Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X16: Disordered and Glassy Materials |
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Sponsoring Units: GSOFT Chair: Patrick Charbonneau, Duke University Room: 275 |
Friday, March 17, 2017 8:00AM - 8:12AM |
X16.00001: Rotational and translational diffusion in a 2D colloidal glass-former Eric Weeks, Skanda Vivek We use video microscopy to observe the diffusive motion of dimer tracers in a quasi-2D sample of colloidal spheres. This sample is a good model for the glass transition, which occurs for a sufficiently high particle concentration. At lower concentrations, the dimer rotational and translational motions are coupled to each other: their ratio is a constant, independent of the concentration of the spherical particles. At higher concentrations of the spherical particles (close to the colloidal glass transition), we observe decoupling between translational and rotational diffusion. In particular, small dimers rotate faster than might be expected. This is because small dimers can rotate within the cage formed by their spherical neighbors with little steric hindrance, in contrast with the larger dimers. [Preview Abstract] |
Friday, March 17, 2017 8:12AM - 8:24AM |
X16.00002: Static and dynamic properties of two dimensional Coulomb clusters Biswarup Ash, Amit Ghosal, Jaydeb Chakrabarti We study the temperature dependence of static and dynamic responses of small number of particles in two-dimensional traps across the thermal crossover from the solid- to liquid-like behaviors. We explore the possibility of observing the signatures of hexatic-glass like behavior for Coulomb interacting particles confined by irregular geometry. While static correlations, that investigate the translational and bond orientational order, show the footprints of hexatic like phase at low temperature, dynamics of the particles slow down considerably as the system approaches the crossover temperature. Using density correlations we probe intriguing signatures of long-lived inhomogeneities due to the interplay of disorder (arising from the irregularity in the confinement) and long-range interactions. The relaxation at multiple time scales show stretched-exponential spatial decay in irregular traps$^1$. Temperature dependence of characteristic time scales, depicting the structural relaxation of the system, show striking similarities with those observed for the glassy systems. Our results indicate that some of the key signatures of supercooled liquids emerge for confined systems with lower spatial symmetries.\\ (1) B.Ash, J.Chakrabarti, and A.Ghosal, Euro.Phys.Lett.,114,4, (2016) [Preview Abstract] |
Friday, March 17, 2017 8:24AM - 8:36AM |
X16.00003: Heterogeneous activation in 2D colloidal glass-forming liquids classified by machine learning Xiaoguang Ma, Zoey Davidson, Tim Still, Robert Ivancic, Sam S. Schoenholz, Daniel M. Sussman, A. J. Liu, A. G. Yodh The trajectories of particles in colloidal glass-forming liquids are often characterized by long periods of ``in-cage'' fluctuations and rapid ``cage-breaking'' rearrangements. We study the rate of such rearrangements and its connection with local cage structures in a 2D binary mixture of poly(N-isopropyl acrylamide) spheres. We use the hopping function, $P_\mathrm{hop}(t)$, to identify rearrangements within particle trajectories. Then we obtain distributions of the residence time $t_R$ between consecutive rearrangements. The mean residence time $\bar{t}_R(S)$ is found to correlate with the local configurations for the rearranging particles, characterized by 70 radial structural features and softness $S$ [PRL 114, 108001 (2015)], which ranks the structural similarities with respect to rearranging particles. Furthermore, $\bar{t}_R(S)$ for particles with similar softness decays monotonically with increasing softness, indicating correlation between rearrangement rates and softness $S$. Finally we find that the conditional and full probability distribution functions, $P(t_R|S)$ and $P(t_R)$, are well explained by a thermal activation model. [Preview Abstract] |
Friday, March 17, 2017 8:36AM - 8:48AM |
X16.00004: Mutual dependence between local stress and geometry in two dimensions Tamoghna Das, Jack Douglas Solids and liquids exhibit a striking change in their resistance to the external stresses associated with the emergence of macroscopic rigidity. While the thermodynamics of the solid-liquid transition is well understood, structural underpinning and dynamics of this transition still remain open. To understand, we simulate a two dimensional Lennard-Jones system in both liquid and crystalline state by varying density at a fixed temperature. The shape of the first coordination shell is quantified and the microscopic density is computed for the generated configurations using standard statistical geometric methods. Next, we attempt to relate these quantities with local virial stress and orientational order using information theoretic measures, namely, Shannon entropy (SE) and mutual information (MI). Interestingly, SE for different stress components shows van der Waals loop like feature with respect to density although they follow distinctly different distributions. MI reveals strong correlation between local geometry and local stress and also captures the transition points. Although the results at the current stage are inadequate to draw any causal connection among the measured quantities, this approach might be useful to understand the emerging rigidity across liquid-solid transition [Preview Abstract] |
Friday, March 17, 2017 8:48AM - 9:00AM |
X16.00005: Critical replica-symmetry-breaking transitions in finite dimensions Sho Yaida, Patrick Charbonneau The transformation of the free-energy landscape from smooth to hierarchical is one of the richest features of mean-field disordered systems. A well-studied example is the de Almeida-Thouless transition for spin glasses in a magnetic field, and a similar phenomenon, the Gardner transition, has recently been predicted for structural glasses. The existence of these replica-symmetry-breaking phase transitions has, however, long been questioned below their upper critical dimension, six. Here, we obtain evidence for the existence of these transitions in physical dimensions, identifying a nontrivial fixed point through a two-loop calculation. We further corroborate the result by resumming the perturbative series with inputs from a three-loop calculation. Our analysis offers a straightforward resolution of the long-lasting controversy surrounding phase transitions in finite-dimensional disordered systems. [Preview Abstract] |
Friday, March 17, 2017 9:00AM - 9:12AM |
X16.00006: Is there a Gardner transition in soft glasses? Camille Scalliet, Ludovic Berthier, Francesco Zamponi Recent theoretical advances in the mean-field theory of hard-sphere glasses predict the existence of the so-called Gardner transition, an ergodicity breaking transition that takes place deep in the glass phase. In hard-sphere glasses, this transition is crucial to make theoretical predictions for the jamming transition occurring at higher densities. Our goal is to determine if the Gardner transition is also a crucial element to understand the low temperature behaviour of soft glasses. We use two complementary theoretical approaches: a mean-field study of a soft glassy model in the limit of infinite dimensions, combined to a numerical investigation of the transition in a simple three-dimensional soft glass-former. Analytical results confirm the existence of the Gardner transition even in soft glasses. Numerical investigations of three-dimensional soft glasses are in progress, and preliminary results are surprisingly more difficult to interpret than originally expected. [Preview Abstract] |
Friday, March 17, 2017 9:12AM - 9:24AM |
X16.00007: A Continuum Approach to Modeling Strain Localization in Amorphous Solids Darius Alix-Williams, Michael Falk Shear Transformation Zone (STZ) theory provides a generalized framework for describing plasticity in sheared amorphous solids. We build upon STZ theory using data from molecular dynamics simulations of strain localization in sheared glassy systems modeled with Lennard-Jones, embedded-atom method (EAM) and Stillinger-Weber (SW) interatomic potentials. We assume that the effective temperature, a local coarse-grained measure of disorder, can be inferred from potential energy. Similarly, it is assumed that yield stress depends on effective temperature, and governs the rate of STZ activation. These assumptions are tested using numerical simulations of the STZ equations in a simple one-dimensional model. The resultant constitutive behavior of the numerical model is compared to the MD simulation results. [Preview Abstract] |
Friday, March 17, 2017 9:24AM - 9:36AM |
X16.00008: Detailed Quantification of String-Like Cooperative Motion Provides Insight into the Dynamic Crossover in Glass-Forming Liquids Dillon Sanders, Jacob Eapen Using atomistic simulations, we conduct a detailed investigation of string-like cooperative motion, and in particular the formation of strings of various lengths in model glass-formers. We show that the maximum values of the average string length and the fraction of atoms that are participating in string-like motion exhibit non-Arrhenius behavior, in which a transition is seen to occur at the dynamic crossover temperature $T_X$. Interestingly, we observe that the population of atoms participating in cooperatively-rearranging pairs (strings composed of two atoms) exhibits a non-monotonic variation in temperature. The population variance with temperature of longer strings is monotonic and becomes increasingly Arrhenius with increasing string length. As a consequence of our analysis, we propose a mechanism for string formation by which single, mobile atoms "latch on" to existing shorter strings to form longer strings. Our findings lend support to the hypothesis that the temperature $T_X$ corresponds to increased presence of activated dynamics in glass-forming liquids at lower temperatures. [Preview Abstract] |
Friday, March 17, 2017 9:36AM - 9:48AM |
X16.00009: Fractional Viscosity Dependence of Reaction Kinetics in Glass-forming liquids Seulki Kwon, Hyun Woo Cho, Jeongmin Kim, Bong June Sung Dynamics of glass-forming systems has been extensively investigated due to its slow and heterogeneous dynamics. The diffusion of molecules in complex systems such as cell cytoplasm also exhibit dynamic heterogeneity and resembles that of glass-forming systems. Chemical reactions in such systems are, therefore, expected to be affected by dynamic heterogeneity and reaction kinetics would differ significantly from that in normal liquids. In this study, we investigate the kinetics of polymer loop formation in Kob-Andersen(KA) glass-forming liquid. The diffusion coefficient (D) of KA liquid deviates from Stokes-Einstein relation due to dynamic heterogeneity, i.e. D \textasciitilde $\eta^{-\xi }$ with $\xi \quad =$ 0.85 According to Kramers theory, reaction kinetics can be projected onto a one-dimensional reaction coordinate and may be described well by Brownian diffusion along the reaction coordinate. We find that the loop formation reaction faithfully follows Kramers theory, but the reaction viscosity ($\eta_{rxn})$ shows a fractional viscosity dependence, i.e. $\eta_{rxn}$ \textasciitilde $\eta ^{\xi }$ with $\xi \quad =$ 0.85, which is contrary to reactions in normal liquids where $\eta_{rxn}$ \textasciitilde $\eta $. [Preview Abstract] |
Friday, March 17, 2017 9:48AM - 10:00AM |
X16.00010: Aging Effects in the Thermal Conductivity of Glass-forming Liquids Chandan Dasgupta, Pranab Jyoti Bhuyan, Rituparno Mandal, Pinaki Chaudhuri, Abhishek Dhar Using extensive numerical simulations of a model glass former (the three dimensional Kob-Andersen binary Lennard-Jones mixture), we have studied the dependence of the thermal conductivity of the supercooled liquid and the low-temperature glass on the history of preparation, such as the rate at which the temperature is decreased to prepare the glass from the high-temperature liquid state. We show that the thermal conductivity at temperatures near and below the ideal glass transition temperature of mode coupling theory depends on the rate of cooling and the age of the glass. Further, we demonstrate that the observed decrease in the thermal conductivity of a glass with increasing age (or with decreasing cooling rate) is linked to the exploration of lower energy local minima (inherent structures) of the underlying potential energy landscape. Finally, by calculating the vibrational density of states of these inherent structures, we show that the variation of the thermal conductivity with age is related to the extent of localization of the low-frequency vibrational modes, with increased localization leading to lower values of the thermal conductivity. [Preview Abstract] |
Friday, March 17, 2017 10:00AM - 10:12AM |
X16.00011: Comparison of a model vapor deposited glass films to equilibrium glass films Elijah Flenner, Ludovic Berthier, Patrick Charbonneau, Francesco Zamponi Vapor deposition of particles onto a substrate held at around 85\% of the glass transition temperature can create glasses with increased density, enthalpy, kinetic stability, and mechanical stability compared to an ordinary glass created by cooling. It is estimated that an ordinary glass would need to age thousands of years to reach the kinetic stability of a vapor deposited glass, and a natural question is how close to the equilibrium is the vapor deposited glass. To understand the process, algorithms akin to vapor deposition are used to create simulated glasses that have a higher kinetic stability than their annealed counterpart, although these glasses may not be well equilibrated either. Here we use novel models optimized for a swap Monte Carlo algorithm in order to create equilibrium glass films and compare their properties with those of glasses obtained from vapor deposition algorithms. This approach allows us to directly assess the non-equilibrium nature of vapor-deposited ultrastable glasses. [Preview Abstract] |
Friday, March 17, 2017 10:12AM - 10:24AM |
X16.00012: Boson Peak in Plastic Crystals Sebastian Emmert, Peter Lunkenheimer, Alois Loidl We present dielectric permittivity data of numerous glassy systems, spanning an extremely broad frequency range. By combining dielectric, terahertz-time-domain, and Fourier-transform-far-infrared spectroscopy, a range from a few $\mu$Hz to several THz is covered.\newline Focus is laid on an absorption that quite universally dominates such spectra at terahertz frequencies. This interesting feature also shows up in other, complementary measurement techniques such as inelastic neutron and light scattering as well as in calorimetric measurements, where it manifests as an excess term in the specific heat. Since its temperature dependent amplitude in the scattering experiments can be described by the Bose-Einstein statistics, it is sometimes referred to as 'boson peak'. Despite its universality, its microscopic origin is still a matter of debate.\newline To shed some light on this issue, we concentrate on the so-called ‘plastic crystals’, which consist of dipolar molecules that form a regular crystal lattice but are still disordered concerning their rotational degrees of freedom. By thoroughly studying the evolution of the boson peak under temperature variation and by comparing it to the results for canonical glass formers, valuable insights into its true nature are gained. [Preview Abstract] |
Friday, March 17, 2017 10:24AM - 10:36AM |
X16.00013: Johari-Goldstein $\beta$ relaxation events are metabasin transitions, and are precursors to $\alpha$ relaxation Marcus Cicerone, Miaochan Zhi, John Bender, Madhusudan Tyagi In 1970, Johari and Goldstein discovered a new relaxation process in liquids ($\beta_{JG}$ relaxation), which is faster than the $\alpha$ relaxation and appears to emerge only when $\alpha$ relaxation times are on the order of ns and longer. Over the intervening decades, much work has been done to understand the origin of this relaxation process, but its nature is still an open question. It is widely felt that $\beta_{JG}$ relaxations are a precursor to $\alpha$ relaxations, and it has been suggested that they may be related to transitions between inherent state (IS) or metabasin (MB) wells in a potential energy landscape. In this work we identify the signatures of IS and MB transitions in quasielastic neutron scattering, and use neutron backscattering to show that the latter are to be identified with $\beta_{JG}$ relaxations.[1] We then use optical Kerr effect measurements to show directly that $\beta_{JG}$ relaxation is a precursor to $\alpha$ relaxation. [1] M.T. Cicerone and M. Tyagi, arXiv:1607.07393v2 [Preview Abstract] |
Friday, March 17, 2017 10:36AM - 10:48AM |
X16.00014: Collapse of Experimental Colloidal Aging using Record Dynamics Dominic Robe, Stefan Boettcher, Paolo Sibani, Peter Yunker The theoretical framework of record dynamics (RD) posits that aging behavior in jammed systems is controlled by short, rare events involving activation of only a few degrees of freedom. RD predicts dynamics in an aging system to progress with the logarithm of $t/t_w$. This prediction has been verified through new analysis of experimental data on an aging 2D colloidal system. MSD and persistence curves spanning three orders of magnitude in waiting time are collapsed. These predictions have also been found consistent with a number of experiments and simulations, but verification of the specific assumptions that RD makes about the underlying statistics of these rare events has been elusive. Here the observation of individual particles allows for the first time the direct verification of the assumptions about event rates and sizes. [D. Robe, et al., EuroPhys. Lett. (to appear, \url{https://arxiv.org/abs/1608.03869})] [Preview Abstract] |
Friday, March 17, 2017 10:48AM - 11:00AM |
X16.00015: Aging near smooth and rough boundaries in a 3D colloidal glass Cong Cao, Eric Weeks We study dense (glassy) bidispesre colloidal samples near a wall with both smooth and rough boundary conditions. Using a confocal microscope we directly observe the slowing of particles' motion (aging phenomena) in both samples. With a smooth boundary, due to the wall induced layer-like structures, we notice that particles' dynamics slow down when near the wall, with aging process quench faster than the bulk area. Motions perpendicular to the wall are severely restricted by the wall, leading to fewer particle exchanges between layers. With the rough boundary, the layer-like structures greatly diminishes. At the same time, the particles' dynamics shows no distinct differences between boundary and bulk. These rough boundary observations indicate the aging process is more strongly influenced by energetic interactions with the wall than by entropic interactions (the latter are due to the confinement imposed by the wall and would be similar for both smooth and rough walls). [Preview Abstract] |
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