Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S8: Disordered and Glassy Systems |
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Sponsoring Units: GSOFT Chair: Megan Valentine, University of California, Santa Barbara Room: 006C |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S8.00001: Network structure of the mussel plaque and its significance for load bearing and adhesion Emmanouela Filippidi, Juntae Kim, J. Herbert Waite, Matthew Helgeson, Megan T. Valentine Marine mussels attach to rocks, each other, and a variety of surfaces via a flat, wide plaque that is interpenetrated by the collagen fibers of a thin, long thread that connects the plaque to the mussel body. The unusually strong adhesion of the plaque has long been attributed to the molecular design of its adhesive proteins that can form a variety of strong chemical bonds. However, the molecular energies for de-adhesion are orders of magnitude smaller than the macroscopic energies measured. We propose that the mesoscopic design of the plaque is critical in enhancing load bearing and eventually adhesion. We present new results on the structure of the plaque studied via electron microscopy and neutron scattering that exhibit a plaque geometry reminiscent of structural foams. Our studies reveal a collection of pores with an inner network, further connected with an outer network. The final structure can be described by two length scales. A synthetic soft system is constructed in an effort to mimic the two-lengthscale structure of the natural plaques. The structure of the native and synthetic systems is compared with the ultimate goal of evaluating the importance of the mesoscopic structure to mechanics and adhesion. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S8.00002: Collapse dynamics of bubble raft under compression Chin-Chang Kuo, Devin Kachan, Alexander Levine, Michael Dennin We report on the collapse of bubble rafts under compression in a closed rectangular geometry. A bubble raft is a single layer of bubbles at the air-water interface. A collapse event occurs when bubbles submerge beneath the neighboring bubbles under applied compression causing the structure of the bubble raft to go from single-layer to multi-layer. We studied the collapse dynamics as a function of compression velocity. At higher compression velocity we observe a more uniform distribution of collapse events, whereas at lower compression velocities, the collapse events accumulate at the system boundaries. We will present results that compare the distribution of collapse probability in the experiments to simulations based on a one-dimensional Ising model with elastic coupling between spin elements. Both the experimental system and simulations are excellent models for collapse in a number of complex systems. By comparing the two systems, we can tune the simulation to better understand the role of the Ising and elastic couplings in determining the collapse dynamics. [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 8:36AM |
S8.00003: The glass-forming ability of patchy repulsive spheres Kai Zhang, Yanhui Liu, Jan Schroers, Mark Shattuck, Corey O'Hern In bulk metallic glasses (BMGs) involving nonmetallic elements, anisotropic interactions are essential to describe their structural relaxation, mechanical properties, and glass-forming ability (GFA). Here, we employ a repulsive sphere model that includes attractive interactions between patches on each sphere to study the glass-forming ability of alloys that include non-metallic components (e.g. metal-metalloid alloys). Using molecular dynamics simulations, we quantify the GFA by measuring the critical cooling rate below which crystallization occurs as a function of the size and spacing of the patches, as well as the symmetry of the crystalline state that competes with the glass. We find that the glasses can dissolve no more than 20-30\% solute nonmetallic atoms (such as B, Si, and P), which explains why non-metallic elements occur at low number fractions in BMGs. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 8:48AM |
S8.00004: Some observations on hyperuniform disordered photonic bandgap materials, from microwave scale study to infrared scale study Sam Tsitrin, Geev Nahal, Marian Florescu, Weining Man A novel class of disordered photonic materials, hyperuniform disordered solids (HUDS), attracted more attention. Recently they have been experimentally proven to provide complete photonic band gap (PBG) when made with Alumina or Si; as well as single-polarization PBG when made with plastic with refract index of 1.6. These PBGs were shown to be real energy gaps with zero density of photonic states, instead of mobility gaps of low transmission due to scattering, etc. Using cm-scale samples and microwave experiments, we reveal the nature of photonic modes existing in these disordered materials by analyzing phase delay and mapping field distribution profile inside them. We also show how to extend the proof-of-concept microwave studies of these materials to proof-of-scale studies for real applications, by designing and fabricating these disordered photonic materials at submicron-scale with functional devices for 1.55 micron wavelength. The intrinsic isotropy of the disordered structure is an inherent advantage associated with the absence of limitations of orientational order, which is shown to provide valuable freedom in defect architecture design impossible in periodical structures. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S8.00005: Characteristics of Johari--Goldstein relaxations in bulk metallic glasses Jichao Qiao, Riccardo Casalini, Jean-Marc Pelletier, Hidemi Kato, Yao Yao The dynamics of Pd-based metallic glasses was studied by mechanical spectroscopy and modulated differential scanning calorimetry. The results show the change in composition has a significant effect on the $\alpha $ relaxation dynamics. All Pd-based metallic glasses have similar fragilities, 59 \textless $m$ \textless 67, and Kohlrausch stretched exponents, 0.59 \textless $\beta_{KWW}$ \textless 0.60. The values of $m$ and $\beta _{KWW}$ correlate well with the general relation proposed by B\"ohmer et al. for other glassy materials and the substitution of the Ni with Cu induced a large change in the time constant of the $\beta $ relaxation, $\tau _{\beta }$. The activation energy, U$_{\beta }$, of the $\beta $ relaxation was generally independent of chemical composition. In all cases, 25 \textless U$_{\beta }$/RT \textless 28, the range shows good agreement compared with the results of other glass formers. From the heat capacity and mechanical loss, the number of dynamically correlated units, \textit{Nc }were obtained; significantly larger \textit{Nc} values for these metallic glasses were observed compared with glassy materials. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S8.00006: Study of shear banding in simulated amorphous solids in the context of shear transformation zone theory Darius Alix-Williams, Michael L. Falk We examine the general framework of the effective temperature formalism of the shear transformation zone (STZ) theory of plasticity via molecular dynamics simulation of two distinct amorphous systems - Silicon and Cu-Zr. In both systems strain localization is observed during simple shear loading. The shear bands differ in the rate of broadening and the sharpness of the interface between the flowing and jammed material. We examine both systems for scaling expected to arise between effective temperature and shear rate. For each system a local dimensionless effective temperature that quantifies structural disorder is extracted by assuming a linear relation to the local potential energy per atom. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S8.00007: Relaxational Dynamics of a Model Glass-forming Metallic Liquid Abhishek Jaiswal, Stephanie O'Keeffe, Andrey Podlesnyak, Georg Ehlers, Rebecca Mills, Konstantin Lokshin, Wojciech Dmowski, Takeshi Egami, Yang Zhang Understanding the diffusional behavior of multi-component glass-forming metallic liquids is of critical importance to the development of novel alloy systems such as bulk metallic glasses (BMG). However, such diffusions are highly activated and complicated because of structural disorder induced by quenching, and chemical disorders induced by size mismatch. Herein, we report temperature and wave-vector transfer ($Q)$ dependence of two-step collective relaxations in the BMG (LM601: ZrCuNiAl) melt measured by quasi-elastic neutron scattering. $Q$-dependence of both fast and slow relaxation time, and the adiabatic sound speed are found to obey the principle of de Gennes narrowing. The measured spectra show a distinct vibrational mode at around 15 meV. Classical Molecular Dynamics (MD) simulation of CuZrAl system, using EAM potential shows that this acoustic mode arises from local vibrations of Al in the cage formed by Cu and Zr atoms. Furthermore, we observed a breakdown of Stokes-Einstein relation in the MD simulated system well above its melting temperature. Accompanied dynamical clustering was detected using unsupervised machine learning techniques. These mechanisms in tandem can be responsible for the excellent glass-forming ability of this material. [Preview Abstract] |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S8.00008: Self-confined dynamics in supercooled liquids during crystallization Alejandro Sanz, Kristine Niss, Tiberio A. Ezquerra, Aurora Nogales, Monica Jimenez, Ines Puente-Orench Within the temperature window limited by the equilibrium melting temperature and the liquid to glass transition temperature, some glass forming systems tend to undergo crystallization. Unlike polymeric materials, low molecular weight liquids are able to self-organize forming fully crystalline structures, in which the dynamics of the remaining disordered regions may be examined along the whole range of crystalline volume fraction when real time studies are assessed. From the point of view of the molecular mobility, dielectric spectroscopy is a unique tool for unraveling the dynamic effects during crystallization. The aim of this contribution is to show a complete picture of the crystallization process in paradigmatic glass formers like 2-propanol, ethanol and glycerol. The interrelationships between structure and dynamics during crystallization will be discussed, paying special attention to the role played by the hydrogen-bonded network across the phase transformation. Novel results on crystallization of 2-propanol studied by real time quasielastic neutron scattering measurements will also be presented. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S8.00009: Shear Rheology of Imidazolium-Based Ionic Liquids with Aromatic Functionality Ran Tao, Sindee Simon As a material class, ionic liquids possess attractive properties and have a wide range of potential uses. In this work, a series of imidazolium-based ionic liquids with varying functionalities from aliphatic to aromatic groups and a fixed anion were characterized using steady shear and dynamic shear rheology. The temperature dependence of shift factors used for constructing the dynamic moduli reduced curves follows the expected WLF relationship, and the dynamic fragility is calculated and compared to the fragility obtained from calorimetry. The retardation spectra are calculated and compared for the series of ionic liquids. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S8.00010: Random sphere packing lattices Yoav Kallus Bravais lattices have always been an important special case of the high-dimensional sphere packing problem, but from the statistical mechanics and random packing perspectives, they have not been studied much until recently. I will discuss the statistical mechanical phenomena exhibited by a system of one sphere under periodic boundary conditions, where the only degrees of freedom are the unit cell parameters. Equilibrium behavior includes a ``crystallization'' transition, but most of the interest comes from studying non-equilibrium behavior: glass transition, random packing, and hysteresis. The random-packed lattices exhibit surprising properties, including a density remarkably higher than amorphous random packing and a quasicontact divergence. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S8.00011: Disordered surface vibrations in jammed sphere packings Daniel Sussman, Andrea Liu, Sidney Nagel We study the vibrational properties of networks derived from jammed packings near a free surface. We find that, in addition to the usual surface modes predicted by continuum elasticity, these systems have a surface density of disordered vibrational modes extending to arbitrarily low frequencies. The spatial profile of the surface modes shows a two-length-scale decay. The length scales diverge at the jamming transition as $\Delta Z^{-1/2}$ and $\Delta Z^{-1}$, respectively, where $\Delta Z$ is the excess coordination number above isostaticity. We speculate that these findings have implications for thin-film Lennard-Jones systems, and argue that the low-temperature jamming perspective may shed light on the physics of mobile surface layers observed in small molecule and polymeric thin films. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S8.00012: On the Marginal Stability of Glassy Systems Le Yan, Marco Baity-Jesi, Markus M\"uller, Matthieu Wyart In various glassy systems that are out of equilibrium, like spin glasses and granular packings, the dynamics appears to be critical: avalanches involving almost the whole system could happen. A recent conceptual breakthrough argues that such glassy systems sample the ensemble of marginal stable states, which inevitably results into critical dynamics. However, it is unclear how the marginal stability is dynamically guaranteed. We investigate this marginal stability assumption by studying specifically the critical athermal dynamics of the Sherrington-Kirkpatrick model. We discuss how a pseudo-gap in the density distribution of local fields characterizing the marginal stability arises dynamically. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S8.00013: Critical scaling of stresses and correlations with strain rate in overdamped sheared disordered solids Joel Clemmer, Kenneth Salerno, Mark Robbins Like many nonequilibrium systems, disordered solids exhibit a power-law distribution of avalanches and other critical behavior when driven slowly. We extend molecular dynamics studies of quasistatic shear of 2D and 3D overdamped binary LJ glasses\footnote{K. M. Salerno and M. O. Robbins, Phys. Rev. E \textbf{88}, 062206 (2013)} to finite strain rate. Finite-size scaling is used to determine the critical behavior of the shear stress and several measures of temporal and spatial correlations in non-affine displacements. With increasing strain rate, there is a power-law rise in the shear stress with exponent $\beta$ extending to lower rates in larger systems. This behavior is governed by the rise in the dynamic correlation length with decreasing stress with exponent $\nu$. The correlation function of non-affine displacements exhibits novel anisotropic power law scaling with $q$, the magnitude of the wave vector. Its strain rate dependence is used to determine the scaling of the dynamic correlation length in various angular directions. In the quasistatic limit, particle diffusion in 2D is proportional to strain with a system-size dependent diffusion constant. Increasing strain rate, the dynamic correlation length drops below the system-size and the diffusion constant begins to fall. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S8.00014: Polyamorphism in tetrahedral substances: similarities between silicon and ice Alex Antonelli, Karl Garcez Tetrahedral substances, such as silicon, water, germanium, and silica, share several thermodynamical anomalies. Among them, the so-called polyamorphism, i.e., the existence of more than one amorphous state, is, perhaps, the most studied one. In this work, we study the transformations between amorphs of silicon using Monte Carlo simulations. The simulations indicate that by compressing the low density amorphous state (LDA), which is obtained by quenching the liquid at high temperature, a new denser amorph is found [1]. The transformation between these two forms of amorphous silicon displays clear hysteresis, similar to the experiment reported by McMillan \textit{et al.} [2]. However, analogously to the case of ice, our simulations indicate that upon annealing the unannealed high density amorphous silicon (uHDA) evolves to more stable forms. The annealing of uHDA at pressures on the order of 20 GPa gives rise to an even denser form, the very high density amorphous silicon (VHDA), while at much lower pressures, about 5 GPa, the uHDA transforms into a lower density form, the expanded high density amorphous silicon (eHDA). [1] K. M. S. Garcez and A. Antonelli, J. Appl. Phys. \textbf{115}, 063504 (2014), [2] P. F. McMillan \textit{et al.}, Nature Mater. \textbf{4}, 680 (2005). [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S8.00015: Thermal Transport in C60 Molecular Crystals Above Room Temperature Caroline S. Gorham, Alan J. H. McGaughey The thermal conductivity of solid fullerene molecular systems has garnered significant interest as an example of materials whose thermal transport is dominated by Einstein-type oscillators. Using classical molecular dynamics simulations, this study isolates the roles of intramolecular and intermolecular vibrational degrees of freedom on the bulk thermal conductivity of the face-centered cubic C$_{60}$ molecular crystal. The Green-Kubo method is used to predict the bulk thermal conductivity. The contributions to thermal transport resulting from collective motions of the molecules, molecular rotations, and intramolecular vibrations are isolated using non-equilibrium methods. These contributions are interpreted using a Debye model, a nearest-neighbor resistance network, and Allen-Feldman theory. [Preview Abstract] |
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