jammed solids, from which Ioffe-Regel limits for transverse and longitudinal modes are obtained. We find that the Ioffe-Regel limit for transverse modes lies at a lower frequency than the boson peak, in contrast to the previous observation that the Ioffe-Regel limit and boson peak coincide. At the unjamming transition, while the Ioffe-Regel limit for transverse modes approaches zero frequency, the Ioffe-Regel limit for longitudinal modes approaches a constant. We also find that the longitudinal dynamical structure factor consists of two components: the liquid-like Rayleigh part and solid-like Brillouin part. At fixed volume fraction, the Rayleigh contribution increases with decreasing the wavelength. We thus determine a crossover wavelength at which contributions of the Rayleigh and Brillouin parts to the dynamical structure factor are equal. This crossover wavelength increases with decreasing the volume fraction following a power-law scaling and diverges at the unjamming transition. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W17.00005: Nonlinear Vibrational Response in Frictional Sphere Packings Thibault Bertrand, Corey S. O'Hern, Mark D. Shattuck The response of frictional granular packings to vibrations can display complex spatiotemporal dynamics due to strong nonlinearities from contact breaking, Hertzian contact interactions, frictional sliding, and other sources that are inherent in granular media. However, most computational and theoretical studies of the vibrational response of packings of frictional spheres have only characterized the linear vibrational response using the dynamical matrix. Here, we directly measure the frequency content of the response of packings of frictional spheres to vibrations as a function of the amplitude and frequency of the perturbations. By doing this, we are able to capture the transition from linear to nonlinear response as a function of the driving and identify the largest source of the nonlinear response for systems with different friction coefficients and packing fraction. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W17.00006: Efficient determination of soft spots in amorphous solids using local structural information Ekin Cubuk, Samuel Schoenholz, Brad Malone, Andrea Liu, Efthimios Kaxiras Structural defects such as dislocations are also flow defects that control plastic flow in crystalline solids. In disordered solids, it is more challenging to identify such local regions that are susceptible to rearrangement. We propose an extremely fast method for identifying soft spots with high accuracy, which scales linearly with number of particles. We achieve this by training a supervised learning model with instances of local neighborhoods and their subsequent plastic flow behavior. By characterizing local neighborhoods with not just one structural quantity, such as bond orientational order, but a combination of multiple structural quantities, we are able to identify a population of regions that correlates just as strongly with rearrangements as do soft spots calculated from vibrational modes. This method does not require knowledge of the interparticle interactions and can readily be applied to experiments that measure the positions of constituent particles in a disordered packing. Furthermore, this also allows for the prediction of plastic behavior in systems like lithiated amorphous silicon, which is important for addressing the durability issues encountered in recent work on improving lithium-ion batteries. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W17.00007: Solitary Wave Interactions in the Hertzian System Paul Anzel, Chiara Daraio It is well known in nonlinear dynamics that when solitons or solitary waves collide, their interaction creates a phase change in the propagating waves. It is natural to expect a similar behavior in highly nonlinear (Nesterenko) solitary waves--waves of mechanical motion in a Hertzian system: a row of elastic spheres which have a non-linear contact force that grows as $F = kx^{3/2}$. However, while this phenomenon has been qualitatively observed in simulations, the size of the change has not been explored systematically and little experimental work has gone into confirming the phase changes. Here we present an experimental and numerical study of the phase shifts created by solitary wave interactions in both co-travelling and head-on collisions. We measure the influence of compressing the spheres, which has the effect of linearizing the system towards a Boussinesq-like equation of motion. Additionally, we measure the creation of secondary solitary waves from the interactions and compare their amplitudes to values previously found in the literature. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W17.00008: Experimental measure of sphere packing probability in a Quasi-2D channel Harry Charalambous, Mark D. Shattuck, Corey S. O'Hern We designed an experiment to test exactly solvable models for packings of frictionless disks in confined geometry. We place a fixed number of monodisperse spheres (grains) of diameter (D=3.2mm) in a quasi 2d rectangular column 1.5D wide by 1D thick by 100D tall. In this arrangement only two possible configurations are allowed for a pair of grains; either consecutive grains are on opposite sides of the column or they are on the same side. We used an electromagnetic shaker to create random states by tossing a range from 4 to 26 grains in the air. After each toss, a vibration (perturbation) was applied to remove frictional effects. We measure the probability of finding each possible state and compare with theory. We find that gravity affects the probability distribution and needs to be incorporated into a new theory. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W17.00009: Frictional families in 2D experimental disks under periodic gravitational compaction Aline Hubard, Mark Shattuck, Corey O'Hern We studied a bidisperse system with diameter ratio 1.2 consisting of four 1.26cm and three 1.57cm stainless steel cylinders confined between two glass plates separated 1.05 times their thickness with the cylinder axis perpendicular to gravity. The particles initially resting on a movable piston are thrown upward and allowed to come to rest. In general this frictional state is stabilized by both normal and tangential (frictional) forces. We then apply short (10ms) small amplitude bursts of 440Hz vibration, temporarily breaking tangential forces and then allow the system to re-stabilize. After N of these compaction steps the number of contacts will increase to an isostatic friction-less state and additional steps do not change the system. Many frictional states reach the same final friction-less state. We find that this evolution is determined by the projection of the gravity vector on the null space of the dynamical matrix of a normal spring network formed from the contacts of the frictional state. Thus each frictional contact network follow a one-dimensional path (or family) through phase space under gravitational compaction. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W17.00010: Conching Chocolate Gary L. Hunter, Paul Chaikin, Elena Blanco, Wilson Poon ``Conching'' is an intermediate step in the processing of chocolate where hydrophilic solid particles, such as sugar and milk proteins, are aggressively mixed into a fatty, fluid phase containing emulsifier, e.g. molten cocoa butter with lecithin. During conching, the system evolves from a fine powder to a coarser granulated material and ultimately into a thick cohesive paste. Our goal is to better understand the evolution of chocolate during conching and the transition from an effectively dry to a wet or immersed granular material. In particular, we focus on how mixing times change in response to variations in solid particle volume fractions and emulsifier concentration. As a function of volume fraction, mixing times are well-described by a conventional form that diverges at a finite volume fraction. Furthermore, mixing times can be collapsed onto a universal curve as a function of mixing speed and emulsifier concentration. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W17.00011: Static quasi-2D emulsion as a granular system Rui Wu, Carlos Orellana, Xia Hong, Kenneth Desmond, Eric Weeks We study the forces between emulsion droplets and the properties of force chains in a static oil-in-water emulsion system near jamming. The emulsion is confined between two parallel glass plates in order to construct a quasi-2D system. Quasi-2D emulsion systems are somewhat analogous to 2D granular disks, except for the absence of static friction between the droplets. We focus on samples at an area fraction $\phi$ that is higher than the jamming point, $\phi_{c}$, and test the robustness of the power law dependence of pressure and the contact numbers on $\phi-\phi_{c}$. Specifically, we vary the surface tension by adding surfactants in the water, and examine the power law relationship under such variations. We also compare our result to simulations as well as established experimental results of true granular systems. [Preview Abstract] |
Thursday, March 6, 2014 4:42PM - 4:54PM |
W17.00012: Starch Suspensions with Different Fluids Melody Lim, Audrey Melville, Joshua Dijksman, Robert Behringer A suspension made of starch particles dispersed in water displays significant non-Newtonian behavior for high enough particulate concentration. This surprising behavior has recently inspired a series of experiments that have shed much light on the possible mechanism behind this phenomenon. In our studies we assess the role of the fluid phase in these suspensions. We find that using fluids other than water can significantly alter the behavior of starch suspensions. Through mechanical tests of various kinds, we assess the interaction between starch particles and different liquids, and how this interaction affects the non-Newtonian behavior of starch suspensions. [Preview Abstract] |
Thursday, March 6, 2014 4:54PM - 5:06PM |
W17.00013: Marginal rigidity and history dependence in packings of attractive athermal emulsions Dylan Bargteil, Lea-Laetitia Pontani, Jasna Brujic The geometry and stress through particulate packings depends on the method of preparation and the interaction potential between the particles. Previously, we discovered that creaming frictionless, athermal emulsions with a short-range depletion attraction leads to an initial increase in the packing density above random close packing, followed by a monotonic decrease in density (Jorjadze et al, PNAS, 2011). This decrease is because the attractive force stabilizes loose voids, thus reducing the average coordination number, $<$z$>$, of the packing. In order to understand the mechanism of packing creation, we investigate whether the final density is influenced by the polydispersity or the initial volume fraction of droplets, as it is in frictional packings. Finally, we compress the attractive packings by centrifugation to probe the scaling laws of pressure versus density and $<$z$>$ and compare them with those found in repulsive packings (Jorjadze et al, PRL, 2013).\\[4pt] [1] I. Jorjadze, L. Pontani, K. A. Newhall, and J. Brujic, Proc. Natl. Acad. Sci. U.S.A. 108, 4286 (2011).\\[0pt] [2] I. Jorjadze, L.-L. Pontani and J. Brujic, Phys. Rev. Lett. 110, 048302 (2013). [Preview Abstract] |
Thursday, March 6, 2014 5:06PM - 5:18PM |
W17.00014: Jamming and free energy landscapes for three caged soft disks Xin Du, Eric Weeks We study jamming in a model of three soft Brownian disks confined in a circular corral. For large corrals, the disks can freely rearrange where one particle passes in between the other two, but for small corrals rearrangements become rare. We use a Monte Carlo simulation to study the dynamics of the three disks, and calculate the Helmholtz free energy from the distribution of configurations in the system. The free-energy landscape in a one-dimensional space contains two symmetric energy minima separated by an energy barrier. Rearrangement events correspond to the system crossing over the free-energy barrier. With low temperature and/or small corral size, the energy barrier becomes larger and the system approaches glass transition. The free energy barrier has both energy and entropy components. We compare our results to a model of hard disks, for which the free energy barrier for rearrangements is entirely entropic. In particular we find that we cannot simply model the soft disks as hard disks with a temperature-dependent effective size. [Preview Abstract] |
Thursday, March 6, 2014 5:18PM - 5:30PM |
W17.00015: Elastic probes of length scales in jammed packings: from global response to point response Kamran Karimi, Craig Maloney We probe amorphous packings in different ways to determine whether or not characteristic length scales govern the elastic response and how these lengths depend on the area fraction of disks, $\phi$. First we drive the system globally using either: i) a homogeneously deforming periodic cell of length $L$, ii) a force field having a plane-wave structure with wavelength $L$, iii) a homogeneously deforming rigid wall of length $L$. Methods i) and ii) give elastic moduli values that converge rapidly to the infinite system size limit and have $\phi$-independent functional forms. Method iii), however shows a dramatic decrease in the shear modulus $\mu$ with increasing $L$. At low $L$, $\mu$ has a value that depends only weakly on $\phi$, whereas, as $L$ goes to infinity, $\mu$ must approach zero near jamming point $\phi_c$. We show that the $\mu$ vs $L$ curves at various $\phi$ can be collapsed into a master curve after scaling $L$ by a quantity $\xi$ that grows near $\phi_c$. Secondly, we study the point response. We show that the response, in Fourier space, crossovers to the Kelvin solution for small wave vectors. This cross-over exhibits a lenghtscale that grows with $\phi$ in a similar fashion to the lengthscale determined by the global shear with a rigid box. [Preview Abstract] |
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