Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V14: Disordered Systems, Glassy Dynamics, and Jamming II |
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Sponsoring Units: DFD GSNP Chair: Peter Schall, University of Amsterdam Room: 315 |
Thursday, March 19, 2009 8:00AM - 8:12AM |
V14.00001: Specific Heat Anomalies in Glassy Fluids Due to Cluster Micro-Melting George Hentschel, Valery Ilyin, Itamar Procaccia, Nurith Schupper We will discuss the specific heat anomalies observed in new simulations of equimolar mixtures of particles interacting via soft core repulsive potentials under external pressure that are known to show glassy dynamics at low temperatures. The simulations show both long-lived states of microcrystalline clusters that do not nucleate a crystalline ground state and also the appearance of two specific heat peaks which were not observable in earlier simulations. We argue that the appearance of two peaks is due to the micro-melting of two types of clusters and discuss the form of the resulting specific heat anomalies. Our arguments suggest that the glass transition will typically show non universal features. [Preview Abstract] |
Thursday, March 19, 2009 8:12AM - 8:24AM |
V14.00002: The building blocks of Dynamical Heterogeneities in dense granular media Raphael Candelier, Olivier Dauchot, Giulio Biroli Unveiling the connection between the short term relaxation and the long term dynamical heterogeneities as observed near the glass transition in super-cooled liquids and the jamming transition in granular materials remains a major challenge in the physics of glassy systems. On one hand, KCM models relate dynamical heterogeneities to a non trivial structure in the trajectory space, inherited from the local dynamical rules. On the other hand, recent studies of hard spheres close to isostaticity suggest that the collective aspect of the relaxation would stem from the extended character of the softest degrees of freedom, along which the system yields from one meta-bassin to another. There is still no direct experimental evidence in favour of one or the other mechanism in super-cooled liquids nor in dense granular media. Here we will show that for a dense granular layer under cyclic shear dynamical heterogeneities result from a two timescales process. Short time but already collective events consist in clustered cage jumps, which concentrate most of the non affine displacements. Such clusters aggregate both temporally and spatially within an avalanche process, which ultimately builds the large scales dynamical heterogeneities. The typical timescale of the dynamical heterogeneities appears as the crossover between the short time separating successive event within the avalanches and the long time separating the successive jumps of any given particle. [Preview Abstract] |
Thursday, March 19, 2009 8:24AM - 8:36AM |
V14.00003: Role of Shape Anisotropy on the Glassy Dynamics of Colloidal Suspensions Mukta Tripathy, Kenneth Schweizer Center-of-mass ideal mode coupling theory (MCT), the nonlinear Langevin activated barrier hopping theory, and the Reference Interaction Site Model have been employed to investigate the structure and slow dynamics of suspensions composed of hard and rigid nonspherical particles. Objects of dimensionality one (rods, rings), two (discs), and three (polyhedra) have been studied. For non-compact particles the volume fraction of ideal kinetic arrest, corresponding to a crossover to activated dynamics, decreases with particle dimensionality and/or aspect ratio. On the other hand, the ideal vitrification volume fraction of compact 3-dimensional objects is a complex and subtle function of particle shape. Calculations of the entropic barrier for activated transport, mean relaxation time, transient localization length, diffusion constant, elastic modulus, and effective fragility have been performed. Deep in the ideal glassy region the barrier height and mean hopping time are controlled by the shape-dependent mean square confining force exerted on a particle by its surroundings. A nearly universal collapse of many dynamical properties is achieved based on a dimensionless difference variable that quantifies the magnitude of the mean square force compared to its critical value at the ideal MCT transition. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V14.00004: Coupled Translational and Rotational Glassy Dynamics in Hard Dicolloid Suspensions Rui Zhang, Kenneth Schweizer Naive mode coupling theory (NMCT) and the nonlinear Langevin equation (NLE) theory of activated glassy dynamics have been generalized to treat the coupled center-of-mass translation and rotational motions of hard linear objects of variable aspect ratio. Two types of ideal nonergodicity transitions are predicted corresponding to localization of only translation (plastic glass for small aspect ratios) or simultaneous arrest of translation and rotation (double glass). The NMCT kinetic arrest transition signals a crossover to activated dynamics controlled by entropic barriers. Specifically, a two-dimensional dynamical free energy surface (function of translational displacement and rotational angle) is constructed which quantifies effective forces in the NLE theory. For all aspect ratios the most efficient activated process corresponding to the trajectory of lowest entropic barrier is associated with a system-specific translation-rotation cooperative motion. Mean alpha relaxation times as a function of dicolloid aspect ratio and volume fraction are computed using multidimensional Kramers theory. [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V14.00005: Constitutive relations in dense granular flows John Drozd, Colin Denniston We use simulations to investigate constitutive relations in dry granular flow. Our system is comprised of mono- and poly-disperse sets of spherical grains falling down a vertical chute under the influence of gravity. We observe three phases or states of granular matter: a free-fall dilute granular gas region at the top of the chute, a granular fluid in the middle and then a glassy region at the bottom. We test various proposed constitutive relations to provide a basis for analytically solving for the stresses in granular flows. Finally, we examine the energy conservation and heat flow in our systems and show that the heat conductivity constitutes distinct power-law dependencies on the granular temperature in the glassy and fluid regions of our system. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V14.00006: Polytetrahedral Frustration of Crystallization: A Study of 4d Hard Spheres Patrick Charbonneau, Jacobus A. van Meel, Daan Frenkel Geometrical frustration is thought to ease the supercooling of a liquid. In $3d$ hard spheres the preferred local cluster is icosahedral and the densest packing is tetrahedral, but no periodic lattice is consistent with either symmetry in Euclidian space, so a crystal phase with a different symmetry nucleates upon compression. For $2d$ disks in contrast triangular or hexagonal order is both locally and globally preferred and crystallization of a metastable fluid is quasi-instantaneous. Yet the precise origin of geometrical frustration remains unclear, because in $2d$ and $3d$ polytetrahedral structures are often equated conceptually to the optimal local cluster. Here, we conduct a computational study of the $4d$ analogue, where the optimal local cluster and global order are commensurate, but the polytetrahedral order is not. We observe no sign of facile crystal formation, which support the polytetrahedral frustration scenario. We also find the fluid to be structurally very different from the crystal. The resulting high interfacial free energy sheds new light on $3d$ geometrical frustration and its role in glass formation. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V14.00007: Noise as a Probe of Ising Spin Glass Transitions Zhi Chen, Clare Yu Noise is ubiquitous and and is often viewed as a nuisance. However, we propose that noise can be used as a probe of the fluctuations of microscopic entities, especially in the vicinity of a phase transition. In recent work we have used simulations to show that the noise increases in the vicinity of phase transitions of ordered systems. We have recently turned our attention to noise near the phase transitions of disordered systems. In particular, we are studying the noise near Ising spin glass transitions using Monte Carlo simulations. We monitor the system as a function of temperature. At each temperature, we obtain the time series of quantities characterizing the properties of the system, i.e., the energy and magnetization. We look at different quantities, such as the noise power spectrum and the second spectrum of the noise, to analyze the fluctuations. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V14.00008: Shear banding in colloidal glasses Vijayakumar Chikkadi, Andrew Schofield, Peter Schall We perform slow shear of colloidal glasses using a confocal microscope and shear-cell set up. The particles are tracked in time and space to construct the local strain field, which is observed to be non-uniform with high strain and low strain zones interspersed in space. Our measurements at a volume fraction $\sim $ 59{\%} show the existence of homogeneously sheared regime at a shear rate $\sim $5x10$^{-5}$ s$^{-1}$ and shear localization at higher shear rates ($>$10$^{-4}$ s$^{-1})$. The set-up offers a unique opportunity to elucidate the evolution of shear-bands using the concept of shear transformations. In particular, the aim is to understand the role of correlation between the shear transformations in the growth of shear bands. We present an overview over the homogeneous versus inhomogeneous shear regime in terms of a deformation map for these systems. [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V14.00009: Correlations between Dynamical Heterogeneity and Viscoelasticity of Confined Colloidal Suspensions under Oscillatory Shear Prasad Sarangapani, Yingxi Elaine Zhu In this talk, we present a recent rheological study of confined amorphous colloidal thin films under oscillatory shear using a home-designed micron-gap rheometer interfaced with a confocal microscope. We visualize the response of ``hard-sphere'' poly-(methyl methacrylate) (PMMA) particles of 1.2 $\mu $m in diameter to applied shear deformation and simultaneously measure the viscous and elastic moduli of PMMA colloidal thin films of bulk volume fraction, \textit{$\phi $}= 0.43-0.57, confined at gaps ranging from 50 $\mu $m to 1-2 $\mu $m. For confined PMMA colloids under shear at gaps where an applied deformation is sufficiently large to induce non-linear responses, we find commonality in particle dynamics where strongly non-affine motion causes particles to move as cooperatively rearranging groups. However, on average the length scale of these groups is larger than the typical length scales of dynamical heterogeneities for the un-sheared thin films and typically approaches the order of confining dimension. We quantify the nature of shear induced flow cooperativity and its relation to a shear thickening transition observed in the limit of large strain amplitudes. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V14.00010: Aggregation of athermal particles induced by capillarity Michael Berhanu, Arshad Kudrolli Aggregation of cohesive particles floating in a medium is a very broad physical phenomena occurring in colloidal systems, soot particles, and intergalactic dust under gravitation. We investigate the geometrically constrained dynamics of aggregation with new experiments using floating spheres at the air-liquid interface. A short range attractive force can be induced by careful choice of buoyancy and capillarity to create self-assembled particle structures which can be tracked by imaging. First, the particles are placed randomly at the interface, and then aggregation is induced by smoothly decreasing the area of the interface which causes the particles to come within the attractive force range caused by capillarity. We measure the area fraction at which the connectivity and rigidity percolation transitions are observed and further characterize the aggregates with two-point correlation functions. We then compare and contrast our results with gelation and jamming transitions reported with colloids and granular matter. Finally, we study the reverse phenomena, where we probe the response of the aggregate to an increase in interface area. [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V14.00011: Correlation range in a supercooled liquid via Green-Kubo expression for viscosity, local atomic stresses, and MD simulations Valentin A. Levashov, Takeshi Egami, James R. Morris We present a new approach to the issue of correlation range in supercooled liquids based on Green-Kubo expression for viscosity. The integrand of this expression is the average stress-stress autocorrelation function. This correlation function could be rewritten in terms of correlations among local atomic stresses at different times and distances. The features of the autocorrelation function decay with time depend on temperature and correlation range. Through this approach we can study the development of spatial correlation with time, thus directly addressing the question of dynamic heterogeneity. We performed MD simulations on a single component system of particles interacting through short range pair potential. Our results indicate that even above the crossover temperature correlations extend well beyond the nearest neighbors. Surprisingly we found that the system size effects exist even on relatively large systems. We also address the role of diffusion in decay of stress-stress correlation function. [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V14.00012: Dynamics in Complex Fluids Formed by Conjugated Polymers Naresh Osti, Madhusudan Tyagi, Dilru Ratnaweera, Uwe Bunz, Dvora Perahia Alkyl di-substituted \textit{para-polyphenyleneethylene} (PPE) associates into several complex fluids in dilute solutions of toluene. At high temperature the molecules are isolated and assume extended configuration. As the temperature decreases, the molecules associate and eventually jam in to a fragile gel. These phases are optically active where the dynamic processes affect their optical characteristics. Inelastic Neutron Back Scattering conjunction with Neutron Spin Echo was used to characterize the dynamics on multiple length scales at different temperatures. The current talk will introduce the neutron backscattering results that follow internal dynamics within the PPE molecules as they are confined into aggregates and jams to form a fragile phase. The data will be discussed in terms of Kohlrausch-Williams-Watt model that provides characteristics time constants for the different dynamic processes. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V14.00013: Spontaneous transition in TiNiFe strain glass system Jian Zhang, Xiaobing Ren, Yu Wang, Kazuhiro Otsuka, Jun Sun Glass has been considered as one major challenge for the statistic mechanics, for the presumption of ergodicity is no longer valid. Hence, glass transition was normally viewed as solely kinetic driven process, including ferroic cluster glasses. Whereas, the ferroic cluster glasses appear once the thermodynamics driven ferroic phase transitions are suppressed by the point defects. It seems quite intriguing why the power of thermodynamics is immediately eliminated when the system reaches the threshold composition, and taken over completely by kinetics. We demonstrate the power of the thermodynamics on the glass state by presenting for the first time the existence of spontaneous transition from strain glass to long range phase in the newly found strain glass in TiNiFe, evidenced with various experimental methods. In addition, we provide one phenomenological model to reveal the underlying mechanism due to the competition between the thermodynamic and kinetic factors. Our results on this relatively simply glass system may bring new ideas in other fields of science and technology, i.e. biophyscis and biochemistry. [Preview Abstract] |
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