Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session L13: Focus Session: Jamming Theory and Experiment III |
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Sponsoring Units: GSNP Chair: Robert Behringer, Duke University Room: D225/226 |
Tuesday, March 22, 2011 2:30PM - 2:42PM |
L13.00001: Relaxation of stresses and dynamical heterogeneities close to jamming in a granular experiment Corentin Coulais, Olivier Dauchot, Robert Behringer Dynamical Heterogeneities have been found to exhibit maximal size and scale invariance at Jamming. We address here the question of the link with stresses in the materials. To that end, we use a confined, vibrated layer of 8000 bidisperse grains under uniaxial compression. The vibration is horizontal, transverse to the direction of compaction. First, an intruder is pulled at constant velocity through the assembly and force measurements reveals maximal time correlations at Jamming. Then, the experimental setup is slightly modified to accept photoelastic grains, made of soft or hard materials. By measuring positions and stresses, decorrelation of forces as well as dynamics in structure, spontaneous fluctuations are probed. Both quenches and intruder pulling protocols are performed, and novel behavior at Jamming is seen. [Preview Abstract] |
Tuesday, March 22, 2011 2:42PM - 2:54PM |
L13.00002: Nonlinear elasticity near jamming probed in bidisperse foams Alexander Siemens, Martin van Hecke An unusual characteristic of the jamming transition is the difference in scaling of the bulk and shear modulus of frictionless soft particles near jamming. We probe this scaling by compressing a bidisperse foam monolayer sandwiched between a glass plate and a fluid surface. We also determine the weakly nonlinear effective bubble-bubble interactions in a 1D chain of bubbles under compression. [Preview Abstract] |
Tuesday, March 22, 2011 2:54PM - 3:06PM |
L13.00003: Reversible plasticity near Jamming in foams Gijs Katgert, Wilson C.K. Poon We study the response of a disordered foam monolayer, confined between a soapy solution and a glass plate to an oscillatory compressive strain brought about by inflating a central bubble. We show that, when driven quasistatically slowly, the foam as a whole can exhibit kinematically reversible plasticity or {\it anelasticity}: the bubble packing alternates between two reproducible configurations, which are separated by multiple plastic events and global displacements. After establishing that the timescale beyond which the foam behaves quasistatically is set by the scaling of the foam compressive modulus with packing fraction $\phi$, we map out the boundary between reversible and irreversible plasticity in the space spanned by $\phi$ and the compressive strain $\varepsilon$ and tentatively find the strain to scale as $\varepsilon \sim (\phi-\phi_c)^{1/4}$, with $\phi_c$ the jamming point. We finally extract a plasticity lengthscale from our experiment and show it to grow on approach to $\phi_c$. [Preview Abstract] |
Tuesday, March 22, 2011 3:06PM - 3:18PM |
L13.00004: Local origins of volume fluctuations in granular materials James Puckett, Frederic Lechenault, Karen Daniels Recent experiments and simulations have observed that the fluctuations in the local volume fraction, $\phi$, decrease as the granular material approaches jamming. We investigate the role of boundary condition and inter-particle friction, $\mu$, on these fluctuations for a dense bidisperse granular monolayer driven at the perimeter. Using a radical Voronoi tessellation, we find a universal linear relationship between the mean variance of $\phi$ independent of boundary condition and $\mu$. We examine the universality and origins of this trend using the recent granocentric model modified to draw neighbors from an arbitrary distribution $P(s)$, the edge-to-edge distance between neighbors. The mean and variance of the observed particle separation $s$ are described by a single length scale controlled by mean $\phi$. We tested diverse functional forms of $P(s)$ and found that each produces the trend of decreasing fluctuations, but only the experimentally-observed $P(s)$ provides quantitative agreement with the measured $\phi$ fluctuations. In conclusion, we find $P(\phi)$ and $P(s)$ encode similar information about the distribution of free volume in a driven granular system under different boundary conditions and inter-particle friction. [Preview Abstract] |
Tuesday, March 22, 2011 3:18PM - 3:30PM |
L13.00005: Intermittent Jamming in Quasi-2D Microfunnels Carlos Ortiz, Karen Daniels, Robert Riehn Both athermal granular jamming and thermal glass transitions have recently received extensive attention. We experimentally investigate the jamming transition in a quasi-2D system of nearly hard-sphere, micron-sized PMMA-PHSA particle suspension in a density and index-matched medium flowing through a microfunnel. We observe a packing fraction driven transition from a gas-like to a liquid-like to a solid-like phase. At sufficiently high packing fractions we observe intermittent jamming under constant pressure. Further increase in the packing fraction forms a stable solid-like jammed phase which is disordered on long-ranges, and susceptible to re-melting by reverse flow, agitation, and diffusion. By displaying properties of both athermal granular jamming and thermal glass transitions, our experiment provides a useful testing ground for understanding the jamming transition as a unifying framework. [Preview Abstract] |
Tuesday, March 22, 2011 3:30PM - 3:42PM |
L13.00006: Controllable jamming of amorphous granular materials applied to robotics Eric Brown, Rodenberg Rodenberg, John Amend, Hod Lipson, Annan Mozeika, Erik Steltz, Mitchell Zakin, Heinrich Jaeger We demonstrate the practicality of using a controlled jamming transition in an amorphous mass of granular material for applications to robotic gripping, and how the gripping capabilities depend on the properties of the jammed state. A mass of granular material contained in a flexible membrane in an unjammed state flows and conforms to almost any object it is pressed against. Upon application of a vacuum, the external pressure on the membrane jams the granular mass with a volumetric contraction $< 1\%$, allowing it to pinch the object. By measuring the holding force on a test sphere at different levels of envelopment, we show that three mechanisms contribute to the holding force: friction, suction, and interlocking. We use a solid mechanics model to relate the holding force from each mechanism to the measured stress response of jammed granular materials to compressional, extensional, and bending strains. This opens up new possibilities for the design of simple systems that excel at gripping objects of arbitrary shape. [Preview Abstract] |
Tuesday, March 22, 2011 3:42PM - 3:54PM |
L13.00007: Jamming in Vertical Channels G. William Baxter, Fiona Steel We study jamming of low aspect-ratio cylindrical Delrin grains in a vertical channel. Grain heights are less than their diameter so the grains resemble antacid tablets, coins, or poker chips. These grains are allowed to fall through a vertical channel with a square cross section where the channel width is greater than the diameter of a grain and constant throughout the length of the channel with no obstructions or constrictions. Grains are sometimes observed to form jams, stable structures supported by the channel walls with no support beneath them. The probability of jam occurrence and the strength or robustness of a jam is effected by grain and channel sizes. We will present experimental measurements of the jamming probability and jam strength in this system and discuss the relationship of these results to other experiments and theories. [Preview Abstract] |
Tuesday, March 22, 2011 3:54PM - 4:06PM |
L13.00008: Geometry Dependence of the Clogging Transition in a Tilted Hopper Charles Thomas, Douglas Durian We report the effect of system geometry on the clogging of granular material flowing out of a flat-bottomed hopper. We vary the hopper tilt angle, aperture shape, and granular media shape, investigating smooth spheres (glass beads), compact angular grains (beach sand), and rod-like grains (rice). We measure the average number of grains discharged before a clog halts the flow. This value grows with hole size as a power law, diverging above a critical hole size. We determine the critical value by performing a least-squares fit to the data. Beyond that critical hole size, the flow does not clog for any given tilt angle. This critical hole size grows with increasing tilt, diverging at $\pi - \theta_{r}$, where $\theta_{r}$ is the angle of repose. The value of the critical hole size as a function of tilt angle describes a well-defined transition on a clogging phase diagram. For circular apertures, the shape of this transition is similar for all grain types. However, this is not the case for the narrow slit apertures, where the rate of growth of the critical hole size with tilt angle depends on the material. The growth rate is the fastest for angular grains, then smooth spheres, with rod-like grains showing the slowest growth. This suggests a profound link between the aperture geometry and the particle shape. [Preview Abstract] |
Tuesday, March 22, 2011 4:06PM - 4:18PM |
L13.00009: Jamming of Granular Flow in a Two-Dimensional Hopper Junyao Tang, Sepehr Sadighpour, Robert Behringer We seek an understanding of the physics of jamming for hopper flow using high speed spatio-temporal video data for photoelastic disks flowing through a two-dimensional hopper. We have found experimental support for the hypothesis that jamming events of granular flow in a hopper is approximately a Poisson process. The mean flow time between two consecutive jams increases rapidly with the hopper opening size, but it is insensitive to changes of the hopper wall angle.Through particle tracking and photoleastic measurements, we measure stress fields, velocity fields and density fields, as well as their fluctuations during the flow. Current work is focusing on understanding how to combine these results to give us further insights of the relation between mean flow properties and jamming and their dependence on hopper configuration.These data are part of an IFPRI-NSF Collaboratory for comparing physical data and simulations. [Preview Abstract] |
Tuesday, March 22, 2011 4:18PM - 4:30PM |
L13.00010: Structural Stability and Jamming of Self-Organized Cluster Conformations in Granular Materials A. Tordesillas, B. Behringer, Q. Lin, J. Shi, J. Zhang We probe emergent self-organized particle cluster conformations in slowly deforming dense granular materials. We invoke structural mechanics to devise a new stability measure for clusters, and use this measure to explore stability of jammed states of cluster conformations consisting of particles in force chains and minimal contact cycles. Knowledge of the spatio-temporal evolution of the (relative) stability of jammed conformations offers valuable clues to granular rheology and self-assembly. We use data from assemblies of bi-/poly-disperse disks subject to 2D deformation in two biaxial strain tests: one computational and one experimental. Self-assembly occurs on multiple length scales with jammed force chains and minimal cycles forming the basic building blocks. Three-cycles are stabilizing agents acting as granular trusses to load-bearing force chain columns. The co-evolution of minimal cycles and force chains form a generic feature of these materials and loading paths. [Preview Abstract] |
Tuesday, March 22, 2011 4:30PM - 4:42PM |
L13.00011: Decoupling of Rotational and Translational Diffusion in Supercooled Colloidal Fluids Kazem V. Edmond, Gary L. Hunter, Mark T. Elsesser, HyunJoo Park, David J. Pine, Eric R. Weeks Using high-speed confocal microscopy, we directly observe the three-dimensional rotational dynamics of rigid clusters of microspheres suspended in dense colloidal suspensions. The clusters are highly ordered packings of fluorescently-labeled PMMA particles, fabricated using a recently developed emulsification technique. Our colloidal suspensions serve as good approximations to hard-sphere fluids, while the clusters probe the system's local rotational and translational dynamics. Far from the colloidal liquid's glass transition, both rotational and translational motion of the clusters are purely Brownian. However, in the liquid's supercooled regime, we observe a decoupling between the two types of motion: as the glass transition is approached, rotational diffusion slows down even more than translational diffusion. Our observation supports the notion that supercooled liquids are not merely liquids with large viscosities but that diffusion takes place by fundamentally changed mechanisms. [Preview Abstract] |
Tuesday, March 22, 2011 4:42PM - 4:54PM |
L13.00012: Confinement of Colloidal Suspensions in a Cylindrical Geometry Nabiha Saklayen, Gary L. Hunter, Kazem V. Edmond, Eric R. Weeks We study binary colloidal suspensions confined within a glass microcapillary to model the glass transition in confined cylindrical geometries. We use high speed three-dimensional confocal microscopy to observe particle dynamics. The use of a slightly tapered microcapillary enables us to probe a range of local volumes for a single colloidal sample. We observe that confinement of the sample slows down particles. In addition, the particles form layers against the capillary walls; these layers also influence particle mobility. We see that even though confinement is primarily responsible for slowing down particles, particles within a layer are seen to move even slower. Within each region of the microcapillary, the mobility perpendicular to the confining boundaries is influenced by distance from the confinement boundary, while the parallel component of mobility is not. [Preview Abstract] |
Tuesday, March 22, 2011 4:54PM - 5:06PM |
L13.00013: Shear-induced dynamics of polydisperse jammed emulsions Eric R. Weeks, Joaquim Clara Rahola We study dense and highly polydisperse emulsions at droplet volume fractions ranging from phi = 0.65 to 0.85. We apply oscillatory shear and observe the subsequent droplet motions using confocal microscopy. Both affine and nonaffine droplet motions are observed, with the large droplets typically moving affinely and pushing the smaller droplets around in non-affine ways. Despite the polydispersity of the sample and the complex droplet trajectories, we observe dynamic correlation length scales. These length scales grow from one to four times the mean droplet diameter, with larger length scales corresponding to higher strain amplitudes (up to strains of about 6\%). [Preview Abstract] |
Tuesday, March 22, 2011 5:06PM - 5:18PM |
L13.00014: A Jamming Phase Diagram for Pressing Polymers Chao Teng, Zexin Zhang, Xiaoliang Wang, Gi Xue Molecular glasses begin to flow when they are heated. Other glassy systems, such as dense foams, emulsions, colloidal suspensions and granular materials, begin to flow when subjected to sufficiently large stresses. The equivalence of these two routes to flow is a basic tenet of jamming, a conceptual means of unifying glassy behavior in a swath of disordered, dynamical arrested systems. However, a full understanding of jamming transition for polymers remains elusive. By controlling the packing densities of polymer glasses, we found that polymer glasses could once flow under cold-pressing at temperatures well below its calorimetric glass transition temperature (Tg). The thermomechanical analysis (TMA) results confirmed that Tg changed with density as well as the applied stress, which is exactly what to be expected within the jamming picture. We propose a jamming phase diagram for polymers based on our laboratory experiments. [Preview Abstract] |
Tuesday, March 22, 2011 5:18PM - 5:30PM |
L13.00015: Visualization of force networks in a three-dimensional granular system Chantal Carpentier, Kinga Lorincz, Peter Schall, Daniel Bonn, Fred Brouwer Force networks form the skeleton of granular matter. The understanding of the rigidity to flow transition of granular materials requires the study of the three-dimensional distribution of forces between the particles. Here we propose a new method to visualize and measure contact forces in three-dimensional suspensions. We use a rigidochromic dye which we attach chemically to the surfaces of the particles to measure local forces at the contact point. This dye exhibits non-fluorescent transitions, when it is free to relax mechanically, but shows strong fluorescence when confinement blocks mechanical relaxation. Preliminary experiments suggest that the fluorescent intensity is a direct measure of the local contact force. We use confocal microscopy to create spatial intensity maps to reconstruct the entire contact force distribution. [Preview Abstract] |
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