Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P9: Jamming: Theory and Experiment I |
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Sponsoring Units: GSNP Chair: Daniel Blair, Georgetown University Room: 303 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P9.00001: Cooperative Particle Dynamics in the Manhattan Model Prasanta Pal, Corey O'Hern, Jerzy Blawzdziewicz We study Brownian dynamics of hard rods in a Manhattan-like traffic grid, in which a series of narrow one-dimensional horizontal and vertical channels intersect at right angles, and particles are forbidden from turning at the intersections. We measure the intermediate scattering function (ISF) and mean-square displacement (msd) as a function of packing fraction $\phi$ and determine $\phi_g$ at which dynamical arrest occurs as a function of the system size, number of intersections, and topology of the grid. As a particular example, we explicitly characterize the cooperative particle dynamics required for structural relaxation for symmetric systems in which all lobes between junctions contain the same number of particles. In these systems, we predict the scaling behavior of the structural relaxation time and self-diffusion coefficient versus $\phi_g - \phi$. We will also quantify the extent to which these systems age and determine whether there is a characteristic number of junctions above which glassy dynamics occurs. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P9.00002: Universal Scaling Relation Near Point J Thomas Haxton, Andrea Liu Recently, several studies (P. Olsson and S. Teitel. \textit{Phys. Rev. Lett.} \textbf{99}, 178001 (2007); T. Hatano. arXiv:0803.2296; L. Berthier and T. A. Witten. arXiv:0810.4405) have indicated the existence of a dynamical phase transition at or near Point J, the point at zero temperature, zero shear stress, and a critical density where repulsive amorphous sphere packings lose rigidity. However, a universal scaling relation connecting the rheology of the jammed solid to that of the viscous liquid has been lacking. We control the temperature, strain rate, and pressure in molecular dynamics simulations to show that the steady-state rheology is described by a universal scaling relation near Point J. [Preview Abstract] |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P9.00003: Scaling of Rheology Near the Colloidal Jamming Transition Zexin Zhang, Anindita Basu, Thomas Haxton, Andrea Liu, Arjun Yodh Recent simulations have proposed that the zero-temperature, zero-shear-stress jamming transition can be understood in the framework of critical phenomena, and thus can be described by various asymptotic scaling laws. We carry out rheology experiments in the vicinity of the jamming transition to study the scaling of flow properties of a bidisperse colloidal soft sphere system. We find, both below and above the jamming transition, a scaling collapse of the rheological data when the shear stress and shear rate are rescaled by proximity to the jamming transition. We extract critical scaling exponents and compared with simulations. C. S. O'Hern et al. Phys. Rev. E 68, 011306 (2003). P. Olsson, S. Teitel, Phys. Rev. Lett., 99, 178001 (2007). T. Hatano, arXiv:0803.2296v4 (2008), arXiv:0804.0477v2 (2008) [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P9.00004: Quenched Disorder as a Fourth Axis to the Jamming Phase Diagram Cynthia Olson Reichhardt, Evan Groopman, Zohar Nussinov, Charles Reichhardt We propose that the general jamming phase diagram proposed by Liu and Nagel [Nature 396, 21, 1998] as a function of shear, density and temperature could also have a fourth axis which is the density of quenched disorder. This could represent jamming in porous media. Using numerical simulations we show that the density at which jamming occurs in a two-dimensional system of disordered disks decreases as the amount of quenched disorder in the sample increases. We argue that when the jamming correlation length is on the same length scale as the average distance between disorder sites, the system will jam. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P9.00005: Critical behavior from geometric confinement in shear thickening suspensions Eric Brown, Heinrich Jaeger We performed rheometry measurements on shear thickening suspensions. The viscosity is measured as a shear stress over shear rate in the shear thickening region to have divergent scalings of both the magnitude and slope at a critical packing fraction $\phi_c$. The yield stress also has a divergent scaling at $\phi_c$. This is qualitatively different form jamming models in which the yield stress grows gradually from an onset packing fraction. The value of $\phi_c$ depends only on particle shape and equals $0.56$ for hard spheres, corresponding to random loose packing and the onset of dilation. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P9.00006: Stress Fluctuations and Nonlinear Dynamical Modes Near Jamming David A. Egolf, Edward J. Banigan The jamming transition is often considered a dynamical transition, but how to properly and quantitatively characterize the changes in dynamical behavior is an open question. We perform numerical simulations of a two-dimensional sheared granular layer over a range of packing fractions spanning the transition. Within these simulations, we calculate a partial spectrum of Lyapunov exponents and vectors, which (at least in one sense) is an optimal decomposition of the dynamics of the system. We find that the Lyapunov exponents and vectors corresponding to the most important dynamical modes of the system tend to localize in space and time near important physical events, such as cooperative rearrangements or redistributions of stresses. In addition, we find that the magnitudes of Lyapunov exponents are directly linked to the size of relative stress fluctuations of the system. At high densities, the system changes from chaotic to non-chaotic, and we measure dynamical time and length scales that diverge as the system jams. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P9.00007: From Spheres to Ellipsoids: The Story of the Density of States Zorana Zeravcic, Ning Xu, Sidney R. Nagel, Andrea J. Liu Packings of frictionless ellipsoids have not only captured the imagination of the public, but also bring up a number of fundamental issues regarding the properties of jammed media. For instance, the average contact number $Z$ of such packings at jamming varies continuously between the spherical isostatic value $Z_{\rm iso}=6$ and the value $Z_{\rm iso}=10$ for ellipsoids of revolution if the ellipticity $\epsilon-1$ is turned on. Here we study the vibrational spectra of soft ellipsoids both as a function of density and $\epsilon$. Our spectra show a two-band structure. For small aspect ratios there is first a rotational band, then a gap and then a second band of translational character. As we increase the aspect ratio, the gap closes and the remaining band has a mixed character. We discuss various surprising features of the spectrum in detail and show how the changes in the gap are related with the change of $Z$ with $\epsilon$. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P9.00008: Growing length scale in gravity-driven dense granular flows Shubha Tewari, Melanie Finn, Allison Ferguson, Bulbul Chakravarty We report on simulations of a two-dimensional, dense, bidisperse system of inelastic hard disks falling down a vertical tube under the influence of gravity. We examine the approach to jamming as the average flow of particles down the tube is slowed by making the outlet narrower. Defining coarse- grained velocity and stress fields, we find a length scale and a time scale can be extracted from two-point spatial and temporal correlations of these fields. Both length and time scales are found to grow as jamming is approached \footnote{ S. Tewari, B. Tithi, A. Ferguson and B. Chakraborty, arXiv:0806.2413}. In an ongoing effort to understand the origin of the growing length and time scales, we have been investigating velocity profiles and distributions, and we will report on these results. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P9.00009: Experimental Study of the 2D Jamming Transition Xiang Cheng We can study a jammed system of particles by following a loosely-packed configuration as the individual particles increase their size until all the particles are constrained by their neighbors. Because tapioca pearls swell to over twice their initial diameter when submerged in water, they offer an ideal medium with which to study properties of the jamming transition in the presence of frictional interactions. Using an array of $\sim $ 10,000 tapioca pearls, we study several static and dynamic signatures of the two-dimensional jamming transition. The amplitude of the first peak of the pair-correlation function changes non-monotonically as the packing fraction of the system increases. This is consistent with recent experiments in a colloidal system of NIPA particles at finite temperatures [1]. This signature is a vestige of the divergence of this peak in the frictionless-sphere limit [2]. A length scale, defined by the spatial velocity correlation function, and the number hexagons in the Voronoi tessellation have pronounced maxima at the transition. [1] Z. Zhang, D. T. N. Chen, A. G. Yodh, K. B. Aptowicz and P. Habdas, Bull. Am. Phys. Soc. Volume 53, Number 2 (2008). [2] C. S. O'Hern, L. E. Silbert, A. J. Liu and S. R. Nagel, Phys. Rev. E 68, 011306 1-19 (2003). [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P9.00010: Influence of Confinement on the Structure of Random Close Packing Kenneth Desmond, Eric R. Weeks We study the structure of many simulated random closing packings confined between two walls. Each packing consists of a binary mixture in equal number with a sizes ratio of 1.4. Our aim is to quantify how a confining boundary and the thickness between the boundaries alters the structure of randomly close packed disks in 2D and spheres in 3D. We find that confinement lowers the packing fraction, and induces heterogeneity in particle density where particles show strong layering near the wall. Both the particle density and the structure of the local packing show oscillations that decay outward from the wall. The decay in the oscillations is rapid, with a characteristic length scale less than the largest particle diameter. We have also developed a simple model for describing the decrease in packing fraction with confinement. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P9.00011: Influence of Confinement on Dynamical Heterogeneities in Dense Colloidal Samples Kazem Edmond, Eric R. Weeks We study a colloidal suspension confined between two parallel walls as a model system for glass transitions in confined geometries. The suspension is a mixture of two particle sizes to prevent wall-induced crystallization. We use confocal microscopy to directly observe the motion of the colloidal particles. This motion is slower in confinement, thus producing glassy behavior in a sample which is a liquid in an unconfined geometry. Like particles in an unconfined near-glassy system, groups of particles in our confined system move together cooperatively. Normally these groups would be spatially isotropic. However, the confining boundaries induce a layering of the particles. We show that the layering modifies the shapes of the mobile groups within the sample so that they are planar. We investigate how the planar restriction of the shapes of the mobile groups may be the cause of the sample's glassy behavior. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P9.00012: Influence of Boundary Mobility on the Dynamics of Confined Colloidal Suspensions Gary L. Hunter, Kazem V. Edmond, Eric R. Weeks We use fast confocal microscopy to study the influence of interfacial mobility and confinement on the dynamics of dense colloidal suspensions. Experiments on confined molecular super-cooled liquids have shown that hard/immobile boundaries result in an increase in relaxation times relative to bulk measurements, whereas soft/mobile boundaries lead to a decrease in relaxation times. We confine suspensions of PMMA microspheres within emulsion droplets of different sizes, thereby probing the consequences of confinement. By changing the viscosity of the external, continuous phase, we also control the interfacial mobility of our samples. In this way, we separate the two effects and draw comparisons between mobility within colloidal suspensions and molecular liquids. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P9.00013: Jamming of Foams Gijs Katgert, Martin van Hecke We experimentally investigate jamming of soft frictionless spheres at zero stress and zero temperature, using static two-dimensional packings of foam bubbles. As a function of the distance to the jamming point, we obtain the distribution of interparticle forces, the scaling of the contact number and the distribution of free Voronoi area per bubble. Our results compare favorably to earlier predictions for soft discs and grains from theory and numerics. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P9.00014: Controlled jamming of particle-laden interfaces using a spinning drop tensiometer Hsin-Ling Cheng, Sachin Velankar Partially-wettable particles often adsorb nearly irreversibly at liquid/liquid interfaces. Under conditions when the interface is crowded with a particle monolayer, ``2D jamming'' can occur, i.e. the interface loses mobility and displays solid- like characteristics. We studied the jamming of iron oxyhydroxide (FeOOH) particles adsorbed at the interface between ethylene glycol and mineral oil using a spinning drop tensiometer (SDT). With decreasing rotational rate, the cylindrical drop retracted due to interfacial tension, thus reducing the interfacial area and increasing interfacial particle concentration. Accordingly, when the specific interfacial area became comparable to that for a close packing of particles, interfacial jamming occurred and drop retraction was arrested. Fast interfacial contraction or low capillary pressures led to less compact jammed monolayers, i.e. with a larger specific interfacial area. There was also significant hysteresis between compressing vs. expanding the jammed monolayer, suggesting that a certain minimum force is required for unjamming. Limited experiments with the same particles at a mineral oil/ silicone oil interface showed altogether different behavior: a particle-free portion of the interface coexisted with a particle-covered portion, suggesting that the monolayer behavior at this non-polar/non-polar interface is dominated by interparticle attraction. [Preview Abstract] |
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