Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K58: Disordered and Glassy Systems I |
Hide Abstracts |
Sponsoring Units: GSOFT Chair: Matthew Abernathy, United States Naval Research Laboratory Room: BCEC 257A |
Wednesday, March 6, 2019 8:00AM - 8:12AM |
K58.00001: Probing the local environment in colloidal glass Wenhai Zheng, David J Pine We developed a method to probe the local environment in colloidal glass by measuring the rotational diffusion of elliptical tracer particles. Using tracers of various aspect ratios as passive micro-probes, we explored the response of the material to different local strains. Special design of the tracers enhances its optical anisotropy, which enables us to follow the 3-dimensional rotation of nearly spherical probes. We found as the volume fraction of the colloidal suspension approaches the glass transition point, the rotational diffusion of the ellipsoids slows down dramatically and differs significantly spatially, which reflects the heterogeneity of the local environment. |
Wednesday, March 6, 2019 8:12AM - 8:24AM |
K58.00002: Tracer Transport Probes Relaxation and Structure of Attractive and
Repulsive Glassy Liquids Ryan Roberts, Ryan Poling-Skutvik, Jeremy C Palmer, Jacinta Conrad Dynamic coupling of small penetrants to slow, cooperative relaxations within crowded cells, supercooled liquids, and polymer matrices has broad consequences for applications ranging from drug delivery to nanocomposite processing. Interactions between the constituents of these and other disordered media alter the cooperative relaxations, but their effect on penetrant dynamics remains incompletely understood. We use molecular dynamics simulations to show that the motions of hard-sphere tracer particles probe differences in local structure and cooperative relaxation processes in attractive and repulsive supercooled liquid matrices with equal bulk packing fractions and long-time diffusivities. Coupling of the tracer dynamics to collective matrix relaxations affects the shape of tracer trajectories, which are string-like within the repulsive matrix and compact in the attractive. These results reveal that the structure of relaxations controls penetrant transport and dispersion in cooperatively relaxing systems. We further explore this connection by calculating the tracer and matrix dynamic susceptibilities, characterizing cooperative rearrangements in the matrices, and simulating tracer diffusion in arrested glasses. |
Wednesday, March 6, 2019 8:24AM - 8:36AM |
K58.00003: Controlling fragility via geometry in hard particle glass-formers Erin Teich, Greg van Anders, Sharon Glotzer We demonstrate that fragility, a technologically relevant measure of glass-forming ability, may be tuned via slight changes to particle shape in monodisperse, super-compressed systems of hard particles. We simulate systems of tetrahedrally symmetric particles, interacting solely through volume exclusion via Monte Carlo sampling, and show that these glass-formers become stronger as the particle shape becomes increasingly tetrahedral. Moreover, we connect strength and local structure in these systems. Our results parallel similar findings for network glass-formers such as silica, in which short-range tetrahedral bonding yields glasses of exceptional strength, and we show that similar effects can arise from geometry alone. |
Wednesday, March 6, 2019 8:36AM - 8:48AM |
K58.00004: Exploring Glassy Physics using Athermal Simulations Francesco Arceri, Eric Corwin Thermal hard spheres simulations are widely used for probing the low temperature physics of glass formers. However, they suffer from the limitations of Monte-Carlo simulations, which are necessarily slow and not easily parallelizable. Although hard sphere interactions present infinitely strong repulsion upon contact, in the infinite pressure limit when the jamming transition occurs, mean-field theory predicts an effective potential, which is a logarithmic function of the gap between particles. This effective potential can be seen as a proxy for frequent collisions, acting as a measure of the allowed space each particle can travel before interacting with one of its neighbors. Thus, by studying the properties of this effective potential we can learn about the thermal system in a high pressure regime which is otherwise inaccessible. Using deterministic minimization schemes to find local minima of the free energy landscape, we can reach extremely dense configurations. We explore the features of such configurations, comparing their vibrational properties with their thermal counterparts as well as with mean field predictions. Furthermore, their dynamics have been tested using thermal simulations with the aim of using them as valid configurations of low temperature glasses. |
Wednesday, March 6, 2019 8:48AM - 9:00AM |
K58.00005: Correlations Between Short- and Long-time Relaxation in Colloidal Supercooled Liquids and Glasses Chandan Kumar, Xiaoguang Ma, Piotr Habdas, Kevin B Aptowicz, Arjun G Yodh The spatiotemporal dynamics of short- (β) and long-time (α) structural relaxation are measured experimentally as a function of packing fraction, φ, in a series of quasi-two-dimensional binary-sphere colloidal supercooled liquids and glasses. The relaxation times associated with both long-time dynamic heterogeneity and short-time intra-cage motion grow by orders of magnitude with increasing φ, and interestingly, the two relaxation times are strongly correlated and suggest power law behavior. Moreover, microscopic analysis of the spatiotemporal dynamics revealed that the fraction of overlapping clusters of most-mobile particles at the long and short timescale increases with φ. Furthermore, the minimum spatial separation between the closest non-overlapping clusters of most-mobile particles across the two distinct timescales shows an exponential distribution. This allows extraction of φ-dependent characteristic length scale that further connects dynamics on short- and long timescales and increases with packing. |
Wednesday, March 6, 2019 9:00AM - 9:12AM |
K58.00006: How glass responses to laser excitation Bo Li, Kai Lou, Walter Kob, Steve Granick Glass is a disordered solid that processes distinct dynamical and elastic properties compared with crystal. Elastically, how heterogeneous a glassy materials can be and to what extend such heterogeneity is determined by structure are long standing puzzles in glass science. In this experiment, we probed the responses of binary colloidal glasses towards the local excitations caused by laser pulses. We observed very similar excitation patterns when the laser was repeated in linear region; directly proving that the dynamical heterogeneity is strongly encoded with structure. In non-linear region, we discovered for the first time a non-monotonic dynamical length scale as a function of $\phi$, resulting from the intriguing interplay between cooperative motion and local structure. Our results highlight the crucial role structure plays in the dynamics and elasticity of glasses. |
Wednesday, March 6, 2019 9:12AM - 9:24AM |
K58.00007: Direct Observation of the Gardner/Marginal Glass Transition within a Colloidal Glass Andrew Hammond, Eric Corwin
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Wednesday, March 6, 2019 9:24AM - 9:36AM |
K58.00008: Frequency-dependent moduli in a supercooled liquid in the close vicinity of the glass transition by molecular dynamics Baoshuang Shang, Joerg Rottler, Pengfei Guan, Jean-Louis BARRAT Amorphous materials have a rich relaxation spectrum which is usually described in terms of alpha, beta, and possibly more complex relaxation mechanism. In this work, we investigate the local dynamic modulus spectrum in a model glass just above glass transition temperature by performing a mechanical spectroscopy analysis using molecular dynamics. We find that the spectrum, at the local as well as on the global scale, can be well depicted by Cole-Davidson formula in the frequency range explored with simulations. Surprisingly, the Cole-Davidson stretching exponent does not change with the size of the local region that is probed. The local relaxation time displays a broad distribution, as expected based on dynamic heterogeneity concepts, but the stretching is obtained independently of this distribution. Furthermore, we find that the size dependence of local relaxation time and modulus can be well explained by the elastic shoving model. |
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K58.00009: Memory in Solid-Solid Interfaces Samuel Dillavou, Shmuel Rubinstein The interface between two solid, static bodies - your chair and the floor, your cup and the table, two books in a stack - is in fact continuously evolving. Due to small-scale roughness, ostensibly flat surfaces typically have a real area of contact several orders of magnitude smaller than apparent area. As a result, these contact points experience enormous pressures, and slowly deform in time. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K58.00010: Extending the phase space of jamming from a jamming point to a jamming plane Yuliang Jin, Hajime Yoshino The concept of jamming has attracted great research interest due to its broad relevance in soft matter such as liquids, glasses, colloids, foams, and granular materials, and its deep connection to the sphere packing problem and phase transitions. Here we show numerically that the phase space of frictionless jammed states can be extended from the well-known jamming point, to a jamming line by using deeply super-cooled liquid states as initial configurations, which can be further extended into a jamming plane by adding shear strains. While all jammed states are isostatic and belong to the same universality class, their various anisotropy and amorphous order can be mapped out on the jammed plane. The jamming point is isotropic, with the minimum amorphous order (or maximum randomness), which, in the thermodynamic limit, sets a sharp lower bound for the jamming density of frictionless packings. |
Wednesday, March 6, 2019 10:00AM - 10:12AM |
K58.00011: Large, growing length scale controls the melting mechanism of stable glasses Ludovic Berthier, Patrick Charbonneau, Elijah Flenner, Christopher J. Fullerton Exceptionally stable vapor-deposited glass films melt via a constant velocity front initiated at the surface, whereas ordinary liquid cooled glass films melt homogeneously. The melting time for stable glass films increase linearly with film thickness until a crossover thickness lc, which can be as large as a micrometer. For films thicker than lc the melting time is constant, suggesting that a bulk transformation mechanism is then prominent. Here we use the swap Monte Carlo algorithm to prepare stable glass films that we subsequently melt films using molecular dynamics simulations, in order to study the microscopic differences between the two melting mechanisms of glass films. Several of our stable films completely melt via a front initiated at the surface for lower melting temperatures, but melt via a bulk mechanism at higher melting temperatures. For intermediate melting temperature we directly determine lc, and then we use bulk melting simulations to approximate |
Wednesday, March 6, 2019 10:12AM - 10:24AM |
K58.00012: Quantifying the Structure of Space-Filling Disordered Cellular Patterns with Hyperuniformity Disorder Length Spectroscopy Anthony Chieco, Douglas Durian A system is hyperuniform if the spectral density decays like χ(q)~q-ε with ε >0 as q goes to zero. In real space the area fraction variance for randomly placed measuring LxL windows can be written σ2(L)=4<a>h(L)/L3 where <a> is the average particle area and h(L) is the hyperuniformity disorder length, which is defined by the distance from the window boundary where number density fluctuations occur [1]. The spectrum of h(L) versus L quantifies the degree of structural order; smaller h(L) indicates more order, and at large L hyperuniform patterns have constant h(L)=he. Here, we compare χ(q) and h(L) spectra for cellular patterns given by Voronoi construction around points that are (1) uncorrelated (Poisson), (2) low discrepancy (Halton), and (3) displaced from a lattice by Gaussian noise (Einstein), as well as (4) the centroids of bubbles in a quasi-2d foam. All four types are hyperuniform and have X(q)~q-4 for small q. The he values indicate that Poisson, Halton, Einstein, and foams are ranked least to most ordered. The foam has he=0.082<a>1/2 and the same value of he is found for the other cellular patterns if analyzed in terms of the Voronoi cell centroids; for comparison, he=0.084<a>1/2 is found at jamming for bidisperse disks [1]. |
Wednesday, March 6, 2019 10:24AM - 10:36AM |
K58.00013: Competition of Crystallization and Vitrification Muhammad Hasyim, Kranthi K Mandadapu The competition between vitrification and crystallization in glass-forming materials manifests as a non-monotonic behavior in the time-temperature transformation (TTT) diagrams. A coarse-grained model, referred to as the Arrow-Potts model, is constructed to explore the physics behind this competition. Using Monte Carlo simulations, the model is shown to produce two regimes of crystal nucleation and coarsening. At high temperatures, crystallization is dominated by the nucleation of compact and fluctuating crystalline clusters. At low temperatures, crystal coarsening proceeds through hierarchical relaxation pathways within the supercooled liquid, producing fractal ramified crystalline clusters. To explain and unify these two regimes, the Kolmogorov-Avrami theory is used as a framework to combine nucleation theory and a random walk theory for crystal coarsening kinetics, both of which govern the high-T and low-T regimes respectively. Finally, we demonstrate how the universal character of low-T crystallization is characterized by scaling exponents which are crucial to accurately account for the timescales observed in the TTT diagram. |
Wednesday, March 6, 2019 10:36AM - 10:48AM |
K58.00014: Measuring Thermophysical Properties of Glassy Materials via Focused Laser Spike Dewetting Tianxing Ma, Adithya Sridhar, Kyle Buznitsky, Matthew Signorelli, Jonathan Singer Focused laser spike (FLaSk) dewetting has been used as a method for the patterning of soft matter thin films for several decades. Through the use of a focused laser beam, a localized heat source is provided along with an extreme thermal gradient. The material melted by the local heating is simultaneously moved down the thermal gradient and forms highly characteristic trench-ridge morphologies. Through micron-scale dot exposures on a universal heating substrate designed in our lab, coupled with optical microscopy, we have studied the characteristic radii of the dewetted ridge feature for various glassy thin films with different molecular weights and glass transition temperatures as a function of time. This was approached through a combination of experiments, simulations, and analytical models. Not only were we able to identify features of the dewetting that revealed differences between the polymer system, but the FLaSk process could give independent information on surface and bulk behavior. In this way, it has been shown that FLaSk dewetting as a metrology method can be employed for high-throughput analysis of thin film materials in high shear, high temperature testing regimes that would otherwise be difficult to reach. |
Wednesday, March 6, 2019 10:48AM - 11:00AM |
K58.00015: How to extract memories from a relaxing granular material Kieran Murphy, Jonathon Kruppe, Heinrich M Jaeger Recent experiments on crumpled sheets have found they can store multiple memories of past loading, and that one can simply watch the system relax over long timescales to read off its memories [1]. The model used to explain the observed nonmonotonic relaxation approximates the system as a population of exponentially relaxing modes with a specific distribution of timescales, though the physical manifestation of the modes in these systems remains ambiguous. |
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