Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z12: Disordered and Glassy Systems II |
Hide Abstracts |
Sponsoring Units: DFD Chair: Jack Douglas, National Institute of Standards and Technology Room: B110-B111 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z12.00001: Microscopic statistical dynamical theory of correlated motion in glassy fluids and suspensions Daniel Sussman, Ken Schweizer The naive mode coupling theory and the stochastic nonlinear Langevin equation theory of single particle activated glassy dynamics has been extended to treat the correlated motion of two tagged particles in a dense fluid. Starting with a generalized Langevin equation deduced using projection and mode coupling approximations, we derive an effective nonequilibrium free energy surface for the stochastic motion of the tagged degrees of freedom. The dynamical free energy surface involves contributions from an ideal entropic term, the potential of mean force, and a many particle `caging' term that is explicitly dependent on the relative separation between the particles. The theory allows the study of space-time dynamic heterogeneity effects, including the length scale beyond which single particle motion of two tagged particles becomes independent and how the emergence of irreversible rearrangements affects the equilibrium pair structure relaxation. Numerical results for hard sphere fluids and colloidal suspensions will be presented. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z12.00002: Improved model for the transit entropy of monatomic liquids Eric Chisolm, Nicolas Bock, Duane Wallace In the original formulation of vibration-transit (V-T) theory for monatomic liquid dynamics, the transit contribution to entropy was taken to be a universal constant, calibrated to the constant-volume entropy of melting. This implied that the transit contribution to energy vanishes, which is incorrect. Here we develop a new formulation that corrects this deficiency. The theory contains two nuclear motion contributions: (a) the dominant vibrational contribution $S_{vib}(T/\theta_0)$, where $T$ is temperature and $\theta_0$ is the vibrational characteristic temperature, and (b) the transit contribution $S_{tr}(T/\theta_{tr})$, where $\theta_{tr}$ is a scaling temperature for each liquid. The appearance of a common functional form of $S_{tr}$ for all the liquids studied is deduced from the experimental data, when analyzed via the V-T formula. The theoretical entropy of melting is derived, in a single formula applying to normal and anomalous melting alike. An \textit{ab initio} calculation of $\theta_0$ for Na and Cu, based on density functional theory, provides verification of our analysis and V-T theory. In view of the present results, techniques currently being applied in \textit{ab initio} simulations of liquid properties can be employed to advantage in the further testing and development of V-T theory. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z12.00003: Free energy landscape theory of glass transition Takashi Odagaki I first present a free energy landscape (FEL) description of statistical mechanics, which is an exact reformulation of statistical mechanics and can be applied to non-equilibrium systems. Then, I discuss thermodynamic and dynamic properties of the vitrification process on the basis of the FEL formalism. I show that thermodynamic and dynamic anomalies at the glass transition, including the cooling rate dependence, can be understood in a unified manner which has not been achieved by any other theories of the glass transition. Namely, I show that the vitrification is a transition from annealed to quenched averages in the FEL and that the fast beta, the JG and the slow alpha relaxations are attributed to stochastic dynamics within a basin of FEL, jumping motion among locally connected basins and diffusive dynamics over barriers of the FEL. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z12.00004: Observation of the Disorder-Induced Crystal-to-Glass Transition Peter Yunker, Zexin Zhang, Arjun Yodh The role of frustration and quenched disorder in driving the transformation of a crystal into a glass is investigated in quasi-two-dimensional binary colloidal suspensions. Frustration is induced by added smaller particles. The crystal-glass transition is measured to differ from the liquid-glass transition in quantitative and qualitative ways. The crystal-glass transition bears structural signatures similar to those of the crystal-fluid transition: at the transition point, the persistence of orientational order decreases sharply from quasi-long-range to short-range, and the orientational order susceptibility exhibits a maximum. The crystal-glass transition also features a sharp variation in particle dynamics: at the transition point, dynamic heterogeneity grows rapidly, and a dynamic correlation length-scale increases abruptly. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z12.00005: Characteristic length scale of the inhomogeneous mode-coupling theory: beyond scaling predictions Elijah Flenner, Grzegorz Szamel The inhomogenous mode-coupling theory of Biroli \textit{et al.}\ [Phys. Rev. Lett. \textbf{97}, 195701 (2006)] allows for the identification of a characteristic length scale that diverges as the mode-coupling transition is approached. We numerically investigate this length scale as a function of time, wave-vector, and distance from the transition by examining the small $\mathbf{q}$ expansion of the dynamic susceptibility $\xi_{\mathbf{q}}(\mathbf{k};t)$ defined by Biroli \textit{et al.} We confirm the scaling predictions of Biroli \textit{et al.}. In addition, we show that the characteristic length is in qualitative agreement with simulations where the length scale is obtained from four-point correlation functions. Finally, we show that the length scale has virtually no $k$ dependence and thus it is well defined. The $k$-independence of the length contrasts with the very strong $k$ dependence of $q\to 0$ limit of the dynamic susceptibility. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z12.00006: On the Molecular Structure of Ge$_{x}$Sb$_{x}$Se$_{1-2x}$ glasses K. Gunasekera, P. Boolchand, A. Jackson The Ge$_{x}$Sb$_{x}$Se$_{100-2x }$ternary is isovalent to the phase-change material, Ge$_{x}$Sb$_{x}$Te$_{100-2x }$, except the Selenides can be prepared as bulk alloy glasses while the Tellurides exist only as amorphous thin-films. Here we report on the Selenides synthesized over a wide composition range, 0 $<$ x $<$ 25{\%}, and examined in modulated-DSC, Raman scattering and molar volume experiments. The enthalpy of relaxation at T$_{g}$ shows the opening of a reversibility window or Intermediate Phase (IP) in the 13{\%} $<$ x $<$ 18{\%} range, or 2.40 $<$ \textbf{\textit{r }}$<$ 2.54 mean coordination number range, where \textbf{\textit{r }}= 2 + 3x. FT- Raman studies reveal frequency of the CS mode of GeSe$_{4}$ tetrahedra to steadily blue-shift with increasing x as networks stiffen. New vibrational modes are observed near 150 cm$^{-1}$ and near 220 cm$^{-1}$ at x $>$ 18.18{\%}, the chemical threshold, and are thought to result from homopolar bonds. Ab-initio cluster calculations place pyramidal SbSe$_{3}$ units and ethylene-like Sb$_{2}$Se$_{2}$ units to reveal Raman activity near 215 cm$^{-1}$ and 228 cm$^{-1}$ respectively. Evolution of glass structure with composition x will be discussed. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z12.00007: Relating the Dynamics of Supercooled Liquids to the Sensitivity of Modes to Small Perturbations Vasile Iulian Clapa, Tsampikos Kottos, Francis Starr We propose an alternate method to relate the structural and dynamical properties of a model supercooled binary Lennard-Jones (BLJ) liquid approaching the glass transition. Our proposal builds on methods from random matrix theory and transport theory of disordered systems, where it was shown that the diffusivity/localization can be probed by an appropriate statistical analysis of the eigenvalues and eigenvectors of the Hamiltonian function. Specifically, we examine the viability of connecting the diffusion constant of the BLJ liquid to: (i) the mean level velocities (MLV) of eigenmodes, (ii) the variance of MLVs, and, (iii) the participation number of the eigenmodes. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z12.00008: Direct evidence of enhanced surface mobility in molecular glass forming system 1,3-bis-(1-naphthyl)-5-(2-naphthyl)benzene Chad Daley, Dan Scifo, Zahra Fakhraai, Mark Ediger, James Forrest We have performed nanoparticle embedding studies on the organic glass forming system 1,3-bis-(1-naphthyl)-5-(2-naphthyl)benzene (TNB). Films are prepared by vapor deposition onto a Si substrate held at a temperature near T$_{g}$ -- 50K (T$_{g}$ = 347K) and subsequently annealed. The surfaces of the films are covered with 20 nm diameter gold nanoparticles. Atomic force microscopy is used to track the apparent height of specific nanoparticles as a function of time elapsed at embedding temperatures of 323K, 333K, and 343K. The experiments reveal direct evidence for surface mobility at temperatures below the bulk glass transition. In addition to changes in the apparent heights of the nanoparticles, there is clear evidence that material surrounding the nanoparticles is being drawn up to engulf the nanoparticles; something not observed in polymeric films. These results directly establish the presence of enhanced surface mobility in molecular glass forming systems. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z12.00009: On the Elastic behavior of Sodium Borate Glasses K. Vignarooban, P. Boolchand, R. Kerner, M. Micoulaut Alkali Borates are industrial glasses and their physical properties are of general interest. We have made a special effort to synthesize dry (Na$_{2}$O)$_{x}$(B$_{2}$O$_{3})_{100-x}$ glasses over a wide composition range, 0 $<$ x $<$ 70{\%}, and have examined them in modulated-DSC, Raman scattering, FTIR, and molar volume experiments. The enthalpy of relaxation at T$_{g}$ shows a global minimum in the 20{\%} $<$ x $<$ 40{\%} range, which we identify with the rigid but stress-free Intermediate Phase (IP). The Boroxyl ring vibrational mode near 808 cm$^{-1}$ in B$_{2}$O$_{3}$, steadily softens by about 4 cm$^{-1}$ as the soda content increases to about 20{\%}. A vibrational mode of mixed rings\footnote{Kamitsos et al., Jour. Mol. Struct 247, 1 (1996).} (containing 3-fold and 4-fold B) is also observed near 775 cm$^{-1}$ at low x, and it also steadily softens by nearly 10 cm$^{-1}$ as x increases in the 20{\%} $<$ x $<$ 40{\%} soda range (IP). We are examining the underlying optical elasticity power-laws to ascertain the nature of the elastic phases. IR reflectance experiments provide the 4-fold coordinated B fraction to increase from 0.17 near x = 20{\%} to 0.44 near x = 40{\%} in broad agreement with NMR results. Evolution of physical properties of these glasses with soda content will be reviewed. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z12.00010: Aging of the generalized density susceptibility in a strong glass Azita Parsaeian, Horacio E. Castillo, Katharina Vollmayr-Lee We investigate dynamical heterogenities in a strong glass below the glass transition temperature. Our model is produced by molecular dynamics simulations of an amorphous silica system, where the atoms interact via the BKS potential. We quantify the heterogenous dynamics by measuring the four-point generalized dynamic susceptibility, i.e., the volume integral of the spatial correlations. We study this quantity as a function of the waiting time and as a function of the global intermediate scattering function. We test for universality by comparing the fluctuations in this model to those of fragile glasses which consist of either small molecules or polymers. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z12.00011: Glass transition and dynamic scaling in soft repulsive particles: a mode-coupling theory study Grzegorz Szamel, Ludovic Berthier, Hugo Jacquin, Elijah Flenner We combine the hypernetted chain approximation with the mode-coupling theory to analyze structure and dynamics of dense systems consisting of soft repulsive particles (harmonic spheres). We investigate the phase diagram for a broad range of temperatures and volume fractions. We find that in the vicinity of the T=0 mode-coupling transition for hard spheres, the dynamics obey a power-law form of dynamic scaling. We find that the critical MCT exponent describing the divergence of the relaxation time at the mode-coupling transition decreases with increasing volume fraction. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z12.00012: Time reparametrization symmetry in a short-range p-spin model Gcina Mavimbela, Horacio E. Castillo We explore the existence of time reparametrization symmetry in the p-spin model. We follow closely the approach previously used to prove the presence of this symmetry in the Edwards-Anderson model. Using the Martin-Siggia-Rose generating functional, we analytically probe the long-time dynamics.We introduce a cut-off in the time difference $\tau_{0}\leq t-t'$ and perform a Renormalization Group analysis where we systematically integrate 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. This continuous symmetry is broken in the glass state and we argue that this gives rise to the presence of Goldstone modes. We expect the Goldstone modes to determine the properties of fluctuations in the glass state. [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z12.00013: Brillouin scattering study of glass-transition dynamics in glycerol at pressures up to 60 kbar William Oliver III, Titus Morris, Taylor Byrum Isothermal pressurization data for glycerol, a prototypic intermediate glass-forming system, will be presented. Brillouin scattering studies were performed at constant temperature to pressures as high as 60 kbar. An equal-angle forward scattering geometry is used for which the pressure dependence of the refractive index is not required to convert Brillouin frequency shift data to sound velocities. Through a careful optical setup acoustic mode frequencies and linewidths are measured, and from data analysis methods that include convolution with the instrument function, both pressure-dependent sound velocities and true linewidths are extracted from these data. Further analysis allow us to model the relaxation time of the glass-forming system as a function of pressure and to calculate the equation of state for this important system to previously unexplored regions of the pressure-temperature phase space. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z12.00014: Triangular Relations in Structural Glasses Karina E. Avila, Horacio E. Castillo, Azita Parsaeian Structural glasses exhibit the phenomenon of dynamical heterogeneity: different regions of the system present different dynamical behavior. To study this phenomenon, we analyze simulations of four models of structural glasses performed in the aging regime. We compute the triangular relations of the local and global two-time correlation functions, i.e., the mathematical relationships among correlators calculated for the time pairs (t1,t2), (t2,t3) and (t1,t3) with t1$>$ t2$>$ t3. We plot the triangular relations of the global and local correlations together to compare their behavior. We find that the probability distribution of local correlations is concentrated along the curve representing the global correlations. Our results provide evidence of time reparametrization invariance and also point toward universality in the aging. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700