Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session V13: Glassy Systems and Jamming II |
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Sponsoring Units: GSNP DFD Chair: Patrick Charbonneau, Duke University Room: D225/226 |
Thursday, March 24, 2011 8:00AM - 8:12AM |
V13.00001: Phonon Spectra in Disordered Clusters of Colloidal Particles with Attractive Interactions Arjun G. Yodh, Peter J. Yunker, Ke Chen, Zexin Zhang The influence of size and morphology on the vibrational properties of disordered clusters of colloidal particles with attractive interactions is studied experimentally. Water- lutidine mixtures induce fluid mediated attraction between micron-sized polystyrene particles, leading to the formation of attractive glasses with high local packing fractions. By measuring displacement correlations between particles, we extract the vibrational properties of these disordered clusters. Surprisingly, the spectra and character of vibrational modes did not depend on the number of particles involved. Rather, it depended strongly on the average number of nearest neighbors. An increase in the number of nearest neighbors shifted the phonon spectrum to higher frequencies, independent of the total number of particles in in the cluster. Simulations of structureless random networks of springs support these results, and further suggest that the dependence of phonon spectrum on number of nearest neighbors is a generic property of disordered networks. [Preview Abstract] |
Thursday, March 24, 2011 8:12AM - 8:24AM |
V13.00002: Dynamics of Small-Molecule Glass Formers Confined in Nanopores Timothy Prisk, Madhusudan Tyagi, Paul Sokol We report a comparative neutron scattering study of the molecular mobility and non-exponential relaxation of three structurally similar glass-forming liquids (isopropanol, propylene glycol, and glycerol) in bulk and confined in porous Vycor glass. Confinement reduces molecular mobility in all three liquids, and suppresses crystallization in isopropanol. High-resolution quasi-elastic neutron scattering spectra were fit to Fourier transformed Kohlrausch functions $\exp[-(t/\tau) ^{\beta}]$, describing $\alpha$-relaxation. The stretching parameter $\beta$ is roughly constant with wavevector $Q$ and temperature. Average relaxation times $\langle\tau(Q)\rangle$ are longer at lower temperatures and in confinement. They obey a power law $\langle\tau(Q)\rangle \propto Q^{-\gamma}$, where the exponent $\gamma$ is modified by both temperature and confinement. Comparison of the bulk and confined liquids lends support to the idea that structural and/or dynamical heterogeneity underlies the non-exponential relaxation of glass- formers, as widely hypothesized in the literature. [Preview Abstract] |
Thursday, March 24, 2011 8:24AM - 8:36AM |
V13.00003: ABSTRACT WITHDRAWN |
Thursday, March 24, 2011 8:36AM - 8:48AM |
V13.00004: Emergence of rigidity at the dynamic glass transition: a replica approach calculation Grzegorz Szamel, Elijah Flenner According to the mean-field replica theory of the glass transition, at the so-called dynamic transition the relaxation stops and the liquid freezes into one of many metastable states. We identify Goldstone modes of the resulting amorphous solid and derive a formal expression for its shear modulus. This expression is complementary to the formula used by Yoshino and Mezard [Phys. Rev. Lett. \textbf{105}, 015504 (2010)]. We combine our formal expression with the recently proposed version of the replica approach [G. Szamel, Europhys. Lett. \textbf{91}, 56004 (2010)] to calculate the shear modulus. [Preview Abstract] |
Thursday, March 24, 2011 8:48AM - 9:00AM |
V13.00005: Experimental study of dynamic rearrangements in repulsive and attractive glasses Zexin Zhang, Peter Yunker, Piotr Habdas, Arjun Yodh The influence of interparticle attraction versus repulsion on heterogeneous glass dynamics is explored with colloidal particles suspended in water-lutidine mixtures. The mixtures permit interparticle potentials to be tuned in situ from short-range repulsive to short-range attractive. Thus, a direct comparison of colloidal glass dynamics in samples composed of the same particles at the same volume fraction is possible. In both types of glasses, dynamics are found to be heterogeneous, and particles rearrange in a cooperative manner. By comparison to repulsive glasses, attractive glasses exhibit dynamics that are heterogeneous over a wider range of time and length scales, and involve more particles. Clusters of rearranging particles form string-like structures in repulsive glasses, and more compact clusters in attractive glasses. The experiments demonstrate explicitly that interparticle interactions affect glass dynamics. [Preview Abstract] |
Thursday, March 24, 2011 9:00AM - 9:12AM |
V13.00006: A family of systematically softened glass-formers Zane Shi, Pablo Debenedetti, Frank Stillinger We present a computational study of a family of binary glass-forming mixtures that interact via the generic $U= 4\epsilon[\lambda (\sigma /r)^n-\alpha (\sigma /r)^6]$, where $n = 7, 8, 9, 10, 11, 12$. $\lambda$ and $\alpha$ are chosen such that the location and depth of the potential minimum are constant across all members of the family. We investigate the effects of softening on thermodynamic quantities such as energy and entropy, as well as dynamic properties such as diffusion and scattering. We also investigate the effects of softening on the energy landscape. In spite of the imposed constraint on well depth and location, we find profound effects of softening on all aspects of liquid and glassy behavior. The stability of the glasses is greatly enhanced by softening (soft liquids make hard glasses), and the relaxation rates in the corresponding liquids increase markedly upon softening. We present a comprehensive analysis of kinetic and thermodynamic fragilities in this family of glass-formers. [Preview Abstract] |
Thursday, March 24, 2011 9:12AM - 9:24AM |
V13.00007: Low-Frequency Vibrational Modes and Rearrangements in a Colloidal Glass Subject to Point Expansion Kevin Aptowicz, Matthew Colagreco, Ryan Margolis, Peter Yunker, Ke Chen, Arjun Yodh We conduct experiments on two-dimensional packings of colloidal thermosensitive hydrogel particles. The packing fraction of the colloidal suspension is tunable from liquid to deeply jammed by varying the global temperature of the sample. In addition, by tightly focusing an infrared laser on the sample, point expansion of the colloidal glass is induced via thermophoretic forces. We utilize displacement correlation matrix techniques employed in recent papers, and we employ video microscopy to derive the vibrational modes. The response of the sample to induced point expansion is analyzed over a range of packing fractions, with particular focus on the correlation between quasi-localized low-frequency vibrational modes and regions of rearrangements. [Preview Abstract] |
Thursday, March 24, 2011 9:24AM - 9:36AM |
V13.00008: Crystallization of the Lewis-Wahnstr\"{o}m ortho-terphenyl model Ulf Pedersen, Toby Hudson, Peter Harrowell Crystallization is observed during long molecular dynamics simulations of bent trimer molecules - one of the standard models in computational studies of viscous supercooled liquids. The crystal was not anticipated, but is surprisingly simple: the three spheres that make up the rigid molecule sit near the sites of a body centered cubic lattice (the trimer bond angle being almost optimal for this structure). Interestingly, the crystal exhibits orientational disorder with molecules aligned randomly along the three Cartesian axis (an example of cubatic orientational order). While crystallization does not disqualify this model for viscous dynamics studies (it may even be valuable that the crystal is known), it illustrates the stubborn ingenuity of molecules to pack in periodic structures and questions our intuition to predict such structures. Finally, this is a rare example of crystallization of a molecular model from melt. [Preview Abstract] |
Thursday, March 24, 2011 9:36AM - 9:48AM |
V13.00009: Vitrification of a monatomic simple liquid in two dimensions Takashi Odagaki, Tomoko Mizuguchi We investigate vitrification and crystallization process of a monatomic system by molecular dynamics simulation, where atoms interact via Lennard-Jones-Gauss potential. We first determine the time-temperature-transformation diagram by observing the crystallization time of the rapidly quenched state from the melt. The crystallization time becomes shortest at a certain temperature T*. The glassy state at low temperatures is shown to be fairly long-lived. In order to examine atomic mechanism of the crystallization, we introduce a modified incoherent intermediate scattering function which measures the structural correlation to a target structure. We show that the crystallization above and below T* take different paths. We also determine the free energy landscape (FEL) and show that the atomic dynamics is consistent with the FEL picture of the glass transition. [Preview Abstract] |
Thursday, March 24, 2011 9:48AM - 10:00AM |
V13.00010: Time reparametrization symmetry in a structural glass model Gcina Mavimbela, Horacio E. Castillo, Claudio Chamon, Leticia Cugliandolo We explore the existence of time reparametrization symmetry in a particle system with quenched disorder. The system's density fluctuations are described by a stochastic equation (D.~S.~Dean,~J.~Phys.~A:Math. Gen \textbf{29}, L613 (1996)). Using the Renormalization Group (RG) on the Martin-Siggia-Rose generating functional, we analytically probe the long time dynamics by systematically integrating over short time scale fluctuations. We find that the RG flow converges to a fixed point that is invariant under reparametrizations of the time variable. [Preview Abstract] |
Thursday, March 24, 2011 10:00AM - 10:12AM |
V13.00011: Viscosity, Shear Waves and Atomic Level Stress Correlations Valentin Levashov, James Morris, Takeshi Egami The Green-Kubo equation relates the macroscopic stress-stress correlation function to a liquid's viscosity. The concept of the atomic level stresses allows the macroscopic stress-stress correlation function in the equation to be expressed in terms of the space/time correlations between the atomic level stress-stress correlation functions. Molecular dynamics studies show surprisingly long spatial extension of stress-stress correlations and also longitudinal and transverse waves propagating in liquids over ranges exceeding the system size. The results reveal that the range of propagation of shear waves corresponds to the range of distances relevant for viscosity. Thus our results show that viscosity is a fundamentally non-local quantity. We also show that periodic boundary conditions play very non-trivial, previously undiscussed, role in molecular dynamics simulations effectively masking the long range nature of viscosity. [Preview Abstract] |
Thursday, March 24, 2011 10:12AM - 10:24AM |
V13.00012: Study of the de Almeida-Thouless line using power-law diluted one-dimensional Heisenberg spin glasses Auditya Sharma, Peter Young In a recent study, we showed that in mean-field theory, there is a de Almeida-Thouless (AT) line, that separates the low-temperature, low-field spin-glass phase from a high-temperature, high-field paramagnetic phase, for arbitrary $m$-component vector spin glasses, provided one applies a magnetic field that is \emph{random in direction.} Building on this piece of work, here, we investigate whether or not there is an AT line beyond mean-field theory for Heisenberg spin glasses by performing Monte Carlo simulations on a power-law diluted one-dimensional Heisenberg spin glass for very large system sizes. [Preview Abstract] |
Thursday, March 24, 2011 10:24AM - 10:36AM |
V13.00013: Renormalization group analysis of the random first order transition Chiara Cammarota, Giulio Biroli, Marco Tarzia, Gilles Tarjus We consider the approach describing glass formation in liquids as a progressive trapping in an exponentially large number of metastable states. To go beyond the mean-field setting, we provide a real-space renormalization group (RG) analysis of the associated replica free-energy functional. The present approximation yields in finite dimensions an ideal glass transition similar to that found in mean field. However, we find that along the RG flow the properties associated with metastable glassy states, such as the configurational entropy, are only defined up to a characteristic length scale that diverges as one approaches the ideal glass transition. The critical exponents characterizing the vicinity of the transition are the usual ones associated with a first-order discontinuity fixed point. [Preview Abstract] |
Thursday, March 24, 2011 10:36AM - 10:48AM |
V13.00014: Influence of pressure on fast relaxation in glass-forming materials Vladimir Novikov, Liang Hong, Alexander Kisliuk, Alexei Sokolov The spectra of GHz-THz dynamics in glass forming materials have two main contributions: the boson peak and the fast relaxation that overlaps with the low-frequency flank of the boson peak. The nature of both contributions remains a subject of active discussions. Applying pressure helps to separate the temperature and volume effects on the fast dynamics. Although the boson peak under pressure was investigated recently by several groups, less attention was devoted to the fast relaxation. In this work we present the study of the fast relaxation measured in some molecular and polymeric glass formers under pressure by light (Raman and Brillouin) scattering. Different experimental conditions were applied: isothermal, isobaric, isokinetic, and isochoric. The results are analyzed within the frames of various theoretical models. In particular, we check in detail the predictions of the soft-potential model of glassy dynamics. [Preview Abstract] |
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