Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C47: Disordered and Glassy Systems |
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Sponsoring Units: GSOFT DCP GSNP Chair: Yang Zhang, University of Illinois at Urbana–Champaign Room: LACC 507 |
Monday, March 5, 2018 2:30PM - 2:42PM |
C47.00001: Cooperative Rearrangements in Aging Colloidal Glass Simulations: Log-Poisson Statistics Dominic Robe, Stefan Boettcher Physical aging is a non-equilibrium relaxation process which takes place after a system is quenched into a glassy state. One of the unexplained features of aging is that the process stagnates on a non-exponential time scale. We posit that the intermittent, irreversible rearrangements noted in aging colloidal glasses are permitted by record-breaking fluctuations of local dynamics. If such events are the sole mechanism of relaxation, this would make aging appear as a Poisson process when viewed on a logarithmic time scale. We examine data from MD simulations, an experimental system, and a coarse grained model. We show that the age-dependent rate of rearrangement events is consistent with a Log-Poisson process, and thus provide a possible explanation for the anomalous time-dependence of dynamical properties of a wide variety of glassy systems. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C47.00002: Structure of (Na2O)x(P2O5)100–x Glasses Probed in IR Reflectance and Raman Scattering Chandi Mohanty, Ralph Chbeir, Aaron Welton, Mathieu Bauchy, Matthieu Micoulaut, Punit Boolchand Modulated differential scanning calorimetry (MDSC) experiments on titled glasses reveal the enthalpy of relaxation at Tg to show a local minimum in the 32.5% < x < 42.5% range of soda, providing evidence of a reversibility window (or intermediate phase). Furthermore, trends in fragility index m(x) of melts deduced from complex Cp measurements using MDSC show a local minimum in the reversibility window. The molecular structure of these glasses is now probed in Raman scattering and IR reflectance. At the stoichiometric composition (x = 50%), the glass and crystal show the symmetric stretching (SS) and asymmetric stretching of P–Ot ( Ot = terminal O) in long chains to reveal complementary behaviors in Raman and IR Transverse Optic response. In the glass, the SS mode of P–Ot bond in chains (1166(1) cm-1), characteristic of Q2 species, and the SS mode characteristic of Q3 species (near 1302 cm-1) are observed and systematically tracked with x in the 0 < x < 50% range. This has permitted extracting the fraction of the Qn (n = 2,3) species as a function of x, which provides a powerful means to elucidate glass structure as in NMR1. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C47.00003: Melt Dynamics and Glass Topological Phases in the GeyAsySe100-2y Ternary Ralph Chbeir, Mathieu Bauchy, Matthieu Micoulaut, Punit Boolchand Recently one found1,2 that the Fragility index (m) of dry and homogenized binary Gex (Se or S)100-x melts are super- strong ( m < 20) in the 20% < x < 26% range (fragility window) and fragile elsewhere. Ab initio MD simulations confirmed3 the behavior. Furthermore, the enthalpy of relaxation of corresponding glasses was found to be near vanishing in the same 20% < x < 26% range, the reversibility window. Is the correlation between the fragility window and reversibility window generic? To explore the issue further, we now examine the GeyAsySe100-2y ternary. Dry and homogeneous melts/glasses were synthesized in the 0 < y < 25% range, and their homogeneity confirmed using FT-Raman profiling. The fragility index and the reversibility window are being measured using Modulated DSC (Complex Cp analysis at variable modulation frequency and Enthalpy of relaxation at a fixed modulation frequency). Results of these experiments will be presented. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C47.00004: Effects of Dryness on the Calorimetric and Vibrational behavior of (Na2O)x[(B2O3)y(GeO2)1−y]1−x glasses Aaron Welton, Ralph Chbeir, Andrew Czaja, Punit Boolchand The two base materials comprising the present ternary, viz., y= 0, i.e., Na2O-GeO binary1 and y = 1, Na2O-B2O3 binary2 have been previously studied and have shown isostatically rigid Intermediate Phases (IPs) to be observed in the x = 0.14 to x = 0.19 range and the x = 0.20 to x = 0.40 range of soda concentration respectively. We had noted earlier that an IP in the present ternary is manifested in the 0.23 < x < 0.30 range of soda. In the present work we have attempted to dry the ternary glasses by vacuum desorbing them while heating close to Tg using a high vacuum pumping line. Re-examination of the reversibility window in the 0.23 < x < 0.30 range of soda shows it to sharpen, get deeper and flatten in the dry glasses providing confidence on the proposed Topological Phases. Raman scattering and IR reflectance experiments are now undertaken to elucidate the role of dryness on glass structure. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C47.00005: The Activated Process of Modifier Cation Migration in Mixed-Network Former Glasses Weimin Wang, John Kieffer We investigated the adiabatic elastic properties and ionic conductivities of two series of mixed network former glasses, sodium borosilicates and sodium borogermanates using Brillouin light scattering and dielectric impedance spectroscopy, respectively. Our analysis reveals strong correlations between these two measures, which allowed us to develop a more detailed formulation of transition state theory describing the modifier cation migration in these materials. We find that the structural deformation during a cation jump is almost entirely controlled by the bulk modulus. Our analysis allows us to assess the spatial extent of this deformation, as well as estimate the relative amounts of configurational and vibrational entropy changes associated with this thermally activated process. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C47.00006: Consequences of homogenization of bulk AsxS100-x glasses on their calorimetric and vibrational behavior Soumendu Chakravarty, Ralph Chbeir, Ping Chen, Punit Boolchand Bulk AsxS100-x melts/glasses of 1.5 gram batch size in the 15% < x < 40% composition range are synthesized by reacting dry As2S3 and S at 700°C in evacuated quartz tubes for several tens of days. Ex-situ FT- Raman scattering of the 1 inch long quenched melt columns were periodically taken till these homogenized. A Q2000 MDSC from TA Instruments is used to examine thermal properties of glasses. The results confirm1 the enthalpy of relaxation at Tg, △Hnr(x) to reveal a sharp square-well like reversibility window in the 22.5% < x < 28.0% range, and Tg(x) to systematically increase with x. FT- Raman scattering experiments reveal the elusive 537 cm-1 mode associated with As=S stretch predicted for the quasi-tetrahedral (QT) S=As(S1/2)3 local structure1 to be observed. The scattering strength of the QT mode shows a global maximum near x = 18%. The Fragility index of these homogenized melts are being examined and will be correlated with the reversibility window. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C47.00007: Experimental and Numerical Evidence of an Intermediate Phase in Sodium Phosphate Glasses Mathieu Bauchy, Kai Yang, Matthieu Micoulaut, Chandi Mohanty, Ralph Chbeir, Punit Boolchand Alkali phosphate glasses are archetypical models for glass sealing materials, bioactive glasses, and solid-state electrolyte. The development of novel glasses with tailored properties requires an accurate knowledge of the linkages between composition, structure, and properties. Such relationships can be elegantly decoded within the framework of topological constraint theory, which reduces complex disordered atomic networks into simpler mechanical trusses. Here, based on modulated differential scanning calorimetry experiments performed on extremely dry sodium phosphate glasses, we report an intermediate phase with sharp boundaries, wherein glass transition is nearly reversible. Based on molecular dynamics simulations, we show that the glass compositions belonging to the intermediate phase exhibit an isostatic network, that is, their atomic network is topologically rigid but free of internal stress. These results shed new light into the origin of rigidity and stress transitions in oxide glasses. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C47.00008: Mechanical annealing of binary glasses: Effects of strain amplitude and temperature Nikolai Priezjev Molecular dynamics simulations are carried out to study the dynamic response of amorphous solids to oscillatory shear at finite temperatures. The data were collected from a poorly annealed binary glass, which was deformed periodically in the elastic regime during several hundred shear cycles. We found that the characteristic time required to reach a steady state with a minimum potential energy is longer at higher temperatures and larger strain amplitudes. With decreasing strain amplitude, the asymptotic value of the potential energy increases but it remains lower than in quiescent samples. The transient decay of the potential energy correlates well with a gradual decrease in the volume occupied by atoms with large nonaffine displacements. By contrast, the maximum amplitude of shear stress oscillations is attained relatively quickly when a large part of the system starts to deform reversibly. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C47.00009: Abstract Withdrawn
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Monday, March 5, 2018 4:18PM - 4:30PM |
C47.00010: A Microscopic View of Stable Glasses via Surface-Initiated Melting Elijah Flenner, Ludovic Berthier, Patrick Charbonneau, Francesco Zamponi Melting fronts have been observed in experimental vapor-deposited glasses, but are absent for ordinary glasses created by cooling a liquid. In order to gain insight into the different melting mechanisms, here we study the melting of an ultrastable glass film into a supercooled liquid using molecular simulations. We identify two mechanisms for this transformation: (i) the uniform melting of the film, and (ii) the initiation of the melting front from its surface. The former takes place in poorly thermalized materials, while the latter only takes place in ultrastable samples. We thus demonstrate that the melting front results from the (ultra-)stability of the glass and not from the vapor deposition process itself. Interestingly, for glass films of intermediate stability, the two mechanisms compete and the growth front propogates a distance l before the glass melts. Experimentally measuring how deep the melting front propogates into the film should be able to validate this proposal. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C47.00011: Testing the paradigms of the glass transition in colloids Jialun Wang, Roseanna Zia Many molecular liquids freeze upon fast enough cooling. This so-called glass state is path dependent and out of equilibrium, as measured by the Kovacs signature experiments, i.e. intrinsic isotherms, asymmetry of approach and memory effect. The reasons for this path- and time-dependence are not fully understood, due to fast molecular relaxations. Colloids provide a natural way to model such behavior, owing to disparity in colloidal versus solvent time scales that can slow dynamics. To shed light on the ambiguity of glass transition, we study via large-scale dynamic simulation of hard-sphere colloidal glass after volume-fraction jumps, where particle size increases at fixed system volume followed by protocols of the McKenna-Kovacs signature experiments. During and following each jump, the positions, velocities, and particle-phase stress are tracked and utilized to characterize relaxation time scales. The impact of both quench depth and quench rate on arrested dynamics and “state” variables are explored. In addition, we expand our view to various structural signatures, and rearrangement mechanism is proposed. The results provide insight into not only the existence of an “ideal” glass transition, but also the role of structure in such a dense amorphous system. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C47.00012: Dynamical criticality in high-dimensional glass-forming liquids. Ludovic Berthier, Patrick Charbonneau, Silvio Franz, Joyjit Kundu The mean-field theory of glass formation predicts the existence of a dynamical critical point at which the relaxation time diverges. Due to the presence of activated processes in physical dimensions (d=2, 3), this critical point is then but a crossover. Some of the associated phenomenology is nonetheless considered to persist. We here aim to identify what, if anything, of this criticality can be clearly identified by systematically varying the dimension of space. Using fluids of polydispersed hard spheres that have been optimized for the swap Monte Carlo algorithm allows us to thermalize very high-density systems and thus to approach the regime of interest easily. We then examine markers of dynamical criticality, such as the fluctuations of dynamical correlators and dynamical heterogeneity. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C47.00013: A diverging length scale in the structure of jammed systems Daniel Hexner, Andrea Liu, Sidney Nagel Super-cooled liquids undergo an enormous slowing down of their dynamics when their temperature is lowered towards the glass transition. Despite the huge growth in time scale there appears to be little change in the structure. This has prompted the suggestion that there is a hidden form of ordering. Motivated by this, we study another amorphous system that undergoes a phase transition into a rigid state: jammed soft repulsive spheres at zero temperature. We have discovered a subtle structural ordering, not seen in the two-point correlation function, g(r), that is associated with the coordination of particles [1]. On scales below a length scale that diverges at the jamming point, the contact fluctuations are sub-extensive (hyperuniform). We argue that this length scale diverges with an exponent 2/(d+1) as the jamming transition is approached. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C47.00014: Low-Frequency Vibrational Modes of Stable Glasses Lijin Wang, Andrea Ninarello, Pengfei Guan, Ludovic Berthier, Grzegorz Szamel, Elijah Flenner There is an excess in the vibrational density of states g(ω) over Debye scaling at low-frequencies, the so-called Boson peak, which results in a peak in g(ω)/ω2. We examine the low-frequency density of states of glasses obtained from quenching supercooled liquids equilibrated at parent temperatures T between temperatures above the onset of supercooling to 62% of the mode coupling temperature TC. The kinetic stability of the glasses at the lowest temperatures examined are comparable to that of experimental glasses. We divide the low-frequency density of states into phonon and quasi-localized modes. We show that the phonon density of states gD(ω) obeys Debye scaling, gD(ω) = ADω2, where AD is the Debye level estimated from the sound velocities. We also show that the quasi-localized density of states obeys g4(ω) = A4ω4 for each T. For parent temperatures above TC, AD and A4 weakly depend on T. For parent temperatures below TC, both AD and A4 decrease with decreasing T, with AD decreasing around 30% and A4 decreasing by an order of magnitude. Additionally, we find that height of the Boson peak scaled by the Debye level AD is independent of T. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C47.00015: Detection of Boson Peak of Densified Silica Glass by Terahertz Time-Domain Spectroscopy Tatsuya Mori, Koki Nakano, Yasuhiro Fujii, Suguru Kitani, Shinji Kohara, Norimasa Nishiyama, Atsunobu Masuno, Akitoshi Koreeda, Hitoshi Kawaji, Seiji Kojima We performed terahertz time-domain spectroscopy on densified silica glasses to investigate the boson peak (BP) dynamics. BP is a low energy excitation universally observed in the THz region of the glass material. In the spectra of α(ν)/ν2 [α(ν) is the absorption coefficient], BP were observed. Infrared light-vibration coupling coefficient CIR(ν) was determined using the α(ν) and vibrational density of states g(ν) obtained from the low-temperature specific heat measurement, and the charge fluctuations of the densified silica glasses were quantitatively evaluated. |
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