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Sample records for glass transition phenomena

  1. Are polymers standard glass-forming systems? The role of intramolecular barriers on the glass-transition phenomena of glass-forming polymers

    NASA Astrophysics Data System (ADS)

    Colmenero, J.

    2015-03-01

    Traditionally, polymer melts have been considered archetypal glass-formers. This has been mainly due to the fact that these systems can easily be obtained as glasses by cooling from the melt, even at low cooling rates. However, the macromolecules, i.e. the structural units of polymer systems in general, are rather different from the standard molecules. They are long objects (‘chains’) made by repetition of a given chemical motif (monomer) and have intra-macromolecular barriers that limit their flexibility. The influence of these properties on, for instance, the glass-transition temperature of polymers, is a topic that has been widely studied by the polymer community almost from the early times of polymer science. However, in the framework of the glass-community, the relevant influence of intra-macromolecular barriers and chain connectivity on glass-transition phenomena of polymers has started to be recognized only recently. The aim of this review is to give an overview and to critically revise the results reported on this topic over the last years. From these results, it seems to be evident that there are two different mechanisms involved in the dynamic arrest in glass-forming polymers: (i) the intermolecular packing effects, which dominate the dynamic arrest of low molecular weight glass-forming systems; and (ii) the effect of intra-macromolecular barriers combined with chain connectivity. It has also been shown that the mode coupling theory (MCT) is a suitable theoretical framework to discuss these questions. The values found for polymers for the central MCT parameter—the so-called λ-exponent—are of the order of 0.9, clearly higher than the standard values (λ ≈ 0.7) found in systems where the dynamic arrest is mainly driven by packing effects (‘standard’ glass-formers). Within the MCT, this is a signature of the presence of two competing mechanisms of dynamic arrest, as it has been observed in short-ranged attractive colloids or two component

  2. Photosensitivity phenomena in multicomponent glasses

    NASA Astrophysics Data System (ADS)

    Czachor, K.; Jedrzejewski, K.; Stępień, R.

    2005-09-01

    Low cost, high bandwidth, narrowband and multifunctionality are main targets for new optical devices development. Planar optics is probably the best solution for future telecom long distance and access transmission networks but also for metrology sensing devices. Many different materials can be used for this purpose like PECVD silica, multicomponent glasses or even polymers. Bragg grating inscription in such material is another advantage to achieve narrowband spectral characteristic of device, which is essential in modern systems. The main purpose of presented work was the development in technology and measurement techniques of channels formed on the surface of the glass. Planar couplers and structures that are more complicated can also be made in the same technology in the future. Special multicomponent glasses SiO2-GeO2-B2O3-Na2O-SnO2 with up to 6 %mol of Sn were synthetized and thin rectangular polished plates were prepared. The UV 244 nm 100 mW Coherent argon ion frequency doubled laser was used in our experiments. Surface relief structures similar to the compaction-densification/expansion model of photosensitivity were developed on the glass surface. The optical microscope and alpha-step profiler were used for preliminary tests of photoinduced structures on the glass surface. The ability of the writing possibility in function of Sn content and different laser power levels were analyzed.

  3. Perspective: The glass transition

    NASA Astrophysics Data System (ADS)

    Biroli, Giulio; Garrahan, Juan P.

    2013-03-01

    We provide here a brief perspective on the glass transition field. It is an assessment, written from the point of view of theory, of where the field is and where it seems to be heading. We first give an overview of the main phenomenological characteristics, or "stylised facts," of the glass transition problem, i.e., the central observations that a theory of the physics of glass formation should aim to explain in a unified manner. We describe recent developments, with a particular focus on real space properties, including dynamical heterogeneity and facilitation, the search for underlying spatial or structural correlations, and the relation between the thermal glass transition and athermal jamming. We then discuss briefly how competing theories of the glass transition have adapted and evolved to account for such real space issues. We consider in detail two conceptual and methodological approaches put forward recently, that aim to access the fundamental critical phenomenon underlying the glass transition, be it thermodynamic or dynamic in origin, by means of biasing of ensembles, of configurations in the thermodynamic case, or of trajectories in the dynamic case. We end with a short outlook.

  4. Glass transition of a particle in a random potential, front selection in nonlinear renormalization group, and entropic phenomena in Liouville and sinh-Gordon models

    NASA Astrophysics Data System (ADS)

    Carpentier, David; Le Doussal, Pierre

    2001-02-01

    We study via renormalization group (RG), numerics, exact bounds, and qualitative arguments the equilibrium Gibbs measure of a particle in a d-dimensional Gaussian random potential with translationally invariant logarithmic spatial correlations. We show that for any d>=1 it exhibits a transition at T=Tc>0. The low-temperature glass phase has a nontrivial structure, being dominated by a few distant states (with replica symmetry breaking phenomenology). In finite dimension this transition exists only in this ``marginal glass'' case (energy fluctuation exponent θ=0) and disappears if correlations grow faster (single ground-state dominance θ>0) or slower (high-temperature phase). The associated extremal statistics problem for correlated energy landscapes exhibits universal features which we describe using a nonlinear Kolmogorov (KPP) RG equation. These include the tails of the distribution of the minimal energy (or free energy) and the finite-size corrections, which are universal. The glass transition is closely related to Derrida's random energy models. In d=2, the connection between this problem and Liouville and sinh-Gordon models is discussed. The glass transition of the particle exhibits interesting similarities with the weak- to strong-coupling transition in Liouville (c=1 barrier) and with a transition that we conjecture for the sinh-Gordon model, with correspondence in some exact results and RG analysis. Glassy freezing of the particle is associated with the generation under RG of new local operators and of nonsmooth configurations in Liouville. Applications to Dirac fermions in random magnetic fields at criticality reveal a peculiar ``quasilocalized'' regime (corresponding to the glass phase for the particle), where eigenfunctions are concentrated over a finite number of distant regions, and allow us to recover the multifractal spectrum in the delocalized regime.

  5. Glass transition of a particle in a random potential, front selection in nonlinear renormalization group, and entropic phenomena in Liouville and sinh-Gordon models.

    PubMed

    Carpentier, D; Le Doussal, P

    2001-02-01

    We study via renormalization group (RG), numerics, exact bounds, and qualitative arguments the equilibrium Gibbs measure of a particle in a d-dimensional Gaussian random potential with translationally invariant logarithmic spatial correlations. We show that for any d>/=1 it exhibits a transition at T=T(c)>0. The low-temperature glass phase has a nontrivial structure, being dominated by a few distant states (with replica symmetry breaking phenomenology). In finite dimension this transition exists only in this "marginal glass" case (energy fluctuation exponent straight theta=0) and disappears if correlations grow faster (single ground-state dominance straight theta>0) or slower (high-temperature phase). The associated extremal statistics problem for correlated energy landscapes exhibits universal features which we describe using a nonlinear Kolmogorov (KPP) RG equation. These include the tails of the distribution of the minimal energy (or free energy) and the finite-size corrections, which are universal. The glass transition is closely related to Derrida's random energy models. In d=2, the connection between this problem and Liouville and sinh-Gordon models is discussed. The glass transition of the particle exhibits interesting similarities with the weak- to strong-coupling transition in Liouville (c=1 barrier) and with a transition that we conjecture for the sinh-Gordon model, with correspondence in some exact results and RG analysis. Glassy freezing of the particle is associated with the generation under RG of new local operators and of nonsmooth configurations in Liouville. Applications to Dirac fermions in random magnetic fields at criticality reveal a peculiar "quasilocalized" regime (corresponding to the glass phase for the particle), where eigenfunctions are concentrated over a finite number of distant regions, and allow us to recover the multifractal spectrum in the delocalized regime.

  6. Physical Phenomena in Containerless Glass Processing

    NASA Technical Reports Server (NTRS)

    Subramanian, R. S.; Cole, R.

    1985-01-01

    An investigation into the various physical phenomena of importance in the space experiments is under way. Theoretical models of thermocapillary flow in drops, thermal migration of bubbles and droplets, the motion of bubbles inside drops, and the migration of bubbles in rotating liquid bodies are being developed. Experiments were conducted on the migration of bubbles and droplets to the axis of a rotating liquid body, and the rise of bubbles in molten glass. Also, experiments on thermocapillary motion in silicone oils as well as glass melts were performed. Experiments are currently being conducted on the migration of bubbles in a thermal gradient, and on their motion inside unconstrained liquid drops in a rotating liquid.

  7. Water's second glass transition.

    PubMed

    Amann-Winkel, Katrin; Gainaru, Catalin; Handle, Philip H; Seidl, Markus; Nelson, Helge; Böhmer, Roland; Loerting, Thomas

    2013-10-29

    The glassy states of water are of common interest as the majority of H2O in space is in the glassy state and especially because a proper description of this phenomenon is considered to be the key to our understanding why liquid water shows exceptional properties, different from all other liquids. The occurrence of water's calorimetric glass transition of low-density amorphous ice at 136 K has been discussed controversially for many years because its calorimetric signature is very feeble. Here, we report that high-density amorphous ice at ambient pressure shows a distinct calorimetric glass transitions at 116 K and present evidence that this second glass transition involves liquid-like translational mobility of water molecules. This "double Tg scenario" is related to the coexistence of two liquid phases. The calorimetric signature of the second glass transition is much less feeble, with a heat capacity increase at Tg,2 about five times as large as at Tg,1. By using broadband-dielectric spectroscopy we resolve loss peaks yielding relaxation times near 100 s at 126 K for low-density amorphous ice and at 110 K for high-density amorphous ice as signatures of these two distinct glass transitions. Temperature-dependent dielectric data and heating-rate-dependent calorimetric data allow us to construct the relaxation map for the two distinct phases of water and to extract fragility indices m = 14 for the low-density and m = 20-25 for the high-density liquid. Thus, low-density liquid is classified as the strongest of all liquids known ("superstrong"), and also high-density liquid is classified as a strong liquid.

  8. Moisture and temperature triggered release of a volatile active agent from soy protein coated paper: effect of glass transition phenomena on carvacrol diffusion coefficient.

    PubMed

    Chalier, Pascale; Ben Arfa, Afef; Guillard, Valerie; Gontard, Nathalie

    2009-01-28

    Carvacrol release from SPI-coated papers was evaluated at different relative humidities (RH; 60, 80, and 100%) and storage temperatures (5, 20, and 30 degrees C). Effective carvacrol diffusivities were determined from experimental release kinetics and by using a mathematical model based on Fick's second law. Increasing storage temperature and RH lead to an increase of carvacrol diffusivity. Depending on the relative humidity, the carvacrol effective diffusivity varied from 1.71 x 10(-16) to 138 x 10(-16) m(2)/s at 30 degrees C, from 0.85 x 10(-16) to 8.78 x 10(-16) m(2)/s at 20 degrees C, and from 0.11 x 10(-16) to 7.50 x 10(-16) m(2)/s at 5 degrees C. The combined effect of relative humidity and temperature on diffusivity was particularly marked at 30 degrees C and 100% RH. The temperature and relative humidity dependence of carvacrol release was related to the glass transition phenomenon and its effect on chain protein mobility and carvacrol diffusivity.

  9. Physical phenomena in containerless glass processing

    NASA Technical Reports Server (NTRS)

    Subramanian, R. S.; Cole, R.; Annamalai, P.; Jayaraj, K.; Kondos, P.; Mcneil, T. J.; Shankar, N.

    1982-01-01

    Experiments were conducted on bubble migration in rotating liquid bodies contained in a sphere. Experiments were initiated on the migration of a drop in a slightly less dense continuous phase contained in a rotating sphere. A refined apparatus for the study of thermocapillar flow in a glass melt was built, and data were acquired on surface velocities in the melt. Similar data also were obtained from an ambient temperature fluid model. The data were analyzed and correlated with the aid of theory. Data were obtained on flow velocities in a pendant drop heated from above. The motion in this system was driven principally by thermocapillarity. An apparatus was designed for the study of volatilization from a glass melt.

  10. Isoconversion Analysis of the Glass Transition

    NASA Astrophysics Data System (ADS)

    Badrinarayanan, Prashanth; Zheng, Wei; Simon, Sindee

    2007-03-01

    At temperatures below their glass transition temperatures (Tgs), glass forming materials deviate from equilibrium density and form a glass. The kinetic nature of the glass transition process is manifested in the cooling rate dependence of the glass transition temperature and by structural relaxation below Tg. Various facets of the glass transition kinetics have been well described by phenomenological models of the glass transition, such as the TNM and KAHR model. An important yet frequently questioned assumption in these models is that the apparent activation energy, which describes the temperature dependence of the relaxation time, does not vary during the glass transition process. Some recent reports suggest that the activation energy varies significantly during the glass transition process. In this work we apply an isoconversion analysis to data in the glass transition region which was obtained on cooling from capillary dilatometry and differential scanning calorimetry (DSC) in order to determine whether the apparent activation energy increases as the glassy state is approached.

  11. Characteristic length of glass transition

    NASA Astrophysics Data System (ADS)

    Donth, E.

    1996-03-01

    The characteristic length of the glass transition (ξ _α ) is based on the concept of cooperatively rearranging regions (CRR's) by Adam & Gibbs (1965): ξ _α is the diameter of one CRR. In the theoretical part of the talk a formula is derived how this length can be calculated from calorimetric data of the transformation interval. The approach is based on fluctuations in natural functional subsystems. The corresponding thermodynamics is represented e.g. in a book of the author (E. Donth, Relaxation and Thermodynamics in Polymers. Glass Transition, Akademie-Verlag, Berlin 1992). A typical value for this length is 3 nanometers. In the experimental part several examples are reported to enlarge the experimental evidence for such a length: Squeezing the glass transition in the amorphous layers of partially crystallized PET (C. Schick, Rostock), glass transition of small-molecule glass formers in a series of nanoscaled pores of porous glasses (F. Kremer, Leipzig), comparison with a concentration fluctuation model in homogeneous polymer mixtures (E.W. Fischer, Mainz), and, from our laboratory, backscaling to ξ _α across the main transition from the entanglement spacing in several amorphous polymers such as PVAC, PS, NR, and some polymer networks. Rouse backscaling was possible in the α β splitting region of several poly(n alkyl methacrylates) resulting in small characteristic lengths of order 1 nanometer near the onset of α cooperativity. In a speculative outlook a dynamic density pattern is presented, having a cellular structure with higher density and lower mobility of the cell walls. It will be explained, with the aid of different thermal expansion of wall and clusters, how the clusters within the cells maintain a certain mobility far below the glass temperature.

  12. Phenomena and mechanisms of crack propagation in glass-ceramics.

    PubMed

    Apel, E; Deubener, J; Bernard, A; Höland, M; Müller, R; Kappert, H; Rheinberger, V; Höland, W

    2008-10-01

    Lithium disilicate, leucite and apatite glass-ceramics have become state-of-the-art framework materials in the fabrication of all-ceramic dental restorative materials. The goal of this study was to examine the crack propagation behaviour of these three known glass-ceramic materials after they have been subjected to Vickers indentation and to characterize their crack opening profiles (delta(meas) vs. (a-r)). For this purpose, various methods of optical examination were employed. Optical microscopy investigations were performed to examine the crack phenomena at a macroscopic level, while high-resolution techniques, such as scanning electron microscopy (SEM) and atomic force microscopy (AFM), were employed to investigate the crack phenomena at a microscopic level. The crack patterns of the three glass-ceramics vary from fairly straightforward to more complex, depending on the amount of residual glass matrix present in the material. The high-strength lithium disilicate crystals feature a high degree of crosslinking, thereby preventing crack propagation. In this material, the crack propagates only through the residual glass phase, which constitutes 30%-40% by volume. Having a high glass content of more than 65% by volume, the leucite and apatite glass-ceramics show far more complex crack patterns. Cracks in the leucite glass-ceramic propagate through both the glass and crystal phase. The apatite glass-ceramic shows a similar crack behaviour as an inorganic-organic composite material containing nanoscale fillers, which are pulled out in the surroundings of the crack tip. The observed crack behaviour and the calculated K(tip) values of the three types of glass-ceramics were compared to the K(IC) values determined according to the SEVNB method.

  13. Assessing transitional phenomena with the transitional object memory probe.

    PubMed

    Fowler, C; Hilsenroth, M J; Handler, L

    1998-01-01

    Winnicott's concept of transitional relatedness has captured the interest of psychoanalysts because it provides an understanding of the dialectical process occurring between inner and outer reality, and by extension, between analyst and analysand. Clinical observations related to transitional phenomena have led the authors to develop a projective early memory probe that assesses transitional phenomena. The transitional object early memory probe was tested both for its empirical validity and for its clinical utility in psychodynamic psychotherapy. Construct validity was assessed by comparing memory scores to the Rorschach Transitional Object Scale, as well as to therapist ratings of patient behaviors. Results demonstrated moderate correlations between early memory scores and Rorschach scale scores. Equally important was the finding that early memory scores were significantly correlated with therapist ratings of key behavioral patterns in therapy. A case vignette highlights the clinical application of the transitional object probe in assessing the capacity for transitional relatedness. In this case, the data gleaned from the patient's memories provided the therapist with a sharper focus on their role in the patient's growing capacity for more vital and creative contact with reality.

  14. Phase transition in a super superspin glass

    NASA Astrophysics Data System (ADS)

    Mathieu, R.; De Toro, J. A.; Salazar, D.; Lee, S. S.; Cheong, J. L.; Nordblad, P.

    2013-06-01

    We here confirm the occurrence of spin glass phase transition and extract estimates of associated critical exponents of a highly monodisperse and densely compacted system of bare maghemite nanoparticles. This system has earlier been found to behave like an archetypal spin glass, with, e.g., a sharp transition from paramagnetic to non-equilibrium behavior, suggesting that this system undergoes a spin glass phase transition at a relatively high temperature, Tg ∼ 140 K.

  15. Ising model of a glass transition.

    PubMed

    Langer, J S

    2013-07-01

    Numerical simulations by Tanaka and co-workers indicate that glass-forming systems of moderately polydisperse hard-core particles, in both two and three dimensions, exhibit diverging correlation lengths. These correlations are described by Ising-like critical exponents, and are associated with diverging, Vogel-Fulcher-Tamann, structural relaxation times. Related simulations of thermalized hard disks indicate that the curves of pressure versus packing fraction for different polydispersities exhibit a sequence of transition points, starting with a liquid-hexatic transition for the monodisperse case, and crossing over with increasing polydispersity to glassy, Ising-like critical points. I propose to explain these observations by assuming that glass-forming fluids contain twofold degenerate, locally ordered clusters of particles, similar to the two-state systems that have been invoked to explain other glassy phenomena. This paper starts with a brief statistical derivation of the thermodynamics of thermalized, hard-core particles. It then discusses how a two-state, Ising-like model can be described within that framework in terms of a small number of statistically relevant, internal state variables. The resulting theory agrees accurately with the simulation data. I also propose a rationale for the observed relation between the Ising-like correlation lengths and the Vogel-Fulcher-Tamann formula.

  16. Glass transition: 'Spin' fluctuations or free volume ?

    NASA Astrophysics Data System (ADS)

    Skomski, R.

    1994-08-01

    Using a simple but statistically well-defined Langevin soft-spin model, the behaviour of suddenly quenched glasses is investigated. The non-equilibrium phase diagram is calculated and utilized to discuss the dependence of the glass-transition temperature on the ground-state properties of the material. The true ground state of the model is ordered, but the glass state remains stable below a non-equilibrium glass-transition temperature T o < T eq, where T eq is the temperature of the accompanying equilibrium phase transition. As opposed to semiphenomenological free-volume theories, it is not necessary to fall back on temperature-dependent energy barriers to explain the glass transition. To rationalize the tendency towards glass formation we derive rules analogous to those known as Zachariasen rules in the case of inorganic glasses.

  17. Temperature dependence of nonlinear optical phenomena in silica glasses

    NASA Astrophysics Data System (ADS)

    Mikami, K.; Motokoshi, S.; Fujita, M.; Jitsuno, T.; Murakami, M.

    2010-11-01

    A linear increase of the laser-induced damage thresholds in silica glasses with decreasing the temperature was reported in this conference at last year. Various nonlinear phenomena should be generated in silica glasses besides the damage in high intensity. Temperature dependences of the nonlinear refractive indices and the SBS (stimulated Brillouin scattering) thresholds in silica glasses at temperature 173 K to 473 K were measured with single-mode Q-switched Nd:YAG laser at fundamental wavelength. As the result, the nonlinear refractive indices increased with decreasing temperature. Because the change was not enough to explain the temperature dependence of laser-induced damage thresholds, the temperature dependence of nonlinear refractive indices would be negligible on laser-induced damage thresholds. On the other hand, the SBS thresholds also increased with decreasing temperature. This result means that acoustic phonons arise easily at high temperature. Probably, the SBS phenomenon is one of reasons for temperature dependence of laser-induced damage thresholds.

  18. Mechanical failure and glass transition in metallic glasses

    SciTech Connect

    Egami, Takeshi

    2011-01-01

    The current majority view on the phenomenon of mechanical failure in metallic glasses appears to be that it is caused by the activity of some structural defects, such as free-volumes or shear transformation zones, and the concentration of such defects is small, only of the order of 1%. However, the recent results compel us to revise this view. Through molecular dynamics simulation it has been shown that mechanical failure is the stress-induced glass transition. According to our theory the concentration of the liquid-like sites (defects) is well over 20% at the glass transition. We suggest that the defect concentration in metallic glasses is actually very high, and percolation of such defects causes atomic avalanche and mechanical failure. In this article we discuss the glass transition, mechanical failure and viscosity from such a point of view.

  19. Electron anions and the glass transition temperature

    PubMed Central

    Sushko, Peter V.; Tomota, Yudai; Hosono, Hideo

    2016-01-01

    Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca12Al14O32]2+ ⋅ (e–)2, we demonstrate that electron anions in this system behave as glass modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. The concentration of such electron anions is a consequential control parameter: It invokes materials evolution pathways and properties not available in conventional glasses, which opens a unique avenue in rational materials design. PMID:27559083

  20. Anomalous dynamics at the hard-sphere glass transition.

    PubMed

    Kwaśniewski, Paweł; Fluerasu, Andrei; Madsen, Anders

    2014-11-21

    We use X-ray photon correlation spectroscopy to study the dynamics of hard sphere suspensions and report the emergence of ergodicity restoring anomalous intermittent relaxation modes in the highest concentration suspension that is estimated to be above the glass transition concentration. We associate these phenomena with non-thermal stress induced relaxations and support our interpretation by a direct comparison of the results with predictions of the mode coupling theory.

  1. Fluctuating hydrodynamics and glass transition theory

    NASA Astrophysics Data System (ADS)

    Rostiashvili, V. G.

    1988-02-01

    Kawasaki's mode-coupling theory is used for deriving and solving non-linear equations of the fluctuating hydrodynamics for a simple fluid. The ergodicity-nonergodicity transition (glass transition) associated with the existence of a zero-frequency pole in the Laplace spectrum of the density correlation function has been discussed. The behaviour of the dynamical viscosity and dynamical moduli in the vicinity of transition has been studied in detail. The physical sense of the glass transition criterion has been considered, and it is compared to the percolation threshold for the overlapping spheres problem.

  2. Glass-glass transition during aging of a colloidal clay.

    PubMed

    Angelini, Roberta; Zaccarelli, Emanuela; de Melo Marques, Flavio Augusto; Sztucki, Michael; Fluerasu, Andrei; Ruocco, Giancarlo; Ruzicka, Barbara

    2014-06-02

    Colloidal suspensions are characterized by a variety of microscopic interactions, which generate unconventional phase diagrams encompassing fluid, gel and glassy states and offer the possibility to study new phase and/or state transitions. Among these, glass-glass transitions are rare to be found, especially at ambient conditions. Here, through a combination of dilution experiments, X-ray photon correlation spectroscopy, small angle X-ray scattering, rheological measurements and Monte Carlo simulations, we provide evidence of a spontaneous glass-glass transition in a colloidal clay. Two different glassy states are distinguished with evolving waiting time: a first one, dominated by long-range screened Coulombic repulsion (Wigner glass) and a second one, stabilized by orientational attractions (Disconnected House of Cards glass), occurring after a much longer time. These findings may have implications for heterogeneously charged systems out-of-equilibrium and for applications where a fine control of the local order and/or long term stability of the amorphous materials are required.

  3. Electron anions and the glass transition temperature

    SciTech Connect

    Johnson, Lewis E.; Sushko, Peter V.; Tomota, Yudai; Hosono, Hideo

    2016-08-24

    Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca12Al14O32]2+ ∙ (e)2, we demonstrate that electron anions in this system behave as glass-modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. Concentration of such electron anions is a consequential control parameter: it invokes materials evolution pathways and properties not available in conventional glasses, which opens a new avenue in rational materials design.

  4. Glass transition and physical hardening of asphalts

    NASA Astrophysics Data System (ADS)

    Kriz, Pavel

    Glass transition and physical hardening was studied in straight-run paving asphalt binders. Two methods, modulated differential scanning calorimetry and dynamic mechanical analysis, were utilized in this study. Kinetic nature of the glass transition was observed in studied asphalts. The glass transition temperature, which represents the transition, was found to be a quantity dependent on observation time and thus meaningless without observation time being specified. The glass transition of asphalts was found to be very broad on the temperature scale due to complexity of the chemical composition. Asphalts were found to be multiphase systems, with glassy amorphous, non-glassy amorphous and crystalline domains existing between approximately 10 and -45°C. Physical hardening was observed in asphalts at broad range of temperatures. Physical aging, i.e. structural relaxation of the glass, was identified as a major process contributing to physical hardening. Direct effect of crystallization was rather insignificant in the temperature range of glass transition. However, the presence of crystals was suggested to affect the molecular mobility of the amorphous phase and thus increase the hardening rate and also extent the phenomenon to higher temperatures outside the normal glass transition range. The concept of rigid amorphous phase was offered. The effect of the physical hardening could generally be reversed upon heating to higher temperature. Although for semi-crystalline asphalt, temperature higher by 50°C than the isothermal storage temperature, was found not to be sufficient to successfully reverse the hardening. Effect of thermal stress on the hardening rate was studied. It was found that the imposed stress was either not significant factor affecting the asphalt hardening or the imposed stress was too low to affect hardening rate significantly. Rheological model able to capture the dependence of relaxation times on the isothermal storage time, reference temperature

  5. Multiple reentrant glass transitions in confined hard-sphere glasses

    NASA Astrophysics Data System (ADS)

    Mandal, Suvendu; Lang, Simon; Gross, Markus; Oettel, Martin; Raabe, Dierk; Franosch, Thomas; Varnik, Fathollah

    2014-07-01

    Glass-forming liquids exhibit a rich phenomenology upon confinement. This is often related to the effects arising from wall-fluid interactions. Here we focus on the interesting limit where the separation of the confining walls becomes of the order of a few particle diameters. For a moderately polydisperse, densely packed hard-sphere fluid confined between two smooth hard walls, we show via event-driven molecular dynamics simulations the emergence of a multiple reentrant glass transition scenario upon a variation of the wall separation. Using thermodynamic relations, this reentrant phenomenon is shown to persist also under constant chemical potential. This allows straightforward experimental investigation and opens the way to a variety of applications in micro- and nanotechnology, where channel dimensions are comparable to the size of the contained particles. The results are in line with theoretical predictions obtained by a combination of density functional theory and the mode-coupling theory of the glass transition.

  6. Application of Glass Transition in Food Processing.

    PubMed

    Balasubramanian, S; Devi, Apramita; Singh, K K; Bosco, S J D; Mohite, Ashish M

    2016-01-01

    The phenomenon of glass transition has been employed to food products to study their stability. It can be applied as an integrated approach along with water activity and physical and chemical changes in food in processing and storage to determine the food stability. Also associated with the changes during agglomeration crystallization, caking, sticking, collapse, oxidation reactions, nonenzymatic browning, and microbial stability of food system. Various techniques such as Differential Scanning Calorimetry, Nuclear Magnetic Resonance, etc. have been developed to determine the glass transition temperature (Tg) of food system. Also, various theories have been applied to explain the concept of Tg and its relation to changes in food system. This review summarizes the understanding of concept of glass transition, its measurement, and application in food technology.

  7. Glass and percolation transitions in dense attractive micellar system

    NASA Astrophysics Data System (ADS)

    Mallamace, F.; Beneduci, R.; Gambadauro, P.; Lombardo, D.; Chen, S. H.

    2001-12-01

    In this work, we study a copolymer-micellar system characterized by clustering processes due to a short-range attractive interaction. This originates a percolation process and a new type of kinetic glass transition. We have studied these intriguing dynamical situations by means of an extensive set of light scattering and viscoelasticity experiments. Obtained data, in both the phenomena, are accounted for by considering in a proper way fractal clustering processes and the related scaling concepts. Near the percolation line the main role in the system structure and dynamics is played by the cluster's partial screening of hydrodynamic interaction, that behaves, on approaching the percolation threshold, dramatic effects on the rheological properties and on the density decay relaxations. The ergodic-nonergodic transition line (glass transition) is studied in terms of the intermediate scattering functions (ISF) in the frame of the mode coupling theory. The measured ISF gives evidence of a logarithmic decay on the density fluctuation followed by a power law behavior. This latter phenomenon is the signature of a high-order glass transition of the A3 type (cusp-like singularity).

  8. Superconducting Metallic Glass Transition-Edge-Sensors

    NASA Technical Reports Server (NTRS)

    Hays, Charles C. (Inventor)

    2013-01-01

    A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

  9. Critical Phenomena of the Disorder Driven Localization-Delocalization Transition

    SciTech Connect

    Ruhlander, Marc

    2002-12-31

    Metal-to-insulator transitions are generally linked to two phenomena: electron-electron correlations and disorder. Although real systems are usually responding to a mixture of both, they can be classified as undergoing a Mott-transition, if the former process dominates, or an Anderson-transition, if the latter dominates. High-Tc superconductors, e.g., are a candidate for the first class. Materials in which disorder drives the metal-to-insulator transition include doped semiconductors and amorphous materials. After briefly reviewing the previous research on transport in disordered materials and the disorder-induced metal-to-insulator transition, a summary of the model and the methods used in subsequent chapters is given.

  10. Mechanisms of Rhyolitic Glass Hydration Below the Glass Transition

    SciTech Connect

    Anovitz, Lawrence {Larry} M; Cole, David R; Fayek, Mostafa

    2008-01-01

    Although a great deal is known about the interaction between water and rhyolitic glasses and melts at temperatures above the glass transition, the nature of this interaction at lower temperatures is much more obscure. Comparisons between high- and low-temperature diffusion studies suggest that several factors play important roles under lower-temperature conditions that are not significant at higher temperatures. Water concentrations in rhyolitic glasses hydrated at low temperatures are significantly greater than in those hydrated at high temperatures and low pressures. Surface concentrations, which equilibrate quickly with the surrounding environment at high temperature, change far more slowly as temperature decreases, and may not equilibrate at room temperature for hundreds or thousands of years. Temperature extrapolations of high- and low-temperature diffusion data are not consistent, suggesting that a change in mechanism occurs. These differences may be due to the inability of "self-stress," caused by the in-diffusing species, to relax at lower temperature. Preliminary calculations suggest that the level of stress caused by glass-water interaction may be greater than the tensile strength of the glass. On a microstuctural scale, extrapolations of high-temperature Fourier transform infrared spectroscopy (FTIR) data to lower temperatures suggests that there should be little or no hydroxyl present in glasses hydrated at low temperature. Comparisons of low-temperature hydration results among SiO2, obsidian, and albite compositions show distinct differences, and features are present in the spectra that do not occur at high temperature. Analysis of H2O and D2O diffusion also suggest that mechanistic differences occur between low- and high-temperature diffusive processes.

  11. Ideal glass transitions by random pinning

    PubMed Central

    Cammarota, Chiara; Biroli, Giulio

    2012-01-01

    We study the effect of freezing the positions of a fraction c of particles from an equilibrium configuration of a supercooled liquid at a temperature T. We show that within the random first-order transition theory pinning particles leads to an ideal glass transition for a critical fraction c = cK(T) even for moderate supercooling; e.g., close to the Mode-Coupling transition temperature. First we derive the phase diagram in the T - c plane by mean field approximations. Then, by applying a real-space renormalization group method, we obtain the critical properties for |c - cK(T)| → 0, in particular the divergence of length and time scales, which are dominated by two zero-temperature fixed points. We also show that for c = cK(T) the typical distance between frozen particles is related to the static point-to-set length scale of the unconstrained liquid. We discuss what are the main differences when particles are frozen in other geometries and not from an equilibrium configuration. Finally, we explain why the glass transition induced by freezing particles provides a new and very promising avenue of research to probe the glassy state and ascertain, or disprove, the validity of the theories of the glass transition. PMID:22623524

  12. Glass transition and enthalpy relaxation of amorphous lactose glass.

    PubMed

    Haque, Md Kamrul; Kawai, Kiyoshi; Suzuki, Toru

    2006-08-14

    The glass transition temperature, T(g), and enthalpy relaxation of amorphous lactose glass were investigated by differential scanning calorimetry (DSC) for isothermal aging periods at various temperatures (25, 60, 75, and 90 degrees C) below T(g). Both T(g) and enthalpy relaxation were found to increase with increasing aging time and temperature. The enthalpy relaxation increased approximately exponentially with aging time at a temperature (90 degrees C) close to T(g) (102 degrees C). There was no significant change observed in the enthalpy relaxation around room temperature (25 degrees C) over an aging period of 1month. The Kohlrausch-Williams-Watts (KWW) model was able to fit the experimental enthalpy relaxation data well. The relaxation distribution parameter (beta) was determined to be in the range 0.81-0.89. The enthalpy relaxation time constant (tau) increased with decreasing aging temperature. The observed enthalpy relaxation data showed that molecular mobility in amorphous lactose glass was higher at temperatures closer to T(g). Lactose glass was stable for a long time at 25 degrees C. These findings should be helpful for improving the processing and storage stability of amorphous lactose and lactose containing food and pharmaceutical products.

  13. Ising spin glass that closely resembles the physical glass transition.

    PubMed

    Mansfield, Marc L

    2002-07-01

    We consider a modification of the one-dimensional Ising model in an external field in which the higher-energy spin state is assumed to be P-fold degenerate. The model shows a transition that becomes first order in the limit of infinite coupling constant. Here we report a study of the dynamical properties of the model by computer simulation in the vicinity of this transition, under the assumption that the model evolves by single spin flips with Metropolis bias, but with certain forbidden flips. The result is a model that exhibits many well-known empirical properties of the physical glass transition, including the "Kauzmann paradox," the Vogel law, stretched-exponential relaxation, and dynamic heterogeneity.

  14. Vortex-glass transition in three dimensions

    SciTech Connect

    Reger, J.D. ); Tokuyasu, T.A. ); Young, A.P. ); Fisher, M.P.A. )

    1991-10-01

    We investigate the possibility of a vortex-glass transition in a disordered type-II superconductor in a magnetic field in three dimensions by numerical studies of a simplified model. Monte Carlo simulations at finite temperature and domain-wall renormalization-group calculations at {ital T}=0 indicate that {ital d}=3 is just above the lower critical dimension {ital d}{sub {ital l}}, though the possibility that {ital d}{sub {ital l}}=3 cannot be definitely ruled out. A comparison is made with {ital XY} and Ising spin glasses. The (effective) correlation-length exponent {nu} and dynamical exponent {ital z} are in fairly good agreement with experiment.

  15. Two glass transitions in miscible polymer blends?

    SciTech Connect

    Dudowicz, Jacek; Freed, Karl F.; Douglas, Jack F.

    2014-06-28

    In contrast to mixtures of two small molecule fluids, miscible binary polymer blends often exhibit two structural relaxation times and two glass transition temperatures. Qualitative explanations postulate phenomenological models of local concentration enhancements due to chain connectivity in ideal, fully miscible systems. We develop a quantitative theory that explains qualitative trends in the dynamics of real miscible polymer blends which are never ideal mixtures. The theory is a synthesis of the lattice cluster theory of blend thermodynamics, the generalized entropy theory for glass-formation in polymer materials, and the Kirkwood-Buff theory for concentration fluctuations in binary mixtures.

  16. Comparison of disaccharide solutions across glass transition

    NASA Astrophysics Data System (ADS)

    Magazù, S.; Branca, C.; Faraone, A.; Migliardo, F.; Migliardo, P.; Romeo, G.

    2001-07-01

    Quasi-elastic neutron scattering (QENS) measurements on trehalose/H 2O and sucrose/H 2O mixtures have been carried out using the spectrometer MIBEMOL at the Laboratoire Leon Brillouin (LLB, Saclay). The study, addressed to the comparison of the vibrational properties of the two homologous disaccharide water mixtures across the glass transition, allows to characterize the different rigidity of both the disaccharide/H 2O mixtures.

  17. Evidence of a glass transition in a ten-state non-mean-field Potts glass.

    PubMed

    Andrist, Ruben S; Larson, Derek; Katzgraber, Helmut G

    2011-03-01

    Potts glasses are prototype models that have been used to understand the structural glass transition. However, in finite space dimensions a glass transition remains to be detected in the 10-state Potts glass. Using a one-dimensional model with long-range power-law interactions we present evidence that a glass transition below the upper critical dimension can exist for short-range systems at low enough temperatures. Gaining insights into the structural glass transition for short-range systems using spin models is thus potentially possible, yet difficult.

  18. Mutarotational kinetics and glass transition of lactose

    NASA Astrophysics Data System (ADS)

    Lefort, Ronan; Caron, Vincent; Willart, Jean-François; Descamps, Marc

    2006-11-01

    We report for the first time real time in situ and quantitative measurements of the mutarotation reaction of lactose in the solid state. The experiments have been performed by 13C NMR. We show that mutarotation is initiated on heating the amorphous state, and reaches chemical equilibrium close above the glass transition temperature Tg. We do not observe this transformation when starting from stable crystalline states. The final ratio of α and β anomers is 1:1, which suggests that the energy profile of the mutarotation reaction pathway in the solid state is actually different from the mechanism proposed for aqueous solution. This chemical equipartition is reached before the crystallization into the corresponding 1:1 molecular compound. These new data clearly illustrate the interrelation between the chemical molecular properties, the physical state of the material, and the relaxational dynamics of the glass.

  19. Chiral-glass transition and replica symmetry breaking of a three-dimensional heisenberg spin glass

    PubMed

    Hukushima; Kawamura

    2000-02-01

    Extensive equilibrium Monte Carlo simulations are performed for a three-dimensional Heisenberg spin glass with the nearest-neighbor Gaussian coupling to investigate its spin-glass and chiral-glass orderings. The occurrence of a finite-temperature chiral-glass transition without the conventional spin-glass order is established. Critical exponents characterizing the transition are different from those of the standard Ising spin glass. The calculated overlap distribution suggests the appearance of a peculiar type of replica-symmetry breaking in the chiral-glass ordered state.

  20. Scaling and universality in glass transition

    PubMed Central

    de Candia, Antonio; Fierro, Annalisa; Coniglio, Antonio

    2016-01-01

    Kinetic facilitated models and the Mode Coupling Theory (MCT) model B are within those systems known to exhibit a discontinuous dynamical transition with a two step relaxation. We consider a general scaling approach, within mean field theory, for such systems by considering the behavior of the density correlator 〈q(t)〉 and the dynamical susceptibility 〈q2(t)〉 − 〈q(t)〉2. Focusing on the Fredrickson and Andersen (FA) facilitated spin model on the Bethe lattice, we extend a cluster approach that was previously developed for continuous glass transitions by Arenzon et al. (Phys. Rev. E 90, 020301(R) (2014)) to describe the decay to the plateau, and consider a damage spreading mechanism to describe the departure from the plateau. We predict scaling laws, which relate dynamical exponents to the static exponents of mean field bootstrap percolation. The dynamical behavior and the scaling laws for both density correlator and dynamical susceptibility coincide with those predicted by MCT. These results explain the origin of scaling laws and the universal behavior associated with the glass transition in mean field, which is characterized by the divergence of the static length of the bootstrap percolation model with an upper critical dimension dc = 8. PMID:27221056

  1. Phenomena of solid state grain boundaries phase transition in technology

    SciTech Connect

    Minaev, Y. A.

    2015-03-30

    The results of study the phenomenon, discovered by author (1971), of the phase transition of grain boundary by the formation of two-dimensional liquid or quasi-liquid films have been done. The described phenomena of the first order phase transition (two-dimensional melting) at temperatures 0.6 – 0.9 T{sub S0} (of the solid state melting point) is a fundamental property of solid crystalline materials, which has allowed to revise radically scientific representations about a solid state of substance. Using the mathematical tools of the film thermodynamics it has been obtained the generalized equation of Clausius - Clapeyron type for two-dimensional phase transition. The generalized equation has been used for calculating grain boundary phase transition temperature T{sub Sf} of any metal, which value lies in the range of (0.55…0.86) T{sub S0}. Based on these works conclusions the develop strategies for effective forming of coatings (by thermo-chemical processing) on surface layers of functional alloys and hard metals have been made. The short overview of the results of some graded alloys characterization has been done.

  2. PREFACE: Fourh Workshop on Non-Equilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Andreozzi, Laura; Giordano, Marco; Leporini, Dino; Tosi, Mario

    2007-04-01

    round-table discussion sessions were organized to discuss issues that have special impact on our current understanding (or lack of it) of the dynamics of glass transition: 'Low-energy excitations and relaxations in glasses' and 'An assessment of current theories: interconnections and relevance to experiments'. We are very grateful to M A Ramos and R Bömer, and to P G Debenedetti and H Z Cummins for organizing and leading these two activities. Two very active and profitable poster sessions collected contributions on the themes of relaxation processes, cooperativity in polymers and mixtures, polyamorphism and water, biomaterials, relaxation, aging phenomena in thin films, confined and complex systems, and theoretical aspect, energy landscape and molecular dynamics, low temperature, glass and PT procedures, tracer dynamics, heterogeneity and relaxation in glass formers We acknowledge the generous support given to the workshop by our institutions, and in particular by Scuola Normale Superiore. The organization of the events in its beautiful rooms and corridors, as well as the lunches and coffee breaks held in its courtyard, especially favoured meetings and discussions between the participants. Several public and private Institutions have also supported our efforts and we would like to thank them warmly: they are the 'Soft Matter' Center of Rome, the INFN Section in Pisa, the CNR/INFM Polylab, and Ital Scientifica, TA Instruments, Novocontrol Technologies, Up Group, Isole e Olena. Finally, we express our gratitude to all those individuals—we mention here in particular Dr Ciro Autiero, Dr Massimo Faetti, Dr Fabio Zulli, Ms Patrizia Pucci, and Ms Caterina D'Elia—who have given their work and time to the making and running of the Workshop.

  3. The correlation between shear elastic modulus and glass transition temperature of bulk metallic glasses

    SciTech Connect

    Lu Zhibin; Li Jiangong; Shao Hang; Ni Xia; Gleiter, H.

    2009-03-02

    Based on Varshni equation, the shear elastic modulus at the glass transition temperature [G(T{sub g})] and the shear elastic modulus at 0 K [G(0)] were calculated from the elastic modulus measured at room temperature for various bulk metallic glasses (BMGs). The G(T{sub g})/G(0) ratios for various BMGs are almost the same and have a value around 0.85. This unique correlation implies that the glass transition occurs when the shear modulus of a BMG decreases to about 85% of G(0). This correlation between shear modulus and glass transition is of significance in understanding the glass transition of BMGs.

  4. Glass transition dynamics of enantiomer (+)-ibuprofen

    NASA Astrophysics Data System (ADS)

    Kim, Tae Hyun; Ko, Jae-Hyeon; Takayama, Haruki; Shibata, Tomohiko; Kojima, Seiji

    2013-02-01

    The acoustic properties and dynamic heat capacity of enantiomer (+)-Ibuprofen were investigated in a wide temperature including glassy and supercooled liquid and equilibrium liquid states. The Brillouin frequency shift and the full width at half maximum of the longitudinal acoustic waves of glassy ibuprofen exhibited clear changes at the glass transition temperature of 223 K. The fragility of (+)-Ibuprofen was determined to be 68 using the temperature dependence of relaxation time obtained from the imaginary part of the complex dynamic heat capacity. The sound velocity, the attenuation coefficient, and the thermal expansion coefficient were determined in the liquid (+)-Ibuprofen based on the measurements of the refractive index.

  5. Characterization of the glass Transition Using a Microindenter.

    DTIC Science & Technology

    1991-02-22

    Glass transition, icroindenter, Poiy(methyl methacrylate), Plasticizers 19 ABSTRACT (Continue on reverse if necessary and identify by block number) The...OFFICE OF NAVAL RESEARCH ContractN00014-85-K-0474 4ir)- It)t Technical Report No. 19 Characterization of the Glass Transition Using a Microindenter...TASK WORK UNIT ELEMENT NO NO. NO ACCESSION NO. I I TITLE (Include Security Classification) Characterization of the Glass Transition Using a icroindenter

  6. PREFACE: Dynamic crossover phenomena in water and other glass-forming liquids Dynamic crossover phenomena in water and other glass-forming liquids

    NASA Astrophysics Data System (ADS)

    Chen, Sow-Hsin; Baglioni, Piero

    2012-02-01

    protein hydration water Francesco Mallamace, Carmelo Corsaro, Piero Baglioni, Emiliano Fratini and Sow-Hsin Chen Common features in the microscopic dynamics of hydration water on organic and inorganic surfacesE Mamontov, H O'Neill, Q Zhang, W Wang and D J Wesolowski Water dynamics as affected by interaction with biomolecules and change of thermodynamic state: a neutron scattering studyA Orecchini, A Paciaroni, C Petrillo, F Sebastiani, A De Francesco and F Sacchetti Temperature dependence of structure and density for D2O confined in MCM-41-SWilliam A Kamitakahara, Antonio Faraone, Kao-Hsiang Liu and Chung-Yuan Mou Density profile of water confined in cylindrical pores in MCM-41 silicaAlan K Soper Dynamic crossover in hydration water of curing cement paste: the effect of superplasticizerHua Li, Wei-Shan Chiang, Emiliano Fratini, Francesca Ridi, Francesco Bausi, Piero Baglioni, Madhu Tyagi and Sow-Hsin Chen Water confined in MCM-41: a mode coupling theory analysisP Gallo, M Rovere and S-H Chen Computer simulations of dynamic crossover phenomena in nanoconfined waterG B Suffritti, P Demontis, J Gulín-Gonźlez and M Masia Hydrophobic nanoconfinement suppresses fluctuations in supercooled waterE G Strekalova, M G Mazza, H E Stanley and G Franzese Other glass-forming liquids Quasi-elastic neutron scattering studies of the slow dynamics of supercooled and glassy aspirinYang Zhang, Madhusudan Tyagi, Eugene Mamontov and Sow-Hsin Chen Colloids Phase diagram of trivalent and pentavalent patchy particlesFlavio Romano, Eduardo Sanz, Piero Tartaglia and Francesco Sciortino Distinguishing the monomer to cluster phase transition in concentrated lysozyme solutions by studying the temperature dependence of the short-time dynamicsPéter Falus, Lionel Porcar, Emiliano Fratini, Wei-Ren Chen, Antonio Faraone, Kunlun Hong, Piero Baglioni and Yun Liu Contrast variation in spin-echo small angle neutron scatteringXin Li, Bin Wu, Yun Liu, Roger Pynn, Chwen-Yang Shew, Gregory S Smith, Kenneth W

  7. Structural relaxation phenomena in silicate glasses modified by irradiation with femtosecond laser pulses

    PubMed Central

    Seuthe, Thomas; Mermillod-Blondin, Alexandre; Grehn, Moritz; Bonse, Jörn; Wondraczek, Lothar; Eberstein, Markus

    2017-01-01

    Structural relaxation phenomena in binary and multicomponent lithium silicate glasses were studied upon irradiation with femtosecond (fs) laser pulses (800 nm central wavelength, 130 fs pulse duration) and subsequent thermal annealing experiments. Depending on the annealing temperature, micro-Raman spectroscopy analyses evidenced different relaxation behaviours, associated to bridging and non-bridging oxygen structures present in the glass network. The results indicate that the mobility of lithium ions is an important factor during the glass modification with fs-laser pulses. Quantitative phase contrast imaging (spatial light interference microscopy) revealed that these fs-laser induced structural modifications are closely related to local changes in the refractive index of the material. The results establish a promising strategy for tailoring fs-laser sensitivity of glasses through structural mobility. PMID:28266615

  8. Structural relaxation phenomena in silicate glasses modified by irradiation with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Seuthe, Thomas; Mermillod-Blondin, Alexandre; Grehn, Moritz; Bonse, Jörn; Wondraczek, Lothar; Eberstein, Markus

    2017-03-01

    Structural relaxation phenomena in binary and multicomponent lithium silicate glasses were studied upon irradiation with femtosecond (fs) laser pulses (800 nm central wavelength, 130 fs pulse duration) and subsequent thermal annealing experiments. Depending on the annealing temperature, micro-Raman spectroscopy analyses evidenced different relaxation behaviours, associated to bridging and non-bridging oxygen structures present in the glass network. The results indicate that the mobility of lithium ions is an important factor during the glass modification with fs-laser pulses. Quantitative phase contrast imaging (spatial light interference microscopy) revealed that these fs-laser induced structural modifications are closely related to local changes in the refractive index of the material. The results establish a promising strategy for tailoring fs-laser sensitivity of glasses through structural mobility.

  9. Approaching the Glass Transition from Various Directions

    NASA Astrophysics Data System (ADS)

    Lipson, Jane

    2015-03-01

    In recent years a significant amount of experimental work has appeared on glassy systems, both polymeric and small molecule. However, this rich explosion in data has not been met with a concomitant leap in fundamental understanding. We have developed a number of approaches to elucidate some of the underlying mechanisms of behaviour in bulk and confined glassy systems. Using our Limited Mobility (LM) coarse-grained simulation model we have characterized the dynamic heterogeneity associated with approaching the glass transition, explored interfacial behaviour when layering materials of differing mobility, and analyzed the effect of a free surface on a supported thin film. Approaching related problems from a different direction we have modified a simple thermodynamic description of the bulk to account for missing interactions at a film surface, and substrate interactions in the case of supported films. Characterizing the systems via bulk data alone, we find our film-averaged predictions for the effects of confinement agree well with experimental data on several freestanding and supported polymer films. That work deals with confined systems; a fundamental understanding of bulk glass transitions also remains incomplete. Most recently we have been applying our Locally Correlated Lattice (LCL) equation of state model, which has met with success in modeling polymer melt and mixture behaviour, to reveal hints of the underlying glassy nature of a bulk polymer sample, even while above its transition temperature (Tg). Correlations between Tg and a variety of equilibrium bulk quantities have lead us to make connections not only with a substantive amount of experimental data on a wide range of polymers, but also with other models of glassy polymeric systems. This talk will comprise an efficient summary of past progress from these different directions, and will then focus on our most recent results and current understanding. This work has been supported by NSF-DMR and GAANN.

  10. Intermolecular forces and the glass transition.

    PubMed

    Hall, Randall W; Wolynes, Peter G

    2008-01-17

    Random first-order transition theory is used to determine the role of attractive and repulsive interactions in the dynamics of supercooled liquids. Self-consistent phonon theory, an approximate mean field treatment consistent with random first-order transition theory, is used to treat individual glassy configurations, whereas the liquid phase is treated using common liquid-state approximations. Free energies are calculated using liquid-state perturbation theory. The transition temperature, T*A, the temperature where the onset of activated behavior is predicted by mean field theory; the lower crossover temperature, T*C, where barrierless motions actually occur through fractal or stringy motions (corresponding to the phenomenological mode coupling transition temperature); and T*K, the Kauzmann temperature (corresponding to an extrapolated entropy crisis), are calculated in addition to T*g, the glass transition temperature that corresponds to laboratory cooling rates. Relationships between these quantities agree well with existing experimental and simulation data on van der Waals liquids. Both the isobaric and isochoric behavior in the supercooled regime are studied, providing results for DeltaCV and DeltaCp that can be used to calculate the fragility as a function of density and pressure, respectively. The predicted variations in the alpha-relaxation time with temperature and density conform to the empirical density-temperature scaling relations found by Casalini and Roland. We thereby demonstrate the microscopic origin of their observations. Finally, the relationship first suggested by Sastry between the spinodal temperature and the Kauzmann temperatures, as a function of density, is examined. The present microscopic calculations support the existence of an intersection of these two temperatures at sufficiently low temperatures.

  11. The Glass Transition of Driven Molecular Materials

    NASA Astrophysics Data System (ADS)

    Descamps, M.; Willart, J. F.; Aumelas, A.

    2008-02-01

    There are many cases of practical interest where materials are maintained in nonequilibrium conditions by some external dynamical forcing: typical examples of these driven materials are provided by irradiation, grinding, extrusion…Contrary to usual phase transitions which are properly addressed by thermal equilibrium states, equilibrium and irreversible thermodynamics, no such general framework is available for driven systems. The purpose of this paper is to show some examples of phase transformations in driven molecular materials. These materials are considered because they are extremely sensitive to external disturbances and are generally very good glass formers. This allows investigating more easily a broad range of the parameters which possibly influence the nature of the end product. We will examine mainly the effect of grinding. Contrary to other materials, metals or minerals, systematic investigations of transformations induced by grinding of molecular materials have not yet been done despite the practical and fundamental interests of such investigations in pharmaceutical and agro-chemical science. We will address several modes of interconversions between crystalline and glassy states of the same compound. We will further discuss specific processing effects on the physical state of the glass itself. It will be shown from these investigations that rationalization and possibilities of prediction are emerging. The use of effective temperature concepts to describe the end product of milling will be discussed. These findings may be of general concern for driven materials of any chemical nature.

  12. Dynamics and thermodynamics of the glass transition

    SciTech Connect

    Langer, J.S.

    2006-04-15

    The principal theme of this paper is that anomalously slow, super-Arrhenius relaxations in glassy materials may be activated processes involving chains of molecular displacements. As pointed out in a preceding paper with Lemaitre, the entropy of critically long excitation chains can enable them to grow without bound, thus activating stable thermal fluctuations in the local density or molecular coordination of the material. I argue here that the intrinsic molecular-scale disorder in a glass plays an essential role in determining the activation rate for such chains, and show that a simple disorder-related correction to the earlier theory recovers the Vogel-Fulcher law in three dimensions. A key feature of this theory is that the spatial extent of critically long excitation chains diverges at the Vogel-Fulcher temperature. I speculate that this diverging length scale implies that, as the temperature decreases, increasingly large regions of the system become frozen and do not contribute to the configurational entropy, and thus ergodicity is partially broken in the super-Arrhenius region above the Kauzmann temperature T{sub K}. This partially broken ergodicity seems to explain the vanishing entropy at T{sub K} and other observed relations between dynamics and thermodynamics at the glass transition.

  13. Dynamics and thermodynamics of the glass transition.

    PubMed

    Langer, J S

    2006-04-01

    The principal theme of this paper is that anomalously slow, super-Arrhenius relaxations in glassy materials may be activated processes involving chains of molecular displacements. As pointed out in a preceding paper with Lemaitre, the entropy of critically long excitation chains can enable them to grow without bound, thus activating stable thermal fluctuations in the local density or molecular coordination of the material. I argue here that the intrinsic molecular-scale disorder in a glass plays an essential role in determining the activation rate for such chains, and show that a simple disorder-related correction to the earlier theory recovers the Vogel-Fulcher law in three dimensions. A key feature of this theory is that the spatial extent of critically long excitation chains diverges at the Vogel-Fulcher temperature. I speculate that this diverging length scale implies that, as the temperature decreases, increasingly large regions of the system become frozen and do not contribute to the configurational entropy, and thus ergodicity is partially broken in the super-Arrhenius region above the Kauzmann temperature T(K). This partially broken ergodicity seems to explain the vanishing entropy at T(K) and other observed relations between dynamics and thermodynamics at the glass transition.

  14. Quantitative field theory of the glass transition

    PubMed Central

    Franz, Silvio; Jacquin, Hugo; Parisi, Giorgio; Urbani, Pierfrancesco; Zamponi, Francesco

    2012-01-01

    We develop a full microscopic replica field theory of the dynamical transition in glasses. By studying the soft modes that appear at the dynamical temperature, we obtain an effective theory for the critical fluctuations. This analysis leads to several results: we give expressions for the mean field critical exponents, and we analytically study the critical behavior of a set of four-points correlation functions, from which we can extract the dynamical correlation length. Finally, we can obtain a Ginzburg criterion that states the range of validity of our analysis. We compute all these quantities within the hypernetted chain approximation for the Gibbs free energy, and we find results that are consistent with numerical simulations. PMID:23112202

  15. Glass transition temperature and its relevance in food processing.

    PubMed

    Roos, Yrjö H

    2010-01-01

    Amorphous, noncrystalline solids are typical of low water content and frozen foods. Solids in these foods, e.g., confectionary, dehydrated foods, cereal foods, and frozen foods, often form nonequilibrium glass-like structures. The glassy state of the solids forms during food processing in a reversible glass transition. Vitrification can occur in numerous glassy states that exhibit various relaxations around the glass transition. The success of freeze drying, spray drying, and extrusion and the stability of dehydrated foods against flow, collapse, and crystallization is based on the control of the glassy state during the dehydration process and storage. Encapsulation processes often use glass-forming materials to entrap dispersed components or improve retention of volatiles. Plasticization of the noncrystalline structures by temperature or water reduce relaxation times exponentially above the glass transition, which results in rapid deterioration. Critical values for water activity and water content express the level of water plasticization leading to glass transition in food storage.

  16. Echoes of the Glass Transition in Athermal Soft Spheres

    NASA Astrophysics Data System (ADS)

    Morse, Peter K.; Corwin, Eric I.

    2017-09-01

    Recent theoretical advances have led to the creation of a unified phase diagram for the thermal glass and athermal jamming transitions. This diagram makes clear that, while related, the mode-coupling—or dynamic—glass transition is distinct from the jamming transition, occurring at a finite temperature and significantly lower density than the jamming transition. Nonetheless, we demonstrate a prejamming transition in athermal frictionless spheres which occurs at the same density as the mode-coupling transition and is marked by percolating clusters of locally rigid particles. At this density in both the thermal and athermal systems, individual motions of an extensive number of particles become constrained, such that only collective motion is possible. This transition, which is well below jamming, exactly matches the definition of collective behavior at the dynamical transition of glasses. Thus, we reveal that the genesis of rigidity in both thermal and athermal systems is governed by the same underlying topological transition in their shared configuration space.

  17. Theoretical study of production of unique glasses in space. [kinetic relationships describing nucleation and crystallization phenomena

    NASA Technical Reports Server (NTRS)

    Larsen, D. C.; Sievert, J. L.

    1975-01-01

    The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate.

  18. Predicting the glass transition temperature of bioactive glasses from their molecular chemical composition.

    PubMed

    Hill, Robert G; Brauer, Delia S

    2011-10-01

    A recently published paper (M.D. O'Donnell, Acta Biomaterialia 7 (2011) 2264-2269) suggests that it is possible to correlate the glass transition temperature (T(g)) of bioactive glasses with their molar composition, based on iterative least-squares fitting of published T(g) data. However, we show that the glass structure is an important parameter in determining T(g). Phase separation, local structural effects and components (intermediate oxides) which can switch their structural role in the glass network need to be taken into consideration, as they are likely to influence the glass transition temperature of bioactive glasses. Although the model suggested by O'Donnell works reasonably well for glasses within the composition range presented, it is oversimplified and fails for glasses outside certain compositional boundaries.

  19. Glass transition in fullerenes: mode-coupling theory predictions.

    PubMed

    Greenall, M J; Voigtmann, Th

    2006-11-21

    We report idealized mode-coupling theory results for the glass transition of ensembles of model fullerenes interacting via phenomenological two-body potentials. Transition lines are found for C60, C70, and C96 in the temperature-density plane. We argue that the observed glass transition behavior is indicative of kinetic arrest that is strongly driven by the interparticle attraction in addition to excluded-volume repulsion. In this respect, these systems differ from most standard glass-forming liquids. They feature arrest that occurs at lower densities and that is stronger than would be expected for repulsion-dominated hard-sphere-like or Lennard-Jones-type systems. The influence of attraction increases with increasing the number of carbon atoms per molecule. However, unrealistically large fullerenes would be needed to yield behavior reminiscent of recently investigated model colloids with strong short-ranged attraction (glass-glass transitions and logarithmic decay of time-correlation functions).

  20. Glass transition in fullerenes: Mode-coupling theory predictions

    NASA Astrophysics Data System (ADS)

    Greenall, M. J.; Voigtmann, Th.

    2006-11-01

    We report idealized mode-coupling theory results for the glass transition of ensembles of model fullerenes interacting via phenomenological two-body potentials. Transition lines are found for C60, C70, and C96 in the temperature-density plane. We argue that the observed glass transition behavior is indicative of kinetic arrest that is strongly driven by the interparticle attraction in addition to excluded-volume repulsion. In this respect, these systems differ from most standard glass-forming liquids. They feature arrest that occurs at lower densities and that is stronger than would be expected for repulsion-dominated hard-sphere-like or Lennard-Jones-type systems. The influence of attraction increases with increasing the number of carbon atoms per molecule. However, unrealistically large fullerenes would be needed to yield behavior reminiscent of recently investigated model colloids with strong short-ranged attraction (glass-glass transitions and logarithmic decay of time-correlation functions).

  1. The glass transition in high-density amorphous ice

    PubMed Central

    Loerting, Thomas; Fuentes-Landete, Violeta; Handle, Philip H.; Seidl, Markus; Amann-Winkel, Katrin; Gainaru, Catalin; Böhmer, Roland

    2015-01-01

    There has been a long controversy regarding the glass transition in low-density amorphous ice (LDA). The central question is whether or not it transforms to an ultraviscous liquid state above 136 K at ambient pressure prior to crystallization. Currently, the most widespread interpretation of the experimental findings is in terms of a transformation to a superstrong liquid above 136 K. In the last decade some work has also been devoted to the study of the glass transition in high-density amorphous ice (HDA) which is in the focus of the present review. At ambient pressure HDA is metastable against both ice I and LDA, whereas at > 0.2 GPa HDA is no longer metastable against LDA, but merely against high-pressure forms of crystalline ice. The first experimental observation interpreted as the glass transition of HDA was made using in situ methods by Mishima, who reported a glass transition temperature Tg of 160 K at 0.40 GPa. Soon thereafter Andersson and Inaba reported a much lower glass transition temperature of 122 K at 1.0 GPa. Based on the pressure dependence of HDA's Tg measured in Innsbruck, we suggest that they were in fact probing the distinct glass transition of very high-density amorphous ice (VHDA). Very recently the glass transition in HDA was also observed at ambient pressure at 116 K. That is, LDA and HDA show two distinct glass transitions, clearly separated by about 20 K at ambient pressure. In summary, this suggests that three glass transition lines can be defined in the p–T plane for LDA, HDA, and VHDA. PMID:25641986

  2. Thermodynamic signature of the dynamic glass transition in hard spheres.

    PubMed

    Hermes, Michiel; Dijkstra, Marjolein

    2010-03-17

    We use extensive event-driven molecular dynamics simulations to study the thermodynamic, structural and dynamic properties of hard-sphere glasses. We determine the equation of state of the metastable fluid branch for hard spheres with a size polydispersity of 10%. Our results show a clear jump in the slope of the isothermal compressibility. The observation of a thermodynamic signature at the transition from a metastable fluid to a glassy state is analogous to the abrupt change in the specific heat or thermal expansion coefficient as observed for molecular liquids at the glass transition. The dynamic glass transition becomes more pronounced and shifts to higher densities for longer equilibration times.

  3. Estimation of the critical glass transition rate and the inorganic glass thickness

    NASA Astrophysics Data System (ADS)

    Belousov, O. K.

    2009-12-01

    Procedures are described for calculating the components of a new equation obtained to estimate critical glass transition rate R c . Reported data on R c are used to calculate critical shear frequency ν t, g( m), and a technique of its calculation using absolute entropy and elastic constants is presented. Procedures for calculating the energy of defect formation in amorphous substances H ν and for estimating glass transition temperature T g are described. It is shown that the ratio H ν / q (where q = N A k BΔ T m-g , N A is Avogadro’s number, k B is the Boltzmann constant, and Δ T m-g is the difference between the melting and glass transition temperatures) can be used to estimate critical glass transition rate R c and critical glass thickness h c .

  4. The Liquid Glass Transition in Sugars and Sugar Mixtures

    NASA Astrophysics Data System (ADS)

    Seo, Jeong-Ah; Oh, Jiyoung; Kwon, Hyun-Joung; Kim, Hyung Kook; Hwang, Yoon-Hwae

    2006-05-01

    The liquid-glass transition in sugars and sugar mixtures was studied with calorimetry, Brillouin scattering, and dielectric spectroscopy. Sugars are particular interest among other glass forming materials because sugars are main constitution of the biological system and sugar glasses play an important role in preservation and protection of biological cells. We studied a number of sugars and sugar mixtures including glucose, galactose, sucrose, maltose, trehalose, glucose/sucrose, sucrose/trehalose, using calorimetry (DTA and DSC), Brillouin scattering, and dielectric spectroscopy. We found the following: (1) Brillouin scattering technique can be used to determine the glass transition temperature. (2) In sugar mixtures, the volume compression effect from the molecule size and shape played an important role in the glass transition temperature. (3) The origin of the secondary relaxation in glucose-water mixtures maybe relate to the rotation-translation coupling constant in the schematic mode coupling theory.

  5. Liquid-Liquid Phase Transition and Glass Transition in a Monoatomic Model System

    PubMed Central

    Xu, Limei; Buldyrev, Sergey V.; Giovambattista, Nicolas; Stanley, H. Eugene

    2010-01-01

    We review our recent study on the polyamorphism of the liquid and glass states in a monatomic system, a two-scale spherical-symmetric Jagla model with both attractive and repulsive interactions. This potential with a parametrization for which crystallization can be avoided and both the glass transition and the liquid-liquid phase transition are clearly separated, displays water-like anomalies as well as polyamorphism in both liquid and glassy states, providing a unique opportunity to study the interplay between the liquid-liquid phase transition and the glass transition. Our study on a simple model may be useful in understanding recent studies of polyamorphism in metallic glasses. PMID:21614201

  6. Thermodynamic consequences of the kinetic nature of the glass transition.

    PubMed

    Koperwas, Kajetan; Grzybowski, Andrzej; Tripathy, Satya N; Masiewicz, Elzbieta; Paluch, Marian

    2015-12-10

    In this paper, we consider the glass transition as a kinetic process and establish one universal equation for the pressure coefficient of the glass transition temperature, dTg/dp, which is a thermodynamic characteristic of this process. Our findings challenge the common previous expectations concerning key characteristics of the transformation from the liquid to the glassy state, because it suggests that without employing an additional condition, met in the glass transition, derivation of the two independent equations for dTg/dp is not possible. Hence, the relation among the thermodynamic coefficients, which could be equivalent to the well-known Prigogine-Defay ratio for the process under consideration, cannot be obtained. Besides, by comparing the predictions of our universal equation for dTg/dp and Ehrenfest equations, we find the aforementioned supplementary restriction, which must be met to use the Prigogine-Defay ratio for the glass transition.

  7. An Overview of the Glass Transition Temperature of Synthetic Polymers.

    ERIC Educational Resources Information Center

    Beck, Keith R.; And Others

    1984-01-01

    Presents an overview of the glass-to-rubber transition, what it is, why it is important, and the major factors that influence it. Indicates that this information should be incorporated into chemistry curricula. (JN)

  8. Thermodynamic glass transition in a spin glass without time-reversal symmetry.

    PubMed

    Baños, Raquel Alvarez; Cruz, Andres; Fernandez, Luis Antonio; Gil-Narvion, Jose Miguel; Gordillo-Guerrero, Antonio; Guidetti, Marco; Iñiguez, David; Maiorano, Andrea; Marinari, Enzo; Martin-Mayor, Victor; Monforte-Garcia, Jorge; Muñoz Sudupe, Antonio; Navarro, Denis; Parisi, Giorgio; Perez-Gaviro, Sergio; Ruiz-Lorenzo, Juan Jesus; Schifano, Sebastiano Fabio; Seoane, Beatriz; Tarancon, Alfonso; Tellez, Pedro; Tripiccione, Raffaele; Yllanes, David

    2012-04-24

    Spin glasses are a longstanding model for the sluggish dynamics that appear at the glass transition. However, spin glasses differ from structural glasses in a crucial feature: they enjoy a time reversal symmetry. This symmetry can be broken by applying an external magnetic field, but embarrassingly little is known about the critical behavior of a spin glass in a field. In this context, the space dimension is crucial. Simulations are easier to interpret in a large number of dimensions, but one must work below the upper critical dimension (i.e., in d < 6) in order for results to have relevance for experiments. Here we show conclusive evidence for the presence of a phase transition in a four-dimensional spin glass in a field. Two ingredients were crucial for this achievement: massive numerical simulations were carried out on the Janus special-purpose computer, and a new and powerful finite-size scaling method.

  9. Thermodynamic glass transition in a spin glass without time-reversal symmetry

    PubMed Central

    Baños, Raquel Alvarez; Cruz, Andres; Fernandez, Luis Antonio; Gil-Narvion, Jose Miguel; Gordillo-Guerrero, Antonio; Guidetti, Marco; Iñiguez, David; Maiorano, Andrea; Marinari, Enzo; Martin-Mayor, Victor; Monforte-Garcia, Jorge; Muñoz Sudupe, Antonio; Navarro, Denis; Parisi, Giorgio; Perez-Gaviro, Sergio; Ruiz-Lorenzo, Juan Jesus; Schifano, Sebastiano Fabio; Seoane, Beatriz; Tarancon, Alfonso; Tellez, Pedro; Tripiccione, Raffaele; Yllanes, David

    2012-01-01

    Spin glasses are a longstanding model for the sluggish dynamics that appear at the glass transition. However, spin glasses differ from structural glasses in a crucial feature: they enjoy a time reversal symmetry. This symmetry can be broken by applying an external magnetic field, but embarrassingly little is known about the critical behavior of a spin glass in a field. In this context, the space dimension is crucial. Simulations are easier to interpret in a large number of dimensions, but one must work below the upper critical dimension (i.e., in d < 6) in order for results to have relevance for experiments. Here we show conclusive evidence for the presence of a phase transition in a four-dimensional spin glass in a field. Two ingredients were crucial for this achievement: massive numerical simulations were carried out on the Janus special-purpose computer, and a new and powerful finite-size scaling method. PMID:22493229

  10. Mechanical spectrum study of glass transition by a composite method

    NASA Astrophysics Data System (ADS)

    Yuan, Y. H.; Zhang, L.; Wang, X. L.; Ying, X. N.; Yan, F.; Huang, Y. N.; Zhu, J. S.; Wang, Y. N.

    2009-11-01

    Normalized mechanical spectra of glycerol, 1,2-propanediol carbonate and poly(vinyl chloride)/di(2-ethyl-hexyl) phthalate (PVC/DOP) blends were studied in the temperature range from 100 to 300 K by a composite method. The dynamic glass transition was observed, which exhibits a peak of temperature-dependent loss modulus. The peak moves toward higher temperature with higher measuring frequency, which accords with the relaxation feature of the dynamic glass transition. Another characteristic temperature can be marked in the mechanical spectrum by the onset of storage modulus change, which is labeled as T gm. T gm is found to be nearly equal to the calorimetric glass transition temperature in glycerol, 1,2-propanediol carbonate and di(2-ethyl-hexyl) phthalate. As we expected, this onset temperature in the mechanical spectrum has an intimate relation with the calorimetric glass transition of materials, and it can be regarded as a representative when the calorimetric glass transition temperature is not available. Finally, normalized mechanical spectra of PVC/DOP blends with different PVC content were obtained and mechanical glass transition temperatures T gm were determined.

  11. Observing the Twinkling Fractal Nature of the Glass Transition

    NASA Astrophysics Data System (ADS)

    Stanzione, Joseph, III; Wool, Richard; Strawhecker, Kenneth

    2010-03-01

    The main idea underlying the Twinkling Fractal Theory (TFT) of the glass transition is the development of dynamic percolating solid fractal structures near Tg, which are in dynamic equilibrium with the surrounding liquid. Solid and liquid clusters interchange at a frequency φTF, which is controlled by the population of intermolecular oscillators in excited energy levels in accord with the Orbach vibrational density of states for a particular fractal cluster g(φ) ˜ φ^df-1, where the fracton dimension df = 4/3. To an observer, these clusters would appear to be ``twinkling.'' A time-lapse tapping-mode atomic force microscopy (AFM) technique has been developed in order to experimentally confirm such phenomena. The twinkling behavior of amorphous, atactic polystyrene with MW = 194,000 g/mol, PDI = 1.07 (GPC) and Tg = 375 K (DSC-heating rate of 3 K/min) has been captured above (383 K), below (358 K), and well below (298 K) its Tg. Two-dimensional space images reveal fractal dimensions consistent with the TFT. The twinkling behavior was analyzed using a statistical autocorrelation function in conjunction with the apparent stretched exponential Kohlrausch-Williams-Watts relaxation function.

  12. Kinetic criteria of glass formation and the pressure dependence of the glass transition temperature.

    PubMed

    Schmelzer, Jürn W P

    2012-02-21

    An overview on different attempts of formulation of kinetic criteria of glass formation is given. It is analyzed which of the characteristic time scales-time of observation, time of relaxation, and time of change of external parameters-have to be employed to appropriately develop such criteria. Based on this analysis, a general model-independent kinetic criterion for glass formation is formulated. As a first consequence, it is shown that it is not-as often claimed-the Deborah number which governs glass formation. Based on this general kinetic criterion for glass formation, general expressions for the dependence of the glass transition temperature on pressure (and vice versa) are obtained being essentially ratios of the partial derivatives of the appropriate relaxation times with respect to pressure and temperature, respectively. Employing, as examples, further two different (free volume and entropy based) models for the description of viscous flow and relaxation, respectively, relations similar but, in general, not identical to the classical Ehrenfest relations describing second-order equilibrium phase transitions are obtained. In this way, it can be explained why one of the Ehrenfest's relations is usually fulfilled in glass transition and the other not and why the Prigogine-Defay ratio in glass transition is not equal to one as this is the case with Ehrenfest's ratio in second-order equilibrium phase transitions. © 2012 American Institute of Physics

  13. Strain glass state as the boundary of two phase transitions

    PubMed Central

    Zhou, Zhijian; Cui, Jian; Ren, Xiaobing

    2015-01-01

    A strain glass state was found to be located between B2-B19’ (cubic to monoclinic) phase transition and B2-R (cubic to rhombohedral) phase transition in Ti49Ni51 alloys after aging process. After a short time aging, strong strain glass transition was observed, because the size of the precipitates is small, which means the strain field induced by the precipitates is isotropic and point-defect-like, and the distribution of the precipitates is random. After a long time aging, the average size of the precipitates increases. The strong strain field induced by the precipitates around them forces the symmetry of the matrix materials to conform to the symmetry of the crystalline structure of the precipitates, which results in the new phase transition. The experiment shows that there exists no well-defined boundary in the evolution from the strain glass transition to the new phase transition. Due to its generality, this glass mediated phase transition divergence scheme can be applied to other proper material systems to induce a more important new phase transition path, which can be useful in the field of phase transition engineering. PMID:26307500

  14. Temperature range of the liquid-glass transition

    NASA Astrophysics Data System (ADS)

    Sanditov, D. S.; Darmaev, M. V.; Sanditov, B. D.

    2016-02-01

    It has been shown that the currently used method for calculating the temperature range of δ T g in the glass transition equation qτ g = δ T g as the difference δ T g = ( T 12- T 13) results in overestimated values, which is explained by the assumption of a constant activation energy of glass transition in deriving the calculation equation ( T 12 and T 13 are the temperatures corresponding to the logarithmic viscosity values of logη = 12 and logη = 13). The methods for the evaluation of δ T g using the Williams-Landel-Ferry equation and the model of delocalized atoms are considered, the results of which are in satisfactory agreement with the product qτ g ( q is the cooling rate of the melt and τ g is the structural relaxation time at the glass transition temperature). The calculation of τ g for inorganic glasses and amorphous organic polymers is proposed.

  15. From Gelation and Glass Transition of Colloidal Systems to Polymers

    NASA Astrophysics Data System (ADS)

    Han, Charles; Yuan, Guangcui; Cheng, He

    Charles C. Han, Guangcui Yuan and He Cheng Joint Laboratory of Polymer Science and Materials, ICCAS, Beijing, China and Institute for Advanced Study, Shenzhen University, Shenzhen, China Aggregation and gelation behavior of mixed suspensions of polystyrene microspheres and poly(N-isopropylacrylamide) microgels have been studied. In dilute microsphere suspensions, with increasing concentration of microgel (MG), microspheres (MS) first aggregated with each other through the bridging of the microgels, then dispersed individually when saturated adsorption was achieved, and finally depletion clusters formed at even higher concentrations of microgel. In concentrated microsphere suspensions, with saturated MG adsorption, a state transition from attractive glass to repulsive glass can be observed. This type of system can be viewed as a molecular model system which has a long range repulsive interaction potential and a short range attractive potential. A comparison between the glass transition of the colloidal systems and the glass transition of polymeric systems can be made.

  16. Transit Scratchitti Removal and Glass Resurfacing by Controlled Fire Polishing

    NASA Astrophysics Data System (ADS)

    Jun, Seongchan; Hong, Shane Y.

    Scratchitti vandalism, a new type of graffiti vandalism, in public transits systems and city neighborhood is a serious problem. To solve this problem, an innovative approach was developed-controlled fire polishing, which incorporates a technique of localized softening and surface tension. Intensive heat is positioned near to the scratch marks on the glass panel. The heat melts a thin layer of glass into liquid, changing the glass’s viscosity to a formable state. The glass is melted to a level close to the depth of the scratch, and allowed to cool down naturally. During the cooling process, the surface tension of the melted glass will even out the scratching indent. After cooling, the glass will be as even and smooth as it was originally. The process will enable the reuse of the damaged window/door and eliminate the otherwise waste by replacement new glass.

  17. Spin-glass transition of the three-dimensional Heisenberg spin glass.

    PubMed

    Campos, I; Cotallo-Aban, M; Martin-Mayor, V; Perez-Gaviro, S; Tarancon, A

    2006-11-24

    It is shown, by means of Monte Carlo simulation and finite size scaling analysis, that the Heisenberg spin glass undergoes a finite-temperature phase transition in three dimensions. There is a single critical temperature, at which both a spin glass and a chiral glass ordering develop. The Monte Carlo algorithm, adapted from lattice gauge theory simulations, makes it possible to thermalize lattices of size L = 32, larger than in any previous spin-glass simulation in three dimensions. High accuracy is reached thanks to the use of the Marenostrum supercomputer. The large range of system sizes studied allows us to consider scaling corrections.

  18. Slowdown of Interhelical Motions Induces a Glass Transition in RNA.

    PubMed

    Frank, Aaron T; Zhang, Qi; Al-Hashimi, Hashim M; Andricioaei, Ioan

    2015-06-16

    RNA function depends crucially on the details of its dynamics. The simplest RNA dynamical unit is a two-way interhelical junction. Here, for such a unit--the transactivation response RNA element--we present evidence from molecular dynamics simulations, supported by nuclear magnetic resonance relaxation experiments, for a dynamical transition near 230 K. This glass transition arises from the freezing out of collective interhelical motional modes. The motions, resolved with site-specificity, are dynamically heterogeneous and exhibit non-Arrhenius relaxation. The microscopic origin of the glass transition is a low-dimensional, slow manifold consisting largely of the Euler angles describing interhelical reorientation. Principal component analysis over a range of temperatures covering the glass transition shows that the abrupt slowdown of motion finds its explanation in a localization transition that traps probability density into several disconnected conformational pools over the low-dimensional energy landscape. Upon temperature increase, the probability density pools then flood a larger basin, akin to a lakes-to-sea transition. Simulations on transactivation response RNA are also used to backcalculate inelastic neutron scattering data that match previous inelastic neutron scattering measurements on larger and more complex RNA structures and which, upon normalization, give temperature-dependent fluctuation profiles that overlap onto a glass transition curve that is quasi-universal over a range of systems and techniques.

  19. A simple method for tuning the glass transition process in inorganic phosphate glasses

    PubMed Central

    Fulchiron, René; Belyamani, Imane; Otaigbe, Joshua U.; Bounor-Legaré, Véronique

    2015-01-01

    The physical modification of glass transition temperature (Tg) and properties of materials via blending is a common practice in industry and academia and has a large economic advantage. In this context, simple production of hitherto unattainable new inorganic glass blends from already existing glass compositions via blending raises much hope with the potential to provide new glasses with new and improved properties, that cannot be achieved with classical glass synthesis, for a plethora of applications such as computers screens, glass-to-metal seals, and storage materials for nuclear wastes. Here, we demonstrate that blends of the specific glass compositions studied are miscible in all proportions, an unreported phenomenon in hard condensed matter like glass. Interestingly, excellent agreement was found between the obtained data and calculated Tgs from theoretical equations (Supplementary information) for predicting the composition dependence of Tg for miscible blends with weak but significant specific interactions between the blend components. That this blending method is at present not applied to inorganic glasses reflects the fact that water and chemically resistant phosphate glasses with relatively low Tgs have become available only recently. PMID:25666949

  20. A simple method for tuning the glass transition process in inorganic phosphate glasses

    NASA Astrophysics Data System (ADS)

    Fulchiron, René; Belyamani, Imane; Otaigbe, Joshua U.; Bounor-Legaré, Véronique

    2015-02-01

    The physical modification of glass transition temperature (Tg) and properties of materials via blending is a common practice in industry and academia and has a large economic advantage. In this context, simple production of hitherto unattainable new inorganic glass blends from already existing glass compositions via blending raises much hope with the potential to provide new glasses with new and improved properties, that cannot be achieved with classical glass synthesis, for a plethora of applications such as computers screens, glass-to-metal seals, and storage materials for nuclear wastes. Here, we demonstrate that blends of the specific glass compositions studied are miscible in all proportions, an unreported phenomenon in hard condensed matter like glass. Interestingly, excellent agreement was found between the obtained data and calculated Tgs from theoretical equations (Supplementary information) for predicting the composition dependence of Tg for miscible blends with weak but significant specific interactions between the blend components. That this blending method is at present not applied to inorganic glasses reflects the fact that water and chemically resistant phosphate glasses with relatively low Tgs have become available only recently.

  1. On relaxation nature of glass transition in amorphous materials

    NASA Astrophysics Data System (ADS)

    Sanditov, Damba S.; Ojovan, Michael I.

    2017-10-01

    A short review on relaxation theories of glass transition is presented. The main attention is paid to modern aspects of the glass transition equation qτg = C, suggested by Bartenev in 1951 (q - cooling rate of the melt, τg - structural relaxation time at the glass transition temperature Tg). This equation represents a criterion of structural relaxation at transition from liquid to glass at T = Tg (analogous to the condition of mechanical relaxation ωτ = 1, where the maximum of mechanical loss is observed). The empirical parameter С = δTg has the meaning of temperature range δTg that characterizes the liquid-glass transition. Different approaches of δTg calculation are reviewed. In the framework of the model of delocalized atoms a modified kinetic criterion of glass transition is proposed (q/Tg)τg = Cg, where Cg ≅ 7·10-3 is a practically universal dimensionless constant. It depends on fraction of fluctuation volume fg, which is frozen at the glass transition temperature Cg = fg/ln(1/fg). The value of fg is approximately constant fg ≅ 0.025. At Tg the process of atom delocalization, i.e. its displacement from the equilibrium position, is frozen. In silicate glasses atom delocalization is reduced to critical displacement of bridge oxygen atom in Si-O-Si bridge necessary to switch a valence bond according to Muller and Nemilov. An equation is derived for the temperature dependence of viscosity of glass-forming liquids in the wide temperature range, including the liquid-glass transition and the region of higher temperatures. Notion of (bridge) atom delocalization is developed, which is related to necessity of local low activation deformation of structural network for realization of elementary act of viscous flow - activated switch of a valence (bridge) bond. Without atom delocalization (;trigger mechanism;) a switch of the valence bond is impossible and, consequently, the viscous flow. Thus the freezing of atom delocalization process at low temperatures

  2. Frustration in Vicinity of Transition Point of Ising Spin Glasses

    NASA Astrophysics Data System (ADS)

    Miyazaki, Ryoji

    2013-09-01

    We conjecture the existence of a relationship between frustration and the transition point at zero temperature of Ising spin glasses. The relation reveals that, in several Ising spin glass models, the concentration of ferromagnetic bonds is close to the critical concentration at zero temperature when the output of a function about frustration is equal to unity. The function is the derivative of the average number of frustrated plaquettes with respect to the average number of antiferromagnetic bonds. This relation is conjectured in Ising spin glasses with binary couplings on two-dimensional lattices, hierarchical lattices, and three-body Ising spin glasses with binary couplings on two-dimensional lattices. In addition, the same argument in the Sherrington--Kirkpatrick model yields a point that is identical to the replica-symmetric solution of the transition point at zero temperature.

  3. Glass transition of repulsive charged rods (fd-viruses).

    PubMed

    Kang, Kyongok

    2014-05-14

    It has recently been shown that suspensions of long and thin charged fibrous viruses (fd) form a glass at low ionic strengths. The corresponding thick electric double layers give rise to long-ranged repulsive electrostatic interactions, which lead to caging and structural arrest at concentrations far above the isotropic-nematic coexistence region. Structural arrest and freezing of the orientational texture are found to occur at the same concentration. In addition, various types of orientational textures are equilibrated below the glass transition concentration, ranging from a chiral-nematic texture with a large pitch (of about 100 μm), an X-pattern, and a tightly packed domain texture, consisting of helical domains with a relatively small pitch (of about 10 μm) and twisted boundaries. The dynamics of both particles as well as the texture are discussed, below and above the glass transition. Dynamic light scattering correlation functions exhibit two dynamical modes, where the slow mode is attributed to the elasticity of helical domains. On approach of the glass-transition concentration, the slow mode increases in amplitude, while as the amplitudes of the fast and slow mode become equal at the glass transition. Finally, interesting features of the "transient" behaviors of charged fd-rod glass are shown as the initial caging due to structural arrest, the propagation of flow originating from stress release, and the transition to the final metastable glass state. In addition to the intensity correlation function, power spectra are presented as a function of the waiting time, at the zero-frequency limit that may access to the thermal anomalities in a charged system.

  4. Effect of dynamical heterogeneity on heat capacity at glass transition in typical silicate glasses

    NASA Astrophysics Data System (ADS)

    Li, Y. Z.; Zhao, L. Z.; Sun, Y. T.; Wen, P.; Bai, H. Y.; Wang, W. H.

    2015-12-01

    The heat capacity jump ΔCp at glass transition and the dynamical heterogeneity are two of the most important features of glass forming liquids. In order to reveal the intrinsic relationship between the two properties, a model glass system (Na2O)x(SiO2)1-x (x = 0.2-0.35) was studied by the systematic measurements of the ΔCp and the mechanical relaxation in the supercooled liquid region. A linear increase in ΔCp with increasing content of Na2O was found, indicating direct contributions of the locally fast dynamics around Na2O to ΔCp. This positive correlation between the locally heterogeneous dynamics and ΔCp was further confirmed by the dynamical heterogeneity analyses. Our results might be helpful for understanding the nature of glass transition.

  5. Fluorinated epoxy resins with high glass transition temperatures

    NASA Technical Reports Server (NTRS)

    Griffith, James R.

    1991-01-01

    Easily processed liquid resins of low dielectric constants and high glass transition temperatures are useful for the manufacture of certain composite electronic boards. That combination of properties is difficult to acquire when dielectric constants are below 2.5, glass transition temperatures are above 200 C and processability is of conventional practicality. A recently issued patent (US 4,981,941 of 1 Jan. 1991) teaches practical materials and is the culmination of 23 years of research and effort and 15 patents owned by the Navy in the field of fluorinated resins of several classes. In addition to high fluorine content, practical utility was emphasized.

  6. Jamming percolation and glass transitions in lattice models.

    PubMed

    Toninelli, Cristina; Biroli, Giulio; Fisher, Daniel S

    2006-01-27

    A new class of lattice gas models with trivial interactions but constrained dynamics is introduced. These models are proven to exhibit a dynamical glass transition: above a critical density rhoc ergodicity is broken due to the appearance of an infinite spanning cluster of jammed particles. The fraction of jammed particles is discontinuous at the transition, while in the unjammed phase dynamical correlation lengths and time scales diverge as exp[C(rhoc-rho)-mu]. Dynamic correlations display two-step relaxation similar to glass formers and jamming systems.

  7. Review: Pressure-Induced Densification of Oxide Glasses at the Glass Transition

    NASA Astrophysics Data System (ADS)

    Kapoor, Saurabh; Wondraczek, Lothar; Smedskjaer, Morten M.

    2017-02-01

    Densification of oxide glasses at the glass transition offers a novel route to develop bulk glasses with tailored properties for emerging applications. Such densification can be achieved in the technologically relevant pressure regime of up to 1GPa. However, the present understanding of the composition-structure-property relationships governing these glasses is limited, with key questions, e.g., related to densification mechanism, remaining largely unanswered. Recent advances in structural characterization tools and high-pressure apparatuses have prompted new research efforts. Here, we review this recent progress and the insights gained in the understanding of the influence of isostatic compression at elevated temperature (so-called hot compression) on the composition-structure-property relationships of oxide glasses. We focus on compression at temperatures at or around the glass transition temperature (Tg), with relevant comparisons made to glasses prepared by pressure quenching and cold compression. We show that permanent densification at 1 GPa sets-in at temperatures above 0.7Tg and the degree of densification increases with increasing compression temperature and time, until attaining an approximately constant value for temperatures above Tg. For glasses compressed at the same temperature/pressure conditions, we demonstrate direct relations between the degree of volume densification and the pressure-induced change in micro-mechanical properties such as hardness, elastic moduli, and extent of the indentation size effect across a variety of glass families. Furthermore, we summarize the results on relaxation behavior of hot compressed glasses. All the pressure-induced changes in the structure and properties exhibit strong composition dependence. The experimental results highlight new opportunities for future investigation and identify research challenges that need to be overcome to advance the field.

  8. Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

    SciTech Connect

    Zhao, K.; Xia, X. X.; Bai, H. Y.; Zhao, D. Q.; Wang, W. H.

    2011-04-04

    We report a high entropy metallic glass of Zn{sub 20}Ca{sub 20}Sr{sub 20}Yb{sub 20}(Li{sub 0.55}Mg{sub 0.45}){sub 20} via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.

  9. Glass transition temperature and conductivity in Li2O and Na2O doped borophosphate glasses

    NASA Astrophysics Data System (ADS)

    Ashwajeet, J. S.; Sankarappa, T.; Ramanna, R.; Sujatha, T.; Awasthi, A. M.

    2015-08-01

    Two alkali doped Borophosphate glasses in the composition, (B2O3)0.2. (P2O5)0.3. (Na2O)(0.5-x). (Li2O)x, where x = 0.05 to 0.50 were prepared by standard melt quenching method at 1200K. Non-crystalline nature was confirmed by XRD studies. Room temperature density was measured by Archimedes principle. DC conductivity in the temperature range from 300K to 575K has been measured. Samples were DSC studied in the temperature range from 423K to 673K and glass transition temperature was determined. Glass transition temperature passed through minima for Li2O con.2centration between 0.25 and 0.30 mole fractions. Activation energy of conduction has been determined by analyzing temperature variation of conductivity determining Arrhenius law. Conductivity passed through minimum and activation passed through maximum for Li2O content from 0.25 to 0.30 mole fractions. Glass transition temperature passed through minimum for the same range of Li2O content. These results revealed mixed alkali effect taking place in these glasses. It is for the first time borophosphate glasses doped with Li2O and Na2O have been studied for density and dc conductivity and, the mixed alkali effect (MAE) has been observed.

  10. Glass transition in binary eutectic systems: best glass-forming composition.

    PubMed

    Wang, Li-Min; Li, Zijing; Chen, Zeming; Zhao, Yue; Liu, Riping; Tian, Yongjun

    2010-09-23

    The glass transition and glass-forming ability in a binary eutectic system of methyl o-toluate (MOT) versus methyl p-toluate (MPT) are studied across the whole composition range. The phase diagram is constructed to explore the best glass-forming composition as the characteristic temperatures of the glass transition, crystallization, eutectic, and liquidus are determined. The best vitrification region is found to locate between the eutectic and the midpoint compositions of the eutectic line, indicating a remarkable deviation from the eutectic composition. The compilation of various simple binary eutectic systems covering inorganic, metallic, ionic, and molecular glass-forming liquids reproduces the rule. Kinetics and thermodynamics in binary systems are investigated to associate with the rule. The composition dependence of the structural relaxation time and the kinetic fragility are presented with dielectric measurements. It is found that whereas mixing of binary miscible liquids kinetically favors glass formation, thermodynamic contribution to the deviation of the best glass-forming composition from eutectics is implied.

  11. EZ lidar dust transit phenomena observations in Seoul, Korea

    NASA Astrophysics Data System (ADS)

    Lolli, S.; Sauvage, L.; Loaec, S.

    2009-09-01

    Duststorms and sandstorms regularly devastate Northeast Asia and cause considerable damage to transportation system and public health; further, these events are conceived to be one of the very important indices for estimating the global warming and desertification. Previously, yellow sand events were considered natural phenomena that originate in deserts and arid areas. However, the greater scale and frequency of these events in recent years are considered to be the result of human activities such as overgrazing and over-cultivation. Japan, Korea, Cina and Mongolia are directly concerned to prevent and control these storms and have been able to some extent to provide forecasts and early warnings. In this framework, to improve the accuracy of forecasting , a compact and rugged eye safe lidar, the EZ LIDATM, developed together by Laboratoire des Sciences du Climat et l'Environnement (LSCE) (CEA-CNRS) and LEOSPHERE, France) to study and investigate structural and optical properties of clouds and aerosols, thanks to the strong know-how of CEA and CNRS in the field of air quality measurements and cloud observation and analysis, was deployed in Seoul, Korea in order to detect and study yellow sand events, thanks to its depolarization channel and scan capabilities. The preliminary results, showed in this paper, of this measurement campaign put in evidence that EZ Lidar, for its capabilities of operating unattended day and night under each atmospheric condition, is mature to be deployed in a global network to study long-range transport, crucial in the forecasting model.

  12. Apparent critical phenomena in the superionic phase transition of Cu2-xSe

    DOE PAGES

    Kang, Stephen Dongmin; Danilkin, Sergey A.; Aydemir, Umut; ...

    2016-01-11

    The superionic phase transition ofmore » $${\\mathrm{Cu}}_{2-x}\\mathrm{Se}$$ accompanies drastic changes in transport properties. The Seebeck coefficient increases sharply while the electrical conductivity and thermal diffusivity drops. Such behavior has previously been attributed to critical phenomena under the assumption of a continuous phase transition. However, applying Landau's criteria suggests that the transition should be first order. Using the phase diagram that is consistent with a first order transition, we show that the observed transport properties and heat capacity curves can be accounted for and modeled with good agreement. The apparent critical phenomena is shown to be a result of compositional degree-of-freedom. In conclusion, understanding of the phase transition allows to explain the enhancement in the thermoelectric figure-of-merit that is accompanied with the transition.« less

  13. Configurational entropy of polar glass formers and the effect of electric field on glass transition

    NASA Astrophysics Data System (ADS)

    Matyushov, Dmitry V.

    2016-07-01

    A model of low-temperature polar liquids is constructed that accounts for the configurational heat capacity, entropy, and the effect of a strong electric field on the glass transition. The model is based on the Padé-truncated perturbation expansions of the liquid state theory. Depending on parameters, it accommodates an ideal glass transition of vanishing configurational entropy and its avoidance, with a square-root divergent enumeration function at the point of its termination. A composite density-temperature parameter ργ/T, often used to represent combined pressure and temperature data, follows from the model. The theory is in good agreement with the experimental data for excess (over the crystal state) thermodynamics of molecular glass formers. We suggest that the Kauzmann entropy crisis might be a signature of vanishing configurational entropy of a subset of degrees of freedom, multipolar rotations in our model. This scenario has observable consequences: (i) a dynamical crossover of the relaxation time and (ii) the fragility index defined by the ratio of the excess heat capacity and excess entropy at the glass transition. The Kauzmann temperature of vanishing configurational entropy and the corresponding glass transition temperature shift upward when the electric field is applied. The temperature shift scales quadratically with the field strength.

  14. Importance of many-body correlations in glass transition: An example from polydisperse hard spheres

    NASA Astrophysics Data System (ADS)

    Leocmach, Mathieu; Russo, John; Tanaka, Hajime

    2013-03-01

    Most of the liquid-state theories, including glass-transition theories, are constructed on the basis of two-body density correlations. However, we have recently shown that many-body correlations, in particular, bond orientational correlations, play a key role in both the glass transition and the crystallization transition. Here we show, with numerical simulations of supercooled polydisperse hard spheres systems, that the length-scale associated with any two-point spatial correlation function does not increase toward the glass transition. A growing length-scale is instead revealed by considering many-body correlation functions, such as correlators of orientational order, which follows the length-scale of the dynamic heterogeneities. Despite the growing of crystal-like bond orientational order, we reveal that the stability against crystallization with increasing polydispersity is due to an increasing population of icosahedral arrangements of particles. Our results suggest that, for this type of systems, many-body correlations are a manifestation of the link between the vitrification and the crystallization phenomena. Whether a system is vitrified or crystallized can be controlled by the degree of frustration against crystallization, polydispersity in this case.

  15. Effect of pressure on fragility and glass transition temperature in fragile glass-former

    NASA Astrophysics Data System (ADS)

    Paluch, M.; Hensel-Bielówka, S.; Zioło, J.

    1999-06-01

    This paper presents the effect of pressure on liquid fragility in poly(bisphenol A-co-epichlorohydrin), glycidyl end capped. On the basis of temperature dependences of dielectric relaxation times measured for several different pressures, the steepness or fragility index mT has been calculated. We proved that liquid fragility is independent of pressure within experimental error. The influence of pressure on glass transition temperature has also been studied. It turned out that pressure dependence of glass transition temperature is well represented by the second-order polynomial.

  16. Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

    2004-01-01

    The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

  17. Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

    2004-01-01

    The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

  18. Glass transition and crystallization kinetics of a barium borosilicate glass by a non-isothermal method

    SciTech Connect

    Lopes, Andreia A. S.; Soares, Roque S.; Lima, Maria M. A.; Monteiro, Regina C. C.

    2014-01-28

    The glass transition and crystallization kinetics of a glass with a molar composition 60BaO-30B{sub 2}O{sub 3}-10SiO{sub 2} were investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves exhibited an endothermic peak associated with the glass transition and two partially overlapped exothermic peaks associated with the crystallization of the glass. The dependence of the glass transition temperature (T{sub g}) and of the maximum crystallization temperature (T{sub p}) on the heating rate was used to determine the activation energy associated with the glass transition (E{sub g}), the activation energy for crystallization (E{sub c}), and the Avrami exponent (n). X-ray diffraction (XRD) revealed that barium borate (β-BaB{sub 2}O{sub 4}) was the first crystalline phase to be formed followed by the formation of barium silicate (Ba{sub 5}Si{sub 8}O{sub 21}). The variations of activation energy for crystallization and of Avrami exponent with the fraction of crystallization (χ) were also examined. When the crystallization fraction (χ) increased from 0.1 to 0.9, the value of local activation energy (E{sub c}(χ)) decreased from 554 to 458 kJ/mol for the first exothermic peak and from 1104 to 831 kJ/mol for the second exothermic peak. The value determined for the Avrami exponent was near 2 indicating a similar one-dimensional crystallization mechanism for both crystalline phases. This was confirmed by the morphological studies performed by scanning electron microscopy (SEM) on glass samples heat-treated at the first and at the second crystallization temperatures.

  19. Crystallization and glass transition of the diols and aminoalcohols, according to DSC data

    NASA Astrophysics Data System (ADS)

    Solonina, I. A.; Rodnikova, M. N.; Kiselev, M. P.; Khoroshilov, A. V.

    2015-05-01

    Overcooling, crystallization, and glass transition of the diol series and aminoalcohols which are the liquids with spatial hydrogen-bond networks, which are the along with the overcooling of dioxane, dimethylsulfoxide, and acetonitrile, which do not have such networks were studied by DSC. The observed phenomena are explained by the stability of H-bond networks. It was concluded that changes in the stability of the networks in and between series of diols and aminoalcohols are due to differences between their molecular structures, the energies of their hydrogen bonds, and their network topologies.

  20. Configurational entropy of binary hard-disk glasses: nonexistence of an ideal glass transition.

    PubMed

    Donev, Aleksandar; Stillinger, Frank H; Torquato, Salvatore

    2007-09-28

    We study the thermodynamics of a binary hard-disk mixture in which the ratio of disk diameters is kappa=1.4. We use a recently developed molecular dynamics algorithm to calculate the free-volume entropy of glassy configurations and obtain the configurational entropy (degeneracy) of the supercompressed liquid as a function of density. We find that the configurational entropy of the glasses near the kinetic glass transition is very close to the mixing entropy, suggesting that the degeneracy is zero only for the phase-separated crystal. We explicitly construct an exponential number of jammed packings with densities spanning the spectrum from the accepted "amorphous" glassy state to the phase-separated crystal, thus showing that there is no ideal glass transition in binary hard-disk mixtures. This construction also demonstrates that the ideal glass, defined as having zero configurational entropy, is not amorphous, but instead is nothing more than a phase-separated crystal. This critique of the presumed existence of an ideal glass parallels our previous critique of the idea that there is a most-dense random (close) packing for hard spheres [Torquato et al., Phys. Rev. Lett. 84, 2064 (2000)]. We also perform free-energy calculations to determine the equilibrium phase behavior of the system. The calculations predict a first-order freezing transition at a density below the kinetic glass transition. However, this transition appears to be strongly kinetically suppressed and is not observed directly. New simulation techniques are needed in order to gain a more complete understanding of the thermodynamic and kinetic behavior of the binary disk mixture and, in particular, of the demixing process during crystallization.

  1. The Structural Bases for Polymer Glass-Transition Temperatures

    NASA Astrophysics Data System (ADS)

    Shen, Jialong

    The glass transition temperatures (Tgs) observed for chemically distinct polymers range over several hundred K, and the molecular bases for this wide variability are largely unknown. Different structural factors are generally interdependent, making it difficult to predict or even rationalize the Tgs of polymers. In this dissertation work, we have synthesized structurally analogous polyesters and polyamides that are wholly amorphous and have compared their Tgs in a well-controlled manner with the aid from their rotational isomeric states (RIS) model. In addition, three tactic PMMAs were selected as model polymers for the search of a possible conformational origin for their vastly different Tgs and dynamic fragility indices. The arrangement of the work is described as follows: In the first chapter, fundamentals of the polymer glass transition temperature and the glass transition problem in general are reviewed. In the second chapter, a series of wholly amorphous linear aliphatic co- and tetra- polyesters are synthesized via bulk melt step-growth polymerization, and their glass transition temperatures were compared as a function of ester group contents. In the third chapter, glass transition temperatures were determined using DSC for melt blended, melt polymerized, interfacial polymerized, and solution polymerized amorphous or low crystallinity aliphatic polyamides. Many of these polyamides are structurally analogous to the polyesters described in the second chapter, with only one varying structural factor; i.e., intermolecular interactions, and their Tgs were compared. In the fourth chapter, dynamic fragility indices for PMMAs with different tacticities were measured using DSC. Rotational Isomeric State (RIS) conformational model results were used to explain the conformational origin of their large differences in T gs and fragilities.

  2. Polaronic Transport in Phosphate Glasses Containing Transition Metal Ions

    NASA Astrophysics Data System (ADS)

    Henderson, Mark

    The goal of this dissertation is to characterize the basic transport properties of phosphate glasses containing various amounts of TIs and to identify and explain any electronic phase transitions which may occur. The P2 O5-V2O5-WO3 (PVW) glass system will be analyzed to find the effect of TI concentration on conduction. In addition, the effect of the relative concentrations of network forming ions (SiO2 and P2O5) on transport will be studied in the P2O5-SiO2-Fe2O 3 (PSF) system. Also presented is a numerical study on a tight-binding model adapted for the purposes of modelling Gaussian traps, mimicking TI's, which are arranged in an extended network. The results of this project will contribute to the development of fundamental theories on the electronic transport in glasses containing mixtures of transition oxides as well as those containing multiple network formers without discernible phase separation. The present study on the PVW follows up on previous investigation into the effect on mixed transition ions in oxide glasses. Past research has focused on glasses containing transition metal ions from the 3d row. The inclusion of tungsten, a 5d transition metal, adds a layer of complexity through the mismatch of the energies of the orbitals contributing to localized states. The data have indicated that a transition reminiscent of a metal-insulator transition (MIT) occurs in this system as the concentration of tungsten increases. As opposed to some other MIT-like transitions found in phosphate glass systems, there seems to be no polaron to bipolaron conversion. Instead, the individual localization parameter for tungsten noticeably decreases dramatically at the transition point as well as the adiabaticity. Another distinctive feature of this project is the study of the PSF system, which contains two true network formers, phosphorous pentoxide (P2O 5) and silicon dioxide (SiO2). It is not usually possible to do a reliable investigation of the conduction properties of

  3. The nature of the colloidal 'glass' transition.

    PubMed

    Dawson, Kenneth A; Lawlor, A; DeGregorio, Paolo; McCullagh, Gavin D; Zaccarelli, Emanuela; Foffi, Giuseppe; Tartaglia, Piero

    2003-01-01

    The dynamically arrested state of matter is discussed in the context of athermal systems, such as the hard sphere colloidal arrest. We believe that the singular dynamical behaviour near arrest expressed, for example, in how the diffusion constant vanishes may be 'universal', in a sense to be discussed in the paper. Based on this we argue the merits of studying the problem with simple lattice models. This, by analogy with the the critical point of the Ising model, should lead us to clarify the questions, and begin the program of establishing the degree of universality to be expected. We deal only with 'ideal' athermal dynamical arrest transitions, such as those found for hard sphere systems. However, it is argued that dynamically available volume (DAV) is the relevant order parameter of the transition, and that universal mechanisms may be well expressed in terms of DAV. For simple lattice models we give examples of simple laws that emerge near the dynamical arrest, emphasising the idea of a near-ideal gas of 'holes', interacting to give the power law diffusion constant scaling near the arrest. We also seek to open the discussion of the possibility of an underlying weak coupling theory of the dynamical arrest transition, based on DAV.

  4. Variation of internal friction with time in metallic glasses near glass transition temperature

    NASA Astrophysics Data System (ADS)

    Hiki, Y.; Miyauchi, Y.; Karasawa, R.; Tamura, R.

    2013-02-01

    Internal friction (IF) of a bulk metallic glass Zr55Cu30Al10Ni5 has been measured near and below/above the glass transition temperature Tg. The specimen is prepared by rapid cooling the liquid mother alloy through casting into a copper ingot. The size of the specimen is about 30 mm × 2 mm × 0.8 mm. The amorphous state of the specimen is checked by the X-ray diffraction, and the temperatures of glass transition (Tg=666 K) and crystallization (Tx=746 K) are determined by the DSC method. The specimen is stabilized by annealing at Tg-10 K for 10 h. The IF measurement is performed by using DMA (TA Instrument) apparatus at the frequency of 0.1 Hz. The deformation mode of vibration is the cantilever bending. The specimen is kept at a constant temperature T, and the IF value Q-1 is measured as a function of duration time t( = 0˜2.5×104s). The temperature is controlled by the apparatus. The measurement is successively carried out at various temperatures T = (Tg-50K)˜(Tg+50K). The Q-1-vs-t behavior is different in different temperature ranges. At lower and higher temperatures, Q-1-vs-t shows the single relaxation. At temperatures near Tg, Q-1-vs-t appears to be quite irregular. These results are considered on the basis of the characteristics of the glass-forming materials and the glass transition.

  5. Investigation of low glass transition temperature on COTS PEM's reliability for space applications

    NASA Technical Reports Server (NTRS)

    Sandor, M.; Agarwal, S.; Peters, D.; Cooper, M. S.

    2003-01-01

    Plastic Encapsulated Microelectronics (PEM) reliability is affected by many factors. Glass transition temperature (Tg) is one such factor. In this presentation issues relating to PEM reliability and the effect of low glass transition temperature epoxy mold compounds are presented.

  6. Thermodynamics of viscous flow and elasticity of glass forming liquids in the glass transition range

    NASA Astrophysics Data System (ADS)

    Rouxel, T.

    2011-11-01

    The elastic moduli of glasses from different chemical systems, including oxide, chalcogenide, oxynitride, and metallic, were investigated through the glass transition (Tg), typically from 0.4 to 1.3 Tg. These data were used to interpret the temperature sensitivity of the shear viscosity coefficient obtained on the same materials. The relevant Gibbs free activation energy was estimated from the apparent heat of flow by means of the temperature dependence of the shear elastic modulus. The activation entropy associated with the viscous flow was also derived and was found to correlate with the fragile versus strong character of the glass forming liquids. Finally, the physicochemistry of the flow process was described on the basis of the glass network de-structuration which shows up through the temperature dependence of Poisson's ratio, and an expression for the shear viscosity coefficient is proposed which is chiefly based on the high temperature elastic behavior.

  7. Glass transition temperature of bulk metallic glasses: A linear connection with the mixing enthalpy

    NASA Astrophysics Data System (ADS)

    Li, Xuelian; Bian, Xiufang; Hu, Lina; Wu, Yuqin; Guo, Jing; Zhang, Junyan

    2007-05-01

    A linear relationship is found between the glass transition temperature Tg and the absolute value of the mixing enthalpy, |ΔHchem|, for bulk metallic glass systems. The increasing (or lowering) of Tg with an admixture of metals or other elements manifests itself in the larger (or smaller) of |ΔHchem| in a given system. The results indicate that the composition dependence of Tg results from the change of excess entropy (Sex) during thermal excitation. The |ΔHchem|, which relates to the strength of interaction among different atoms, corresponds to part of the Sex at Tg [Sex(Tg)]. The glass transition temperatures for Cu-Zr (Hf)-, Zr-Cu-, and La-Al-based glassy alloys are correlated with the interaction intensity between their based binary eutectic compositions, respectively.

  8. Evidence for Glass and Spin-Glass Phase Transitions From the Dynamic Susceptibility

    PubMed Central

    Bitko, D.; Coppersmith, S. N.; Leheny, R. L.; Menon, N.; Nagel, S. R.; Rosenbaum, T. F.

    1997-01-01

    We present evidence that there is a phase transition, with a diverging static susceptibility, underlying the transformation of a liquid into a glass. The dielectric susceptibility, at frequencies above its characteristic value, shows a power-law tail extending over many decades to higher frequencies. An extrapolation of this behavior to the temperature where the dynamics becomes arrested indicates a diverging susceptibility. We present evidence for analogous behavior in the magnetic susceptibility of a paramagnet approaching the spin-glass transition. The similarity of the response in these two glassy systems suggests that some conventional lore, such as that the spin glass shows evidence for a diverging correlation length only in a nonlinear but not in the linear susceptibility, may be invalid. PMID:27805138

  9. Glass transitions in the cellular Potts model

    NASA Astrophysics Data System (ADS)

    Chiang, M.; Marenduzzo, D.

    2016-10-01

    We study the dynamical transition between a fluid-like and a solid-like phase in a confluent cell monolayer, by using the cellular Potts model and computer simulations. We map out the phase diagram as a function of interfacial tension and of cell motility. While in the fluid phase there is normal diffusion, in the solid phase we observe sub-diffusion, very slow relaxation, and ageing, thereby strongly suggesting that this phase is glassy. Our results complement previous theoretical work within the vertex model and show that the cellular Potts model can account for the experimentally observed glassy dynamics of some biological tissues.

  10. Rotational and Translational Diffusion Near the Colloidal Glass Transition

    NASA Astrophysics Data System (ADS)

    Edmond, Kazem V.; Elsesser, Mark T.; Hunter, Gary L.; Pine, David J.; Weeks, Eric R.

    2010-03-01

    We study concentrated colloidal suspensions, a model system which has a glass transition. Using confocal microscopy we observe the three-dimensional translational and rotational motion of rigid clusters of particles suspended in a dense colloidal suspension of spheres. The clusters are highly ordered packings of fluorescently-labeled, core-shell PMMA particles, fabricated using a variation of a previously developed emulsification technique [1]. We use the dense suspension of spheres as the supercooled glass-forming liquid, while the clusters serve as tracers possessing rotational and translational dynamics. With image analysis and particle tracking software, we track both the translational and rotational motion of the tracer clusters in three dimensions. Far from the glass transition, both types of motion are purely Brownian in character. In contrast, near the glass transition, we observe both types of motion become temporally intermittent. [4pt] [1] V. N. Manoharan, M. T. Elsesser, and D. J. Pine, ``Dense Packing and Symmetry in Small Clusters of Microspheres'' Science 301, 483 (2003)

  11. Finite-size scaling for the glass transition: the role of a static length scale.

    PubMed

    Karmakar, Smarajit; Procaccia, Itamar

    2012-12-01

    Over the past decade, computer simulations have had an increasing role in shedding light on difficult statistical physical phenomena, and in particular on the ubiquitous problem of the glass transition. Here in a wide variety of materials the viscosity of a supercooled liquid increases by many orders of magnitude upon decreasing the temperature over a modest range. A natural concern in these computer simulations is the very small size of the simulated systems compared to experimental ones, raising the issue of how to assess the thermodynamic limit. Here we turn this limitation to our advantage by performing finite size scaling on the system size dependence of the relaxation time for supercooled liquids to emphasize the importance of a growing static length scale in the theory of glass transition. We demonstrate that the static length scale that was discovered by us in Physica A 391, 1001 (2012) fits the bill extremely well, allowing us to provide a finite-size scaling theory for the α-relaxation time of the glass transition, including predictions for the thermodynamic limit based on simulations in small systems.

  12. Application of liquid dynamics theory to the glass transition.

    PubMed

    Wallace, D C

    1999-12-01

    In monatomic liquid dynamics theory, the system moves among a large number of intersecting nearly harmonic valleys in the many-particle potential energy surface. The same potential surface underlies the motion of atoms in the supercooled liquid. As temperature is decreased below the melting temperature, the motion among the potential valleys will begin to freeze out, and the system will pass out of equilibrium. It is therefore necessary to develop a nonequilibrium theory, based on the Hamiltonian motion. The motion is separated into two distinct parts, and idealized as follows: (a) the vibrational motion within a single valley is assumed to be purely harmonic, and remaining in equilibrium; and (b) the transit motion, which carries the system from one valley to another, is assumed to be instantaneous, and energy and momentum conserving. This idealized system is capable of exhibiting a glass transition behavior. An elementary model, incorporating the idealized motion, is the independent atom model, originally developed to treat self diffusion in monatomic liquids. For supercooled liquids, in the independent atom model, the vanishing of self diffusion at a finite temperature implies the same property for the transit probability. The vanishing of the transit probability at a finite temperature supports the view that transits are not merely thermally activated, but are controlled by phase-space correlations. For supercooled liquid sodium, the transit probability has Vogel-Tamann-Fulcher temperature dependence. The independent atom model is shown to be capable of exhibiting all the essential glass transition properties, including rate dependence of the glass transition temperature, and both exponential and nonexponential relaxation.

  13. Role of Quantum Effects in the GlassTransition.

    SciTech Connect

    Novikov, Vladimir; Sokolov, Alexei P

    2013-01-01

    It is shown that quantum effects lead to a significant decrease of the glass transition temperature Tg with respect to the melting temperature Tm, so that the ratio Tg=Tm can be much smaller than the typical value of 2=3 in materials where Tg is near or below 60 K. Furthermore, it is demonstrated that the viscosity or structural relaxation time in such low temperature glass formers should exhibit highly unusual temperature dependence, namely a decrease of the apparent activation energy upon approaching Tg (instead of traditional increase).

  14. Glass transition temperatures in nanoscale equilibrated polystyrene droplets

    NASA Astrophysics Data System (ADS)

    Daley, Chad; Forrest, James

    2013-03-01

    Measurements of thin film glass transition temperature (Tg) in thin polymer films are only made possible through the metastability of the film with respect to dewetting. Even in the melt state, such samples are not in thermal equilibrium, and resulting Tg values may not be conclusive. In this talk we discuss recent measurements of Tg for equilibrium polystyrene droplets on silicon substrates as measured through their thermal expansion with true non-contact atomic force microscopy. These measurements show promise to not only definitively address the continuing controversy surrounding thin film Tg measurements, but are also readily applied to study non-polymeric glass formers.

  15. Multiple glass transitions and freezing events of aqueous citric acid.

    PubMed

    Bogdan, Anatoli; Molina, Mario J; Tenhu, Heikki; Loerting, Thomas

    2015-05-14

    Calorimetric and optical cryo-microscope measurements of 10-64 wt % citric acid (CA) solutions subjected to moderate (3 K/min) and slow (0.5 and 0.1 K/min) cooling/warming rates and also to quenching/moderate warming between 320 and 133 K are presented. Depending on solution concentration and cooling rate, the obtained thermograms show one freezing event and from one to three liquid-glass transitions upon cooling and from one to six liquid-glass and reverse glass-liquid transitions, one or two freezing events, and one melting event upon warming of frozen/glassy CA/H2O. The multiple freezing events and glass transitions pertain to the mother CA/H2O solution itself and two freeze-concentrated solution regions, FCS1 and FCS2, of different concentrations. The FCS1 and FCS2 (or FCS22) are formed during the freezing of CA/H2O upon cooling and/or during the freezing upon warming of partly glassy or entirely glassy mother CA/H2O. The formation of two FCS1 and FCS22 regions during the freezing upon warming to our best knowledge has never been reported before. Using an optical cryo-microscope, we are able to observe the formation of a continuous ice framework (IF) and its morphology and reciprocal distribution of IF/(FCS1 + FCS2). Our results provide a new look at the freezing and glass transition behavior of aqueous solutions and can be used for the optimization of lyophilization and freezing of foods and biopharmaceutical formulations, among many other applications where freezing plays a crucial role.

  16. Low-frequency optical dielectric response and rigidity transitions in network glasses

    SciTech Connect

    Gonzalez-Leal, J. M.; Angel, J. A.; Marquez, E.; Jimenez-Garay, R.; Krecmer, P.

    2006-11-15

    Self-organization occurring in As{sub x}S{sub 1-x} and As{sub x}Se{sub 1-x} glass alloy films reflects in their low-frequency optical dielectric response, and valuable information about the building blocks conforming their structure, can be derived from the analysis of the refractive-index dispersion data. The experimental results are discussed in the framework of the single-oscillator approach proposed by Wemple and DiDomenico, which provides a meaningful parametrization of the phenomena ruling the coupling between the photon-probe and the electron plasma in the near-infrared spectral region. Rigidity transitions occurring in both binary glassy systems are discussed in terms of the differences observed in the oscillator parameters, and these electronic evidences are linked to those arguments found in the literature, based on calorimetric and Raman measurements, that point to a segregated-phase view of glass materials.

  17. The glass and jamming transitions in dense granular matter

    NASA Astrophysics Data System (ADS)

    Coulais, Corentin; Candelier, Raphaël; Dauchot, Olivier

    2013-06-01

    Everyday life tells us that matter acquires rigidity either when it cools down, like lava flows which turn into solid rocks, or when it is compacted, like tablets simply formed by powder compression. As suggested by these examples, solidification is not the sole privilege of crystals but also happens for disordered media such as glass formers, granular media, foams, emulsions and colloidal suspensions. Fifteen years ago the "Jamming paradigm" emerged to encompass in a unique framework the glass transition and the emergence of yield stress, two challenging issues in modern condensed matter physics. One must realize how bold this proposal was, given that the glass transition is a finite temperature transition governing the dynamical properties of supercooled liquids, while Jamming is essentially a zero temperature, zero external stress and purely geometric transition which occurs when a given packing of particles reaches the maximum compression state above which particles start to overlap. More recently, the observation of remarkable scaling properties on the approach to jamming led to the conjecture that this zero temperature "critical point" could determine the properties of dense particle systems within a region of the parameter space to be determined, which in principle could include thermal and stressed systems. Fifteen years of intense theoretical and experimental work later, what have we learned about Jamming and glassy dynamics? In this paper, we discuss these issues in the light of the experiments we have been conducting with vibrated grains.

  18. Lost transparency! Weathering phenomena on the archaeological window glass collection of the Cistercian Abbey of the Dunes - Koksijde (Belgium)

    NASA Astrophysics Data System (ADS)

    Wouters, Hilde; Nuyts, Gert; Cagno, Simone; Minten, Nicole; Meulebroeck, Wendy; Baert, Kitty; Terryn, Herman; Janssens, Koen; Thienpont, Hugo; Nys, Karin

    As far as Belgium and archaeological window glass is concerned, the most important site is the Dunes Abbey, a former Cistercian abbey near the Flemish coastline. The collection contains approximately 15,000 fragments dating from the 13th to the 16th century. This glass was exposed to atmospheric weathering while in situ for several hundred years, buried for up to 400 years, excavated by different individual excavators in different eras and for over half a century stored in uncontrolled conditions. Moreover, different conservation treatments have been applied to the glass. Due to this, the collection was in a friable condition and we assume half of it has already been completely lost. The remaining collection retains fragments whose condition ranges between almost perfectly preserved material to being completely weathered to the point that no original glass survives. In this research, an important asset is recognizing what has already been lost and maximizing what is still available. During recent conservation and stock making campaigns, the different weathering phenomena were separated into 9 groups based on empirical criteria and detailed registration. As a first step to further investigation of the weathering processes, quantitative SEM-EDX analyses are used to give better insight into the chemical composition of these groups. The aim is to bridge the gap between interpretative archaeologically and archaeological science and to develop a common terminology to evaluate the complexity of weathering phenomena in archaeological window glass collections which can be used as a tool for the assembling and interpretation of these collections.

  19. Instantaneous Normal Modes and the Protein Glass Transition

    SciTech Connect

    Schultz, Roland; Krishnan, Marimuthu; Daidone, Isabella; Smith, Jeremy C

    2009-01-01

    In the instantaneous normal mode method, normal mode analysis is performed at instantaneous configurations of a condensed-phase system, leading to modes with negative eigenvalues. These negative modes provide a means of characterizing local anharmonicities of the potential energy surface. Here, we apply instantaneous normal mode to analyze temperature-dependent diffusive dynamics in molecular dynamics simulations of a small protein (a scorpion toxin). Those characteristics of the negative modes are determined that correlate with the dynamical (or glass) transition behavior of the protein, as manifested as an increase in the gradient with T of the average atomic mean-square displacement at 220 K. The number of negative eigenvalues shows no transition with temperature. Further, although filtering the negative modes to retain only those with eigenvectors corresponding to double-well potentials does reveal a transition in the hydration water, again, no transition in the protein is seen. However, additional filtering of the protein double-well modes, so as to retain only those that, on energy minimization, escape to different regions of configurational space, finally leads to clear protein dynamical transition behavior. Partial minimization of instantaneous configurations is also found to remove nondiffusive imaginary modes. In summary, examination of the form of negative instantaneous normal modes is shown to furnish a physical picture of local diffusive dynamics accompanying the protein glass transition.

  20. Interfacial instabilities and the glass transition in polymer thin films

    NASA Astrophysics Data System (ADS)

    Besancon, Brian Matthew

    Lithography, lubrication and active components in organic electronic devices are diverse applications of polymer thin films. Confinement and interfacial interactions have a profound effect on the properties of thin films and are responsible for behavior that is often counterintuitive and difficult to predict. Phenomena ranging from interfacial instabilities to thickness-dependent properties such as the glass transition (Tg) and viscosity are challenges associated with the design, processing, fabrication and performance of polymer thin films. In this dissertation, we examined three basic problems: the first concerns the morphology of interfacial instabilities, the second is the film thickness dependence of the viscosity, and the third is the thickness dependence of the Tg of thin film polymer-polymer mixtures. Thin liquid films in the nanometer thickness range often succumb to interfacial instabilities leading to break-up and droplet formation. While the destabilization process is well understood, the mechanisms by which the instability proceeds are not. One mechanism by which the dewetting process begins is with the formation and subsequent growth of circular holes. We show that fingering instabilities can develop at the periphery of these holes and that the morphology of the instability depends on chain length and the nature of the substrate-polymer interactions. The details of this secondary instability are examined and compared to fingering instabilities observed in macroscopic liquid fronts. A related issue in these systems is that the dynamics can be film thickness dependent. Since the viscosity and capillary forces determine the dynamics of interfacial instabilities, the time dependence of the hole size provides a method to measure the viscosity of the film. We used this approach to examine the influence of carbon nanotubes on the dewetting dynamics and determine the thickness dependence of the viscosity, which was found to depend on the thickness dependent

  1. Stability analysis of IV-V-VI chalcogenide glasses using glass transition and crystallization temperature

    NASA Astrophysics Data System (ADS)

    Sharma, Neha; Sharda, Sunanda; Sharma, Vineet; Sharma, Pankaj

    2013-06-01

    Selenium based chalcogenide glasses are attractive candidates for IR devices due to their low transmission loss. Thermal studies for Ge19Se81-xSbx (x = 0, 4, 8, 12, 16, 17.2, 20) have been carried out using differential thermal analysis. Glass transition temperature has been calculated using Tanaka's relation. Marseglia's and Ozawa's methods have been used for the calculation of activation energy for crystallization. Effect of Sb addition on GeSe base system shows that resistance to devitrification increases up to x = 17.2.

  2. Correlation between average melting temperature and glass transition temperature in metallic glasses

    NASA Astrophysics Data System (ADS)

    Lu, Zhibin; Li, Jiangong

    2009-02-01

    The correlation between average melting temperature (⟨Tm⟩) and glass transition temperature (Tg) in metallic glasses (MGs) is analyzed. A linear relationship, Tg=0.385⟨Tm⟩, is observed. This correlation agrees with Egami's suggestion [Rep. Prog. Phys. 47, 1601 (1984)]. The prediction of Tg from ⟨Tm⟩ through the relationship Tg=0.385⟨Tm⟩ has been tested using experimental data obtained on a large number of MGs. This relationship can be used to predict and design MGs with a desired Tg.

  3. Josephson-Vortex-Glass Transition in Strong Fields

    NASA Astrophysics Data System (ADS)

    Ikeda, Ryusuke; Adachi, Hiroto

    2000-09-01

    A vortex-glass transition due to point disorder in layered superconductors is studied for the case with an applied field parallel to the layers. Our calculation of tilt responses indicates that, irrespective of the magnitude of the field, the resulting glass phase, Josephson-vortex-glass (JG), should have a transverse Meissner effect, as in a planar splayed glass phase, only for a tilt perpendicular to the layers. Further, focusing on the high field (and/or high anisotropy) region B \\sqrt{{\\mitΓ}} > φ0/d2, where Γ is the mass anisotropy in the Lawrence-Doniach model, the JG transition line TJG(B) is shown to have a similar form to a B-T line following from the disorder-free Lindemann criterion and to decrease withincreasing B \\sqrt{{\\mitΓ}}, in marked contrast to the disorder-free melting line insensitive to B \\sqrt{{\\mitΓ}} in such the high field region. This TJG(B) line seems to have been recently observed in a.c. susceptibility and in-plane resistivitymeasurements in BSCCO and qualitatively explains a field dependence at lower temperatures of previous BSCCO resistivity data showing the so-called in-plane Lorentz force-free behavior.

  4. Protein's unfolding and the glass transition: a common thermodynamic signature.

    NASA Astrophysics Data System (ADS)

    Olivares-Quiroz, L.; Garcia-Colin, L. S.

    2008-02-01

    Recently, it has been recognized that protein's folding and unfolding mechanisms exhibit a wide range of common features with the glass transition observed in supercooled organic and inorganic liquids. Such similarities range from pure thermodynamic aspects such an anomalous ΔCp and a substantial entropy decrease ΔS<0, to strictly kinetic aspects as the existence of an excess of vibrational modes at low frequencies (bosonic peak) revealed by Raman and neutron scattering experiments. In this work, we discuss both the experimental and theoretical facts that might enable an extrapolation of the Adam-Gibbs scheme for the standard glass transition to describe the relaxation time τ as function of temperature T in biological macromolecules' unfolding.

  5. Ductile-to-brittle transition in spallation of metallic glasses

    SciTech Connect

    Huang, X.; Ling, Z.; Dai, L. H.

    2014-10-14

    In this paper, the spallation behavior of a binary metallic glass Cu{sub 50}Zr{sub 50} is investigated with molecular dynamics simulations. With increasing the impact velocity, micro-voids induced by tensile pulses become smaller and more concentrated. The phenomenon suggests a ductile-to-brittle transition during the spallation process. Further investigation indicates that the transition is controlled by the interaction between void nucleation and growth, which can be regarded as a competition between tension transformation zones (TTZs) and shear transformation zones (STZs) at atomic scale. As impact velocities become higher, the stress amplitude and temperature rise in the spall region increase and micro-structures of the material become more unstable. Therefore, TTZs are prone to activation in metallic glasses, leading to a brittle behavior during the spallation process.

  6. Structural relaxation in the glass transition region of water

    NASA Astrophysics Data System (ADS)

    Giovambattista, Nicolas; Angell, C. Austen; Sciortino, Francesco; Stanley, H. Eugene

    2005-07-01

    We perform molecular dynamics (MD) simulations using the extended simple-point-charge (SPC/E) model for water to study the structural relaxation through the glass transition region. We follow the same standard protocol used in differential scanning calorimetry experiments. Specifically, we cool liquid configurations at different cooling rates to produce a glass, and then we heat the glass back to the liquid state. We also study aging effects in the glass before heating. We find that MD simulations can reproduce the phenomenology observed in experiments. We review the Tool-Narayanaswamy-Moynihan (TNM) phenomenological approach, introduced to describe the behavior of the specific heat upon heating glass to the liquid phase. The TNM approach requires, as an ansatz, an expression for the temperature dependence of the relaxation time. We compare the simulation results with the prediction of the TNM approach supplemented with two well-known expressions for the relaxation time: the Narayanaswamy-Moynihan (NM) and the Adam-Gibbs-Scherer (AGS) expressions. We find that, in the case of slow cooling rates, our simulations are well represented by the TNM approach, but only if the AGS expression is adopted. We also find that the TNM approach fails in the case of fast cooling rates for both NM and AGS expressions. Several attempts to provide more freedom to the fitting procedure by allowing the fitting parameters to depend on temperature, cooling, and/or heating rates do not improve the agreement between the simulation data and the TNM predictions.

  7. Vibrational Excitations in Glasses — B. Vibrational Excitations in Glasses: Rigidity Transition and Lamb-Mössbauer Factors

    NASA Astrophysics Data System (ADS)

    Boolchand, P.

    The following sections are included: * Glass Forming Tendency and Rigidity Transition * Vibrational Density of States and Lamb-Mössbauer Factors * Experimental Considerations * Mössbauer spectrometer * Measurements of Lamb-Mössbauer factors * 119Sn Lamb-Mössbauer Factors and Nanophase Separation in GeSe2 Glass * Rigidity Transition and Lamb-Mössbauer Factors in Glasses * Chalcogenides * GexSe1-x * GexTe1-x * Oxide glasses * (Na2O)x(TeO2)1-x * Complementary Probes of Rigidity Transition * Temperature modulated differential scanning calorimetry * Raman scattering * Mössbauer hyperfine structure * Conclusions and Future Work * Acknowledgments * References

  8. Multiple Glass Transitions and Freezing Events of Aqueous Citric Acid

    PubMed Central

    2014-01-01

    Calorimetric and optical cryo-microscope measurements of 10–64 wt % citric acid (CA) solutions subjected to moderate (3 K/min) and slow (0.5 and 0.1 K/min) cooling/warming rates and also to quenching/moderate warming between 320 and 133 K are presented. Depending on solution concentration and cooling rate, the obtained thermograms show one freezing event and from one to three liquid–glass transitions upon cooling and from one to six liquid–glass and reverse glass–liquid transitions, one or two freezing events, and one melting event upon warming of frozen/glassy CA/H2O. The multiple freezing events and glass transitions pertain to the mother CA/H2O solution itself and two freeze-concentrated solution regions, FCS1 and FCS2, of different concentrations. The FCS1 and FCS2 (or FCS22) are formed during the freezing of CA/H2O upon cooling and/or during the freezing upon warming of partly glassy or entirely glassy mother CA/H2O. The formation of two FCS1 and FCS22 regions during the freezing upon warming to our best knowledge has never been reported before. Using an optical cryo-microscope, we are able to observe the formation of a continuous ice framework (IF) and its morphology and reciprocal distribution of IF/(FCS1 + FCS2). Our results provide a new look at the freezing and glass transition behavior of aqueous solutions and can be used for the optimization of lyophilization and freezing of foods and biopharmaceutical formulations, among many other applications where freezing plays a crucial role. PMID:25482069

  9. Energy Transfer between Post-Transition Elements & Rare Earths in Oxide & Chalcogenide Glasses.

    DTIC Science & Technology

    1979-08-27

    narrow- 37 line excitation F. Optical transitions of Sm3+ in oxide glasses 41 G. Energy transfer from U i+ to Sm3+ in phosphate glass 45 H. Transition...probabilities of europium(III) in zirconium 50 and beryllium fluoride glasses, phosphate glass and pentaphosphate crystals I. Multiphonon relaxation in...in phosphate , borate, germa- nate and tellurite glasses. The level fluorescent lifetime was derived from these rates and from the calculated radiative

  10. Noise as a Probe of Ising Spin Glass Transitions

    NASA Astrophysics Data System (ADS)

    Chen, Zhi; Yu, Clare

    2009-03-01

    Noise is ubiquitous and and is often viewed as a nuisance. However, we propose that noise can be used as a probe of the fluctuations of microscopic entities, especially in the vicinity of a phase transition. In recent work we have used simulations to show that the noise increases in the vicinity of phase transitions of ordered systems. We have recently turned our attention to noise near the phase transitions of disordered systems. In particular, we are studying the noise near Ising spin glass transitions using Monte Carlo simulations. We monitor the system as a function of temperature. At each temperature, we obtain the time series of quantities characterizing the properties of the system, i.e., the energy and magnetization. We look at different quantities, such as the noise power spectrum and the second spectrum of the noise, to analyze the fluctuations.

  11. Motility-Driven Glass and Jamming Transitions in Biological Tissues

    NASA Astrophysics Data System (ADS)

    Bi, Dapeng; Yang, Xingbo; Marchetti, M. Cristina; Manning, M. Lisa

    2016-04-01

    Cell motion inside dense tissues governs many biological processes, including embryonic development and cancer metastasis, and recent experiments suggest that these tissues exhibit collective glassy behavior. To make quantitative predictions about glass transitions in tissues, we study a self-propelled Voronoi model that simultaneously captures polarized cell motility and multibody cell-cell interactions in a confluent tissue, where there are no gaps between cells. We demonstrate that the model exhibits a jamming transition from a solidlike state to a fluidlike state that is controlled by three parameters: the single-cell motile speed, the persistence time of single-cell tracks, and a target shape index that characterizes the competition between cell-cell adhesion and cortical tension. In contrast to traditional particulate glasses, we are able to identify an experimentally accessible structural order parameter that specifies the entire jamming surface as a function of model parameters. We demonstrate that a continuum soft glassy rheology model precisely captures this transition in the limit of small persistence times and explain how it fails in the limit of large persistence times. These results provide a framework for understanding the collective solid-to-liquid transitions that have been observed in embryonic development and cancer progression, which may be associated with epithelial-to-mesenchymal transition in these tissues.

  12. Water mobility, denaturation and the glass transition in proteins.

    PubMed

    Porter, David; Vollrath, Fritz

    2012-06-01

    A quantitative mechanism is presented that links protein denaturation and the protein-water glass transition through an energy criterion for the onset of mobility of strong protein-water bonds. Differences in the zero point vibrational energy in the ordered and disordered bonded states allow direct prediction of the two transition temperatures. While the onset of water mobility induces the same change in heat capacity for both transitions, the order-disorder transition of denaturation also predicts the observed excess enthalpy gain. The kinetics of the water and protein components through the glass transition are predicted and compared with dielectric spectroscopy observations. The energetic approach provides a consistent mechanism for processes such as refolding and aggregation of proteins involved in protein maintenance and adaptability, as the conformational constraints of strong water-amide bonds are lost with increased molecular mobility. Moreover, we suggest that the ordered state of peptide-water bonds is induced at the point of protein synthesis and could play a key role in the function of proteins through the enhancement of electronic activity by ferroelectric domains in the protein hydration shell, which is lost upon denaturation. Copyright © 2012 Elsevier B.V. All rights reserved.

  13. Glass transition dynamics of stacked thin polymer films

    NASA Astrophysics Data System (ADS)

    Fukao, Koji; Terasawa, Takehide; Oda, Yuto; Nakamura, Kenji; Tahara, Daisuke

    2011-10-01

    The glass transition dynamics of stacked thin films of polystyrene and poly(2-chlorostyrene) were investigated using differential scanning calorimetry and dielectric relaxation spectroscopy. The glass transition temperature Tg of as-stacked thin polystyrene films has a strong depression from that of the bulk samples. However, after annealing at high temperatures above Tg, the stacked thin films exhibit glass transition at a temperature almost equal to the Tg of the bulk system. The α-process dynamics of stacked thin films of poly(2-chlorostyrene) show a time evolution from single-thin-film-like dynamics to bulk-like dynamics during the isothermal annealing process. The relaxation rate of the α process becomes smaller with increase in the annealing time. The time scale for the evolution of the α dynamics during the annealing process is very long compared with that for the reptation dynamics. At the same time, the temperature dependence of the relaxation time for the α process changes from Arrhenius-like to Vogel-Fulcher-Tammann dependence with increase of the annealing time. The fragility index increases and the distribution of the α-relaxation times becomes smaller with increase in the annealing time for isothermal annealing. The observed change in the α process is discussed with respect to the interfacial interaction between the thin layers of stacked thin polymer films.

  14. Glass transitions in nanoscale heated volumes of thin polystyrene films

    NASA Astrophysics Data System (ADS)

    Li, Alex G.; Burggraf, Larry W.

    2010-12-01

    Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic force microscopy incorporating a thermal tip. Three-dimensional spatial nanoconfinements were achieved by controlling size and boundary conditions of small heated volumes of polymer nanostrands drawn from the polymer surface with the thermal tip, using appropriate loads and temperatures at the tip-polymer contact. Finite element analysis was performed to model mechanical contact and thermal transport, including the effects of contact radius, film thickness, and load on temperature and pressure distributions in the confined volume at the contact. The glass transition temperature (Tg) was measured by observing the softening of polymers with increasing temperature. The measured surface Tg exhibited a strong size dependence, while the subsurface Tg increased with decreasing the distance to the substrate. A large increase in the surface Tg was observed when the radius of contact was reduced below about 10 nm. The increase in the glass transition temperature at the surface was attributed to the presence of surface and line tension at the nanometer contact, while the enhanced Tg near the substrate was attributed to the pinning effects that reduces the mobility of the polymer molecules in the film over several hundreds of nanometers away from the polymer-substrate interface.

  15. The glass-liquid transition of water on hydrophobic surfaces.

    PubMed

    Souda, Ryutaro

    2008-09-28

    Interactions of thin water films with surfaces of graphite and vitrified room-temperature ionic liquid [1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)])] were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature and annealing time to elucidate the glass-liquid transition of water at the molecular level. Surface diffusion of water occurs at temperatures higher than 120 K, thereby forming three-dimensional clusters (a two-dimensional layer) on the [bmim][PF(6)] (graphite) surface. The hydrophobic effect of the surface decreases with increasing coverage of water; the bulklike properties evolve up to 40 ML, as evidenced by the occurrence of film dewetting at around the conventional glass transition temperature (140 K). Results also showed that aging is necessary for the water monolayer (a 40 ML water film) to dewet the graphite ([bmim][PF(6)]) surface. The occurrence of aging is explainable by the successive evolution of two distinct liquids during the glass-liquid transition: low density liquid is followed by supercooled liquid water. The water monolayer on graphite is characterized by the preferred orientation of unpaired OH groups toward the surface; this structure is arrested during the aging time despite the occurrence of surface diffusion. However, the water monolayer formed on the [bmim][PF(6)] surface agglomerates immediately after the commencement of surface diffusion. The structure of low density liquid tends to be arrested by the attractive interaction with the neighbors.

  16. Dynamical and structural signatures of the glass transition in emulsions

    NASA Astrophysics Data System (ADS)

    Zhang, Chi; Gnan, Nicoletta; Mason, Thomas G.; Zaccarelli, Emanuela; Scheffold, Frank

    2016-09-01

    We investigate structural and dynamical properties of moderately polydisperse emulsions across an extended range of droplet volume fractions ϕ, encompassing fluid and glassy states up to jamming. Combining experiments and simulations, we show that when ϕ approaches the glass transition volume fraction {φg} , dynamical heterogeneities and amorphous order arise within the emulsion. In particular, we find an increasing number of clusters of particles having five-fold symmetry (i.e. the so-called locally favoured structures, LFS) as ϕ approaches {φg} , saturating to a roughly constant value in the glassy regime. However, contrary to previous studies, we do not observe a corresponding growth of medium-range crystalline order; instead, the emergence of LFS is decoupled from the appearance of more ordered regions in our system. We also find that the static correlation lengths associated with the LFS and with the fastest particles can be successfully related to the relaxation time of the system. By contrast, this does not hold for the length associated with the orientational order. Our study reveals the existence of a link between dynamics and structure close to the glass transition even in the absence of crystalline precursors or crystallization. Furthermore, the quantitative agreement between our confocal microscopy experiments and Brownian dynamics simulations indicates that emulsions are and will continue to be important model systems for the investigation of the glass transition and beyond.

  17. Simple solvable energy-landscape model that shows a thermodynamic phase transition and a glass transition.

    PubMed

    Naumis, Gerardo G

    2012-06-01

    When a liquid melt is cooled, a glass or phase transition can be obtained depending on the cooling rate. Yet, this behavior has not been clearly captured in energy-landscape models. Here, a model is provided in which two key ingredients are considered in the landscape, metastable states and their multiplicity. Metastable states are considered as in two level system models. However, their multiplicity and topology allows a phase transition in the thermodynamic limit for slow cooling, while a transition to the glass is obtained for fast cooling. By solving the corresponding master equation, the minimal speed of cooling required to produce the glass is obtained as a function of the distribution of metastable states.

  18. Predicting bioactive glass properties from the molecular chemical composition: glass transition temperature.

    PubMed

    O'Donnell, Matthew D

    2011-05-01

    The glass transition temperature (T(g)) of inorganic glasses is an important parameter than can be used to correlate with other glass properties, such as dissolution rate, which governs in vitro and in vivo bioactivity. Seven bioactive glass compositional series reported in the literature (77 in total) were analysed here with T(g) values obtained by a number of different methods: differential thermal analysis, differential scanning calorimetry and dilatometry. An iterative least-squares fitting method was used to correlate T(g) from thermal analysis of these compositions with the levels of individual oxide and fluoride components in the glasses. When all seven series were fitted a reasonable correlation was found between calculated and experimental values (R(2)=0.89). When the two compositional series that were designed in weight percentages (the remaining five were designed in molar percentage) were removed from the model an improved fit was achieved (R(2)=0.97). This study shows that T(g) for a wide range in compositions (e.g. SiO(2) content of 37.3-68.4 mol.%) can be predicted to reasonable accuracy enabling processing parameters to be predicted such as annealing, fibre-drawing and sintering temperatures.

  19. First-principles computation of random-pinning glass transition, glass cooperative length scales, and numerical comparisons

    NASA Astrophysics Data System (ADS)

    Cammarota, Chiara; Seoane, Beatriz

    2016-11-01

    As a guideline for experimental tests of the ideal glass transition (random-pinning glass transition, RPGT) that shall be induced in a system by randomly pinning particles, we performed first-principle computations within the hypernetted chain approximation and numerical simulations of a hard-sphere model of a glass former. We obtain confirmation of the expected enhancement of glassy behavior under the procedure of random pinning. We present the analytical phase diagram as a function of c and of the packing fraction ϕ , showing a line of RPGT ending in a critical point. We also obtain microscopic results on cooperative length scales characterizing medium-range amorphous order in hard-sphere glasses and indirect quantitative information on a key thermodynamic quantity defined in proximity to ideal glass transitions, the amorphous surface tension. Finally, we present numerical results of pair correlation functions able to differentiate the liquid and the glass phases, as predicted by the analytic computations.

  20. Raman scattering boson peak and differential scanning calorimetry studies of the glass transition in tellurium-zinc oxide glasses.

    PubMed

    Stavrou, E; Tsiantos, C; Tsopouridou, R D; Kripotou, S; Kontos, A G; Raptis, C; Capoen, B; Bouazaoui, M; Turrell, S; Khatir, S

    2010-05-19

    Raman scattering and differential scanning calorimetry (DSC) measurements have been carried out on four mixed tellurium-zinc oxide (TeO(2))(1 - x)(ZnO)(x) (x = 0.1, 0.2, 0.3, 0.4) glasses under variable temperature, with particular attention being given to the respective glass transition region. From the DSC measurements, the glass transition temperature T(g) has been determined for each glass, showing a monotonous decrease of T(g) with increasing ZnO content. The Raman study is focused on the low-frequency band of the glasses, the so-called boson peak (BP), whose frequency undergoes an abrupt decrease at a temperature T(d) very close to the respective T(g) values obtained by DSC. These results show that the BP is highly sensitive to dynamical effects over the glass transition and provides a means for an equally reliable (to DSC) determination of T(g) in tellurite glasses and other network glasses. The discontinuous temperature dependence of the BP frequency at the glass transition, along with the absence of such a behaviour by the high-frequency Raman bands (due to local atomic vibrations), indicates that marked changes of the medium range order (MRO) occur at T(g) and confirms the correlation between the BP and the MRO of glasses.

  1. Nonlinear phenomena of acridine orange in inorganic glasses at nanosecond scale

    NASA Astrophysics Data System (ADS)

    Gaponenko, S. V.; Gribkovskii, V. P.; Zimin, L. G.; Lebed, V. Yu.; Malinovskii, I. E.; Graham, S.; Klingshirn, C.; Eyal, M.; Brusilovsky, D.; Reisfeld, R.

    1993-04-01

    Nonlinear optical behavior of acridine orange dye has been studied in lead-tin-flouride glass. We found that this material possess nonlinear saturable absorption and power-dependent lifetimes, both on nanosecond time scale. This short response is explained by an efficient S-T transfer induced by the heavy atoms of the glass. The glass has a good potential as a nonlinear material on a nanosecond time scale.

  2. Brittle-to-Ductile Transition in Metallic Glass Nanowires.

    PubMed

    Şopu, D; Foroughi, A; Stoica, M; Eckert, J

    2016-07-13

    When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure.

  3. The old problems of glass and the glass transition, and the many new twists.

    PubMed Central

    Angell, C A

    1995-01-01

    In this paper I review the ways in which the glassy state is obtained both in nature and in materials science and highlight a "new twist"--the recent recognition of polymorphism within the glassy state. The formation of glass by continuous cooling (viscous slowdown) is then examined, the strong/fragile liquids classification is reviewed, and a new twist-the possibility that the slowdown is a result of an avoided critical point-is noted. The three canonical characteristics of relaxing liquids are correlated through the fragility. As a further new twist, the conversion of strong liquids to fragile liquids by pressure-induced coordination number increases is demonstrated. It is then shown that, for comparable systems, it is possible to have the same conversion accomplished via a first-order transition within the liquid state during quenching. This occurs in the systems in which "polyamorphism" (polymorphism in the glassy state) is observed, and the whole phenomenology is accounted for by Poole's bond-modified van der Waals model. The sudden loss of some liquid degrees of freedom through such weak first-order transitions is then related to the polyamorphic transition between native and denatured hydrated proteins, since the latter are also glass-forming systems--water-plasticized, hydrogen bond-cross-linked chain polymers (and single molecule glass formers). The circle is closed with a final new twist by noting that a short time scale phenomenon much studied by protein physicists-namely, the onset of a sharp change in d/dT ( is the Debye-Waller factor)--is general for glass-forming liquids, including computer-simulated strong and fragile ionic liquids, and is closely correlated with the experimental glass transition temperature. The latter thus originates in strong anharmonicity in certain components of the vibrational density of states, which permits the system to access the multiple minima of its configuration space. The connection between the anharmonicity

  4. Magnetic Fluctuations, Precursor Phenomena, and Phase Transition in MnSi under a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Pappas, C.; Bannenberg, L. J.; Lelièvre-Berna, E.; Qian, F.; Dewhurst, C. D.; Dalgliesh, R. M.; Schlagel, D. L.; Lograsso, T. A.; Falus, P.

    2017-07-01

    The reference chiral helimagnet MnSi is the first system where Skyrmion lattice correlations have been reported. At a zero magnetic field the transition at TC to the helimagnetic state is of first order. Above TC, in a region dominated by precursor phenomena, neutron scattering shows the buildup of strong chiral fluctuating correlations over the surface of a sphere with radius 2 π /ℓ, where ℓ is the pitch of the helix. It has been suggested that these fluctuating correlations drive the helical transition to first order following a scenario proposed by Brazovskii for liquid crystals. We present a comprehensive neutron scattering study under magnetic fields, which provides evidence that this is not the case. The sharp first order transition persists for magnetic fields up to 0.4 T whereas the fluctuating correlations weaken and start to concentrate along the field direction already above 0.2 T. Our results thus disconnect the first order nature of the transition from the precursor fluctuating correlations. They also show no indication for a tricritical point, where the first order transition crosses over to second order with increasing magnetic field. In this light, the nature of the first order helical transition and the precursor phenomena above TC, both of general relevance to chiral magnetism, remain an open question.

  5. Nonequilibrium and nonhomogeneous phenomena around a first-order quantum phase transition

    NASA Astrophysics Data System (ADS)

    Del Re, Lorenzo; Fabrizio, Michele; Tosatti, Erio

    2016-03-01

    We consider nonequilibrium phenomena in a very simple model that displays a zero-temperature first-order phase transition. The quantum Ising model with a four-spin exchange is adopted as a general representative of first-order quantum phase transitions that belong to the Ising universality class, such as for instance the order-disorder ferroelectric transitions, and possibly first-order T =0 Mott transitions. In particular, we address quantum quenches in the exactly solvable limit of infinite connectivity and show that, within the coexistence region around the transition, the system can remain trapped in a metastable phase, as long as it is spatially homogeneous so that nucleation can be ignored. Motivated by the physics of nucleation, we then study in the same model static but inhomogeneous phenomena that take place at surfaces and interfaces. The first-order nature implies that both phases remain locally stable across the transition, and with that the possibility of a metastable wetting layer showing up at the surface of the stable phase, even at T =0 . We use mean-field theory plus quantum fluctuations in the harmonic approximation to study quantum surface wetting.

  6. Dynamic thermal expansivity of liquids near the glass transition.

    PubMed

    Niss, Kristine; Gundermann, Ditte; Christensen, Tage; Dyre, Jeppe C

    2012-04-01

    Based on previous works on polymers by Bauer et al. [Phys. Rev. E 61, 1755 (2000)], this paper describes a capacitative method for measuring the dynamical expansion coefficient of a viscous liquid. Data are presented for the glass-forming liquid tetramethyl tetraphenyl trisiloxane (DC704) in the ultraviscous regime. Compared to the method of Bauer et al., the dynamical range has been extended by making time-domain experiments and by making very small and fast temperature steps. The modeling of the experiment presented in this paper includes the situation in which the capacitor is not full because the liquid contracts when cooling from room temperature down to around the glass-transition temperature, which is relevant when measuring on a molecular liquid rather than a polymer.

  7. The length and time scales of water's glass transitions.

    PubMed

    Limmer, David T

    2014-06-07

    Using a general model for the equilibrium dynamics of supercooled liquids, I compute from molecular properties the emergent length and time scales that govern the nonequilibrium relaxation behavior of amorphous ice prepared by rapid cooling. Upon cooling, the liquid water falls out of equilibrium whereby the temperature dependence of its relaxation time is predicted to change from super-Arrhenius to Arrhenius. A consequence of this crossover is that the location of the apparent glass transition temperature depends logarithmically on cooling rate. Accompanying vitrification is the emergence of a dynamical length-scale, the size of which depends on the cooling rate and varies between angstroms and tens of nanometers. While this protocol dependence clarifies a number of previous experimental observations for amorphous ice, the arguments are general and can be extended to other glass forming liquids.

  8. Single-particle dynamics near the glass transition of a metallic glass.

    PubMed

    Lü, Y J; Wang, W H

    2016-12-01

    The single-particle dynamics of the glass-forming Cu_{50}Zr_{50} alloy, from the supercooled liquid well above the glass-transition temperature, T_{g} to the glassy state, is studied by using the molecular dynamics simulations. When the liquid is cooled below 1.2T_{g}, the dynamics heterogeneity characterized by the cage-jump motion becomes increasingly pronounced. The analyses based on the continuous time random walk method indicate that the liquid falls out of equilibrium in the present simulation time scale when it is cooled into the regime below 1.02T_{g}. However, we find that the jump length and the jump rate do not display the non-equilibrium behaviors even in the glassy state below T_{g}, which allows us to study the intrinsic dynamic characteristics through T_{g}. The mean waiting time between two successive jumps has a rapid growth following the Vogel-Fulcher-Tammann law as the non-equilibrium regime is approached, in analogy with the temperature behaviors of transport properties for fragile supercooled liquids. In contrast, the jump rate maintains the Arrhenius decay and the jump length has even a weaker temperature dependence when the liquid is cooled into glassy state. We find that a pronounced enhancement of the spatial correlation of jumps occurs accompanied by the glass transition: the string-like cooperative jumps dominate the fast motion instead of the uncorrelated and individual jumps. Our work offers an insight into the equilibrium effect of the single-particle dynamics in glass transition.

  9. Single-particle dynamics near the glass transition of a metallic glass

    NASA Astrophysics Data System (ADS)

    Lü, Y. J.; Wang, W. H.

    2016-12-01

    The single-particle dynamics of the glass-forming C u50Z r50 alloy, from the supercooled liquid well above the glass-transition temperature, Tg to the glassy state, is studied by using the molecular dynamics simulations. When the liquid is cooled below 1.2 Tg , the dynamics heterogeneity characterized by the cage-jump motion becomes increasingly pronounced. The analyses based on the continuous time random walk method indicate that the liquid falls out of equilibrium in the present simulation time scale when it is cooled into the regime below 1.02 Tg . However, we find that the jump length and the jump rate do not display the non-equilibrium behaviors even in the glassy state below Tg, which allows us to study the intrinsic dynamic characteristics through Tg. The mean waiting time between two successive jumps has a rapid growth following the Vogel-Fulcher-Tammann law as the non-equilibrium regime is approached, in analogy with the temperature behaviors of transport properties for fragile supercooled liquids. In contrast, the jump rate maintains the Arrhenius decay and the jump length has even a weaker temperature dependence when the liquid is cooled into glassy state. We find that a pronounced enhancement of the spatial correlation of jumps occurs accompanied by the glass transition: the string-like cooperative jumps dominate the fast motion instead of the uncorrelated and individual jumps. Our work offers an insight into the equilibrium effect of the single-particle dynamics in glass transition.

  10. Affinity and its derivatives in the glass transition process

    NASA Astrophysics Data System (ADS)

    Garden, J.-L.; Guillou, H.; Richard, J.; Wondraczek, L.

    2012-07-01

    The thermodynamic treatment of the glass transition remains an issue of intense debate. When associated with the formalism of non-equilibrium thermodynamics, the lattice-hole theory of liquids can provide new insight in this direction, as has been shown by Schmelzer and Gutzow [J. Chem. Phys. 125, 184511 (2006)], 10.1063/1.2374894, by Möller et al. [J. Chem. Phys. 125, 094505 (2006)], 10.1063/1.2346673, and more recently by Tropin et al. [J. Non-Cryst. Solids 357, 1291 (2011), 10.1016/j.jnoncrysol.2010.11.111; Tropin et al., J. Non-Cryst. Solids 357, 1303 (2011)], 10.1016/j.jnoncrysol.2010.12.005. Here, we employ a similar approach. We include pressure as an additional variable, in order to account for the freezing-in of structural degrees of freedom upon pressure increase. Second, we demonstrate that important terms concerning first order derivatives of the affinity-driving-force with respect to temperature and pressure have been previously neglected. We show that these are of crucial importance in the approach. Macroscopic non-equilibrium thermodynamics is used to enlighten these contributions in the derivation of Cp,κT, and αp. The coefficients are calculated as a function of pressure and temperature following different theoretical protocols, revealing classical aspects of vitrification and structural recovery processes. Finally, we demonstrate that a simple minimalist model such as the lattice-hole theory of liquids, when being associated with rigorous use of macroscopic non-equilibrium thermodynamics, is able to account for the primary features of the glass transition phenomenology. Notwithstanding its simplicity and its limits, this approach can be used as a very pedagogical tool to provide a physical understanding on the underlying thermodynamics which governs the glass transition process.

  11. Pressure Dependence of the Glass Transition Temperature in the Fragile Glass Former Cumene

    NASA Astrophysics Data System (ADS)

    Raty, Jean-Yves; Baris Malcioglu, Osman; Bichara, Christophe

    2013-03-01

    The glass transition temperature, Tg, is one of the most important characteristics of glassy systems. While Tg has been measured for many systems at atmospheric pressure, direct measurement of the glass transition is difficult at high pressures due to small sample sizes and long time scales. Tg(P) measurements to date mostly involve extrapolations of high-pressure viscosity or relaxation data to η = 1013 P or t = 100 s, respectively. In this study we present direct measurement of Tg at pressures up to several GPa through a combination of pressure gradient tracking and observation of increases in the thermal expansion coefficient upon heating from the glass to the viscous liquid state. High pressures are attained through the use of a diamond anvil cell and precise temperatures are maintained via custom heating and cryogenic systems. By directly mapping this phase boundary, we can compare models for Tg(P). In addition, high-pressure analysis requiring knowledge of Tg at pressure will be greatly aided.

  12. Magnetic imaging of a supercooling glass transition in a weakly disordered ferromagnet.

    PubMed

    Wu, Weida; Israel, Casey; Hur, Namjung; Park, Soonyong; Cheong, Sang-Wook; de Lozanne, Alex

    2006-11-01

    Spin glasses are founded in the frustration and randomness of microscopic magnetic interactions. They are non-ergodic systems where replica symmetry is broken. Although magnetic glassy behaviour has been observed in many colossal magnetoresistive manganites, there is no consensus that they are spin glasses. Here, an intriguing glass transition in (La,Pr,Ca)MnO3 is imaged using a variable-temperature magnetic force microscope. In contrast to the speculated spin-glass picture, our results show that the observed static magnetic configuration seen below the glass-transition temperature arises from the cooperative freezing of the first-order antiferromagnetic (charge ordered) to ferromagnetic transition. Our data also suggest that accommodation strain is important in the kinetics of the phase transition. This cooperative freezing idea has been applied to structural glasses including window glasses and supercooled liquids, and may be applicable across many systems to any first-order phase transition occurring on a complex free-energy landscape.

  13. Quantum critical behavior of the superfluid-Mott glass transition

    NASA Astrophysics Data System (ADS)

    Vojta, Thomas; Crewse, Jack; Puschmann, Martin; Arovas, Daniel; Kiselev, Yury

    2016-10-01

    We investigate the zero-temperature superfluid to insulator transitions in a diluted two-dimensional quantum rotor model with particle-hole symmetry. We map the Hamiltonian onto a classical (2 +1 ) -dimensional X Y model with columnar disorder which we analyze by means of large-scale Monte Carlo simulations. For dilutions below the lattice percolation threshold, the system undergoes a generic superfluid-Mott glass transition. In contrast to other quantum phase transitions in disordered systems, its critical behavior is of conventional power-law type with universal (dilution-independent) critical exponents z =1.52 (3 ) , ν =1.16 (5 ) , β /ν =0.48 (2 ) , γ /ν =2.52 (4 ) , and η =-0.52 (4 ) . These values agree with and improve upon earlier Monte Carlo results [Phys. Rev. Lett. 92, 015703 (2004)], 10.1103/PhysRevLett.92.015703 while (partially) excluding other findings in the literature. As a further test of universality, we also consider a soft-spin version of the classical Hamiltonian. In addition, we study the percolation quantum phase transition across the lattice percolation threshold; its critical behavior is governed by the lattice percolation exponents in agreement with recent theoretical predictions. We relate our results to a general classification of phase transitions in disordered systems, and we briefly discuss experiments.

  14. Structure of Li(x)Rb(1-x)PO(3) glasses near the glass transition.

    PubMed

    Hall, Andreas; Swenson, Jan; Bowron, Daniel T; Adams, Stefan

    2009-06-17

    The temperature dependence of mixed alkali metaphosphate Li(x)Rb(1-x)PO(3) (x = 1, 0.5, 0) structures has been studied from room temperature up to about 20 K above the glass transition temperature (T(g)) by means of neutron diffraction and reverse Monte Carlo modelling. The results show that the structural changes are limited to a slight temperature-induced broadening of the peaks in S(Q) and a linear thermal expansion of 50-100 ppm K(-1). Furthermore, the possible diffusion pathways of the mobile ions have been investigated by the bond valence technique and the results show that they are not significantly affected as the glass is brought above T(g). The decrease in activation energy that occurs above T(g) is thus attributed to an increased coupling between the motions of the mobile ions and the relaxation of the phosphate network.

  15. Glassy nature and glass-to-crystal transition in the binary metallic glass CuZr

    NASA Astrophysics Data System (ADS)

    Wei, Zi-Yang; Shang, Cheng; Zhang, Xiao-Jie; Liu, Zhi-Pan

    2017-06-01

    The prediction for the stability of glassy material is a key challenge in physical science. Here, we report a theoretical framework to predict the glass stability based on stochastic surface walking global optimization and reaction pathway sampling. This is demonstrated by revealing for the first time the global potential energy surface (PES) of two systems, CuZr binary metallic glass and nonglassy pure Cu systems, and establishing the lowest energy pathways linking glassy/amorphous structures with crystalline structures. The CuZr system has a significant number of glassy structures on PES that are ˜0.045 eV /atom above the crystal structure. Two clear trends are identified from global PES in the glass-to-crystal transition of the CuZr system: (i) the local Zr-Cu coordination (nearest neighbor) increases, and (ii) the local Zr bonding environment becomes homogeneous. This allows us to introduce quantitative structural and energetics conditions to distinguish the glassy structures from the crystalline structures. Because of the local Zr-Cu exchange in the glass-to-crystal transition, a high reaction barrier (>0.048 eV /atom ) is present to separate the glassy structures and the crystals in CuZr. By contrast, the Cu system, although it does possess amorphous structures that appear at much higher energy (˜0.075 eV /atom ) with respect to the crystal structure, has very low reaction barriers for the crystallization of amorphous structures, i.e. <0.011 eV /atom . The quantitative data on PES now available from global optimization techniques deepens our understanding on the microscopic nature of glassy material and might eventually facilitate the design of stable glassy materials.

  16. Glass transition of ionic liquids under high pressure.

    PubMed

    Ribeiro, Mauro C C; Pádua, Agílio A H; Gomes, Margarida F Costa

    2014-06-28

    The glass transition pressure at room temperature, pg, of six ionic liquids based on 1-alkyl-3-methylimidazolium cations and the anions [BF4](-), [PF6](-), and bis(trifluromethanesulfonyl)imide, [NTf2](-), has been obtained from the pressure dependence of the bandwidth of the ruby fluorescence line in diamond anvil cells. Molar volume, Vm(pg), has been estimated by a group contribution model (GCM) developed for the ionic liquids. A density scaling relation, TV(γ), has been considered for the states Vm(pg, 295 K) and Vm(Tg, 0.1 MPa) using the simplifying condition that the viscosity at the glass transition is the same at pg at room temperature and at atmospheric pressure at Tg. Assuming a constant γ over this range of density, a reasonable agreement has been found for the γ determined herein and that of a previous density scaling analysis of ionic liquids viscosities under moderate conditions. Further support for the appropriateness of extrapolating the GCM equation of state to the GPa pressure range is provided by comparing the GCM and an equation of state previously derived in the power law density-scaling regime.

  17. Measurement of the glass transition temperature of elastomer systems

    SciTech Connect

    Sircar, A.K.; Chartoff, R.P.

    1994-09-01

    The glass transition temperature of polymers depends on both the experimental procedures and the experimental techniques used for its evaluation. However, the value of the published data is often diminished because these details are omitted. Examples are cited to show how the magnitude of differential scanning calorimetry (DSC) T{sub g} depends on the T{sub g} location and different calibration methods. Some comments are also made about thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) methods, although these are treated only briefly. The factors that are unique to elastomer glass transition temperatures are: (1) the difficulties of calibration of the instruments at subambient temperature, (2) increase of T{sub g} by the extent of vulcanization and filler loading, (3) differences due to microstructure and microphase separation, and (4) the availability of different grades of the same elastomer with different composition or added components, which alter their T{sub g}. Thus, the literature value of T{sub g} should include not only the calibration and procedure for the experiment, but also the exact name and description of the elastomer with the number index, the recipe used, and the cure conditions.

  18. Glass transition of charged particles in two-dimensional confinement.

    PubMed

    Yazdi, Anoosheh; Heinen, Marco; Ivlev, Alexei; Löwen, Hartmut; Sperl, Matthias

    2015-05-01

    The glass transition of mesoscopic charged particles in two-dimensional confinement is studied by mode-coupling theory. We consider two types of effective interactions between the particles, corresponding to two different models for the distribution of surrounding ions that are integrated out in coarse-grained descriptions. In the first model, a planar monolayer of charged particles is immersed in an unbounded isotropic bath of ions, giving rise to an isotropically screened Debye-Hückel (Yukawa)-type effective interaction. The second, experimentally more relevant system is a monolayer of negatively charged particles that levitate atop a flat horizontal electrode, as frequently encountered in laboratory experiments with complex (dusty) plasmas. A steady plasma current toward the electrode gives rise to an anisotropic effective interaction potential between the particles, with an algebraically long-ranged in-plane decay. In a comprehensive parameter scan that covers the typical range of experimentally accessible plasma conditions, we calculate and compare the mode-coupling predictions for the glass transition in both kinds of systems.

  19. Glass transition and relaxation processes of nanocomposite polymer electrolytes.

    PubMed

    Money, Benson K; Hariharan, K; Swenson, Jan

    2012-07-05

    This study focus on the effect of δ-Al(2)O(3) nanofillers on the dc-conductivity, glass transition, and dielectric relaxations in the polymer electrolyte (PEO)(4):LiClO(4). The results show that there are three dielectric relaxation processes, α, β, and γ, in the systems, although the structural α-relaxation is hidden in the strong conductivity contribution and could therefore not be directly observed. However, by comparing an enhanced dc-conductivity, by approximately 2 orders of magnitude with 4 wt % δ-Al(2)O(3) added, with a decrease in calorimetric glass transition temperature, we are able to conclude that the dc-conductivity is directly coupled to the hidden α-relaxation, even in the presence of nanofillers (at least in the case of δ-Al(2)O(3) nanofillers at concentrations up to 4 wt %). This filler induced speeding up of the segmental polymer dynamics, i.e., the α-relaxation, can be explained by the nonattractive nature of the polymer-filler interactions, which enhance the "free volume" and mobility of polymer segments in the vicinity of filler surfaces.

  20. Local Glass Transition Temperature Gradients Near Polymer-Polymer Interfaces

    NASA Astrophysics Data System (ADS)

    Baglay, Roman; Roth, Connie

    2015-03-01

    For decades the glass transition in confined systems has been studied with the hopes of uncovering the governing length scales that impact these dynamics. However, understanding length scales of local gradients in glass transition temperature (Tg) near a free surface have been hampered by limitations of how to treat the enhanced mobility at the free surface theoretically. We have previously reported on the local Tg in multilayer structures made from high molecular weight polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA), a weakly immiscible system with a ~ 7 nm interfacial width. Using ultrathin (10-15 nm) pyrene-labeled layers inserted into the multilayer structure at different positions (z) from the glassy-rubbery interface, we were able to map the local Tg(z) profile across this glassy-rubbery interface with temperature-dependent fluorescence intensity measurements. Our work revealed an asymmetric local mobility gradient propagating hundreds of nanometers away from the glassy-rubbery PS-PnBMA interface into the glassy PS and rubbery PnBMA sides before bulk Tgs were recovered far from the interface. Here we extend these measurements to investigate how the local Tg(z) profile in PS varies when in contact with a variety of immiscible polymers whose Tgs vary between +90 K to -80 K relative to the Tg of PS, so-called hard vs soft confinement.

  1. Glass transition of ionic liquids under high pressure

    NASA Astrophysics Data System (ADS)

    Ribeiro, Mauro C. C.; Pádua, Agílio A. H.; Gomes, Margarida F. Costa

    2014-06-01

    The glass transition pressure at room temperature, pg, of six ionic liquids based on 1-alkyl-3-methylimidazolium cations and the anions [BF4]-, [PF6]-, and bis(trifluromethanesulfonyl)imide, [NTf2]-, has been obtained from the pressure dependence of the bandwidth of the ruby fluorescence line in diamond anvil cells. Molar volume, Vm(pg), has been estimated by a group contribution model (GCM) developed for the ionic liquids. A density scaling relation, TVγ, has been considered for the states Vm(pg, 295 K) and Vm(Tg, 0.1 MPa) using the simplifying condition that the viscosity at the glass transition is the same at pg at room temperature and at atmospheric pressure at Tg. Assuming a constant γ over this range of density, a reasonable agreement has been found for the γ determined herein and that of a previous density scaling analysis of ionic liquids viscosities under moderate conditions. Further support for the appropriateness of extrapolating the GCM equation of state to the GPa pressure range is provided by comparing the GCM and an equation of state previously derived in the power law density-scaling regime.

  2. Structure of glasses containing transition metal ions. Progress report, February 1, 1979-January 31, 1980

    SciTech Connect

    White, W B; Furukawa, T; Tsong, I S.T.; Fox, K; Herman, J S; Houser, C; Nelson, C

    1980-02-01

    New normal coordinate calculations were used to relate the vibrational frequencies of silicate glasses to Si-O force constants. These appear to account for the observed frequency shifts with degree of silica polymerization. Raman spectroscopy has been used to elucidate the structure of sodium borosilicate glasses and of sodium aluminosilicate glasses. Structures of compositionally complex glasses can be understood if spectra are measured on many glasses spaced at small compositional intervals. Optical absorption spectra were used to investigate the structural setting of iron in alkali silicate glasses. Research on the alkali-hydrogen exchange in alkali silicate glasses was completed and additional work on ternary glasses is under way. A series of appendices present completed work on the structural investigations of alkali borosilicate glasses, on the structural setting of transition metal ions in glasses, and on the diffusion of hydrogen in alkali silicate glasses.

  3. Resolving the controversy on the glass transition temperature of water?

    PubMed

    Capaccioli, S; Ngai, K L

    2011-09-14

    We consider experimental data on the dynamics of water (1) in glass-forming aqueous mixtures with glass transition temperature T(g) approaching the putative T(g) = 136 K of water from above and below, (2) in confined spaces of nanometer in size, and (3) in the bulk at temperatures above the homogeneous nucleation temperature. Altogether, the considered relaxation times from the data range nearly over 15 decades from 10(-12) to 10(3) s. Assisted by the various features in the isothermal spectra and theoretical interpretation, these considerations enable us to conclude that relaxation of un-crystallized water is highly non-cooperative. The exponent β(K) of its Kohlrausch stretched exponential correlation function is not far from having the value of one, and hence the deviation from exponential time decay is slight. Albeit the temperature dependence of its α-relaxation time being non-Arrhenius, the corresponding T(g)-scaled temperature dependence has small steepness index m, likely less than 44 at T(g), and hence water is not "'fragile" as a glassformer. The separation in time scale of the α- and the β-relaxations is small at T(g), becomes smaller at higher temperatures, and they merge together shortly above T(g). From all these properties and by inference, water is highly non-cooperative as a glass-former, it has short cooperative length-scale, and possibly smaller configurational entropy and change of heat capacity at T(g) compared with other organic glass-formers. This conclusion is perhaps unsurprising because water is the smallest molecule. Our deductions from the data rule out that the T(g) of water is higher than 160 K, and suggest that it is close to the traditional value of 136 K.

  4. Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties.

    PubMed

    Möncke, D; Kamitsos, E I; Palles, D; Limbach, R; Winterstein-Beckmann, A; Honma, T; Yao, Z; Rouxel, T; Wondraczek, L

    2016-09-28

    A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn(2+) enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb(2+) and Bi(3+) induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was

  5. Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties

    NASA Astrophysics Data System (ADS)

    Möncke, D.; Kamitsos, E. I.; Palles, D.; Limbach, R.; Winterstein-Beckmann, A.; Honma, T.; Yao, Z.; Rouxel, T.; Wondraczek, L.

    2016-09-01

    A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb2+ and Bi3+ induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was determined

  6. Pressure dependence of glass transition in As2Te3 glass.

    PubMed

    Ramesh, K

    2014-07-24

    Amorphous solids prepared from their melt state exhibit glass transition phenomenon upon heating. Viscosity, specific heat, and thermal expansion coefficient of the amorphous solids show rapid changes at the glass transition temperature (Tg). Generally, application of high pressure increases the Tg and this increase (a positive dT(g)/dP) has been understood adequately with free volume and entropy models which are purely thermodynamic in origin. In this study, the electrical resistivity of semiconducting As(2)Te(3) glass at high pressures as a function of temperature has been measured in a Bridgman anvil apparatus. Electrical resistivity showed a pronounced change at Tg. The Tg estimated from the slope change in the resistivity-temperature plot shows a decreasing trend (negative dT(g)/dP). The dT(g)/dP was found to be -2.36 °C/kbar for a linear fit and -2.99 °C/kbar for a polynomial fit in the pressure range 1 bar to 9 kbar. Chalcogenide glasses like Se, As(2)Se(3), and As(30)Se(30)Te(40) show a positive dT(g)/dP which is very well understood in terms of the thermodynamic models. The negative dT(g)/dP (which is generally uncommon in liquids) observed for As(2)Te(3) glass is against the predictions of the thermodynamic models. The Adam-Gibbs model of viscosity suggests a direct relationship between the isothermal pressure derivative of viscosity and the relaxational expansion coefficient. When the sign of the thermal expansion coefficient is negative, dT(g)/dP = Δk/Δα will be less than zero, which can result in a negative dT(g)/dP. In general, chalcogenides rich in tellurium show a negative thermal expansion coefficient (NTE) in the supercooled and stable liquid states. Hence, the negative dT(g)/dP observed in this study can be understood on the basis of the Adams-Gibbs model. An electronic model proposed by deNeufville and Rockstad finds a linear relation between Tg and the optical band gap (Eg) for covalent semiconducting glasses when they are grouped

  7. The glass transition and crystallization of propylene carbonate investigated by mechanical spectroscopy

    NASA Astrophysics Data System (ADS)

    Ying, X. N.

    2013-08-01

    A composite reed flexural vibration method is used to investigate the dynamic mechanical responses of propylene carbonate below room temperature. The mechanical spectrum of propylene carbonate is subtracted from a composite system consisting of the substrate and of propylene carbonate deposited on it. The mechanical spectrum relating to the glass transition and crystallization is identified. It suggests that an interfacial effect occurs in the crystalline state rather than the glass transition. This work supports the reliability of the composite reed flexural vibration method in the investigation on the glass transition of propylene carbonate. Finally, the determination of the glass transition temperature of propylene carbonate by mechanical spectroscopy was discussed.

  8. Evidence for a simple monatomic ideal glass former: the thermodynamic glass transition from a stable liquid phase.

    PubMed

    Elenius, Måns; Oppelstrup, Tomas; Dzugutov, Mikhail

    2010-11-07

    Under cooling, a liquid can undergo a transition to the glassy state either as a result of a continuous slowing down or by a first-order polyamorphous phase transition. The second scenario has so far always been observed in a metastable liquid domain below the melting point where crystalline nucleation interfered with the glass formation. We report the first observation of the liquid-glass transition by a first-order polyamorphous phase transition from the equilibrium stable liquid phase. The observation was made in a molecular dynamics simulation of a one-component system with a model metallic pair potential. In this way, the model, demonstrating the thermodynamic glass transition from a stable liquid phase, may be regarded as a candidate for a simple monatomic ideal glass former. This observation is of conceptual importance in the context of continuing attempts to resolve the long-standing Kauzmann paradox. The possibility of a thermodynamic glass transition from an equilibrium melt in a metallic system also indicates a new strategy for the development of bulk metallic glass-forming alloys.

  9. Breaking Through the Glass Ceiling: Recent Experimental Approaches to Probe the Properties of Supercooled Liquids near the Glass Transition.

    SciTech Connect

    Smith, R. Scott; Kay, Bruce D.

    2012-03-15

    Experimental measurements of the properties supercooled liquids at temperatures near their respective glass transition temperatures, Tg, are requisite for understanding the behavior of glasses and amorphous solids. Unfortunately, many supercooled molecular liquids rapidly crystallize at temperatures far above their Tg making such measurements difficult to nearly impossible. In this perspective we discuss some recent alternative approaches to obtain experimental data in the temperature regime near Tg. These new approaches may yield the additional experimental data necessary to test current theoretical models of the dynamical slowdown that occurs in supercooled liquids approaching the glass transition.

  10. Breaking Through the Glass Ceiling: Recent Experimental Approaches to Probe the Properties of Supercooled Liquids near the Glass Transition.

    PubMed

    Smith, R Scott; Kay, Bruce D

    2012-03-15

    Experimental measurements of the properties of supercooled liquids at temperatures near their glass transition temperatures, Tg, are requisite for understanding the behavior of glasses and amorphous solids. Unfortunately, many supercooled molecular liquids rapidly crystallize at temperatures far above their Tg, making such measurements difficult to nearly impossible. In this Perspective, we discuss some recent alternative approaches to obtain experimental data in the temperature regime near Tg. These new approaches may yield the additional experimental data necessary to test current theoretical models of the dynamical slowdown that occurs in supercooled liquids approaching the glass transition.

  11. Mid-gap phenomena in chalcogenide glasses and barrier-cluster-heating model

    SciTech Connect

    Banik, Ivan Kubliha, Marián; Lukovičová, Jozefa; Pavlendová, Gabriela

    2015-12-07

    The physical mechanism of photoluminescence spectrum formation of chalcogenide glasses (CHG) belongs to the important unsolved problems in physics of non-crystalline materials. Photoluminescence is an important means of the electron spectrum investigation. PL spectrum in CHG is produced mostly in the middle of the band gap, and its profile is normal - Gaussian. Several features of PL spectra in CHG is still a great mystery. The aim of the paper is to make reader acquainted with the new insight into the problem. In this article we also deal with the issue of clarifying the nature of mid-gap absorption. From the experiments it is known that after excitation of the glass As{sub 2}S{sub 3} (or As{sub 2}Se{sub 3}) with primary radiation from Urbach-tail region the glass will be able to absorb the photons of low energy (IR) radiation from mid-gap region of spectra. This low photon absorption without action of the primary excitation radiation of the higher photon energy is impossible. Mid-gap absorption yields boost in the photoluminescence. The paper gives the reader the new insights into some, until now, unexplained effects and contexts in chalcogenide glasses from the position of barrier-cluster-heating model.

  12. Finite-size scaling study of dynamic critical phenomena in a vapor-liquid transition

    NASA Astrophysics Data System (ADS)

    Midya, Jiarul; Das, Subir K.

    2017-01-01

    Via a combination of molecular dynamics (MD) simulations and finite-size scaling (FSS) analysis, we study dynamic critical phenomena for the vapor-liquid transition in a three dimensional Lennard-Jones system. The phase behavior of the model has been obtained via the Monte Carlo simulations. The transport properties, viz., the bulk viscosity and the thermal conductivity, are calculated via the Green-Kubo relations, by taking inputs from the MD simulations in the microcanonical ensemble. The critical singularities of these quantities are estimated via the FSS method. The results thus obtained are in nice agreement with the predictions of the dynamic renormalization group and mode-coupling theories.

  13. Finite-size scaling study of dynamic critical phenomena in a vapor-liquid transition.

    PubMed

    Midya, Jiarul; Das, Subir K

    2017-01-28

    Via a combination of molecular dynamics (MD) simulations and finite-size scaling (FSS) analysis, we study dynamic critical phenomena for the vapor-liquid transition in a three dimensional Lennard-Jones system. The phase behavior of the model has been obtained via the Monte Carlo simulations. The transport properties, viz., the bulk viscosity and the thermal conductivity, are calculated via the Green-Kubo relations, by taking inputs from the MD simulations in the microcanonical ensemble. The critical singularities of these quantities are estimated via the FSS method. The results thus obtained are in nice agreement with the predictions of the dynamic renormalization group and mode-coupling theories.

  14. Reconsideration of inviscid shock interactions and transition phenomena on double-wedge geometries in a M ∞ = 9 hypersonic flow

    NASA Astrophysics Data System (ADS)

    Hu, Z. M.; Myong, R. S.; Yang, Y. R.; Cho, T. H.

    2010-12-01

    Shock polar analysis as well as 2-D numerical computation technique are used to illustrate a diverse flow topology induced by shock/shock interaction in a M ∞ = 9 hypersonic flow. New flow features associated with inviscid shock wave interaction on double-wedge-like geometries are reported in this study. Transition of shock interaction, unsteady oscillation, and hysteresis phenomena in the RR ↔ MR transition, and the physical mechanisms behind these phenomena are numerically studied and analyzed.

  15. Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water

    PubMed Central

    Giovambattista, Nicolas; Loerting, Thomas; Lukanov, Boris R.; Starr, Francis W.

    2012-01-01

    Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature Tg. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of Tg(P) for LDA and HDA by performing computer simulations of two water models – one with a LLPT, and one without. In the absence of a LLPT, Tg(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different Tg(P) which are directly linked with the LLPT. Available experimental data for Tg(P) are only consistent with the scenario including a LLPT. PMID:22550566

  16. Two-dimensional electronic spectroscopy signatures of the glass transition

    DOE PAGES

    Lewis, K. L. .. M.; Myers, J. A.; Fuller, F.; ...

    2010-01-01

    Two-dimensional electronic spectroscopy is a sensitive probe of solvation dynamics. Using a pump–probe geometry with a pulse shaper [ Optics Express 15 (2007), 16681-16689; Optics Express 16 (2008), 17420-17428], we present temperature dependent 2D spectra of laser dyes dissolved in glass-forming solvents. At low waiting times, the system has not yet relaxed, resulting in a spectrum that is elongated along the diagonal. At longer times, the system loses its memory of the initial excitation frequency, and the 2D spectrum rounds out. As the temperature is lowered, the time scale of this relaxation grows, and the elongation persists for longermore » waiting times. This can be measured in the ratio of the diagonal width to the anti-diagonal width; the behavior of this ratio is representative of the frequency–frequency correlation function [ Optics Letters 31 (2006), 3354–3356]. Near the glass transition temperature, the relaxation behavior changes. Understanding this change is important for interpreting temperature-dependent dynamics of biological systems.« less

  17. Dynamically disordered hopping, glass transition, and polymer electrolytes

    NASA Astrophysics Data System (ADS)

    Lonergan, Mark C.; Nitzan, Abraham; Ratner, Mark A.; Shriver, D. F.

    1995-08-01

    The central parameter of the dynamically disordered hopping (DDH) model, the renewal time, is correlated with the characteristic time constant of the glass transition relaxation in polymer-salt complexes. With this identification, the frequency-dependent permittivity of these materials can be quite adequately described. In particular, experimental evidence for a high-frequency relaxation predicted by the DDH model is presented. This relaxation corresponds to the polarization of ions in their local percolation clusters as they wait for a renewal event to occur. In light of information on the renewal time, the direct current properties of polymer-salt complexes are used to calculate the size of these local clusters. These calculations suggest that the motion of an ion in the absence of renewal (polymer segmental motion) corresponds to displacements within its local coordination ``cage'' rather than hopping between several available coordination sites.

  18. Simultaneous Determination of Glass Transition Temperatures of Several Polymers

    PubMed Central

    He, Jiang; Liu, Wei; Huang, Yao-Xiong

    2016-01-01

    Aims A simple and easy optical method is proposed for the determination of glass transition temperature (Tg) of polymers. Methods & Results Tg was determined using the technique of microsphere imaging to monitor the variation of the refractive index of polymer microsphere as a function of temperature. It was demonstrated that the method can eliminate most thermal lag and has sensitivity about six fold higher than the conventional method in Tg determination. So the determined Tg is more accurate and varies less with cooling/heating rate than that obtained by conventional methods. The most attractive character of the method is that it can simultaneously determine the Tg of several polymers in a single experiment, so it can greatly save experimental time and heating energy. Conclusion The method is not only applicable for polymer microspheres, but also for the materials with arbitrary shapes. Therefore, it is expected to be broadly applied to different fundamental researches and practical applications of polymers. PMID:26985670

  19. Anomalously large isotope effect in the glass transition of water

    DOE PAGES

    Gainaru, Catalin; Agapov, Alexander L.; Fuentes-Landete, Violeta; ...

    2014-11-24

    Here we present the discovery of an unusually large isotope effect in the structural relaxation and the glass transition temperature Tg of water. Dielectric relaxation spectroscopy of low-density as well as of vapor deposited amorphous water reveal Tg differences of 10±2K between H2O and D2O, sharply contrasting with other hydrogen bonded liquids for which H/D exchange increases Tg by typically less than 1K. We show that the large isotope effect and the unusual variation of relaxation times in water at low temperatures can be explained in terms of quantum effects. Thus, our findings shed new light on water's peculiar low-temperaturemore » dynamics and the possible role of quantum effects in its structural relaxation, and possibly in dynamics of other low molecular weight liquids.« less

  20. The vortex glass to liquid transition in Bi2212 whisker

    NASA Astrophysics Data System (ADS)

    Zheng, P.; Zhou, Y. Q.; Chen, Z. J.; Luo, S.; Wang, W. H.; He, Y. S.; Duo, J.

    1999-05-01

    Through scaling the dc I- V isotherms of Bi2212 whisker in magnetic field H‖ c, the vortex glass-liquid transition is found in Bi2212 whisker whereas it does not appear in Bi2212 crystal slab [R. Behr, J. Kotzler, G. Nakielski, M. Baumann, M. Kaufmann, J. Kowalewski, Physica C 235 (1994) 2669]. The critical exponents are ν=0.5, z=4.0. We found that the critical exponents are influenced by the planar defects of the sample. The result was compared to those of single crystals and films [Behr et al., 1994; H. Yamasaki, K. Endo, S. Kosaka, M. Umeda, S. Yoshida, K. Kajimura, Phys. Rev. B 50 (17) (1994) 12959].

  1. Moisture adsorption isotherms and glass transition temperature of pectin.

    PubMed

    Basu, Santanu; Shivhare, U S; Muley, S

    2013-06-01

    The moisture adsorption isotherms of low methoxyl pectin were determined at 30-70°C and water activity ranging from 0.11 to 0.94. The moisture adsorption isotherms revealed that the equilibrium moisture content increased with water activity. Increase in temperature, in general, resulted in decreased equilibrium moisture content. However in some cases, equilibrium moisture content values increased with temperature at higher water activities. Selected sorption models (GAB, Halsey, Henderson, Oswin, modified Oswin) were tested for describing the adsorption isotherms. Parameters of each sorption models were determined by nonlinear regression analysis. Oswin model gave the best fit for pectin sorption behaviour. Isosteric heat of sorption decreased with increase in moisture content and varied between 14.607 and 0.552 kJ/mol. Glass transition temperature decreased with increase in moisture content of pectin.

  2. Comparison of static length scales characterizing the glass transition.

    PubMed

    Biroli, Giulio; Karmakar, Smarajit; Procaccia, Itamar

    2013-10-18

    The dramatic dynamic slowing down associated with the glass transition is considered by many to be related to the existence of a static length scale that grows when temperature decreases. Defining, identifying, and measuring such a length is a subtle problem. Recently, two proposals, based on very different insights regarding the relevant physics, were put forward. One approach is based on the point-to-set correlation technique and the other on the scale where the lowest eigenvalue of the Hessian matrix becomes sensitive to disorder. Here we present numerical evidence that the two approaches might result in the same identical length scale. This provides mutual support for their relevance and, at the same time, raises interesting theoretical questions, discussed in the conclusion.

  3. Local elastic response measured near the colloidal glass transition

    NASA Astrophysics Data System (ADS)

    Anderson, D.; Schaar, D.; Hentschel, H. G. E.; Hay, J.; Habdas, Piotr; Weeks, Eric R.

    2013-03-01

    We examine the response of a dense colloidal suspension to a local force applied by a small magnetic bead. For small forces, we find a linear relationship between the force and the displacement, suggesting the medium is elastic, even though our colloidal samples macroscopically behave as fluids. We interpret this as a measure of the strength of colloidal caging, reflecting the proximity of the samples' volume fractions to the colloidal glass transition. The strain field of the colloidal particles surrounding the magnetic probe appears similar to that of an isotropic homogeneous elastic medium. When the applied force is removed, the strain relaxes as a stretched exponential in time. We introduce a model that suggests this behavior is due to the diffusive relaxation of strain in the colloidal sample.

  4. Relaxation and possible dynamical transition in electron glass

    NASA Astrophysics Data System (ADS)

    Bhandari, Preeti; Malik, Vikas; Kumar, Deepak

    2017-05-01

    We have considered here the relaxation properties of three dimensional lattice model of an electron glass. We have modeled the kinetics of site-occupation numbers as Ising spins by Kawasaki Dynamics. The master equation governing the dynamics is approximated by making mean field approximation. We have calculated the eigenvalues and localization characteristics of the linear dynamical matrix. The behavior of the eigenvalues at different temperatures is used to detect the presence of a possible dynamical transition. We have also calculated eigenvalues of inverse susceptibility matrix and its behavior with temperature is used as additional input to analyze the slow dynamics and aging. Due to localized states having long lifetime the dynamics of the system slows down with decreasing temperature. We found the gap exponent of density of states of Hartree energy to be close to δ≈d-1 as predicted by Efros and Shklovskii.

  5. The glass transition process in humid biopolymers. DSC study

    NASA Astrophysics Data System (ADS)

    Grunina, N. A.; Belopolskaya, T. V.; Tsereteli, G. I.

    2006-05-01

    Thermal properties of native and denatured biopolymers with quite different chemical and steric structure (globular and fibrillar proteins, DNA, starches) were studied by means of differential scanning calorimetry in a wide range of temperatures and concentrations of water. It was shown that both native and denatured humid biopolymers are glassy systems. The glass transition temperature of these systems strongly depends on percentage of water, with water being simultaneously an intrinsic element of systems' ordered structure and a plasticizer of its amorphous state. On the base of the absolute values of heat capacities for biopolymer-water systems as a whole, heat capacities for biopolymers themselves were calculated as functions on water concentration at fixed temperatures. The S-shaped change of heat capacity observed on diagrams of state both for native and denatured biopolymers is the manifestation of biopolymers' passing through the vitrification region, as it occurs for denatured samples at heating.

  6. Definition of a mechanical glass transition temperature for dehydrated foods.

    PubMed

    Kasapis, Stefan

    2004-04-21

    A new concept of the mechanical glass transition temperature (T(g)) is presented with application in dehydrated high-sugar/gelatin mixtures, fish, and fruits. The macroscopic basis and manner of relaxation processes during vitrification of these foodstuffs are developed using small deformation dynamic oscillation, the master curve of viscoelasticity, and the time-temperature superposition principle. The quantitative features of the mechanical T(g) are based on the combined framework of free volume/WLF theory and the Andrade equation. It is proposed that the thermal profile of storage modulus on shear is a fundamental index of monitoring changes in a glassy structure, and several cases are presented in support of this concept.

  7. Anomalously large isotope effect in the glass transition of water

    SciTech Connect

    Gainaru, Catalin; Agapov, Alexander L.; Fuentes-Landete, Violeta; Amann-Winkel, Katrin; Nelson, Helge; Köster, Karsten W.; Kolesnikov, Alexander I.; Novikov, Vladimir N.; Richert, Ranko; Böhmer, Roland; Loerting, Thomas; Sokolov, Alexei P.

    2014-11-24

    Here we present the discovery of an unusually large isotope effect in the structural relaxation and the glass transition temperature Tg of water. Dielectric relaxation spectroscopy of low-density as well as of vapor deposited amorphous water reveal Tg differences of 10±2K between H2O and D2O, sharply contrasting with other hydrogen bonded liquids for which H/D exchange increases Tg by typically less than 1K. We show that the large isotope effect and the unusual variation of relaxation times in water at low temperatures can be explained in terms of quantum effects. Thus, our findings shed new light on water's peculiar low-temperature dynamics and the possible role of quantum effects in its structural relaxation, and possibly in dynamics of other low molecular weight liquids.

  8. Changes in the Atomic Structure through Glass Transition Observed by X-Ray Scattering

    SciTech Connect

    Egami, Takeshi

    2012-01-01

    The glass transition involves a minor change in the internal energy, and yet the physical and mechanical properties of a glass change dramatically. In order to determine the evolution of the atomic structure through the glass transition, we employed in-situ synchrotron X-ray scattering measurements as a function of temperature on a model material: Zr-Cu-Al metallic glass. We found that the thermal expansion at the atomic level is smaller than the macroscopic thermal expansion, and significantly increases above the glass transition temperature. The observed changes in the pair-distribution function (PDF) are explained in terms of the fluctuations in the local atomic volume and their change through the glass transition.

  9. Critical phenomena and noise-induced phase transitions in neuronal networks.

    PubMed

    Lee, K-E; Lopes, M A; Mendes, J F F; Goltsev, A V

    2014-01-01

    We study numerically and analytically first- and second-order phase transitions in neuronal networks stimulated by shot noise (a flow of random spikes bombarding neurons). Using an exactly solvable cortical model of neuronal networks on classical random networks, we find critical phenomena accompanying the transitions and their dependence on the shot noise intensity. We show that a pattern of spontaneous neuronal activity near a critical point of a phase transition is a characteristic property that can be used to identify the bifurcation mechanism of the transition. We demonstrate that bursts and avalanches are precursors of a first-order phase transition, paroxysmal-like spikes of activity precede a second-order phase transition caused by a saddle-node bifurcation, while irregular spindle oscillations represent spontaneous activity near a second-order phase transition caused by a supercritical Hopf bifurcation. Our most interesting result is the observation of the paroxysmal-like spikes. We show that a paroxysmal-like spike is a single nonlinear event that appears instantly from a low background activity with a rapid onset, reaches a large amplitude, and ends up with an abrupt return to lower activity. These spikes are similar to single paroxysmal spikes and sharp waves observed in electroencephalographic (EEG) measurements. Our analysis shows that above the saddle-node bifurcation, sustained network oscillations appear with a large amplitude but a small frequency in contrast to network oscillations near the Hopf bifurcation that have a small amplitude but a large frequency. We discuss an amazing similarity between excitability of the cortical model stimulated by shot noise and excitability of the Morris-Lecar neuron stimulated by an applied current.

  10. Determination of glass transition temperature for polymers by methods of thermoactivation spectroscopy

    NASA Astrophysics Data System (ADS)

    Yurov, V. M.; Laurinas, V. C.; Eremin, E. N.; Gyngazova, M. S.

    2016-02-01

    For rapid determination of glass transition temperature for polymers, we propose a method of thermally stimulated luminescence. The experiments were carried for epoxy polymers dyed and undyed with organic dyes. It is shown that glass transition temperature depends on curing temperature and concentration of the dye. The comparison with the thermogravimetric analysis showed coincidence of the results obtained.

  11. Modeling the nonlinear PMMA behavior near glass transition temperature: application to its thermoforming

    NASA Astrophysics Data System (ADS)

    Gilormini, P.; Chevalier, L.; Régnier, G.

    2011-01-01

    Using suitable constitutive equations, numerical simulation allows predicting the properties of transparencies that are thermoformed near their glass transition temperature. Such equations are presented, which describe the nonlinear viscoelastic behavior of poly(methyl methacrylate) at large deformations near glass transition. The simulation of the thermoforming of a transparency at constant and uniform temperature is performed and compared with experimental results.

  12. Effects of forming conditions on structure, relaxation phenomena, and aging behaviors of glass fibers

    NASA Astrophysics Data System (ADS)

    Shen, Changqing

    DSC analysis and DRIFT spectroscopy were combined to study the effects of fiber forming conditions and fiber aging behaviors. An external pressure set-up was incorporated into the former fiber drawing system to manipulate the fiber diameter. Soda-aluminosilicate glass fibers of the same diameter were prepared with this system at the same temperature with various rates. Pre-Tg exotherm of the fibers increased first with drawing rate and decreased when the rate exceeded 8.0 m/s, presumably caused by the shear thinning effects. When the rate is greater than 8.0 m/s, a new structure-related band at 877 cm-1 appeared as a shoulder to the band at 850 cm-1. The band at 877 cm -1 remained intact during the annealing and aging processes, while the band at 850 cm-1 responded sensitively to these processes. Evidence was found for structural orientation in silicate fibers. Four endothermic peaks were found in the DSC curves of long-term aged fibers. The assignments for the peaks were provided. The aging behavior of glass fibers was found to be affected by both the glass composition and the fiber forming conditions.

  13. Pressure coefficient of the glass transition temperature in the thermodynamic scaling regime

    NASA Astrophysics Data System (ADS)

    Koperwas, K.; Grzybowski, A.; Grzybowska, K.; Wojnarowska, Z.; Pionteck, J.; Sokolov, A. P.; Paluch, M.

    2012-10-01

    We report that the pressure coefficient of the glass transition temperature, dTg/dp, which is commonly used to determine the pressure sensitivity of the glass transition temperature Tg, can be predicted in the thermodynamic scaling regime. We show that the equation derived from the isochronal condition combined with the well-known scaling, TVγ = const, predicts successfully values of dTg/dp for a variety of glass-forming systems, including van der Waals liquids, polymers, and ionic liquids.

  14. The structural origin of the hard-sphere glass transition in granular packing

    SciTech Connect

    Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie

    2015-09-28

    Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.

  15. The structural origin of the hard-sphere glass transition in granular packing

    DOE PAGES

    Xia, Chengjie; Li, Jindong; Cao, Yixin; ...

    2015-09-28

    Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleationmore » process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.« less

  16. The structural origin of the hard-sphere glass transition in granular packing

    PubMed Central

    Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie

    2015-01-01

    Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden' polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. Our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses. PMID:26412008

  17. A thermally tunable inverse opal photonic crystal for monitoring glass transition.

    PubMed

    Sun, Liguo; Xie, Zhuoying; Xu, Hua; Xu, Ming; Han, Guozhi; Wang, Cheng; Bai, Xuduo; Gu, ZhongZe

    2012-03-01

    An optical method was developed to monitor the glass transition of the polymer by taking advantage of reflection spectrum change of the thermally tunable inverse opal photonic crystal. The thermally tunable photonic bands of the polymer inverse opal photonic crystal were traceable to the segmental motion of macromolecules, and the segmental motion was temperature dependent. By observing the reflection spectrum change of the polystyrene inverse opal photonic crystal during thermal treatment, the glass transition temperature of polystyrene was gotten. Both changes of the position and intensity of the reflection peak were observed during the glass transition process of the polystyrene inverse opal photonic crystal. The optical change of inverse opal photonic crystal was so large that the glass transition temperature could even be estimated by naked eyes. The glass transition temperature derived from this method was consistent with the values measured by differential scanning calorimeter.

  18. Thermal glass transition beyond the Vogel-Fulcher-Tammann behavior for glass forming diglycidylether of bisphenol A.

    PubMed

    Krüger, J K; Britz, T; Baller, J; Possart, W; Neurohr, H

    2002-12-31

    For the low molecular weight fragile liquid diglycidyl ether of bisphenol A we report, based on Brillouin and dielectric spectroscopy, on a thermal glass transition where the relaxation time of the alpha process does not go to infinity. Instead, the structural alpha relaxation disappears spontaneously at the transition point. That discontinuity in relaxation time coincides with a kink in the longitudinal hypersonic velocity and determines unambiguously the transition from the liquid to the glassy state.

  19. Laser-induced glass-crystallization phenomena of GeSe2 investigated by light scattering

    NASA Astrophysics Data System (ADS)

    Haro, E.; Xu, Z. S.; Morhange, J.-F.; Balkanski, M.; Espinosa, G. P.; Phillips, J. C.

    1985-07-01

    Recrystallization of glassy GeSe2 under laser irradiation has been studied with use of Raman spectroscopy. A threshold irradiation power level below which no changes in the local molecular structure of the system can be detected has been defined. For an irradiation power above the threshold, three stages of transformation have been identified: The first stage is characterized by the nucleation of clusters or submicrocrystallites which remain embedded in a continuum glass matrix. The second stage is characterized by the coexistence of clusters of various sizes. Up to this stage, the system is fully reversible. The last stage is reached when the crystallites coalesce to form a polycrystalline material.

  20. Analysis of early medieval glass beads - Glass in the transition period

    NASA Astrophysics Data System (ADS)

    Šmit, Žiga; Knific, Timotej; Jezeršek, David; Istenič, Janka

    2012-05-01

    Glass beads from graves excavated in Slovenia and dated archaeologically to the 7th-10th century AD were analysed by the combined PIXE-PIGE method. The results indicate two groups of glass; natron glass made in the Roman tradition and glass made with alkalis from the ash of halophytic plants, which gradually replaced natron glass after c. 800 AD. The alkalis used in the second group of glass seem to be in close relation to a variant of the Venetian white glass that appeared several centuries later. The origin of this glass may be traced to glass production in Mesopotamia and around the Aral Sea. All the mosaic beads with eye decoration, as well as most of the drawn-segmented and drawn-cut beads analysed, are of plant-ash glass, which confirms their supposed oriental origin.

  1. Long-wavelength fluctuations and the glass transition in two dimensions and three dimensions

    NASA Astrophysics Data System (ADS)

    Vivek, Skanda; Kelleher, Colm P.; Chaikin, Paul M.; Weeks, Eric R.

    2017-02-01

    Phase transitions significantly differ between 2D and 3D systems, but the influence of dimensionality on the glass transition is unresolved. We use microscopy to study colloidal systems as they approach their glass transitions at high concentrations and find differences between two dimensions and three dimensions. We find that, in two dimensions, particles can undergo large displacements without changing their position relative to their neighbors, in contrast with three dimensions. This is related to Mermin-Wagner long-wavelength fluctuations that influence phase transitions in two dimensions. However, when measuring particle motion only relative to their neighbors, two dimensions and three dimensions have similar behavior as the glass transition is approached, showing that the long-wavelength fluctuations do not cause a fundamental distinction between 2D and 3D glass transitions.

  2. Long-wavelength fluctuations and the glass transition in two dimensions and three dimensions.

    PubMed

    Vivek, Skanda; Kelleher, Colm P; Chaikin, Paul M; Weeks, Eric R

    2017-02-21

    Phase transitions significantly differ between 2D and 3D systems, but the influence of dimensionality on the glass transition is unresolved. We use microscopy to study colloidal systems as they approach their glass transitions at high concentrations and find differences between two dimensions and three dimensions. We find that, in two dimensions, particles can undergo large displacements without changing their position relative to their neighbors, in contrast with three dimensions. This is related to Mermin-Wagner long-wavelength fluctuations that influence phase transitions in two dimensions. However, when measuring particle motion only relative to their neighbors, two dimensions and three dimensions have similar behavior as the glass transition is approached, showing that the long-wavelength fluctuations do not cause a fundamental distinction between 2D and 3D glass transitions.

  3. Effect of UV exposure on photochromic glasses doped with transition metal oxides

    NASA Astrophysics Data System (ADS)

    El-Zaiat, S. Y.; Medhat, M.; Omar, Mona F.; Shirif, Marwa A.

    2016-07-01

    Silver halide photochromic glasses doped with one of the transition metal oxides, (Ti O2) , (CoO) ,(Cr2 O3) are prepared using the melt quench technique. Glass samples are exposed to a UV source for 20 min. Spectral reflectance and transmittance at normal incidence of the prepared glasses are recorded before and after UV exposure with a double beam spectrophotometer in the spectral range 200-2500 nm. Dispersion parameters such as: single oscillator energy, dispersion energy and Abbe's number are deduced and compared. Absorption dispersion parameters, like optical energy gap for direct and indirect transitions, Urbach energy and steepness parameter, are deduced for the different glass prepared. Reflection loss, molar refractivity and electronic polarizability are deduced and compared. The effect of UV light exposure of these glasses on transmittance, reflectance, the linear and the predicted nonlinear optical parameters are investigated and discussed for the three transition metals. Nonlinear parameters increase in the three glass samples after UV exposure.

  4. Roles of water and solids composition in the control of glass transition and stickiness of milk powders.

    PubMed

    Silalai, Nattiga; Roos, Yrjö H

    2010-06-01

    Plasticization and glass transition of amorphous components in food powders often result in stickiness and caking. The glass transition temperature (T(g)) of milk powders was measured by differential scanning calorimetry (DSC) and a viscometer method was used to determine sticky-point temperatures. Water sorption isotherms were established for varying solids compositions. Lactose contents were analyzed by high-performance anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) and proteins were identified using SDS-PAGE gel electrophoresis. Solids composition and water affected both the T(g) and stickiness behavior. Stickiness was governed by carbohydrates and water plasticization. At low protein contents, precrystallization of lactose decreased the sticky point temperature, but increasing protein content in all milk powders decreased stickiness at all water activities. The results showed that glass transition can be used to describe time-dependent stickiness and crystallization phenomena, and it can be used as a parameter to control and reduce stickiness of dairy solids with various compositions.

  5. Conformational Fluctuations of Polymers in a Melt Associated with Glass Transition

    NASA Astrophysics Data System (ADS)

    Iwaoka, Nobuyuki; Takano, Hiroshi

    2017-03-01

    The conformational fluctuations of a glassy short polymer melt are studied by coarse-grained molecular dynamics simulations and principal component analysis (PCA). The distribution of PCA eigenvalues, which measure static fluctuations of the polymers, shows a clear difference between above and below the conventional glass transition temperature Tg. The approximate conformational entropy of the polymers also indicates a transition near Tg. This is evidence that the static properties of polymers in the melt signal the glass transition.

  6. Signature of a Type-A Glass Transition and Intrinsic Confinement Effects in a Binary Glass-Forming System

    NASA Astrophysics Data System (ADS)

    Blochowicz, Thomas; Schramm, Sebastian; Lusceac, Sorin; Vogel, Michael; Stühn, Bernd; Gutfreund, Philipp; Frick, Bernhard

    2012-07-01

    We study dynamically highly asymmetric binary mixtures comprised of small methyl tetrahydrofuran (MTHF) molecules and polystyrene. Combined use of dielectric spectroscopy, H2 nuclear magnetic resonance, incoherent quasielastic neutron scattering, and depolarized dynamic light scattering allows us to selectively probe the dynamics of the components in a broad dynamic range. It turns out that the mixtures exhibit two glass transitions in a wide concentration range although being fully miscible on a macroscopic scale. In between both glass transition temperatures, the dynamics of the small molecules show strong confinement effects, e.g., a crossover from Vogel-Fulcher to Arrhenius behavior of the time constants. Moreover, the dynamical behavior of small molecules close to the slow matrix is consistent with mode coupling theory predictions for a type-A glass transition, which was expected from recent theoretical and simulation studies in comparable systems.

  7. Apparent critical phenomena in the superionic phase transition of Cu2-xSe

    SciTech Connect

    Kang, Stephen Dongmin; Danilkin, Sergey A.; Aydemir, Umut; Avdeev, Maxim; Studer, Andrew; Snyder, G. Jeffrey

    2016-01-11

    The superionic phase transition of ${\\mathrm{Cu}}_{2-x}\\mathrm{Se}$ accompanies drastic changes in transport properties. The Seebeck coefficient increases sharply while the electrical conductivity and thermal diffusivity drops. Such behavior has previously been attributed to critical phenomena under the assumption of a continuous phase transition. However, applying Landau's criteria suggests that the transition should be first order. Using the phase diagram that is consistent with a first order transition, we show that the observed transport properties and heat capacity curves can be accounted for and modeled with good agreement. The apparent critical phenomena is shown to be a result of compositional degree-of-freedom. In conclusion, understanding of the phase transition allows to explain the enhancement in the thermoelectric figure-of-merit that is accompanied with the transition.

  8. Glass transition temperatures and fermentative activity of heat-treated commercial active dry yeasts.

    PubMed

    Schebor, C; Galvagno, M; del Pilar Buera, M; Chirife, J

    2000-01-01

    Differential scanning calorimetry thermograms of various samples of commercial instant active dry yeasts revealed a clear glass transition typical of amorphous carbohydrates and sugars. The resulting glass transition temperatures were found to decrease with increasing moisture content. The observed glass curve was similar to that of pure trehalose, which is known to accumulate in large amounts in baker's yeast. The effect of heat treatment at various temperatures on the fermentative activity (as measured by the metabolic production of CO(2)) of dry yeast was studied. First-order plots were obtained representing the loss of fermentative activity as a function of heating time at the various temperatures assayed. Significant losses of fermentative activity were observed in vitrified yeast samples. The dependence of rate constants with temperature was found to follow Arrhenius behavior. The relationship between the loss of fermentative activity and glass transition was not verified, and the glass transition was not reflected on the temperature dependence of fermentative activity loss.

  9. Evidence of glass transition in thin films of maleic anhydride derivatives: Effect of the surfactant coadsorption

    NASA Astrophysics Data System (ADS)

    López-Dıaz, D.; Velázquez, M. M.

    2008-08-01

    The glass transition temperature of poly (maleic anhydride-alt-1-octadecen) and poly (styrene-co-maleic anhydride) cumene-terminated thin films has been measured by mechanical relaxation of Langmuir films of these polymers. The dynamical properties show glass-like features (non-Arrhenius relaxation times and non-Debye mechanical response) interpreted by the coupling model. The glass transition temperature values determined by a mechanical relaxation experiment (step-compression) agree very well with those obtained by surface potential measurements. It is found that the glass transition temperature values in thin films decrease by about 100K as compared with those corresponding to the bulk polymers. The coadsorption of the water-insoluble surfactant DODAB decreases the glass transition temperature.

  10. Replica symmetry breaking transition of the weakly anisotropic Heisenberg spin glass in magnetic fields.

    PubMed

    Imagawa, Daisuke; Kawamura, Hikaru

    2004-02-20

    The spin and the chirality orderings of the three-dimensional Heisenberg spin glass with the weak random anisotropy are studied under applied magnetic fields by equilibrium Monte Carlo simulations. A replica symmetry breaking transition occurs in the chiral sector accompanied by the simultaneous spin-glass order. The ordering behavior differs significantly from that of the Ising spin glass, despite the similarity in the global symmetry. Our observation is consistent with the spin-chirality decoupling-recoupling scenario of a spin-glass transition.

  11. Precise Measurements of the Density and Critical Phenomena Near Phase Transitions in Liquid Helium

    NASA Technical Reports Server (NTRS)

    Yeh, Nai-Chang

    1997-01-01

    The first-year progress for the project of precise measurements of the density and critical phenomena of helium near phase transitions is summarized below: (1) completion of a cryogenic sample probe for the proposed measurements, and the rehabilitation of a designated laboratory at Caltech for this project; (2) construction and testing of a superconducting niobium cavity; (3) acquisition of one phase-locked-loop system for high-resolution frequency control and read- out; (4) setting up high-resolution thermometry (HRT) for temperature readout and control; (5) developing new approaches for calibrating the coefficient between the resonant frequency shift (delta f) and the helium density (rho), as well as for measuring the effect of gravity on T(sub lambda) to a much better precision; (6) programming of the interface control of all instruments for automatic data acquisition; and (7) improving data analyses and fitting procedures.

  12. Investigation of the atypical glass transition and recrystallization behavior of amorphous prazosin salts.

    PubMed

    Kumar, Lokesh; Popat, Dharmesh; Bansal, Arvind K

    2011-08-25

    This manuscript studied the effect of counterion on the glass transition and recrystallization behavior of amorphous salts of prazosin. Three amorphous salts of prazosin, namely, prazosin hydrochloride, prazosin mesylate and prazosin tosylate were prepared by spray drying, and characterized by optical-polarized microscopy, differential scanning calorimetry and powder X-ray diffraction. Modulated differential scanning calorimetry was used to determine the glass transition and recrystallization temperature of amorphous salts. Glass transition of amorphous salts followed the order: prazosin mesylate > prazosin tosylate ~ prazosin hydrochloride. Amorphous prazosin mesylate and prazosin tosylate showed glass transition, followed by recrystallization. In contrast, amorphous prazosin hydrochloride showed glass transition and recrystallization simultaneously. Density Functional Theory, however, suggested the expected order of glass transition as prazosin hydrochloride > prazosin mesylate > prazosin tosylate. The counterintuitive observation of amorphous prazosin hydrochloride having lower glass transition was explained in terms of its lower activation energy (206.1 kJ/mol) for molecular mobility at Tg, compared to that for amorphous prazosin mesylate (448.5 kJ/mol) and prazosin tosylate (490.7 kJ/mol), and was further correlated to a difference in hydrogen bonding strength of the amorphous and the corresponding recrystallized salts. This study has implications in selection of an optimal amorphous salt form for pharmaceutical development.

  13. The Gardner Transition: A new approach for understanding low-temperature glasses

    NASA Astrophysics Data System (ADS)

    Charbonneau, Patrick

    Recent theoretical advances in the mean-field theory of glasses predict the existence deep in the glass phase of a novel phase transition, a so-called Gardner transition. This transition signals the emergence of a complex free energy landscape composed of a marginally stable hierarchy of sub-basins within a broad glass metabasin. It is thus the onset of marked changes in thermal and transport properties of glasses, and ultimately leads to the unusual critical behavior at jamming. The Gardner transition itself is immediately related to a diverging (i) characteristic relaxation time, (ii) caging susceptibility and (iii) correlation length of the caging heterogeneity as well as aging, even in well-thermalized glasses. We have detected some of these signatures both in a mean-field model and in standard hard-sphere glass formers. We find the results to quantitatively agree with theory in the former and qualitatively so in the latter, which suggest that the transition should be detectable in a wide array of numerical and experimental systems. Interestingly, although the Gardner transitions is primarily associated with structural glass formers, we also find features of the transition in crystals of polydisperse particles once the landscape becomes rough.

  14. Using Dielectric Relaxation Spectroscopy to Characterize the Glass Transition Time of Polydextrose.

    PubMed

    Buehler, Martin G; Kindle, Michael L; Carter, Brady P

    2015-06-01

    Dielectric relaxation spectroscopy was used to characterize the glass transition time, tg , of polydextrose, where the glass transition temperature, Tg , and water activity, aw (relative humidity), were held constant during polydextrose relaxation. The tg was determined from a shift in the peak frequency of the imaginary capacitance spectrum with time. It was found that when the peak frequency reaches 30 mHz, polydextrose undergoes glass transition. Glass transition time, tg , is the time for polydextrose to undergo glass transition at a specific Tg and aw . Results lead to a modified state diagram, where Tg is depressed with increasing aw . This curve forms a boundary: (a) below the boundary, polydextrose does not undergo glass transition and (b) above the boundary, polydextrose rapidly undergoes glass transition. As the boundary curve is specified by a tg value, it can assist in the selection of storage conditions. An important point on the boundary curve is at aw = 0, where Tg0 = 115 °C. The methodology can also be used to calculate the stress-relaxation viscosity of polydextrose as a function of Tg and aw , which is important when characterizing the flow properties of polydextrose initially in powder form.

  15. Investigation of the Atypical Glass Transition and Recrystallization Behavior of Amorphous Prazosin Salts

    PubMed Central

    Kumar, Lokesh; Popat, Dharmesh; Bansal, Arvind K.

    2011-01-01

    This manuscript studied the effect of counterion on the glass transition and recrystallization behavior of amorphous salts of prazosin. Three amorphous salts of prazosin, namely, prazosin hydrochloride, prazosin mesylate and prazosin tosylate were prepared by spray drying, and characterized by optical-polarized microscopy, differential scanning calorimetry and powder X-ray diffraction. Modulated differential scanning calorimetry was used to determine the glass transition and recrystallization temperature of amorphous salts. Glass transition of amorphous salts followed the order: prazosin mesylate > prazosin tosylate ∼ prazosin hydrochloride. Amorphous prazosin mesylate and prazosin tosylate showed glass transition, followed by recrystallization. In contrast, amorphous prazosin hydrochloride showed glass transition and recrystallization simultaneously. Density Functional Theory, however, suggested the expected order of glass transition as prazosin hydrochloride > prazosin mesylate > prazosin tosylate. The counterintuitive observation of amorphous prazosin hydrochloride having lower glass transition was explained in terms of its lower activation energy (206.1 kJ/mol) for molecular mobility at Tg, compared to that for amorphous prazosin mesylate (448.5 kJ/mol) and prazosin tosylate (490.7 kJ/mol), and was further correlated to a difference in hydrogen bonding strength of the amorphous and the corresponding recrystallized salts. This study has implications in selection of an optimal amorphous salt form for pharmaceutical development. PMID:24310595

  16. Ideal quantum glass transitions: Many-body localization without quenched disorder

    SciTech Connect

    Schiulaz, M.; Müller, M.

    2014-08-20

    We explore the possibility for translationally invariant quantum many-body systems to undergo a dynamical glass transition, at which ergodicity and translational invariance break down spontaneously, driven entirely by quantum effects. In contrast to analogous classical systems, where the existence of such an ideal glass transition remains a controversial issue, a genuine phase transition is predicted in the quantum regime. This ideal quantum glass transition can be regarded as a many-body localization transition due to self-generated disorder. Despite their lack of thermalization, these disorder-free quantum glasses do not possess an extensive set of local conserved operators, unlike what is conjectured for many-body localized systems with strong quenched disorder.

  17. High Glass Transition Temperature Renewable Polymers via Biginelli Multicomponent Polymerization.

    PubMed

    Boukis, Andreas C; Llevot, Audrey; Meier, Michael A R

    2016-04-01

    A novel and straightforward one-pot multicomponent polycondensation method was established in this work. The Biginelli reaction is a versatile multicomponent reaction of an aldehyde, a β-ketoester (acetoacetate) and urea, which can all be obtained from renewable resources, yielding diversely substituted 3,4-dihydropyrimidin-2(1H)-ones (DHMPs). In this study, renewable diacetoacetate monomers with different spacer chain lengths (C3, C6, C10, C20) were prepared via simple transesterification of renewable diols and commercial acetoacetates. The diacetoacetate monomers were then reacted with renewable dialdehydes, i.e., terephthalaldehyde and divanillin in a Biginelli type step-growth polymerization. The obtained DHMP polymers (polyDHMPs) displayed high molar masses, high glass transition temperatures (Tg) up to 203 °C and good thermal stability (Td5%) of 280 °C. The Tg of the polyDHMPs could be tuned by variation of the structure of the dialdehyde or the diacetoacetate component. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Control parameter dependence of transport coefficients near the glass transition

    NASA Astrophysics Data System (ADS)

    Tokuyama, Michio

    2013-02-01

    The master curves for transport coefficients, such as self-diffusion coefficient D, shear viscosity η, and electrical conductivity σ, near the glass transition are studied based on the fact recently proposed by the present author that the long-time self-diffusion coefficients in both fragile and strong liquids are well described by the following two types of master curves, depending on whether the control parameter is an intensive one (X) or an extensive one (Y); f(x) = (1-x)2+ɛexp[62x3+ɛ(1-x)2+ɛ] and g(y) = (1-y)2/y, where x = X/Xf and y = Y/Yf, Xf and Yf being fictive singular points to be determined. Here ɛ = 4/3 for fragile liquids and 5/3 for strong liquids. The thermodynamic function Y = h(X) is then used to relate f(x) with g(y) and vice versa. The experimental data and the simulation results for the shear viscosity and the electrical conductivity are also analyzed by using the master curves f(x) and g(y). Thus, it is shown that any transport coefficients are well described by those master curves up to the deviation point, above which all the data start to deviate from the master curves and the system becomes out of equilibrium.

  19. Magnetically ordered phase near transition to Bose-glass phase

    NASA Astrophysics Data System (ADS)

    Syromyatnikov, A. V.; Sizanov, A. V.

    2017-01-01

    We discuss a magnetically ordered ("superfluid") phase near quantum transition to the Bose-glass phase in a simple modeling system, a Heisenberg antiferromagnet with spatial dimension d >2 in an external magnetic field with disorder in exchange coupling constants. Our analytical consideration is based on hydrodynamic description of long-wavelength excitations. Results obtained are valid in the entire critical region near the quantum critical point (QCP), allowing us to describe a possible crossover from one critical behavior to another. We demonstrate that the system behaves in full agreement with predictions by M. P. Fisher et al. [Phys. Rev. B 40, 546 (1989), 10.1103/PhysRevB.40.546] in close vicinity to the QCP. We find as an extension to that analysis that the anomalous dimension η =2 -d and β =ν d /2 , where β and ν are critical exponents of the order parameter and the correlation length, respectively. The density of states per spin of low-energy localized excitations is found to be independent of d ("superuniversal"). We show that many recent experimental and numerical results obtained in various three-dimensional (3D) systems can be described by our formulas using percolation critical exponents. Then, it is a possibility that a percolation critical regime arises in the ordered phase in some 3D systems not very close to the QCP.

  20. Thermal Features and Glass Transition in Polystyrene-Nanodiamond Composites

    NASA Astrophysics Data System (ADS)

    Cristian Chipara, Alin; Mion, Thomas; Villegas, Rafael; Lozano, Karen; Magdalena Chipara, Dorina; Tidrow, Steven; Chipara, Mircea

    2010-03-01

    Polystyrene-Nanodiamond composites were obtained by dissolving the polymeric matrix into a theta solvent (cyclohexane) followed by the addition of diamond nanoparticles from Aldrich (with a particle size ranging between 3 and 8 nm) and subsequent sonication for about 100 minutes by using a Hielscher high power (1 kW) sonicator. The homogeneous solution was poured onto microscope slides and the solvent has been removed by heating in an oven at 125 ^oC for about 3 hours. Composites containing various amounts (from 0 % to 25 % nanodiamonds within polystyrene) have been investigated. The physical properties of the as obtained nanocomposites were investigated by DSC, TGA, Raman, and WAXS. Glass transition temperature was shifted to higher temperatures and the thermal stability was enhanced by the addition of nanodiamonds. A phenomenological model for the observed changes is proposed (within the free volume approximation) and discussed in detail. Acknowledgements: This research was supported by US Army Research Laboratory (W911NF-08-1-0353) and LSAMP -UTPA.

  1. Computational approaches for investigating interfacial adhesion phenomena of polyimide on silica glass.

    PubMed

    Min, Kyoungmin; Rammohan, Aravind R; Lee, Hyo Sug; Shin, Jaikwang; Lee, Sung Hoon; Goyal, Sushmit; Park, Hyunhang; Mauro, John C; Stewart, Ross; Botu, Venkatesh; Kim, Hyunbin; Cho, Eunseog

    2017-09-05

    This manuscript provides a comprehensive study of adhesion behavior and its governing mechanisms when polyimide undergoes various modes of detachment from silica glass. Within the framework of steered molecular dynamics, we develop three different adhesion measurement techniques: pulling, peeling, and sliding. Such computational methodologies can be applied to investigate heterogeneous materials with differing interfacial adhesion modes. Here, a novel hybrid potential involving a combination of the INTERFACE force field in conjunction with ReaxFF and including Coulombic and Lennard-Jones interactions is employed to study such interfaces. The studies indicate that the pulling test requires the largest force and the shortest distance to detachment as the interfacial area is separated instantaneously, while the peeling test is observed to exhibit the largest distance for detachment because it separates via line-by-line adhesion. Two kinds of polyimides, aromatic and aliphatic type, are considered to demonstrate the rigidity dependent adhesion properties. The aromatic polyimide, which is more rigid due to the stronger charge transfer complex between chains, requires a greater force but a smaller distance at detachment than the aliphatic polyimide for all of the three methodologies.

  2. Non-monotonic effect of confinement on the glass transition.

    PubMed

    Varnik, Fathollah; Franosch, Thomas

    2016-04-06

    The relaxation dynamics of glass forming liquids and their structure are influenced in the vicinity of confining walls. This effect has mostly been observed to be a monotonic function of the slit width. Recently, a qualitatively new behaviour has been uncovered by Mittal and coworkers, who reported that the single particle dynamics in a hard-sphere fluid confined in a planar slit varies in a non-monotonic way as the slit width is decreased from five to roughly two particle diametres (Mittal et al 2008 Phys. Rev. Lett. 100 145901). In view of the great potential of this effect for applications in those fields of science and industry, where liquids occur under strong confinement (e.g. nano-technology), the number of researchers studying various aspects and consequences of this non-monotonic behaviour has been rapidly growing. This review aims at providing an overview of the research activity in this newly emerging field. We first briefly discuss how competing mechanisms such as packing effects and short-range attraction may lead to a non-monotonic glass transition scenario in the bulk. We then analyse confinement effects on the dynamics of fluids using a thermodynamic route which relates the single particle dynamics to the excess entropy. Moreover, relating the diffusive dynamics to the Widom's insertion probability, the oscillations of the local dynamics with density at moderate densities are fairly well described. At high densities belonging to the supercooled regime, however, this approach breaks down signaling the onset of strongly collective effects. Indeed, confinement introduces a new length scale which in the limit of high densities and small pore sizes competes with the short-range local order of the fluid. This gives rise to a non-monotonic dependence of the packing structure on confinement, with a corresponding effect on the dynamics of structural relaxation. This non-monotonic effect occurs also in the case of a cone-plate type channel, where the degree

  3. Non-monotonic effect of confinement on the glass transition

    NASA Astrophysics Data System (ADS)

    Varnik, Fathollah; Franosch, Thomas

    2016-04-01

    The relaxation dynamics of glass forming liquids and their structure are influenced in the vicinity of confining walls. This effect has mostly been observed to be a monotonic function of the slit width. Recently, a qualitatively new behaviour has been uncovered by Mittal and coworkers, who reported that the single particle dynamics in a hard-sphere fluid confined in a planar slit varies in a non-monotonic way as the slit width is decreased from five to roughly two particle diametres (Mittal et al 2008 Phys. Rev. Lett. 100 145901). In view of the great potential of this effect for applications in those fields of science and industry, where liquids occur under strong confinement (e.g. nano-technology), the number of researchers studying various aspects and consequences of this non-monotonic behaviour has been rapidly growing. This review aims at providing an overview of the research activity in this newly emerging field. We first briefly discuss how competing mechanisms such as packing effects and short-range attraction may lead to a non-monotonic glass transition scenario in the bulk. We then analyse confinement effects on the dynamics of fluids using a thermodynamic route which relates the single particle dynamics to the excess entropy. Moreover, relating the diffusive dynamics to the Widom’s insertion probability, the oscillations of the local dynamics with density at moderate densities are fairly well described. At high densities belonging to the supercooled regime, however, this approach breaks down signaling the onset of strongly collective effects. Indeed, confinement introduces a new length scale which in the limit of high densities and small pore sizes competes with the short-range local order of the fluid. This gives rise to a non-monotonic dependence of the packing structure on confinement, with a corresponding effect on the dynamics of structural relaxation. This non-monotonic effect occurs also in the case of a cone-plate type channel, where the degree

  4. Minimal cooling speed for glass transition in a simple solvable energy landscape model

    NASA Astrophysics Data System (ADS)

    Toledo-Marín, J. Quetzalcóatl; Castillo, Isaac Pérez; Naumis, Gerardo G.

    2016-06-01

    The minimal cooling speed required to form a glass is obtained for a simple solvable energy landscape model. The model, made from a two-level system modified to include the topology of the energy landscape, is able to capture either a glass transition or a crystallization depending on the cooling rate. In this setup, the minimal cooling speed to achieve glass formation is then found to be related with the crystallization relaxation time, energy barrier and with the thermal history. In particular, we obtain that the thermal history encodes small fluctuations around the equilibrium population which are exponentially amplified near the glass transition, which mathematically corresponds to the boundary layer of the master equation. The change in the glass transition temperature is also found as a function of the cooling rate. Finally, to verify our analytical results, a kinetic Monte Carlo simulation was implemented.

  5. Effects of confinement on the glass transition temperature of molecular liquids

    SciTech Connect

    Zhang, J.; Liu, G.; Jonas, J.

    1992-04-16

    Differential scanning calorimetry was used to analyze the effects of confinement on the glass transition of temperature, T{sub g}, of several molecular liquids in porous silica glasses. For all the liquids, confinement lowers the observed T{sub g}. A linear relationship between the inverse of the silica glass pore radius and T{sub g} was also observed. The relative temperature depression due to confinement was less than the freezing point depression. 40 refs., 1 fig., 1 tab.

  6. Striking role of non-bridging oxygen on glass transition temperature of calcium aluminosilicate glass-formers

    NASA Astrophysics Data System (ADS)

    Bouhadja, M.; Jakse, N.; Pasturel, A.

    2014-06-01

    Molecular dynamics simulations are used to study the structural and dynamic properties of calcium aluminosilicate, (CaO-Al2O3)1-x(SiO2)x, glass formers along three joins, namely, R = 1, 1.57, and 3, in which the silica content x can vary from 0 to 1. For all compositions, we determined the glass-transition temperature, the abundances of the non-bridging oxygen, triclusters, and AlO5 structural units, as well as the fragility from the temperature evolution of the α-relaxation times. We clearly evidence the role played by the non-bridging oxygen linked either to Al atoms or Si atoms in the evolution of the glass-transition temperature as well as of the fragility as a function of silica content along the three joins.

  7. Striking role of non-bridging oxygen on glass transition temperature of calcium aluminosilicate glass-formers

    SciTech Connect

    Bouhadja, M.; Jakse, N.; Pasturel, A.

    2014-06-21

    Molecular dynamics simulations are used to study the structural and dynamic properties of calcium aluminosilicate, (CaO-Al{sub 2}O{sub 3}){sub 1−x}(SiO{sub 2}){sub x}, glass formers along three joins, namely, R = 1, 1.57, and 3, in which the silica content x can vary from 0 to 1. For all compositions, we determined the glass-transition temperature, the abundances of the non-bridging oxygen, triclusters, and AlO{sub 5} structural units, as well as the fragility from the temperature evolution of the α-relaxation times. We clearly evidence the role played by the non-bridging oxygen linked either to Al atoms or Si atoms in the evolution of the glass-transition temperature as well as of the fragility as a function of silica content along the three joins.

  8. Fast scanning calorimetry studies of the glass transition in doped amorphous solid water: Evidence for the existence of a unique vicinal phase

    NASA Astrophysics Data System (ADS)

    McCartney, Stephanie A.; Sadtchenko, Vlad

    2013-02-01

    The fast scanning calorimetry (FSC) was employed to investigate glass transition phenomena in vapor deposited amorphous solid water (ASW) films doped with acetic acid, pentanol, and carbon tetrachloride. In all three cases, FSC thermograms of doped ASW films show well pronounced glass transitions at temperatures near 180 K. Systematic FSC studies of the glass transition temperature and the excess heat capacity dependence on the concentration of impurities indicate the possible existence of two distinct non-crystalline phases of H2O in binary aqueous solutions. According to our conjecture, bulk pure ASW is a glass at temperatures up to its crystallization near 205 K. However, guest molecules in the ASW matrix may be enveloped in an H2O phase which undergoes a glass transition prior to crystallization. In the case of CH3COOH, we estimate that such a viscous liquid shell contains approximately 25 H2O molecules. We discuss the implications of these findings for past studies of molecular kinetics in pure vitreous water and in binary aqueous solutions.

  9. Fast scanning calorimetry studies of the glass transition in doped amorphous solid water: evidence for the existence of a unique vicinal phase.

    PubMed

    McCartney, Stephanie A; Sadtchenko, Vlad

    2013-02-28

    The fast scanning calorimetry (FSC) was employed to investigate glass transition phenomena in vapor deposited amorphous solid water (ASW) films doped with acetic acid, pentanol, and carbon tetrachloride. In all three cases, FSC thermograms of doped ASW films show well pronounced glass transitions at temperatures near 180 K. Systematic FSC studies of the glass transition temperature and the excess heat capacity dependence on the concentration of impurities indicate the possible existence of two distinct non-crystalline phases of H2O in binary aqueous solutions. According to our conjecture, bulk pure ASW is a glass at temperatures up to its crystallization near 205 K. However, guest molecules in the ASW matrix may be enveloped in an H2O phase which undergoes a glass transition prior to crystallization. In the case of CH3COOH, we estimate that such a viscous liquid shell contains approximately 25 H2O molecules. We discuss the implications of these findings for past studies of molecular kinetics in pure vitreous water and in binary aqueous solutions.

  10. Emergence of long-range correlations and rigidity at the dynamic glass transition.

    PubMed

    Szamel, Grzegorz; Flenner, Elijah

    2011-09-02

    At the so-called dynamic glass transition predicted by the mean-field replica approach equilibrium liquid's translational symmetry is spontaneously broken, albeit at the microscopic level. We show that this fact implies the emergence of Goldstone modes and long-range density correlations. We derive and evaluate a new statistical mechanical expression for the glass shear modulus.

  11. Direct evidence of entropy driven fluid-like - glass-like transition in microgel suspensions

    NASA Astrophysics Data System (ADS)

    Guo, Yun Xia; Liu, Ying Dan; Liu, Riping; Tian, Yongjun; Chen, Ke; Wang, Li-Min

    2017-02-01

    The phase transitions in poly (N-isopropylacrylamide) (PNIPAM) microgel suspensions are studied using rheological and calorimetric measurements at various concentrations. Two transitions are resolved, one being the hydrophilic-hydrophobic transition imposed by the gain/release of H2O molecules in PNIPAM particles via H-bond interactions, the other the fluid-like - glass-like transition of the hydrated microgels. The relaxation behaviors in the frozen glass-like states are observed by monitoring the shear modulus upon aging. Nevertheless, no enthalpic signature is detected in the relaxation process, suggesting entropy-driven relaxation dynamics.

  12. Optical absorption and heating rate dependent glass transition in vanadyl doped calcium oxy-chloride borate glasses

    NASA Astrophysics Data System (ADS)

    Dahiya, M. S.; Khasa, S.; Agarwal, A.

    2015-04-01

    Some important results pertaining to optical and thermal properties of vanadyl doped oxy-halide glasses in the chemical composition CaCl2-CaO-B2O3 are discussed. These glasses have been prepared by conventional melt quench technique. From X-ray diffraction (XRD) profiles the amorphous nature of the doped glasses has been confirmed. The electronic polarizability is calculated and found to increase with increase in chloride content. The optical absorption spectra have been recorded in the frequency range of 200-3200 nm. Recorded spectra are analyzed to evaluate cut-off wavelength (λcut-off), optical band gap (Eg), band tailing (B), Urbach energy (ΔE) and refractive index (n). Thermal analysis has been carried out for the prepared glasses at three different heating rates viz. 5, 10 and 20 °C/min. The glass transition temperature (Tg) along with thermal activation energy (Ea) corresponding to each heating rate are evaluated from differential scanning calorimetry (DSC) thermographs. It is found that Ea decrease and Tg increase with increase in heating rate. The variation in Tg is also observed with the substitution of calcium chloride in place of calcium oxide. The increasing and higher values of Ea suggest that prepared glasses have good thermal stability. Variation in Tg and Eg suggests that Cl- anions enter into the voids of borate network at low concentrations (<5.0%) and contribute to the network formation at high concentration (>5.0%).

  13. Sharp semiconductor-to-metal transition of VO{sub 2} thin films on glass substrates

    SciTech Connect

    Jian, Jie; Chen, Aiping; Zhang, Wenrui; Wang, Haiyan

    2013-12-28

    Outstanding phase transition properties of vanadium dioxide (VO{sub 2}) thin films on amorphous glass were achieved and compared with the ones grown on c-cut sapphire and Si (111) substrates, all by pulsed laser deposition. The films on glass substrate exhibit a sharp semiconductor-to-metal transition (∼4.3 °C) at a near bulk transition temperature of ∼68.4 °C with an electrical resistance change as high as 3.2 × 10{sup 3} times. The excellent phase transition properties of the films on glass substrate are correlated with the large grain size and low defects density achieved. The phase transition properties of VO{sub 2} films on c-cut sapphire and Si (111) substrates were found to be limited by the high defect density.

  14. Numerical detection of the Gardner transition in a mean-field glass former.

    PubMed

    Charbonneau, Patrick; Jin, Yuliang; Parisi, Giorgio; Rainone, Corrado; Seoane, Beatriz; Zamponi, Francesco

    2015-07-01

    Recent theoretical advances predict the existence, deep into the glass phase, of a novel phase transition, the so-called Gardner transition. This transition is associated with the emergence of a complex free energy landscape composed of many marginally stable sub-basins within a glass metabasin. In this study, we explore several methods to detect numerically the Gardner transition in a simple structural glass former, the infinite-range Mari-Kurchan model. The transition point is robustly located from three independent approaches: (i) the divergence of the characteristic relaxation time, (ii) the divergence of the caging susceptibility, and (iii) the abnormal tail in the probability distribution function of cage order parameters. We show that the numerical results are fully consistent with the theoretical expectation. The methods we propose may also be generalized to more realistic numerical models as well as to experimental systems.

  15. Subcritical transition to turbulence: What we can learn from the physics of glasses.

    PubMed

    Dauchot, Olivier; Bertin, Eric

    2012-09-01

    In this note, we discuss possible analogies between the subcritical transition to turbulence in shear flows and the glass transition in supercooled liquids. We briefly review recent experimental and numerical results, as well as theoretical proposals, and compare the difficulties arising in assessing the divergence of the turbulence lifetime in subcritical shear flow with that encountered for the relaxation time in the study of the glass transition. In order to go beyond the purely methodological similarities, we further elaborate on this analogy and propose a simple model for the transition to turbulence, inspired by the random energy model (a standard model for the glass transition), with the aim to possibly foster yet-unexplored directions of research in subcritical shear flows.

  16. Numerical detection of the Gardner transition in a mean-field glass former

    NASA Astrophysics Data System (ADS)

    Charbonneau, Patrick; Jin, Yuliang; Parisi, Giorgio; Rainone, Corrado; Seoane, Beatriz; Zamponi, Francesco

    2015-07-01

    Recent theoretical advances predict the existence, deep into the glass phase, of a novel phase transition, the so-called Gardner transition. This transition is associated with the emergence of a complex free energy landscape composed of many marginally stable sub-basins within a glass metabasin. In this study, we explore several methods to detect numerically the Gardner transition in a simple structural glass former, the infinite-range Mari-Kurchan model. The transition point is robustly located from three independent approaches: (i) the divergence of the characteristic relaxation time, (ii) the divergence of the caging susceptibility, and (iii) the abnormal tail in the probability distribution function of cage order parameters. We show that the numerical results are fully consistent with the theoretical expectation. The methods we propose may also be generalized to more realistic numerical models as well as to experimental systems.

  17. Cluster Glass Transition of Ultrasoft-Potential Fluids at High Density

    NASA Astrophysics Data System (ADS)

    Miyazaki, Ryoji; Kawasaki, Takeshi; Miyazaki, Kunimasa

    2016-10-01

    Using molecular dynamics simulation, we investigate the slow dynamics of a supercooled binary mixture of soft particles interacting with a generalized Hertzian potential. At low density, it displays typical slow dynamics near its glass transition temperature. At higher densities, particles bond together, forming clusters, and the clusters undergo the glass transition. The number of particles in a cluster increases one by one as the density increases. We demonstrate that there exist multiple cluster-glass phases characterized by a different number of particles per cluster, each of which is separated by distinct minima. Surprisingly, a so-called higher order singularity of the mode-coupling theory signaled by a logarithmic relaxation is observed in the vicinity of the boundaries between monomer and cluster glass phases. The system also exhibits rich and anomalous dynamics in the cluster glass phases, such as the decoupling of the self- and collective dynamics.

  18. Irreversible transitions in the exchange-striction model of spin-glass state

    NASA Astrophysics Data System (ADS)

    Valkov, V. I.; Golovchan, A. V.

    2014-08-01

    Based on the assumption of a negative volume dependence of random exchange integrals, it is possible to switch to a compressible Sherrington-Kirkpatrick spin-glass model. Within the proposed model, temperature-pressure phase diagrams were calculated and pressure- and magnetic-field-induced first-order phase transitions from the initial paramagnetic and spin-glass states to the ferromagnetic state were predicted. It was shown that the application of pressure in the spin-glass state not only increases and shifts magnetic susceptibility, but also reduces the critical magnetic fields of irreversible induced phase transitions from the spin-glass to the ferromagnetic state. The obtained results are used to describe the spin-glass state in (Sm1-xGdx)0.55Sr0.45MnO3.

  19. Cluster Glass Transition of Ultrasoft-Potential Fluids at High Density.

    PubMed

    Miyazaki, Ryoji; Kawasaki, Takeshi; Miyazaki, Kunimasa

    2016-10-14

    Using molecular dynamics simulation, we investigate the slow dynamics of a supercooled binary mixture of soft particles interacting with a generalized Hertzian potential. At low density, it displays typical slow dynamics near its glass transition temperature. At higher densities, particles bond together, forming clusters, and the clusters undergo the glass transition. The number of particles in a cluster increases one by one as the density increases. We demonstrate that there exist multiple cluster-glass phases characterized by a different number of particles per cluster, each of which is separated by distinct minima. Surprisingly, a so-called higher order singularity of the mode-coupling theory signaled by a logarithmic relaxation is observed in the vicinity of the boundaries between monomer and cluster glass phases. The system also exhibits rich and anomalous dynamics in the cluster glass phases, such as the decoupling of the self- and collective dynamics.

  20. Calorimetric glass transition in a mean-field theory approach

    PubMed Central

    Mariani, Manuel Sebastian; Parisi, Giorgio; Rainone, Corrado

    2015-01-01

    The study of the properties of glass-forming liquids is difficult for many reasons. Analytic solutions of mean-field models are usually available only for systems embedded in a space with an unphysically high number of spatial dimensions; on the experimental and numerical side, the study of the properties of metastable glassy states requires thermalizing the system in the supercooled liquid phase, where the thermalization time may be extremely large. We consider here a hard-sphere mean-field model that is solvable in any number of spatial dimensions; moreover, we easily obtain thermalized configurations even in the glass phase. We study the 3D version of this model and we perform Monte Carlo simulations that mimic heating and cooling experiments performed on ultrastable glasses. The numerical findings are in good agreement with the analytical results and qualitatively capture the features of ultrastable glasses observed in experiments. PMID:25675523

  1. Dependence of the width of the glass transition interval on cooling and heating rates.

    PubMed

    Schmelzer, Jürn W P; Tropin, Timur V

    2013-01-21

    In a preceding paper [J. W. P. Schmelzer, J. Chem. Phys. 136, 074512 (2012)], a general kinetic criterion of glass formation has been advanced allowing one to determine theoretically the dependence of the glass transition temperature on cooling and heating rates (or similarly on the rate of change of any appropriate control parameter determining the transition of a stable or metastable equilibrium system into a frozen-in, non-equilibrium state of the system, a glass). In the present paper, this criterion is employed in order to develop analytical expressions for the dependence of the upper and lower boundaries and of the width of the glass transition interval on the rate of change of the external control parameters. It is shown, in addition, that the width of the glass transition range is strongly correlated with the entropy production at the glass transition temperature. The analytical results are supplemented by numerical computations. Analytical results and numerical computations as well as existing experimental data are shown to be in good agreement.

  2. Dependence of the width of the glass transition interval on cooling and heating rates

    NASA Astrophysics Data System (ADS)

    Schmelzer, Jürn W. P.; Tropin, Timur V.

    2013-01-01

    In a preceding paper [J. W. P. Schmelzer, J. Chem. Phys. 136, 074512 (2012), 10.1063/1.3685510], a general kinetic criterion of glass formation has been advanced allowing one to determine theoretically the dependence of the glass transition temperature on cooling and heating rates (or similarly on the rate of change of any appropriate control parameter determining the transition of a stable or metastable equilibrium system into a frozen-in, non-equilibrium state of the system, a glass). In the present paper, this criterion is employed in order to develop analytical expressions for the dependence of the upper and lower boundaries and of the width of the glass transition interval on the rate of change of the external control parameters. It is shown, in addition, that the width of the glass transition range is strongly correlated with the entropy production at the glass transition temperature. The analytical results are supplemented by numerical computations. Analytical results and numerical computations as well as existing experimental data are shown to be in good agreement.

  3. Percolation effects on entangled polymer rheology and the glass transition

    NASA Astrophysics Data System (ADS)

    Wool, Richard P.

    2012-07-01

    Current thinking on the fundamentals of entangled polymer melt rheology suggests that stress relaxation in the terminal zone occurs via Reptation, chain-end fluctuation and (convective) constraint release. This scenario is not correct. It is shown through a series of experiments with selectively deuterated model polymers that relaxation occurs through a percolation process which permits large clusters of entangled polymers to stress relax before their conformations are fully relaxed. The percolation model of entanglements (R.P. Wool, Macromolecules 26, 1564, 1993) makes unique predictions regarding the dynamics of polymer chains in the terminal relaxation zone. These include: (a) Reptating homopolymer chains with molecular weight M >> Mc appear to be non-Reptating as their ends and centers relax at the same rate in a Rouse-like manner during percolation. (b) The mechanical relaxation time τ(M) is related to the Reptation time Tr˜ M3 by τ(M) = Tr[(1-Mc/M)Me/Mc]2, which is the origin of the zero shear viscosity behaving as ηo˜M3.4 (c) The biggest surprise is that during stress relaxation, the random coil dimensions Rg(//) and Rg(⊥) are not fully relaxed when the stress and birefringence relax to zero. (d) Matrix molecular weight P effects on relaxation time τ(M) of the probe chain M are as follows: When the probe chain M>>P, the matrix P-chains percolate and Rouse-like dynamics is observed for the M-Reptating chains with τ(M) ˜ P1M2. (e) When the matrix P>>M, percolation does not occur for the M-chain and the relaxation time of the probe chain τ(M) ˜ PoM3 is in accord with DeGennes Reptation theory. These unusual results predicted by entanglement percolation are supported by extensive experimental data (NR, SANS, DSIMS, FTIR, BR) from selectively deuterated polystyrene chains HDH, DHD, HPS and DPS. These results clearly suggest that current notions of polymer rheology need to be reconsidered. Near Tg, a new perspective on the Glass Transition of amorphous

  4. Transition from glass to graphite in manufacture of composite aircraft structure

    NASA Technical Reports Server (NTRS)

    Buffum, H. E.; Thompson, V. S.

    1978-01-01

    The transition from fiberglass reinforced plastic composites to graphite reinforced plastic composites is described. Structural fiberglass design and manufacturing background are summarized. How this experience provides a technology base for moving into graphite composite secondary structure and then to composite primary structure is considered. The technical requirements that must be fulfilled in the transition from glass to graphite composite structure are also included.

  5. Testing the paradigms of the glass transition in colloids via dynamic simulation

    NASA Astrophysics Data System (ADS)

    Wang, Jialun; Peng, Xiaoguang; Li, Qi; McKenna, Gregory; Zia, Roseanna

    2016-11-01

    Upon cooling, molecular glass-formers undergo a glass transition during which viscosity appears to diverge, and the material transitions from a liquid to an amorphous solid. However, the new state is not an equilibrium phase: material properties such as enthalpy continue to evolve in time. Rather, the material evolves toward an "intransient" state, as measured by the Kovacs signature experiments, e.g. the intrinsic isotherm, which reveals a paradoxical dependence of transition time on quench depth, and suggests that whether the glass transition occurs at the beginning or end of this transition is an open question. Colloidal glass formers provide a natural way to model such behavior, owing to the disparity in time scales that allow tracking of particle dynamics. We interrogate these ideas via dynamic simulation of a hard-sphere colloidal glassy state induced by jumps in volume fraction. We explore three methods to model the jump: evaporation, aspiration, and particle-size jumps. During and following each jump, the positions, velocities, and particle-phase stress are tracked and utilized to characterize relaxation time scales and structural changes. Analogs for the intrinsic isotherms are developed. The results provide insight into the existence of an "ideal" glass transition.

  6. Glass Transition Temperature of Saccharide Aqueous Solutions Estimated with the Free Volume/Percolation Model.

    PubMed

    Constantin, Julian Gelman; Schneider, Matthias; Corti, Horacio R

    2016-06-09

    The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions has been predicted as a function of the water content by using the free volume/percolation model (FVPM). This model only requires the molar volume of water in the liquid and supercooled regimes, the molar volumes of the hypothetical pure liquid sugars at temperatures below their pure glass transition temperatures, and the molar volumes of the mixtures at the glass transition temperature. The model is simplified by assuming that the excess thermal expansion coefficient is negligible for saccharide-water mixtures, and this ideal FVPM becomes identical to the Gordon-Taylor model. It was found that the behavior of the water molar volume in trehalose-water mixtures at low temperatures can be obtained by assuming that the FVPM holds for this mixture. The temperature dependence of the water molar volume in the supercooled region of interest seems to be compatible with the recent hypothesis on the existence of two structure of liquid water, being the high density liquid water the state of water in the sugar solutions. The idealized FVPM describes the measured glass transition temperature of sucrose, glucose, and fructose aqueous solutions, with much better accuracy than both the Gordon-Taylor model based on an empirical kGT constant dependent on the saccharide glass transition temperature and the Couchman-Karasz model using experimental heat capacity changes of the components at the glass transition temperature. Thus, FVPM seems to be an excellent tool to predict the glass transition temperature of other aqueous saccharides and polyols solutions by resorting to volumetric information easily available.

  7. Glass Former Effects on Photoluminescence and Optical Properties of Some Heavy Metal Oxide Glasses Doped with Transition Metal Ions

    NASA Astrophysics Data System (ADS)

    Marzouk, M. A.; Abo-Naf, S. M.; Zayed, H. A.; Hassan, N. S.

    2017-03-01

    Heavy metal oxide (PbO and Bi2O3) glasses doped with transition metal (TM) ions (TiO2, V2O5, Cr2O3, and MnO2) and having low content of common glass formers (B2O3, SiO2, or P2O5) were prepared by the conventional melt annealing method. Ultraviolet, visible absorption, and photoluminescence properties of these glasses were measured, and the data were employed to investigate the prepared glassy samples. The optical absorption spectra of TiO2 and V2O5 exhibited three bands centered at about 240, 305, and 380 nm, followed by a broad asymmetrical near-visible band centered at 425-432 nm, while Cr2O3 and MnO2 exhibited an extended visible peak at 517-548 nm. Results showed that the luminescence intensity changed with different transition metal oxides. From the absorption edge data, the values of the optical band gap Eopt and Urbach energy (ΔE) were calculated. The calculated values of the optical energy gap were found to be dependent on the glass composition. The changing values of optical band gap and band tail can be related to the structural changes that are taking place in the glass samples. The variations of the luminescence intensity, values of optical band gap, band tail, and refractive index gave an indication of the potential use of the prepared glasses to design novel optical functional materials with higher optical performance.

  8. Bond orientational order in liquids: Towards a unified description of water-like anomalies, liquid-liquid transition, glass transition, and crystallization: Bond orientational order in liquids.

    PubMed

    Tanaka, Hajime

    2012-10-01

    There are at least three fundamental states of matter, depending upon temperature and pressure: gas, liquid, and solid (crystal). These states are separated by first-order phase transitions between them. In both gas and liquid phases a complete translational and rotational symmetry exist, whereas in a solid phase both symmetries are broken. In intermediate phases between liquid and solid, which include liquid crystal and plastic crystal phases, only one of the two symmetries is preserved. Among the fundamental states of matter, the liquid state is the most poorly understood. We argue that it is crucial for a better understanding of liquids to recognize that a liquid generally has the tendency to have a local structural order and its presence is intrinsic and universal to any liquid. Such structural ordering is a consequence of many-body correlations, more specifically, bond angle correlations, which we believe are crucial for the description of the liquid state. We show that this physical picture may naturally explain difficult unsolved problems associated with the liquid state, such as anomalies of water-type liquids (water, Si, Ge, ...), liquid-liquid transition, liquid-glass transition, crystallization and quasicrystal formation, in a unified manner. In other words, we need a new order parameter representing a low local free-energy configuration, which is a bond orientational order parameter in many cases, in addition to a density order parameter for the physical description of these phenomena. Here we review our two-order-parameter model of liquid and consider how transient local structural ordering is linked to all of the above-mentioned phenomena. The relationship between these phenomena is also discussed.

  9. Spin glass transition in canonical AuFe alloys: A numerical study

    NASA Astrophysics Data System (ADS)

    Zhang, Kai-Cheng; Li, Yong-Feng; Liu, Gui-Bin; Zhu, Yan

    2012-05-01

    Although spin glass transitions have long been observed in diluted magnetic alloys, e.g. AuFe and CuMn alloys, previous numerical studies are not completely consistent with the experiment results. The abnormal critical exponents of the alloys remain still puzzling. By employing parallel tempering algorithm with finite-size scaling analysis, we investigated the phase transitions in canonical AuFe alloys. Our results strongly support that spin glass transitions occur at finite temperatures in the alloys. The calculated critical exponents agree well with those obtained from experiments.

  10. Effects of configurational changes on electrical resistivity during glass-liquid transition of two bulk metal-alloy glasses

    NASA Astrophysics Data System (ADS)

    Aji, D. P. B.; Johari, G. P.

    2014-12-01

    Consequences of increase in structural fluctuations on heating Pd40Ni10Cu30P20 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 through their glass to liquid transition range were investigated by measuring the electrical resistivity, ρ, an electron scattering property. The temperature coefficient of resistivity (TCR = (1/ρ) dρ/dT) of the liquid and glassy states is negative. The plots of their ρ against T in the Tg (glass to liquid transition) range show a gradual change in the slope similar to the change observed generally for the plots of the density, elastic modulus, and refractive index. As fluctuations in the melt structure involve fewer configurations on cooling, ρ increases. In the energy landscape description, the melt's structure explores fewer minima with decrease in T, vibrational frequencies increase, and electron scattering and ρ increase. Plots of (-dρ/dT) against T resemble the plot of the specific heat of other glasses and show a sub-Tg feature and a rapid rise at T near Tg. Analysis shows that the magnitude of negative TCR is dominated by change in the phonon characteristics, and configurational fluctuations make it more negative. The TCR of the liquid and glassy states seems qualitatively consistent with the variation in the structure factor in Ziman's model for pure liquid metals as extended by Nagel to metal alloys and used to explain the negative TCR of a two-component metal glass.

  11. Discontinuous nature of the repulsive-to-attractive colloidal glass transition

    PubMed Central

    van de Laar, T.; Higler, R.; Schroën, K.; Sprakel, J.

    2016-01-01

    In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale. PMID:26940737

  12. Kinetics of the glass transition of fragile soft colloidal suspensions.

    PubMed

    Saha, Debasish; Joshi, Yogesh M; Bandyopadhyay, Ranjini

    2015-12-07

    Microscopic relaxation time scales are estimated from the autocorrelation functions obtained by dynamic light scattering experiments for Laponite suspensions with different concentrations (CL), added salt concentrations (CS), and temperatures (T). It has been shown in an earlier work [D. Saha, Y. M. Joshi, and R. Bandyopadhyay, Soft Matter 10, 3292 (2014)] that the evolutions of relaxation time scales of colloidal glasses can be compared with molecular glass formers by mapping the waiting time (tw) of the former with the inverse of thermodynamic temperature (1/T) of the latter. In this work, the fragility parameter D, which signifies the deviation from Arrhenius behavior, is obtained from fits to the time evolutions of the structural relaxation time scales. For the Laponite suspensions studied in this work, D is seen to be independent of CL and CS but is weakly dependent on T. Interestingly, the behavior of D corroborates the behavior of fragility in molecular glass formers with respect to equivalent variables. Furthermore, the stretching exponent β, which quantifies the width w of the spectrum of structural relaxation time scales, is seen to depend on tw. A hypothetical Kauzmann time tk, analogous to the Kauzmann temperature for molecular glasses, is defined as the time scale at which w diverges. Corresponding to the Vogel temperature defined for molecular glasses, a hypothetical Vogel time tα (∞) is also defined as the time at which the structural relaxation time diverges. Interestingly, a correlation is observed between tk and tα (∞), which is remarkably similar to that known for fragile molecular glass formers. A coupling model that accounts for the tw-dependence of the stretching exponent is used to analyse and explain the observed correlation between tk and tα (∞).

  13. Kinetics of the glass transition of fragile soft colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Saha, Debasish; Joshi, Yogesh M.; Bandyopadhyay, Ranjini

    2015-12-01

    Microscopic relaxation time scales are estimated from the autocorrelation functions obtained by dynamic light scattering experiments for Laponite suspensions with different concentrations (CL), added salt concentrations (CS), and temperatures (T). It has been shown in an earlier work [D. Saha, Y. M. Joshi, and R. Bandyopadhyay, Soft Matter 10, 3292 (2014)] that the evolutions of relaxation time scales of colloidal glasses can be compared with molecular glass formers by mapping the waiting time (tw) of the former with the inverse of thermodynamic temperature (1/T) of the latter. In this work, the fragility parameter D, which signifies the deviation from Arrhenius behavior, is obtained from fits to the time evolutions of the structural relaxation time scales. For the Laponite suspensions studied in this work, D is seen to be independent of CL and CS but is weakly dependent on T. Interestingly, the behavior of D corroborates the behavior of fragility in molecular glass formers with respect to equivalent variables. Furthermore, the stretching exponent β, which quantifies the width w of the spectrum of structural relaxation time scales, is seen to depend on tw. A hypothetical Kauzmann time tk, analogous to the Kauzmann temperature for molecular glasses, is defined as the time scale at which w diverges. Corresponding to the Vogel temperature defined for molecular glasses, a hypothetical Vogel time tα ∞ is also defined as the time at which the structural relaxation time diverges. Interestingly, a correlation is observed between tk and tα ∞ , which is remarkably similar to that known for fragile molecular glass formers. A coupling model that accounts for the tw-dependence of the stretching exponent is used to analyse and explain the observed correlation between tk and tα ∞ .

  14. Reversible atomic processes as basic mechanisms of the glass transition

    PubMed Central

    Ye, Feng; Sprengel, Wolfgang; Wunderlich, Rainer K.; Fecht, Hans-Jörg; Schaefer, Hans-Eckhardt

    2007-01-01

    Reversible formation and disappearance of vacant spaces (vacancy-type defects) in bulk Zr57Cu15.4Ni12.6Nb5Al10 glass are directly evidenced by high-resolution, time-differential dilatometry studies. The vacancy kinetics are strongly temperature-dependent, with an effective migration enthalpy of HVM = 3.34 eV. This may explain the strong temperature dependence of glass properties such as viscosity. The results presented here are of general importance for understanding amorphous condensed matter and biomaterials and for the technical development of amorphous steels. PMID:17664428

  15. Icosahedral Order, Frustration, and the Glass Transition: Evidence from Time-Dependent Nucleation and Supercooled Liquid Structure Studies

    SciTech Connect

    Shen, Y.T.; Kim, T.H.; Gangopadhyay, A.K.; Kelton, K.F.

    2009-06-05

    One explanation for the glass transition is a geometrical frustration owing to the development of non-space-filling short-range order (icosahedral, tetrahedral). However, experimental demonstrations of this are lacking. Here, the first quantitative measurements of the time-dependent nucleation rate in a Zr59Ti3Cu20Ni8Al10 bulk metallic glass are combined with the first measurements of the evolution of the supercooled liquid structure to near the glass transition temperature to provide strong support for an icosahedral-order-based frustration model for the glass transition in Zr-based glasses.

  16. Glass transition in thin supported polystyrene films probed by temperature-modulated ellipsometry in vacuum.

    PubMed

    Efremov, Mikhail Yu; Kiyanova, Anna V; Last, Julie; Soofi, Shauheen S; Thode, Christopher; Nealey, Paul F

    2012-08-01

    Glass transition in thin (1-200 nm thick) spin-cast polystyrene films on silicon surfaces is probed by ellipsometry in a controlled vacuum environment. A temperature-modulated modification of the method is used alongside a traditional linear temperature scan. A clear glass transition is detected in films with thicknesses as low as 1-2 nm. The glass transition temperature (T(g)) shows no substantial dependence on thickness for coatings greater than 20 nm. Thinner films demonstrate moderate T(g) depression achieving 18 K for thicknesses 4-7 nm. Less than 4 nm thick samples are excluded from the T(g) comparison due to significant thickness nonuniformity (surface roughness). The transition in 10-20 nm thick films demonstrates excessive broadening. For some samples, the broadened transition is clearly resolved into two separate transitions. The thickness dependence of the glass transition can be well described by a simple 2-layer model. It is also shown that T(g) depression in 5 nm thick films is not sensitive to a wide range of experimental factors including molecular weight characteristics of the polymer, specifications of solvent used for spin casting, substrate composition, and pretreatment of the substrate surface.

  17. Kinetic Glass Transition in a Micellar System with Short-Range Attractive Interaction

    SciTech Connect

    Mallamace, F.; Gambadauro, P.; Micali, N.; Chen, S.-H.

    2000-06-05

    We show that percolation and structural arrest transitions coexist in different regions of the phase diagram of a copolymer-micellar system and relate them to short-range intermicellar attraction. The intermediate scattering function shows a nonergodic transition along a temperature and concentration dependent line. Analyses show a logarithmic time dependence, attributed to a higher-order glass transition singularity predicted by mode-coupling theory, followed by a power law. (c) 2000 The American Physical Society.

  18. Glass transition-related thermorheological complexity in polystyrene melts

    NASA Astrophysics Data System (ADS)

    Lin, Y.-H.

    2007-11-01

    The relaxation-modulus G(t) functional forms covering the whole time range are given by incorporating a stretched exponential for the structural- (glassy-) relaxation process into the extended reptation theory (ERT; for entangled systems) or the Rouse theory (for entanglement-free systems). The creep compliance J(t) curves of two entangled (A and B) and one entanglement-free (C) polystyrene samples (Plazek) as well as the viscoelastic spectra G*(ω) of four entanglement-free polystyrene samples (Inoue et al) have been quantitatively analyzed in terms of the given G(t) functional forms. In such quantitatively successful analyses, the ERT or the Rouse theory works as the frame of reference in both the line shape and timescale. The thermorheological complexity in the J(t) curves is explained naturally and precisely by the temperature dependence of the energetic-interaction-derived structural relaxation being stronger than that of the entropic ERT or Rouse dynamics in a simple way. Structural-relaxation times τS (= 18s'K') of all the studied samples are equally well separated into two decoupled quantities: the structural-growth parameter s' and the frictional factor K' (for the Rouse-Mooney or Rouse modes of motion). The separation is fundamentally a clean-cut process: s' is determined entirely by the line shape of J(t) or G*(ω) while K' is calculated from the timescale shifting factor obtained from the superposition of the calculated curves onto the measured. The glassy-relaxation strength AGf and the stretching parameter β extracted from the J(t) and G*(ω) results over the glassy-relaxation region are in good agreement. The glass-transition temperature Tg is defined as corresponding to τS = 1000 s for all the studied samples. The τS, s' and K' data points of samples A, B and C extracted from their J(t) curves individually fall closely on the same curves when expressed as a function of ΔT = T-Tg, revealing a Tg-related universality within the polystyrene system

  19. Polymeric nanoparticles - Influence of the glass transition temperature on drug release.

    PubMed

    Lappe, Svenja; Mulac, Dennis; Langer, Klaus

    2017-01-30

    The physico-chemical characterisation of nanoparticles is often lacking the determination of the glass transition temperature, a well-known parameter for the pure polymer carrier. In the present study the influence of water on the glass transition temperature of poly (DL-lactic-co-glycolic acid) nanoparticles was assessed. In addition, flurbiprofen and mTHPP as model drugs were incorporated in poly (DL-lactic-co-glycolic acid), poly (DL-lactic acid), and poly (L-lactic acid) nanoparticles. For flurbiprofen-loaded nanoparticles a decrease in the glass transition temperature was observed while mTHPP exerted no influence on this parameter. Based on this observation, the release behaviour of the drug-loaded nanoparticles was investigated at different temperatures. For all preparations an initial burst release was measured that could be attributed to the drug adsorbed to the large nanoparticle surface. At temperatures above the glass transition temperature an instant drug release of the nanoparticles was observed, while at lower temperatures less drug was released. It could be shown that the glass transition temperature of drug loaded nanoparticles in suspension more than the corresponding temperature of the pure polymer is the pivotal parameter when characterising a nanostructured drug delivery system. Copyright © 2016 Elsevier B.V. All rights reserved.

  20. Direct evidence for local symmetry breaking during a strain glass transition.

    PubMed

    Zhou, Yumei; Xue, Dezhen; Tian, Ya; Ding, Xiangdong; Guo, Shengwu; Otsuka, Kazuhiro; Sun, Jun; Ren, Xiaobing

    2014-01-17

    Strain glass transition is a unique nanoscale displacive transition with local symmetry breaking while maintaining the macroscopic symmetry or average structure unchanged. It usually occurs in the "nonmartensitic" composition range of a martensitic system. So far, only indirect evidence exists for such a transition, essentially from macroscopic measurements and low-resolution transmission electron microscopy observations, and there is a lack of direct evidence for the speculated local symmetry breaking and the sluggish nature of the glass transition. In this Letter we report in situ high-resolution transmission electron microscopy observations on a Ti50(Pd41Cr9) strain glass alloy and direct evidence for these key issues. Our results show that at temperatures well above the strain glass transition temperature (Tg), the lattice is essentially an undistorted B2 structure. With approaching Tg, the local symmetry breaking gradually occurs with the formation and growth of nanomartensite clusters with a combined stacking period of three and four plane intervals, but the average structure measured by x-ray diffraction remains B2. These nanomartensite clusters become finally frozen below Tg. Our results provide not only a microscopic basis for the macroscopic properties of strain glass, but also new insights into a range of possible applications of this unique class of materials.

  1. Size-Dependent Brittle-to-Ductile Transition in Silica Glass Nanofibers.

    PubMed

    Luo, Junhang; Wang, Jiangwei; Bitzek, Erik; Huang, Jian Yu; Zheng, He; Tong, Limin; Yang, Qing; Li, Ju; Mao, Scott X

    2016-01-13

    Silica (SiO2) glass, an essential material in human civilization, possesses excellent formability near its glass-transition temperature (Tg > 1100 °C). However, bulk SiO2 glass is very brittle at room temperature. Here we show a surprising brittle-to-ductile transition of SiO2 glass nanofibers at room temperature as its diameter reduces below 18 nm, accompanied by ultrahigh fracture strength. Large tensile plastic elongation up to 18% can be achieved at low strain rate. The unexpected ductility is due to a free surface affected zone in the nanofibers, with enhanced ionic mobility compared to the bulk that improves ductility by producing more bond-switching events per irreversible bond loss under tensile stress. Our discovery is fundamentally important for understanding the damage tolerance of small-scale amorphous structures.

  2. A study of the glass transition of polypropylene surfaces by sum-frequency vibrational spectroscopy and scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Gracias, D. H.; Zhang, D.; Lianos, L.; Ibach, W.; Shen, Y. R.; Somorjai, G. A.

    1999-07-01

    Sum-frequency generation (SFG) vibrational spectroscopy and scanning force microscopy (SFM) were used to probe structural changes of atactic polypropylene (APP) and isotactic polypropylene (IPP) surfaces in the glass transition. The results indicate that below the glass transition, the surface polymer chains are better oriented with the CH 2 groups pointing outward and the surface elastic modulus is higher. The SFG and SFM results correlate well in the transition towards the glass phase. No discernible difference between the glass transition temperatures of the bulk and surface was observed.

  3. Thermal analysis of specific heat measurements in glassy Se80-xTe20Sbx alloys in glass transition region

    NASA Astrophysics Data System (ADS)

    Saraswat, S.; Mehta, N.; Sharma, S. D.

    2016-01-01

    In the present report, we have done specific heat measurements in glassy Se80-xTe20Sbx (0 ≤ x ≤ 15) alloys in glass transition region. Differential scanning calorimetry (DSC) technique is used for this purpose. We have observed a tremendously huge increase in the specific heat (Cp) values at the glass transition temperature. The thermal analysis shows that the values of Cp below glass transition temperature and the difference of Cp values before and after glass transition (∆Cp) are highly composition-dependent.

  4. Dynamical State Transition by Neuromodulation Due to Acetylcholine in Neural Network Model for Oscillatory Phenomena in Thalamus

    NASA Astrophysics Data System (ADS)

    Omori, Toshiaki; Horiguchi, Tsuyoshi

    2004-12-01

    We propose a two-layered neural network model for oscillatory phenomena in the thalamic system and investigate an effect of neuromodulation due to the acetylcholine on the oscillatory phenomena by numerical simulations. The proposed model consists of a layer of the thalamic reticular neurons and that of the cholinergic neurons. We introduce a dynamics of concentration of the acetylcholine which depends on a state of the cholinergic neurons, and assume that the conductance of the thalamic reticular neurons is dynamically regulated by the acetylcholine. From the results obtained by numerical simulations, we find that a dynamical transition between a bursting state and a resting state occurs successively in the layer of the thalamic reticular neurons due to the acetylcholine. Therefore it turns out that the neuromodulation due to the acetylcholine is important for the dynamical state transition in the thalamic system.

  5. Glass transitions and scaling laws within an alternative mode-coupling theory

    NASA Astrophysics Data System (ADS)

    Götze, Wolfgang; Schilling, Rolf

    2015-04-01

    Idealized glass transitions are discussed within an alternative mode-coupling theory (TMCT) proposed by Tokuyama [Physica A 395, 31 (2014), 10.1016/j.physa.2013.10.028]. This is done in order to identify common ground with and differences from the conventional mode-coupling theory (MCT). It is proven that both theories imply the same scaling laws for the transition dynamics, which are characterized by two power-law decay functions and two diverging power-law time scales. However, the values for the corresponding anomalous exponents calculated within both theories differ from each other. It is proven that the TMCT, contrary to the MCT, does not describe transitions with continuously vanishing arrested parts of the correlation functions. It is also demonstrated for a schematic model that the TMCT does not lead to the MCT scenarios either for transition-line crossings or for the appearance of higher-order glass-transition singularities.

  6. Glass transitions and scaling laws within an alternative mode-coupling theory.

    PubMed

    Götze, Wolfgang; Schilling, Rolf

    2015-04-01

    Idealized glass transitions are discussed within an alternative mode-coupling theory (TMCT) proposed by Tokuyama [Physica A 395, 31 (2014)]. This is done in order to identify common ground with and differences from the conventional mode-coupling theory (MCT). It is proven that both theories imply the same scaling laws for the transition dynamics, which are characterized by two power-law decay functions and two diverging power-law time scales. However, the values for the corresponding anomalous exponents calculated within both theories differ from each other. It is proven that the TMCT, contrary to the MCT, does not describe transitions with continuously vanishing arrested parts of the correlation functions. It is also demonstrated for a schematic model that the TMCT does not lead to the MCT scenarios either for transition-line crossings or for the appearance of higher-order glass-transition singularities.

  7. Adam-Gibbs Formulation of Enthalpy Relaxation Near the Glass Transition

    PubMed Central

    Hodge, Ian M.

    1997-01-01

    The entropically based nonlinear Adam-Gibbs equation is discussed in the context of phenomenologies for nonlinear enthalpy relaxation within the glass transition temperature range. In many materials for which adequate data are available, the nonlinear Adam-Gibbs parameters are physically reasonable and agree with those obtained from linear relaxation data and thermodynamic extrapolations. Observed correlations between the traditional Tool-Narayanaswamy-Moynihan parameters are rationalized in terms of the Adam-Gibbs primary activation energy (Δμ) determining how close the kinetic glass transition temperature can get to the thermodynamic Kauzmann temperature. It is shown that increased nonlinearity in the glass transition temperature range is associated with greater fragility in the liquid/rubber state above Tg. PMID:27805137

  8. Constrained Methods in the Understanding of the Calorimetric Glass Transition in Simple Liquids.

    NASA Astrophysics Data System (ADS)

    Gonzalez Padilla, Francisco; Harrowell, Peter R.

    2001-03-01

    In spite of the intensive work and the important improvements in understanding the glass transition, the detailed microcopical behaviour and its thermodynamical implications are not understood yet. We will focus in the calorimetric glass transition, namely the non-monotonic variation of the specific heat with temperature. We will also be interested in recent suggestions that try to deal with the definition of an ideal glassy phase. We use different types of constrains to understand which degrees of freedom are important in understanding the calorimetric glass transition. We deal with geometrical constrain and with constrains obtain from the study of the hessian matrix. Indication on the importance of the anharmonicities to obtain a non-monotonic behaviour of the specific heat are obtained.

  9. Resolving glass transition in Te-based phase-change materials by modulated differential scanning calorimetry

    NASA Astrophysics Data System (ADS)

    Chen, Yimin; Mu, Sen; Wang, Guoxiang; Shen, Xiang; Wang, Junqiang; Dai, Shixun; Xu, Tiefeng; Nie, Qiuhua; Wang, Rongping

    2017-10-01

    Glass transitions of Te-based phase-change materials (PCMs) were studied by modulated differential scanning calorimetry. It was found that both Ge2Sb2Te5 and GeTe are marginal glass formers with ΔT (= T x ‑ T g) less than 2.1 °C when the heating rate is below 3 °C min‑1. The fragilities of Ge2Sb2Te5 and GeTe can be estimated as 46.0 and 39.7, respectively, around the glass transition temperature, implying that a fragile-to-strong transition would be presented in such Te-based PCMs. The above results provide direct experimental evidence to support the investigation of crystallization kinetics in supercooled liquid PCMs.

  10. Use of glass transitions in carbohydrate excipient design for lyophilized protein formulations

    PubMed Central

    Roughton, Brock C.; Topp, E.M.; Camarda, Kyle V.

    2013-01-01

    This work describes an effort to apply methods from process systems engineering to a pharmaceutical product design problem, with a novel application of statistical approaches to comparing solutions. A computational molecular design framework was employed to design carbohydrate molecules with high glass transition temperatures and low water content in the maximally freeze-concentrated matrix, with the objective of stabilizing lyophilized protein formulations. Quantitative structure–property relationships were developed for glass transition temperature of the anhydrous solute, glass transition temperature of the maximally concentrated solute, melting point of ice and Gordon–Taylor constant for carbohydrates. An optimization problem was formulated to design an excipient with optimal property values. Use of a stochastic optimization algorithm, Tabu search, provided several carbohydrate excipient candidates with statistically similar property values, as indicated by prediction intervals calculated for each property. PMID:24385675

  11. Liquid-liquid transition in a strong bulk metallic glass-forming liquid.

    PubMed

    Wei, Shuai; Yang, Fan; Bednarcik, Jozef; Kaban, Ivan; Shuleshova, Olga; Meyer, Andreas; Busch, Ralf

    2013-01-01

    Polymorphic phase transitions are common in crystalline solids. Recent studies suggest that phase transitions may also exist between two liquid forms with different entropy and structure. Such a liquid-liquid transition has been investigated in various substances including water, Al2O3-Y2O3 and network glass formers. However, the nature of liquid-liquid transition is debated due to experimental difficulties in avoiding crystallization and/or measuring at high temperatures/pressures. Here we report the thermodynamic and structural evidence of a temperature-induced weak first-order liquid-liquid transition in a bulk metallic glass-forming system Zr(41.2)Ti(13.8)Cu(12.5)Ni10Be(22.5) characterized by non- (or weak) directional bonds. Our experimental results suggest that the local structural changes during the transition induce the drastic viscosity changes without a detectable density anomaly. These changes are correlated with a heat capacity maximum in the liquid. Our findings support the hypothesis that the 'strong' kinetics (low fragility) of a liquid may arise from an underlying lambda transition above its glass transition.

  12. Structural relaxation time and cooling rate of a melt in the glass transition region

    NASA Astrophysics Data System (ADS)

    Sanditov, D. S.; Sydykov, B. S.

    2015-03-01

    The nature of the parameter involved in the Bartenev equation qτg = C relating the cooling rate of a glass-forming melt to its structural relaxation time in the glass transition region is discussed on the basis of the Volkenshtein-Ptitsyn theory using a number of known relationships. It is established that parameter C for amorphous substances with the same fragility is linearly temperature dependent. This parameter is shown to equal the narrow temperature range δ T g characterizing the liquid-glass transition region (by Nemilov); i.e., C = δ T g. It is concluded that δ T g for most glassy systems is only ˜0.7% of the glass transition temperature T g. The narrowness of temperature range δ T g is explained by the small fluctuation volume fraction f g "frozen" at the glass transition temperature. The concept of a close relationship between constant C and the structural order at T g (i.e., the characteristic of the inner state of a nonequilibrium "frozen" amorphous system) is developed.

  13. Two rigidity-percolation transitions on binary Bethe networks and the intermediate phase in glass

    NASA Astrophysics Data System (ADS)

    Moukarzel, Cristian F.

    2013-12-01

    Rigidity percolation is studied analytically on randomly bonded networks with two types of nodes, respectively, with coordination numbers z1 and z2, and with g1 and g2 degrees of freedom each. For certain cases that model chalcogenide glass networks, two transitions, both of first order, are found, with the first transition usually rather weak. The ensuing intermediate pase, although not isostatic in its entirety, has very low self-stress. Our results suggest a possible mechanism for the appearance of intermediate phases in glass that does not depend on a self-organization principle.

  14. Relaxation functions and dynamical heterogeneities in a model of chemical gel interfering with glass transition

    NASA Astrophysics Data System (ADS)

    Candia, Antonio de; Fierro, Annalisa; Pastore, Raffaele; Pica Ciamarra, Massimo; Coniglio, Antonio

    2017-02-01

    We investigate the heterogeneous dynamics in a model, where chemical gelation and glass transition interplay, focusing on the dynamical susceptibility. Two independent mechanisms give raise to the correlations, which are manifested in the dynamical susceptibility: one is related to the presence of permanent clusters, while the other is due to the increase of particle crowding as the glass transition is approached. The superposition of these two mechanisms originates a variety of different behaviours. We show that these two mechanisms can be unentangled considering the wave vector dependence of the dynamical susceptibility.

  15. Dynamics of an epoxy system near the glass transition studied by Brillouin and dielectric spectroscopies

    NASA Astrophysics Data System (ADS)

    Comez, L.; Fioretto, Daniele; Verdini, L.; Livi, A.; Rolla, Pierangelo A.

    1997-06-01

    The relaxation processes of an epoxy resin were investigated by light scattering and broadband dielectric spectroscopy around the glass transition temperature Tg. Dielectric spectroscopy measurements give evidence of tow relaxations, a structural and a secondary one, merging into a single process well above Tg. Besides the regular divergence of the structural relaxation time, the glass transition is also evidenced by changes of the shape parameters and of the relaxation strength of the secondary process. A comparison between dielectric and Brillouin data shows that Brillouin spectra are markedly sensitive to the secondary relaxation.

  16. Glass transition behavior of ternary disaccharide-ethylene glycol-water solutions

    NASA Astrophysics Data System (ADS)

    Yu, Tongxu; Zhao, Lishan; Wang, Qiang; Cao, Zexian

    2017-06-01

    Glass transition behavior of ternary disaccharide-ethylene glycol-water solutions, in reference to that of the binary combinations, has been investigated towards a better understanding of their cryoprotective ability. In water-deficient solutions, the disaccharides, including trehalose, sucrose and maltose, can associate with more than 100 ethylene glycol molecules to form amorphous complex, one order of magnitude larger than the corresponding hydration numbers. In water-rich solutions, a second glass transition emerges with increasing molar fraction of ethylene glycol, indicating the possible synergy of disaccharides and ethylene glycol in vitrification of the ternary aqueous solution.

  17. Thermal conductivity of Glycerol’s liquid, glass, and crystal states, glass-liquid-glass transition, and crystallization at high pressures

    SciTech Connect

    Andersson, Ove; Johari, G. P.

    2016-02-14

    To investigate the effects of local density fluctuations on phonon propagation in a hydrogen bonded structure, we studied the thermal conductivity κ of the crystal, liquid, and glassy states of pure glycerol as a function of the temperature, T, and the pressure, p. We find that the following: (i) κ{sub crystal} is 3.6-times the κ{sub liquid} value at 140 K at 0.1 MPa and 2.2-times at 290 K, and it varies with T according to 138 × T{sup −0.95}; (ii) the ratio κ{sub liquid} (p)/κ{sub liquid} (0.1 MPa) is 1.45 GPa{sup −1} at 280 K, which, unexpectedly, is about the same as κ{sub crystal} (p)/κ{sub crystal} (0.1 MPa) of 1.42 GPa{sup −1} at 298 K; (iii) κ{sub glass} is relatively insensitive to T but sensitive to the applied p (1.38 GPa{sup −1} at 150 K); (iv) κ{sub glass}-T plots show an enhanced, pressure-dependent peak-like feature, which is due to the glass to liquid transition on heating; (v) continuous heating cold-crystallizes ultraviscous glycerol under pressure, at a higher T when p is high; and (vi) glycerol formed by cooling at a high p and then measured at a low p has a significantly higher κ than the glass formed by cooling at a low p. On heating at a fixed low p, its κ decreases before its glass-liquid transition range at that p is reached. We attribute this effect to thermally assisted loss of the configurational and vibrational instabilities of a glass formed at high p and recovered at low p, which is different from the usual glass-aging effect. While the heat capacity, entropy, and volume of glycerol crystal are less than those for its glass and liquid, κ{sub crystal} of glycerol, like its elastic modulus and refractive index, is higher. We discuss these findings in terms of the role of fluctuations in local density and structure, and the relations between κ and the thermodynamic quantities.

  18. Thermal and fragility aspects of microwave synthesized glasses containing transition metal ions and heavy metal ions

    NASA Astrophysics Data System (ADS)

    Renuka, C.; Viswanatha, R.; Reddy, C. Narayana

    2017-02-01

    A simple, clean and energy efficient microwave heating route is used to prepare glasses in the systems xMnO-33(0.09PbCl2:0.91PbO)-(67-x) NaPO3 and xPbCl2-33PbO-(67-x) NaPO3 where 0.1 ≤ x ≤ 4 (mol%). Thermal data extracted from differential scanning calorimetry (DSC) thermograms are used to study the composition dependence of glass transition temperature (Tg), heat capacity, thermal stability and fragility. The decrease in glass transition temperature with modifier oxide (Na2O + MnO) content can be ascribed to network degradation and the volume increasing effect caused by PbCl2. The change in heat capacity of MnPb glass being greater than that of PbNP glass, suggests that MnPb glasses are more covalent than PbNP glasses. DSC thermograms taken at different heating rates (φ) reveal the dependence of Tg on φ, and the thermal stability of the glass increases due to MnO addition. Fragility aspects have also been studied by calculating the fragility functions ( {{Δ {{C}}_{{p}} }/{{{C}_{{pl}} }}{{and}}{[ {{NBO}} ]}/{{{V}_{{m}}3 {{T}}_{{g}} }}} ). Results obtained from both the fragility functions compare well and reveal the dependence of fragility functions on modifier content and PbCl2 mol%. Further, the decrease in Tg and Hv are suggested to be due to the increase in the number of non-bridging oxygens, which results in the lowering of stiffness and rigidity of the glass network. Analysis of the infrared spectra confirms that the glassy matrix is composed of P-O-P, P-O-Pb, P=O and P-O- bonding.

  19. Reversible transition of deformation mode by structural rejuvenation and relaxation in bulk metallic glass

    NASA Astrophysics Data System (ADS)

    Meng, Fanqiang; Tsuchiya, Koichi; Seiichiro; Yokoyama, Yoshihiko

    2012-09-01

    A transition of the deformation mode from heterogeneous, localized deformation to homogeneous deformation was observed in Zr50Cu40Al10 bulk metallic glass (BMG) by giant straining using the high-pressure torsion (HPT) method. The transition is accompanied by a pronounced decrease in hardness and elastic modulus as measured by nanoindentation. Annealing of the deformed BMG resulted in the restoration of the localized deformation, hardness, and elastic modulus; thus, the transition is reversible. The observed reversible transition can be attributed to a change in the local atomic environment in the rejuvenated volume and the relaxed one.

  20. Effects of configurational changes on electrical resistivity during glass-liquid transition of two bulk metal-alloy glasses

    SciTech Connect

    Aji, D. P. B.; Johari, G. P.

    2014-12-14

    Consequences of increase in structural fluctuations on heating Pd{sub 40}Ni{sub 10}Cu{sub 30}P{sub 20} and Zr{sub 46.75}Ti{sub 8.25}Cu{sub 7.5}Ni{sub 10}Be{sub 27.5} through their glass to liquid transition range were investigated by measuring the electrical resistivity, ρ, an electron scattering property. The temperature coefficient of resistivity (TCR = (1/ρ) dρ/dT) of the liquid and glassy states is negative. The plots of their ρ against T in the T{sub g} (glass to liquid transition) range show a gradual change in the slope similar to the change observed generally for the plots of the density, elastic modulus, and refractive index. As fluctuations in the melt structure involve fewer configurations on cooling, ρ increases. In the energy landscape description, the melt's structure explores fewer minima with decrease in T, vibrational frequencies increase, and electron scattering and ρ increase. Plots of (−dρ/dT) against T resemble the plot of the specific heat of other glasses and show a sub-T{sub g} feature and a rapid rise at T near T{sub g}. Analysis shows that the magnitude of negative TCR is dominated by change in the phonon characteristics, and configurational fluctuations make it more negative. The TCR of the liquid and glassy states seems qualitatively consistent with the variation in the structure factor in Ziman's model for pure liquid metals as extended by Nagel to metal alloys and used to explain the negative TCR of a two-component metal glass.

  1. Analyses of kinetic glass transition in short-range attractive colloids based on time-convolutionless mode-coupling theory.

    PubMed

    Narumi, Takayuki; Tokuyama, Michio

    2017-03-01

    For short-range attractive colloids, the phase diagram of the kinetic glass transition is studied by time-convolutionless mode-coupling theory (TMCT). Using numerical calculations, TMCT is shown to recover all the remarkable features predicted by the mode-coupling theory for attractive colloids: the glass-liquid-glass reentrant, the glass-glass transition, and the higher-order singularities. It is also demonstrated through the comparisons with the results of molecular dynamics for the binary attractive colloids that TMCT improves the critical values of the volume fraction. In addition, a schematic model of three control parameters is investigated analytically. It is thus confirmed that TMCT can describe the glass-glass transition and higher-order singularities even in such a schematic model.

  2. Analyses of kinetic glass transition in short-range attractive colloids based on time-convolutionless mode-coupling theory

    NASA Astrophysics Data System (ADS)

    Narumi, Takayuki; Tokuyama, Michio

    2017-03-01

    For short-range attractive colloids, the phase diagram of the kinetic glass transition is studied by time-convolutionless mode-coupling theory (TMCT). Using numerical calculations, TMCT is shown to recover all the remarkable features predicted by the mode-coupling theory for attractive colloids: the glass-liquid-glass reentrant, the glass-glass transition, and the higher-order singularities. It is also demonstrated through the comparisons with the results of molecular dynamics for the binary attractive colloids that TMCT improves the critical values of the volume fraction. In addition, a schematic model of three control parameters is investigated analytically. It is thus confirmed that TMCT can describe the glass-glass transition and higher-order singularities even in such a schematic model.

  3. On the quantum spin glass transition on the Bethe lattice

    NASA Astrophysics Data System (ADS)

    Mossi, G.; Parolini, T.; Pilati, S.; Scardicchio, A.

    2017-01-01

    We investigate the ground-state properties of a disorderd Ising model with uniform transverse field on the Bethe lattice, focusing on the quantum phase transition from a paramagnetic to a glassy phase that is induced by reducing the intensity of the transverse field. We use a combination of quantum Monte Carlo algorithms and exact diagonalization to compute Rényi entropies, quantum Fisher information, correlation functions and order parameter. We locate the transition by means of the peak of the Rényi entropy and we find agreement with the transition point estimated from the emergence of finite values of the Edwards-Anderson order parameter and from the peak of the correlation length. We interpret the results by means of a mean-field theory in which quantum fluctuations are treated as massive particles hopping on the interaction graph. We see that the particles are delocalized at the transition, a fact that points towards the existence of possibly another transition deep in the glassy phase where these particles localize, therefore leading to a many-body localized phase.

  4. Evidence of phase transition in Nd3+ doped phosphate glass determined by thermal lens spectrometry.

    PubMed

    Andrade, Acácio A; Lourenço, Sidney A; Pilla, Viviane; Silva, Anielle C Almeida; Dantas, Noelio O

    2014-01-28

    Thermal lens spectroscopy (TLS), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) techniques were applied to the thermo-optical property analysis of a new phosphate glass matrix PANK with nominal composition 40P2O5·20Al2O3·35Na2O·5K2O (mol%), doped with different Nd(3+) compositions. This glass system, synthesized by the fusion protocol, presents high transparency from UV to the near infrared, excellent thermo-optical properties at room temperature and high fluorescence quantum efficiency. Thermal lens phase shift parameters, thermal diffusivity and the DSC signal present pronounced changes at about 61 °C for the PANK glass system. This anomalous behavior was associated with a phase transition in the nanostructured glass materials. The FTIR signal confirms the presence of isolated PO4 tetrahedron groups connected to different cations in PANK glass. As a main result, our experimental data suggest that these tetrahedron groups present a structural phase transition, paraelectric-ferroelectric phase transition, similar to that in potassium dihydrogen phosphate, KH2PO4, nanocrystals and which TLS technique can be used as a sensitive method to investigate changes in the structural level of nanostructured materials.

  5. Ultra-slow dynamics in low density amorphous ice revealed by deuteron NMR: indication of a glass transition.

    PubMed

    Löw, Florian; Amann-Winkel, Katrin; Loerting, Thomas; Fujara, Franz; Geil, Burkhard

    2013-06-21

    The postulated glass-liquid transition of low density amorphous ice (LDA) is investigated with deuteron NMR stimulated echo experiments. Such experiments give access to ultra-slow reorientations of water molecules on time scales expected for structural relaxation of glass formers close to the glass-liquid transition temperature. An involved data analysis is necessary to account for signal contributions originating from a gradual crystallization to cubic ice. Even if some ambiguities remain, our findings support the view that pressure amorphized LDA ices are of glassy nature and undergo a glass-liquid transition before crystallization.

  6. Spin-glass transition in Heisenberg spin system with ± J random bonds

    NASA Astrophysics Data System (ADS)

    Ghazali, A.; Lallemand, P.; Diep, H. T.

    1986-02-01

    We investigate by Monte Carlo simulations the simple cubic lattice with Heisenberg spins interacting via short range ± J random bonds for different antiferromagnetic bond concentrations x. We find that for x<0.25, a transition of the para-ferromagnetic type occurs. For 0.25⪅ x⩽0.5, the existence of a remanant magnetization and of a rounded peak of the specific heat together with other data support a paramagnetic-spin-glass transition at finite temperature.

  7. Dynamics of Bragg glass in high-Tc superconductors near depinning transition

    NASA Astrophysics Data System (ADS)

    Luo, Meng-Bo; Hu, Xiao

    2010-12-01

    The dynamics of vortices near depinning transition is studied in terms of a three-dimensional flux-line model with point-like pinning centers. The zero-temperature critical depinning force F is determined with two methods consistently. We find two universal exponents β≈0.64 and δ≈2.3 which characterize the critical behaviors of depinning transition of Bragg glass (BrG). The dynamical modes of flux lines near F are also discussed.

  8. Thermal analysis of frozen solutions: multiple glass transitions in amorphous systems.

    PubMed

    Sacha, Gregory A; Nail, Steven L

    2009-09-01

    Frozen aqueous solutions of sucrose exhibit two "glass transition-like" thermal events below the melting endotherm of ice when examined by DSC, but the physical basis of these events has been a source of some disagreement. In this study, a series of sugars, including sucrose, lactose, trehalose, maltose, fructose, galactose, fucose, mannose, and glucose were studied by modulated DSC and freeze-dry microscopy in order to better understand whether sucrose is unique in any way with respect to this behavior, as well as to explore the physical basis, and the pharmaceutical significance of these multiple transitions. Double transitions were found to be a common feature of all sugars examined. The results are consistent with both thermal events being glass transitions in that (1) both events have second-order characteristics that appear in the reversing signals, (2) annealing experiments reveal that enthalpy recovery is associated with each transition, and (3) Lissajous plots indicate that no detectable latent heat of melting is associated with either transition. The data in this study are consistent with the idea that the lower temperature transition arises from a metastable glassy mixture containing more water than that in the maximally freeze-concentrated solute. Freeze-dry microscopy observations show that for all of the sugars examined, it is the higher temperature transition that is associated with structural collapse during freeze-drying. There is no apparent pharmaceutical significance associated with the lower-temperature transition.

  9. Dynamical transition in the D=3 Edwards-Anderson spin glass in an external magnetic field.

    PubMed

    Baity-Jesi, M; Baños, R A; Cruz, A; Fernandez, L A; Gil-Narvion, J M; Gordillo-Guerrero, A; Iñiguez, D; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Muñoz Sudupe, A; Navarro, D; Parisi, G; Perez-Gaviro, S; Pivanti, M; Ricci-Tersenghi, F; Ruiz-Lorenzo, J J; Schifano, S F; Seoane, B; Tarancon, A; Tripiccione, R; Yllanes, D

    2014-03-01

    We study the off-equilibrium dynamics of the three-dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses.

  10. Glass transition in driven granular fluids: A mode-coupling approach

    NASA Astrophysics Data System (ADS)

    Kranz, W. T.; Sperl, M.; Zippelius, A.

    2013-02-01

    We consider the stationary state of a fluid comprised of inelastic hard spheres or disks under the influence of a random, momentum-conserving external force. Starting from the microscopic description of the dynamics, we derive a nonlinear equation of motion for the coherent scattering function in two and three space dimensions. A glass transition is observed for all coefficients of restitution, ɛ, at a critical packing fraction φc(ɛ) below random close packing. The divergence of timescales at the glass transition implies a dependence on compression rate upon further increase of the density—similar to the cooling-rate dependence of a thermal glass. The critical dynamics for coherent motion as well as tagged particle dynamics is analyzed and shown to be nonuniversal with exponents depending on space dimension and degree of dissipation.

  11. Dynamical transition in the D =3 Edwards-Anderson spin glass in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Baity-Jesi, M.; Baños, R. A.; Cruz, A.; Fernandez, L. A.; Gil-Narvion, J. M.; Gordillo-Guerrero, A.; Iñiguez, D.; Maiorano, A.; Mantovani, F.; Marinari, E.; Martin-Mayor, V.; Monforte-Garcia, J.; Muñoz Sudupe, A.; Navarro, D.; Parisi, G.; Perez-Gaviro, S.; Pivanti, M.; Ricci-Tersenghi, F.; Ruiz-Lorenzo, J. J.; Schifano, S. F.; Seoane, B.; Tarancon, A.; Tripiccione, R.; Yllanes, D.; Janus Collaboration

    2014-03-01

    We study the off-equilibrium dynamics of the three-dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses.

  12. The glass transition, crystallization and melting in Au-Pb-Sb alloys

    NASA Technical Reports Server (NTRS)

    Lee, M. C.; Allen, J. L.; Fecht, H. J.; Perepezko, J. H.; Ohsaka, K.

    1988-01-01

    The glass transition, crystallization and melting of Au(55)Pb(22.5)Sb(22.5) alloys have been studied by differential scanning calorimetry DSC. Crystallization on heating above the glass transition temperature Tg (45 C) begins at 64 C. Further crystallization events are observed at 172 C and 205 C. These events were found to correspond to the formation of the intermetallic compounds AuSb2, Au2Pb, and possibly AuPb2, respectively. Isothermal DSC scans of the glassy alloy above Tg were used to monitor the kinetics of crystallization. The solidification behavior and heat capacity in the glass-forming composition range were determined with droplet samples. An undercooling level of 0.3T(L) below the liquidus temperature T(L) was achieved, resulting in crystallization of different stable and metastable phases. The heat capacity C(P) of the undercooled liquid was measured over an undercooling range of 145 C.

  13. Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition.

    PubMed

    Brambilla, G; El Masri, D; Pierno, M; Berthier, L; Cipelletti, L; Petekidis, G; Schofield, A B

    2009-02-27

    We use dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres. Our study covers an unprecedented density range and spans seven decades in structural relaxation time, tau(alpha0, including equilibrium measurements above phi(c), the location of the glass transition deduced from fitting our data to mode-coupling theory. Instead of falling out of equilibrium, the system remains ergodic above phi(c) and enters a new dynamical regime where tau(alpha) increases with a functional form that was not anticipated by previous experiments, while the amplitude of dynamic heterogeneity grows slower than a power law with tau(alpha), as found in molecular glass formers close to the glass transition.

  14. Evidence for Spin Glass Ordering Near the Weak to Strong Localization Transition in Hydrogenated Graphene.

    PubMed

    Matis, Bernard R; Houston, Brian H; Baldwin, Jeffrey W

    2016-04-26

    We provide evidence that magnetic moments formed when hydrogen atoms are covalently bound to graphene exhibit spin glass ordering. We observe logarithmic time-dependent relaxations in the remnant magnetoresistance following magnetic field sweeps, as well as strong variances in the remnant magnetoresistance following field-cooled and zero-field-cooled scenarios, which are hallmarks of canonical spin glasses and provide experimental evidence for the hydrogenated graphene spin glass state. Following magnetic field sweeps, and over a relaxation period of several minutes, we measure changes in the resistivity that are more than 3 orders of magnitude larger than what has previously been reported for a two-dimensional spin glass. Magnetotransport measurements at the Dirac point, and as a function of hydrogen concentration, demonstrate that the spin glass state is observable as the zero-field resistivity reaches a value close to the quantum unit h/2e(2), corresponding to the point at which the system undergoes a transition from weak to strong localization. Our work sheds light on the critical magnetic-dopant density required to observe spin glass formation in two-dimensional systems. These findings have implications to the basic understanding of spin glasses as well the fields of two-dimensional magnetic materials and spintronics.

  15. CORRELATION OF THE GLASS TRANSITION TEMPERATURE OF PLASTICIZED PVC USING A LATTICE FLUID MODEL

    EPA Science Inventory

    A model has been developed to describe the composition dependence of the glass transition temperature (Tg) of polyvinyl chloride (PVC) + plasticizer mixtures. The model is based on Sanchez-Lacombe equation of state and the Gibbs-Di Marzio criterion, which states that th...

  16. Molecular Motion in Polymers: Mechanical Behavior of Polymers Near the Glass-Rubber Transition Temperature.

    ERIC Educational Resources Information Center

    Sperling, L. H.

    1982-01-01

    The temperature at which the onset of coordinated segmental motion begins is called the glass-rubber transition temperature (Tg). Natural rubber at room temperature is a good example of a material above its Tg. Describes an experiment examining the response of a typical polymer to temperature variations above and below Tg. (Author/JN)

  17. Practical Considerations for Determination of Glass Transition Temperature of a Maximally Freeze Concentrated Solution.

    PubMed

    Pansare, Swapnil K; Patel, Sajal Manubhai

    2016-08-01

    Glass transition temperature is a unique thermal characteristic of amorphous systems and is associated with changes in physical properties such as heat capacity, viscosity, electrical resistance, and molecular mobility. Glass transition temperature for amorphous solids is referred as (T g), whereas for maximally freeze concentrated solution, the notation is (T g'). This article is focused on the factors affecting determination of T g' for application to lyophilization process design and frozen storage stability. Also, this review provides a perspective on use of various types of solutes in protein formulation and their effect on T g'. Although various analytical techniques are used for determination of T g' based on the changes in physical properties associated with glass transition, the differential scanning calorimetry (DSC) is the most commonly used technique. In this article, an overview of DSC technique is provided along with brief discussion on the alternate analytical techniques for T g' determination. Additionally, challenges associated with T g' determination, using DSC for protein formulations, are discussed. The purpose of this review is to provide a practical industry perspective on determination of T g' for protein formulations as it relates to design and development of lyophilization process and/or for frozen storage; however, a comprehensive review of glass transition temperature (T g, T g'), in general, is outside the scope of this work.

  18. Liquid-glass transition as the freezing of characteristic acoustic frequencies

    SciTech Connect

    Sanditov, D. S.

    2010-11-15

    Half-quantum interpretation is proposed for the liquid-glass transition as the freezing of characteristic acoustic frequencies (degrees of freedom) that are related to the molecular mobility of delocalized excited kinetic units, namely, linear quantum oscillators. There exists a correlation between the energy quantum of an elementary excitation (atom delocalization energy) and the glass transition temperature, which is proportional to the characteristic Einstein temperature. By analogy with the Einstein theory of the heat capacity of solids, the temperature range of the concentration of excited atoms in an amorphous medium is divided into the following two regions: a high-temperature region with a linear temperature dependence of this concentration and a low-temperature region, where the concentration of excited atoms decreases exponentially to the limiting minimum value (about 3%). At this value, the viscosity increases to a critical value (about 10{sup 12} Pa s), which corresponds to the glass transition temperature, i.e., the temperature of freezing the mobility of excited kinetic units. The temperature dependence of the free activation energy of viscous flow in the glass transition range is specified by the temperature dependence of the relative number of excited atoms.

  19. CORRELATION OF THE GLASS TRANSITION TEMPERATURE OF PLASTICIZED PVC USING A LATTICE FLUID MODEL

    EPA Science Inventory

    A model has been developed to describe the composition dependence of the glass transition temperature (Tg) of polyvinyl chloride (PVC) + plasticizer mixtures. The model is based on Sanchez-Lacombe equation of state and the Gibbs-Di Marzio criterion, which states that th...

  20. Structural studies of an organic liquid through the glass transition

    SciTech Connect

    Leheny, R.L.; Menon, N.; Nagel, S.R.; Long Price, D.; Suzuya, K.; Thiyagarajan, P.

    1996-11-01

    We have performed neutron diffraction experiments on deuterated propylene glycol, an organic glass former, at temperatures ranging from where its dynamical response approaches that of normal liquids to below the point where relaxation times appear to diverge. Our studies extend over a very broad range of scattering wave vector (0.01{lt}{ital Q}{lt}30 A{sup {minus}1}). In contrast to models which predict clustering, we find no evidence in the liquid at any temperature for heterogeneities large on molecular scales. However, we do note subtle changes at shorter lengths. Using molecular dynamics simulations to model our results, we identify these changes with increasing density and increasing orientational order induced by hydrogen bonding in the liquid as it cools. Analysis of the orientational correlations between molecules reveals a strong dependence on their relative positions. {copyright} {ital 1996 American Institute of Physics.}

  1. Physical stability of drugs after storage above and below the glass transition temperature: Relationship to glass-forming ability.

    PubMed

    Alhalaweh, Amjad; Alzghoul, Ahmad; Mahlin, Denny; Bergström, Christel A S

    2015-11-10

    Amorphous materials are inherently unstable and tend to crystallize upon storage. In this study, we investigated the extent to which the physical stability and inherent crystallization tendency of drugs are related to their glass-forming ability (GFA), the glass transition temperature (Tg) and thermodynamic factors. Differential scanning calorimetry was used to produce the amorphous state of 52 drugs [18 compounds crystallized upon heating (Class II) and 34 remained in the amorphous state (Class III)] and to perform in situ storage for the amorphous material for 12h at temperatures 20°C above or below the Tg. A computational model based on the support vector machine (SVM) algorithm was developed to predict the structure-property relationships. All drugs maintained their Class when stored at 20°C below the Tg. Fourteen of the Class II compounds crystallized when stored above the Tg whereas all except one of the Class III compounds remained amorphous. These results were only related to the glass-forming ability and no relationship to e.g. thermodynamic factors was found. The experimental data were used for computational modeling and a classification model was developed that correctly predicted the physical stability above the Tg. The use of a large dataset revealed that molecular features related to aromaticity and π-π interactions reduce the inherent physical stability of amorphous drugs. Copyright © 2015 Elsevier B.V. All rights reserved.

  2. Transport properties of glass-forming liquids suggest that dynamic crossover temperature is as important as the glass transition temperature

    PubMed Central

    Mallamace, Francesco; Branca, Caterina; Corsaro, Carmelo; Leone, Nancy; Spooren, Jeroen; Chen, Sow-Hsin; Stanley, H. Eugene

    2010-01-01

    It is becoming common practice to partition glass-forming liquids into two classes based on the dependence of the shear viscosity η on temperature T. In an Arrhenius plot, ln η vs 1/T, a strong liquid shows linear behavior whereas a fragile liquid exhibits an upward curvature [super-Arrhenius (SA) behavior], a situation customarily described by using the Vogel–Fulcher–Tammann law. Here we analyze existing data of the transport coefficients of 84 glass-forming liquids. We show the data are consistent, on decreasing temperature, with the onset of a well-defined dynamical crossover η×, where η× has the same value, η× ≈ 103 Poise, for all 84 liquids. The crossover temperature, T×, located well above the calorimetric glass transition temperature Tg, marks significant variations in the system thermodynamics, evidenced by the change of the SA-like T dependence above T× to Arrhenius behavior below T×. We also show that below T× the familiar Stokes–Einstein relation D/T ∼ η-1 breaks down and is replaced by a fractional form D/T ∼ η-ζ, with ζ ≈ 0.85. PMID:21148100

  3. Flight-measured laminar boundary-layer transition phenomena including stability theory analysis

    NASA Technical Reports Server (NTRS)

    Obara, C. J.; Holmes, B. J.

    1985-01-01

    Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows.

  4. Phenomena at the QCD phase transition in nonequilibrium chiral fluid dynamics (Nχ FD)

    NASA Astrophysics Data System (ADS)

    Nahrgang, Marlene; Herold, Christoph

    2016-08-01

    Heavy-ion collisions performed in the beam energy range accessible by the NICA collider facility are expected to produce systems of extreme net-baryon densities and can thus reach yet unexplored regions of the QCD phase diagram. Here, one expects the phase transition between the plasma of deconfined quarks and gluons and the hadronic matter to be of first order. A discovery of the first-order phase transition would as well prove the existence of the QCD critical point, a landmark in the phase diagram. In order to understand possible signals of the first-order phase transition in heavy-ion collision experiments it is very important to develop dynamical models of the phase transition. Here, we discuss the opportunities of studying dynamical effects at the QCD first-order phase transition within our model of nonequilibrium chiral fluid dynamics.

  5. Spectroscopic and ultrasonic investigations on structural characterization of borate glass specimen doped with transition metal ions

    NASA Astrophysics Data System (ADS)

    Sathish, K.; Thirumaran, S.

    2015-08-01

    The present work describes the glass samples of composition (x% V2O5-(80-x)% B2O3-20% Na2CO3) VBS glass system and (x% MnO2-(80-x)% B2O3-20% Na2CO3) in MBS glass system with mol% ranging from x = 3, 6, 9, 12, 15 and 18 in steps of 3 mol% are prepared by melt quenching technique. For these prepared glass systems, sound velocity (longitudinal and shear velocities) and density have been measured. The sound velocity (longitudinal and shear) was measured by using pulse-echo technique at 5 MHz. The XRD study was carried to out to ascertain the amorphous nature of the glass specimen. Using these measured values, the elastic moduli, Poisson's ratio, Debye temperature, acoustic impedance and thermal expansion coefficient of the two glass systems were evaluated. The elastic and mechanical properties of the prepared glass systems are analyzed from ultrasonic study and the structural characterization from spectroscopic study. The effects due to the doping of transition metal ions with borate have been discussed. In the V2O5 doped glass system, (VBS glass system) the sound velocity, density and elastic moduli, steeply increases after 12 mol% comparatively with MnO2 doped glass system (VBS glass system). The present study critically observes the doping of V2O5 with borate enhances the strengthening of network linkage and hardening of the glassy network structure than MnO2. The IR spectral analysis reveals depolymerization of the borate network and conversion of BO3 or BO4 units with the formation of non-bridging oxygen. The FTIR spectral studies confirm the presence of various functional groups of the sample. FTIR spectrum of sample exhibits broad absorption bands indicating the wide distribution of borate structural units. The effect of Na2CO3, V2O5 and MnO2 contents on the structures of borate glass is evaluated from the FTIR spectra. The topological aspects of the prepared glass samples are exhaustively reported from SEM micrographs.

  6. Spectroscopic and ultrasonic investigations on structural characterization of borate glass specimen doped with transition metal ions.

    PubMed

    Sathish, K; Thirumaran, S

    2015-08-05

    The present work describes the glass samples of composition (x% V₂O₅-(80-x)% B₂O₃-20% Na₂CO₃) VBS glass system and (x%MnO₂-(80-x)% B₂O₃-20% Na₂CO₃) in MBS glass system with mol% ranging from x=3, 6, 9, 12, 15 and 18 in steps of 3 mol% are prepared by melt quenching technique. For these prepared glass systems, sound velocity (longitudinal and shear velocities) and density have been measured. The sound velocity (longitudinal and shear) was measured by using pulse-echo technique at 5 MHz. The XRD study was carried to out to ascertain the amorphous nature of the glass specimen. Using these measured values, the elastic moduli, Poisson's ratio, Debye temperature, acoustic impedance and thermal expansion coefficient of the two glass systems were evaluated. The elastic and mechanical properties of the prepared glass systems are analyzed from ultrasonic study and the structural characterization from spectroscopic study. The effects due to the doping of transition metal ions with borate have been discussed. In the V₂O₅ doped glass system,(VBS glass system) the sound velocity, density and elastic moduli, steeply increases after 12 mol% comparatively with MnO₂ doped glass system (VBS glass system). The present study critically observes the doping of V₂O₅ with borate enhances the strengthening of network linkage and hardening of the glassy network structure than MnO₂. The IR spectral analysis reveals depolymerization of the borate network and conversion of BO₃ or BO4 units with the formation of non-bridging oxygen. The FTIR spectral studies confirm the presence of various functional groups of the sample. FTIR spectrum of sample exhibits broad absorption bands indicating the wide distribution of borate structural units. The effect of Na₂CO₃, V₂O₅ and MnO₂ contents on the structures of borate glass is evaluated from the FTIR spectra. The topological aspects of the prepared glass samples are exhaustively reported from SEM micrographs.

  7. Effect of mixed transition metal ions on DC conductivity in lithium bismuth borate glasses

    SciTech Connect

    Khasa, S.; Yadav, Arti Dahiya, M. S.; Seema,; Ashima; Agarwal, A.

    2015-06-24

    The DC conductivities of glasses having composition x(2NiO·V{sub 2}O{sub 5})·(30-x)Li{sub 2}O·20Bi{sub 2}O{sub 3}·50B{sub 2}O{sub 3} (with x=0, 2, 5, 7 and 10, i.e. NVLBB glasses) and glass samples having composition 7NiO·23 Li{sub 2}O·20Bi{sub 2}O{sub 3}·50B{sub 2}O{sub 3} and 7V{sub 2}O{sub 5}·23Li{sub 2}O·20Bi{sub 2}O{sub 3}·50B{sub 2}O{sub 3} (NLBB and VLBB respectively) are investigated as a function of temperature. Conductivity for glasses containing higher percentage of lithium ions is predominantly ionic and in glasses containing higher percentage of transition metal (TM) ions is predominantly electronic. The observed increase in conductivity with x and peak-like behavior at x=7 in NVLBB glasses due to competitive transport of small polaron contributing to a significant structural change in NVLBB glasses. Variation of molar volume and density was also observed with x. In NVLBB glasses, as x increases density increases except a slight decrease at x=7. Also density increases in NLBB whereas in case of VLBB it decreases in comparison to NVLBB1 glass composition. Mott’s small polaron hopping (SPH) model has been applied to analyze the high temperature conductivity data and activation energy.

  8. Impact-Induced Glass Transition in Elastomeric Coatings

    NASA Astrophysics Data System (ADS)

    Roland, C. M.

    2013-03-01

    When an elastomer layer is applied to the front surface of steel, the resistance to penetration by hard projectiles increases significantly. It is not obvious why a soft polymer should affect this property of metals, and most rubbers do not. However, we have found that a few are very effective; the requirement is that the polymer undergo a viscoelastic phase transition upon impact. This means that the frequency of its segmental dynamics correspond to the impact frequency. The latter is estimated as the ratio of the projectile velocity to the coating thickness, and is on the order of 105 s-1 for the experiments herein. Our data and a non-linear dynamics finite-element analysis offer support for this resonance condition as a primary mechanism underlying the penetration-resistance of elastomer-coated metal substrates. The impact-induced phase transition causes large energy absorption, decreasing the kinetic energy of the impacting projectile. However, this energy absorption only accounts for about half the enhanced stopping power of the elastomer/steel bilayer. An additional mechanism is lateral spreading of the impact force, resulting from the transient hardening of the elastomeric during its transition to the glassy state - the modulus of the rubber increases 1000-fold over a time period of microseconds. The penetration-resistance is a very nonlinear function of the coating thickness. Moreover, tests on various metals show that hardness is the principal substrate parameter controlling the contribution of the coating. This work was supported by the Office of Naval Research.

  9. On the nature of the liquid-to-glass transition equation

    NASA Astrophysics Data System (ADS)

    Sanditov, D. S.

    2016-09-01

    Within the model of delocalized atoms, it is shown that the parameter δ T g , which enters the glasstransition equation qτ g = δ T g and characterizes the temperature interval in which the structure of a liquid is frozen, is determined by the fluctuation volume fraction {f_g} = {( {{{Δ {V_e}} / V _{T = {T_g}}} frozen at the glass-transition temperature T g and the temperature T g itself. The parameter δ T g is estimated by data on f g and T g . The results obtained are in agreement with the values of δ T g calculated by the Williams-Landel-Ferry (WLF) equation, as well as with the product qτ g —the left-hand side of the glass-transition equation ( q is the cooling rate of the melt, and τ g is the structural relaxation time at the glass-transition temperature). Glasses of the same class with f g ≈ const exhibit a linear correlation between δ T g and T g . It is established that the currently used methods of Bartenev and Nemilov for calculating δ T g yield overestimated values, which is associated with the assumption, made during deriving the calculation formulas, that the activation energy of the glass-transition process is constant. A generalized Bartenev equation is derived for the dependence of the glass-transition temperature on the cooling rate of the melt with regard to the temperature dependence of the activation energy of the glasstransition process. A modified version of the kinetic glass-transition criterion is proposed. A conception is developed that the fluctuation volume fraction f = Δ V e / V can be interpreted as an internal structural parameter analogous to the parameter ξ in the Mandelstam-Leontovich theory, and a conjecture is put forward that the delocalization of an active atom—its critical displacement from the equilibrium position—can be considered as one of possible variants of excitation of a particle in the Vol'kenshtein-Ptitsyn theory. The experimental data used in the study refer to a constant cooling rate of q = 0.05 K

  10. Glass-to-cryogenic-liquid transitions in aqueous solutions suggested by crack healing

    PubMed Central

    Kim, Chae Un; Tate, Mark W.; Gruner, Sol M.

    2015-01-01

    Observation of theorized glass-to-liquid transitions between low-density amorphous (LDA) and high-density amorphous (HDA) water states had been stymied by rapid crystallization below the homogeneous water nucleation temperature (∼235 K at 0.1 MPa). We report optical and X-ray observations suggestive of glass-to-liquid transitions in these states. Crack healing, indicative of liquid, occurs when LDA ice transforms to cubic ice at 160 K, and when HDA ice transforms to the LDA state at temperatures as low as 120 K. X-ray diffraction study of the HDA to LDA transition clearly shows the characteristics of a first-order transition. Study of the glass-to-liquid transitions in nanoconfined aqueous solutions shows them to be independent of the solute concentrations, suggesting that they represent an intrinsic property of water. These findings support theories that LDA and HDA ice are thermodynamically distinct and that they are continuously connected to two different liquid states of water. PMID:26351671

  11. Glass-to-cryogenic-liquid transitions in aqueous solutions suggested by crack healing.

    PubMed

    Kim, Chae Un; Tate, Mark W; Gruner, Sol M

    2015-09-22

    Observation of theorized glass-to-liquid transitions between low-density amorphous (LDA) and high-density amorphous (HDA) water states had been stymied by rapid crystallization below the homogeneous water nucleation temperature (∼235 K at 0.1 MPa). We report optical and X-ray observations suggestive of glass-to-liquid transitions in these states. Crack healing, indicative of liquid, occurs when LDA ice transforms to cubic ice at 160 K, and when HDA ice transforms to the LDA state at temperatures as low as 120 K. X-ray diffraction study of the HDA to LDA transition clearly shows the characteristics of a first-order transition. Study of the glass-to-liquid transitions in nanoconfined aqueous solutions shows them to be independent of the solute concentrations, suggesting that they represent an intrinsic property of water. These findings support theories that LDA and HDA ice are thermodynamically distinct and that they are continuously connected to two different liquid states of water.

  12. Low-temperature fabrication of VO2 thin film on ITO glass with a Mott transition

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen

    2016-09-01

    Polycrystalline Vanadium dioxide (VO2) thin film can be fabricated on glass substrates by high power impulse magnetron sputtering at a relative high temperature. In order to apply an effective bias voltage on substrate and control the energy of the ions impinged to the substrate, conductive indium-tin oxide (ITO) glass was used as the substrate. UV-visible-near IR transmittance spectra and X-ray diffraction (XRD) patterns of the as-deposited films exhibited that M-VO2 thin film with a metal-insulator transition temperature of 37∘C was fabricated successfully at 300∘C with a bias voltage of -200V, and the calculated average crystalline size of this film was about 12nm. XRD patterns at varied temperatures showed that the structural change of MIT of the VO2 thin film was suppressed during the phase transition process, and a pure Mott transition was obtained.

  13. Spacelab experiment definition study on phase transition and critical phenomena in fluids: Interim report on experimental justification

    NASA Technical Reports Server (NTRS)

    Moldover, M. R.; Hocken, M. R.; Gammon, R. W.; Sengers, J. V.

    1976-01-01

    Pure fluids and fluid mixtures near critical points are identified and are related to the progress of several disciplines. Consideration is given to thermodynamic properties, transport properties, and the complex nonlinear phenomena which occur when fluids undergo phase transitions in the critical region. The distinction is made between practical limits which may be extended by advances in technology and intrinsic ones which arise from the modification of fluid properties by the earth's gravitational field. The kinds of experiments near critical points which could best exploit the low gravity environment of an orbiting laboratory are identified. These include studies of the index of refraction, constant volume specific heat, and phase separation.

  14. Glass Transition Temperature and Density Scaling in Cumene at Very High Pressure

    NASA Astrophysics Data System (ADS)

    Ransom, T. C.; Oliver, W. F.

    2017-07-01

    We present a new method that allows direct measurements of the glass transition temperature Tg at pressures up to 4.55 GPa in the glass-forming liquid cumene (isopropylbenzene). This new method uses a diamond anvil cell and can measure Tg at pressures of 10 GPa or greater. Measuring Tg at the glass →liquid transition involves monitoring the disappearance of pressure gradients initially present in the glass, but also takes advantage of the large increase in the volume expansion coefficient αp at Tg as the supercooled or superpressed liquid is entered. Accurate Tg(P ) values in cumene allow us to show that density scaling holds along this isochronous line up to pressures much higher than any previous study, corresponding to a density increase of 29%. Our results for cumene over this huge compression range yield ργ/T =C , where C is a constant and where γ =4.77 ±0.02 for this nonassociated glass-forming system. Finally, high-pressure cumene viscosity data from the literature taken at much lower pressures and at several different temperatures, corresponding to a large dynamic range of nearly 13 orders of magnitude, are shown to superimpose on a plot of η vs ργ/T for the same value of γ .

  15. X-ray tomography of feed-to-glass transition of simulated borosilicate waste glasses

    DOE PAGES

    Harris, William H.; Guillen, Donna P.; Klouzek, Jaroslav; ...

    2017-05-10

    The feed composition of a high level nuclear waste (HLW) glass melter affects the overall melting rate by influencing the chemical, thermophysical, and morphological properties of a relatively insulating cold cap layer over the molten phase where the primary feed vitrification reactions occur. Data from X ray computed tomography imaging of melting pellets comprised of a simulated high-aluminum HLW feed heated at a rate of 10°C/min reveal the distribution and morphology of bubbles, collectively known as primary foam, within this layer for various SiO2/(Li2CO3+H3BO3+Na2CO3) mass fractions at temperatures between 600°C and 1040°C. To track melting dynamics, cross-sections obtained through themore » central profile of the pellet were digitally segmented into primary foam and a condensed phase. Pellet dimensions were extracted using Photoshop CS6 tools while the DREAM.3D software package was used to calculate pellet profile area, average and maximum bubble areas, and two-dimensional void fraction. The measured linear increase in the pellet area expansion rates – and therefore the increase in batch gas evolution rates – with SiO2/(Li2CO3+H3BO3+Na2CO3) mass fraction despite an exponential increase in viscosity of the final waste glass at 1050°C and a lower total amount of gas-evolving species suggest that the retention of primary foam with large average bubble size at higher temperatures results from faster reaction kinetics rather than increased viscosity. However, viscosity does affect the initial foam collapse temperature by supporting the growth of larger bubbles. Because the maximum bubble size is limited by the pellet dimensions, larger scale studies are needed to understand primary foam morphology at high temperatures. This temperature-dependent morphological data can be used in future investigations to synthetically generate cold cap structures for use in models of heat transfer within a HLW glass melter.« less

  16. Systematic Field Theory of the RNA Glass Transition

    NASA Astrophysics Data System (ADS)

    David, Francois; Wiese, Kay Jörg

    2007-03-01

    We prove that the Lässig-Wiese (LW) field theory for the freezing transition of the secondary structure of random RNA is renormalizable to all orders in perturbation theory. The proof relies on a formulation of the model in terms of random walks and on the use of the multilocal operator product expansion. Renormalizability allows us to work in the simpler scheme of open polymers, and to obtain the critical exponents at 2-loop order. It also allows us to prove some exact exponent identities, conjectured by LW.

  17. Electronic bonding transition in compressed SiO{sub 2} glass

    SciTech Connect

    Lin, J.-F.; Yoo, Choong-Shik; Trave, Andrea; Fukui, Hiroshi; Prendergast, David; Okuchi, Takuo; Cai, Yong Q.; Hiraoka, Nozomu; Eng, Peter; Hu, Michael Y.; Chow, Paul

    2007-01-01

    Knowledge of the electronic structure of amorphous and liquid silica at high pressures is essential to understanding their complex properties ranging from silica melt in magma to silica glass in optics, electronics, and material science. Here we present oxygen near K-edge spectra of SiO{sub 2} glass to 51 GPa obtained using x-ray Raman scattering in a diamond-anvil cell. The x-ray Raman spectra below {approx}10 GPa are consistent with those of quartz and coesite, whereas the spectra above {approx}22 GPa are similar to that of stishovite. This pressure-induced spectral change indicates an electronic bonding transition occurring from a fourfold quartzlike to a sixfold stishovitelike configuration in SiO{sub 2} glass between 10 GPa and 22 GPa. In contrast to the irreversible densification, the electronic bonding transition is reversible upon decompression. The observed reversible bonding transition and irreversible densification call for a coherent understanding of the transformation mechanism in compressed SiO{sub 2} glass.

  18. Non-linear Phenomena of Wing Flutter and the Effect of Laminar-Turbulent Transition

    NASA Astrophysics Data System (ADS)

    Marti, Ferran

    A Navier-Stokes Computational Fluid Dynamics (CFD) code is coupled with a Computa- tional Structural Dynamics (CSD) code to study the flutter boundary of the NACA64A010 airfoil using Isogai's structural model in transonic conditions. This model simulates aeroelas- tic conditions on a sweptback wing. A well-known feature, only present in the inviscid flutter boundary of this airfoil, is the existence of multiple flutter points for a fixed freestream Mach number. The fully-turbulent flutter boundary has not been studied by many researchers us- ing a Reynolds-Averaged Navier-Stokes approach. In the present study, the fully-turbulent flutter boundary reveals the existence of multiple equilibrium positions for a narrow range of flight conditions. The system moves away from the initial equilibrium position, finding a new set of equilibrium points and oscillating around it. This new set of equilibrium points reveals as stable or unstable for different structural properties of the wing. We then proceed to study the effect of turbulent transition on flutter boundary. A laminar- to-turbulent transition model is implemented in the CFD code and validated. The effect of using a free-transition CFD code vs. a fully-turbulent approach is evaluated on three airfoils with different characteristics for subsonic and transonic conditions. While free-transition does not affect the pressure distribution at subsonic conditions, the transonic simulations reveal a change in the shock-wave position when laminar-turbulent effects are included. The effect of transition on the flutter boundary of the NACA64A010 airfoil at transonic conditions is then investigated. A comparison between the free-transition, inviscid and fully-turbulent flutter boundaries reveals similarities between the inviscid and free-transition elastic re- sponses. Those similarities are due to the shift in the fully-turbulent shock-wave position, when accounting for free-transition effects, moving closer to the inviscid

  19. Boundary layer transition: A review of theory, experiment and related phenomena

    NASA Technical Reports Server (NTRS)

    Kistler, E. L.

    1971-01-01

    The overall problem of boundary layer flow transition is reviewed. Evidence indicates a need for new, basic physical hypotheses in classical fluid mechanics math models based on the Navier-Stokes equations. The Navier-Stokes equations are challenged as inadequate for the investigation of fluid transition, since they are based on several assumptions which should be expected to alter significantly the stability characteristics of the resulting math model. Strong prima facie evidence is presented to this effect.

  20. Direct Measurement of the Pressure Dependence of the Glass Transition Temperature: A Comparison of Methods

    NASA Astrophysics Data System (ADS)

    Oliver, William, III; Ransom, Timothy; Cooper, James, III

    2013-03-01

    Two methods for the direct measurement of the pressure dependence of the glass-transition temperature Tg are presented and compared. These methods involve the use of the diamond anvil cell (DAC), and hence, enable the ability to measure Tg(P) to record high pressures of several GPa. Such studies are increasingly relevant as new methods have pushed other high-pressure experimental investigations of glass-forming systems into the same pressure regime. Both methods use careful ruby fluorescence measurements in the DAC as temperature is increased from the glass (TTg) . Method 1 observes the disappearance of pressure gradients as the viscous liquid region is entered, whereas method 2 involves observation of slope changes in the P-T curve during temperature ramps. Such slope changes are associated with the significant change in the volume expansion coefficient between the highly viscous, metastable, supercooled liquid state and the solid glassy state. In most cases, the two methods yield good agreement in the Tg(P) curve. Data will be presented for more than one glass-forming system, including the intermediate strength glass-forming system glycerol and the fragile glass former salol. We acknowledge support from the NSF under DMR-0552944

  1. Deuteron NMR (Nuclear Magnetic Resonance) in relation to the glass transition in polymers

    NASA Technical Reports Server (NTRS)

    Roessler, E.; Sillescu, H.; Spiess, H. W.; Wallwitz, R.

    1983-01-01

    H-2NMR is introduced as a tool for investigating slow molecular motion in the glass transition region of amorphous polymers. In particular, we compare H-2 spin alignment echo spectra of chain deuterated polystyrene with model calculations for restricted rotational Brownian motion. Molecular motion in the polyztyrene-toluene system has been investigated by analyzing H-2NMR of partially deuterated polystyrene and toluene, respectively. The diluent mobility in the mixed glass has been decomposed into solid and liquid components where the respective average correlation times differ by more than 5 decades.

  2. Deuteron NMR (Nuclear Magnetic Resonance) in relation to the glass transition in polymers

    NASA Technical Reports Server (NTRS)

    Roessler, E.; Sillescu, H.; Spiess, H. W.; Wallwitz, R.

    1983-01-01

    H-2NMR is introduced as a tool for investigating slow molecular motion in the glass transition region of amorphous polymers. In particular, we compare H-2 spin alignment echo spectra of chain deuterated polystyrene with model calculations for restricted rotational Brownian motion. Molecular motion in the polyztyrene-toluene system has been investigated by analyzing H-2NMR of partially deuterated polystyrene and toluene, respectively. The diluent mobility in the mixed glass has been decomposed into solid and liquid components where the respective average correlation times differ by more than 5 decades.

  3. Effects of dynamic heterogeneity and density scaling of molecular dynamics on the relationship among thermodynamic coefficients at the glass transition

    SciTech Connect

    Koperwas, K. Grzybowski, A.; Grzybowska, K.; Wojnarowska, Z.; Paluch, M.

    2015-07-14

    In this paper, we define and experimentally verify thermodynamic characteristics of the liquid-glass transition, taking into account a kinetic origin of the process. Using the density scaling law and the four-point measure of the dynamic heterogeneity of molecular dynamics of glass forming liquids, we investigate contributions of enthalpy, temperature, and density fluctuations to spatially heterogeneous molecular dynamics at the liquid-glass transition, finding an equation for the pressure coefficient of the glass transition temperature, dTg/dp. This equation combined with our previous formula for dTg/dp, derived solely from the density scaling criterion, implies a relationship among thermodynamic coefficients at Tg. Since this relationship and both the equations for dTg/dp are very well validated using experimental data at Tg, they are promising alternatives to the classical Prigogine-Defay ratio and both the Ehrenfest equations in case of the liquid-glass transition.

  4. The superspin glass transition in zinc ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Kaman, O.; Kořínková, T.; Jirák, Z.; Maryško, M.; Veverka, M.

    2015-05-01

    Nanoparticles of the ZnxFe3-xO4 (x = 0.3-0.4) spinel phase having 5 and 15 nm size were synthesized by thermal decomposition of the respective acetylacetonates in a high boiling-point solvent employing surfactants. The collective behaviour of the nanoparticles was probed by dc and ac magnetic measurements of tightly compressed pellets of the particles and silica coated products which were prepared by reverse microemulsion technique. The assembly of bare 5 nm particles remains in the superparamagnetic state with Curie-Weiss characteristics down to 35 K when a rather sharp freezing of superspins is detected. The larger particles show a similar but more diffusive transition at 250 K. The cores encapsulated into the diamagnetic silica do not exhibit glassy freezing.

  5. Fragility, network adaptation, rigidity- and stress- transitions in homogenized binary GexS100-x glasses

    NASA Astrophysics Data System (ADS)

    Chakraborty, Shibalik; Boolchand, Punit

    2014-03-01

    Binary GexS100-x glasses reveal elastic and chemical phase transitions driven by network topology. With increasing Ge content x, well defined rigidity (xc(1) =19.3%) and stress(xc(2) =24.85%) transitions and associated optical elasticity power-laws are observed in Raman scattering. Calorimetric measurements reveal a square-well like minimum with window walls that coincide with the two elastic phase transitions. Molar volumes show a trapezoidal-like minimum with edges that nearly coincide with the reversibility window. These results are signatures of the isostatically rigid nature of the elastic phase formed between the rigidity and stress transitions. Complex Cp measurements show melt fragility index, m(x) to also show a global minimum in the reversibility window, underscoring that melt dynamics encode the elastic behavior of the glass formed at Tg. The strong nature of melts formed in the IP has an important practical consequence; they lead to slow homogenization of non-stoichiometric batch compositions reacted at high temperatures. Homogenization of chalcogenides melts/glasses over a scale of a few microns is a pre-requisite to observe the intrinsic physical properties of these materials. Supported by NSF Grant DMR 0853957.

  6. Probing the Bose glass-superfluid transition using quantum quenches of disorder

    NASA Astrophysics Data System (ADS)

    Meldgin, Carolyn; Ray, Ushnish; Russ, Philip; Chen, David; Ceperley, David M.; Demarco, Brian

    2016-07-01

    The disordered Bose-Hubbard model--a paradigm for strongly correlated and disordered bosonic systems--is central to our understanding of quantum phase transitions. Despite extensive theoretical work on the disordered Bose-Hubbard model, little is known about the impact of temperature, the dynamical behaviour of quantum phases, and how equilibrium is affected during quantum phase transitions. These issues are critically important to applications such as quantum annealing and electronics based on quantum phase transitions. Here, we use a quantum quench of disorder in an ultracold lattice gas to dynamically probe the superfluid-Bose glass quantum phase transition at non-zero temperature ( Fig. 1). By measuring excitations generated during the quench, we provide evidence for superfluid puddles in the Bose glass phase and produce a superfluid-Bose glass phase diagram consistent with completely constrained, finite temperature, and equilibrium quantum Monte Carlo simulations. The residual energy from the quench, which is an efficacy measure for optimization through quantum annealing, is unchanged for quench times spanning nearly a hundred tunnelling times.

  7. Characterization of amorphous solids with weak glass transitions using high ramp rate differential scanning calorimetry.

    PubMed

    Katayama, Derrick S; Carpenter, John F; Manning, Mark Cornell; Randolph, Theodore W; Setlow, Peter; Menard, Kevin P

    2008-02-01

    Measurement of the glass transition temperature (T(g)) of proteins and other high molecular weight polymers in the amorphous state is often difficult, since the transition is extremely weak, that is, the DeltaC(p) at the glass transition temperature is small. For example, little is known about the solid-state properties of hydroxyethyl starch (HES), which is beginning to become more commonly evaluated as a bulking agent in pharmaceutical products. For weak thermal events, such as the change in heat capacity at the T(g) of a pure protein or large synthetic polymer, increased heating rate should produce greater sensitivity in terms of heat flow. Recent innovations in rapid scanning technology for differential scanning calorimetry (DSC) allow measurements on materials where the thermal events are difficult to detect by conventional DSC. In the current study, measurements of the T(g) of proteins in the solid state, amorphous pharmaceutical excipients which have small DeltaC(p) at the glass transition temperature, and bacterial spores, have all been made using high ramp rate DSC, providing information on materials that was inaccessible using conventional DSC methods.

  8. Critical Phenomena at the Normal-Incommensurate Phase Transition in Rb2ZnCl4

    NASA Astrophysics Data System (ADS)

    Mashiyama, Hiroyuki

    1981-08-01

    The X-ray reflection intensity and the dielectric constant are measured around the normal-incommensurate phase transition. From the temperature dependence of a satellite reflection at \\includegraphics{dummy.eps}, the critical exponent 2β is determined to be 0.69± 0.01. This value is very close to the exponent of the three-dimensional n{=}2-vector model. The dielectric constant along the ferroelectric axis shows a weak anomaly at the transition point, which is discussed with the aid of the remormalization-group method.

  9. Survey and research on up-conversion emission character and energy transition of Yb3+/Er3+/Tm3+ co-doped phosphate glass and glass ceramic

    NASA Astrophysics Data System (ADS)

    Yu, Yin; Song, Feng; Ming, Chengguo; Liu, Jiadong; Li, Wei; Liu, Yanling; Zhao, Hongyan

    2012-11-01

    By conventional high-temperature melting method, Yb3+/Er3+/Tm3+ co-doped phosphate glass was synthesized. After annealing the precursor glass, the phosphate glass ceramic (GC) was obtained. By measuring the X-ray diffraction (XRD) spectrum, it is proved that the LiYbP4O12 and Li6P6O18 nano-crystals have existed in the phosphate GC. The up-conversion (UC) emission intensity of the GC is obvious stronger compared to that of the glass. The reason is that the shorter distance between rare earth ions in the glass ceramic increases the energy transitions from the sensitized ions (Yb3+) to the luminous ions (Er3+ and Tm3+). By studying the dependence of UC emissions on the pump power, the 523 and 546 nm green emissions of Er3+ ions in the glass are two-photon processes. But in the glass ceramic, they are two/three-photon processes. The phenomenon implies that a three-photon process has participated in the population of the two green emissions. Using Dexter theory, we discuss the energy transitions of Er3+ and Tm3+. The results indicate the energy transition of Tm3+ to Er3+ is very strong in the GC, which changes the population mechanism of UC emissions of Er3+.

  10. Structural influence of mixed transition metal ions on lithium bismuth borate glasses

    NASA Astrophysics Data System (ADS)

    Yadav, Arti; Dahiya, Manjeet S.; Hooda, A.; Chand, Prem; Khasa, S.

    2017-08-01

    Lithium bismuth borate glasses containing mixed transition metals having composition 7CoO·23Li2O·20Bi2O3·50B2O3 (CLBB), 7V2O5·23Li2O·20Bi2O3·50B2O3 (VLBB) and x(2CoO·V2O5)·(30 - x)Li2O·20Bi2O3·50B2O3 (x = 0.0 (LBB) and x = 2.0, 5.0, 7.0, 10.0 mol% (CVLBB1-4)) are synthesized via melt quench route. The synthesized compositions are investigated for their physical properties using density (D) and molar volume (Vm), thermal properties by analyzing DSC/TG thermo-graphs, structural properties using IR absorption spectra in the mid-IR range and optical properties using UV-Vis-NIR spectroscopy. The Electron Paramagnetic Resonance (EPR) spectra of vanadyl and cobalt ion have been analyzed to study compositional effects on spin-Hamiltonian parameters. The non linear variations in physical properties depict a strong structural influence of Co/V- oxides on the glassy matrix. The compositional variations in characteristic temperatures (glass transition temperature Tg, glass crystallization temperature Tp and glass melting temperature Tm) reveals that Tg for glass samples CLBB is relatively less than that of pure lithium bismuth borate (LBB) glass sample wherein Tg for sample VLBB is higher than that of LBB. The increase in Tg (as compared with LBB) with an enhanced substitution of mixed transition metal oxides (2CoO·V2O5) shows a progressive structure modification of bismuth borate matrix. These predictions are very well corroborated by corresponding compositional trends of Tp and Tm. FTIR studies reveal that Co2+& VO2+ ions lead to structural rearrangements through the conversion of three-coordinated boron into four coordinated boron and thereby reducing number of non-bridging oxygen atoms. Bismuth is found to exist in [BiO6] octahedral units only, whereas boroxol rings are not present in the glass network. The theoretical values of optical basicity (Λth) and corresponding oxide ion polarizability (αo2-) have also been calculated to investigate oxygen covalency of

  11. Effect of free surface roughness on the apparent glass transition temperature in thin polymer films measured by ellipsometry.

    PubMed

    Efremov, Mikhail Yu

    2014-12-01

    Ellipsometry is one of the standard methods for observation of glass transition in thin polymer films. This work proposes that sensitivity of the method to surface morphology can complicate manifestation of the transition in a few nm thick samples. Two possible mechanisms of free surface roughening in the vicinity of glass transition are discussed: roughening due to lateral heterogeneity and roughening associated with thermal capillary waves. Both mechanisms imply an onset of surface roughness in the glass transition temperature range, which affects the experimental data in a way that shifts apparent glass transition temperature. Effective medium approximation models are used to introduce surface roughness into optical calculations. The results of the optical modeling for a 5 nm thick polystyrene film on silicon are presented.

  12. Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions

    NASA Astrophysics Data System (ADS)

    Zhou, Hongwei; Xue, Changguo; Weis, Philipp; Suzuki, Yasuhito; Huang, Shilin; Koynov, Kaloian; Auernhammer, Günter K.; Berger, Rüdiger; Butt, Hans-Jürgen; Wu, Si

    2016-10-01

    The development of polymers with switchable glass transition temperatures (Tg) can address scientific challenges such as the healing of cracks in high-Tg polymers and the processing of hard polymers at room temperature without using plasticizing solvents. Here, we demonstrate that light can switch the Tg of azobenzene-containing polymers (azopolymers) and induce reversible solid-to-liquid transitions of the polymers. The azobenzene groups in the polymers exhibit reversible cis-trans photoisomerization abilities. Trans azopolymers are solids with Tg above room temperature, whereas cis azopolymers are liquids with Tg below room temperature. Because of the photoinduced solid-to-liquid transitions of these polymers, light can reduce the surface roughness of azopolymer films by almost 600%, repeatedly heal cracks in azopolymers, and control the adhesion of azopolymers for transfer printing. The photoswitching of Tg provides a new strategy for designing healable polymers with high Tg and allows for control over the mechanical properties of polymers with high spatiotemporal resolution.

  13. Difference in variation of glass transition activation energy between 1,2-propanediamine and 1,2-propanediol

    NASA Astrophysics Data System (ADS)

    Terashima, Yukio

    2016-05-01

    Variations of the effective activation energy (Eα) throughout the glass transition were determined for 1,2-propanediamine (12PDA) and 1,2-propanediol (12PDO) by applying an isoconversional method to differential scanning calorimetry (DSC) data. Eα was found to markedly decrease throughout the glass transition of 12PDA, whereas such drastic change in Eα was not observed for 12PDO. Although the two simple liquids are similar in molecular structure and size, their trends in Eα and fragility m throughout the glass transition can be quite different. The significant disparity in the kinetic parameters can be caused by differences in hydrogen-bonding structure between 12PDA and 12PDO.

  14. Common behaviors associated with the glass transitions of water-like models

    NASA Astrophysics Data System (ADS)

    Horstmann, R.; Vogel, M.

    2017-07-01

    We perform molecular dynamics simulations to ascertain effects of the molecular polarity on structural and dynamical properties of water-like systems, in particular, on their glassy slowdown. To systematically vary the molecular dipole moments, we scale the partial charges of the established SPC/E and TIP4P/2005 models. In broad ranges of the molecular polarity, the studied SPC/E and TIP4P/2005 descendants show a density anomaly, which can be attributed to the removal of water molecules interstitial between the first and the second neighbor shells upon cooling. While all considered modified water models behave as typical glass formers, the structural relaxation time τ heavily depends on the molecular dipole moment. This large dynamical diversity is exploited to systematically ascertain characteristic properties of glass-forming liquids. For all studied water-like systems, we observe a close relation between the activation energy E∞ describing the Arrhenius behavior of the regular liquid and the glass transition temperature Tg characterizing the supercooled liquid, explicitly, E∞/Tg≈10 . Moreover, decomposing the activation energy of the structural relaxation according to E (T ) =E∞+Ec(T ) , we show that the glassy slowdown of all modified water molecules can fully be traced back to an exponential temperature dependence of the contribution Ec(T) related to cooperative dynamics. Extrapolation of this behavior suggests a common value at the glass transition temperature, Ec(Tg ) /Tg≈25 . Finally, we discuss links between the structural relaxation and the vibrational displacement, as proposed in various theoretical approaches to the glass transition.

  15. Elastic Anomaly and Polyamorphic Transition in (La, Ce)-based Bulk Metallic Glass under Pressure.

    PubMed

    Qi, Xintong; Zou, Yongtao; Wang, Xuebing; Chen, Ting; Welch, David O; Jiang, Jianzhong; Li, Baosheng

    2017-04-07

    Pressure-induced polyamorphism in Ce-based metallic glass has attracted significant interest in condensed matter physics. In this paper, we discover that in association with the polyamorphism of La32Ce32Al16Ni5Cu15 bulk metallic glass, the acoustic velocities, measured up to 12.3 GPa using ultrasonic interferometry, exhibit velocity minima at 1.8 GPa for P wave and 3.2 GPa for S wave. The low and high density amorphous states are distinguished by their distinct pressure derivatives of the bulk and shear moduli. The elasticity, permanent densification, and polyamorphic transition are interpreted by the topological rearrangement of solute-centered clusters in medium-range order (MRO) mediated by the 4f electron delocalization of Ce under pressure. The precisely measured acoustic wave travel times which were used to derive the velocities and densities provided unprecedented data to document the evolution of the bulk and shear elastic moduli associated with a polyamorphic transition in La32Ce32Al16Ni5Cu15 bulk metallic glass and can shed new light on the mechanisms of polyamorphism and structural evolution in metallic glasses under pressure.

  16. Disorder-Assisted Melting and the Glass Transition in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Zaccone, Alessio; Terentjev, Eugene M.

    2013-04-01

    The mechanical response of solids depends on temperature, because the way atoms and molecules respond collectively to deformation is affected at various levels by thermal motion. This is a fundamental problem of solid state science and plays a crucial role in materials science. In glasses, the vanishing of shear rigidity upon increasing temperature is the reverse process of the glass transition. It remains poorly understood due to the disorder leading to nontrivial (nonaffine) components in the atomic displacements. Our theory explains the basic mechanism of the melting transition of amorphous (disordered) solids in terms of the lattice energy lost to this nonaffine motion, compared to which thermal vibrations turn out to play only a negligible role. The theory is in good agreement with classic data on melting of amorphous polymers (for which no alternative theory can be found in the literature) and offers new opportunities in materials science.

  17. The Glass Transition and Dynamics in Athermal Poly(a-Methyl Styrene)/Oligomer Blends

    NASA Astrophysics Data System (ADS)

    Zheng, Wei; Simon, Sindee

    2008-03-01

    The glass transition and dynamics in athermal blends of poly(a-methyl styrene) (PaMS) and its short chain oligomers are investigated using differential scanning calorimetry (DSC). A methodology is described to partition the calorimetric transition in order to obtain effective Tgs for each component of the blend. The dependences of these effective Tgs on overall blend composition are described by the Lodge-McLeish model although the self-concentration effect is less than expected based on the Kuhn length. The kinetics associated with the glass temperature, Tg, are examined by studying the cooling rate dependence of Tg for the pure components and the blends, as well as by examining the enthalpy overshoots in the heating DSC scans. Extension of Colmenero's model to describe the dynamics in these materials will be discussed.

  18. Effect of sodium chloride on the glass transition of condensed starch systems.

    PubMed

    Chuang, Lillian; Panyoyai, Naksit; Shanks, Robert; Kasapis, Stefan

    2015-10-01

    The present investigation deals with the structural properties of condensed potato starch-sodium chloride systems undergoing a thermally induced glass transition. Sample preparation included hot pressing at 120°C for 7 min to produce extensive starch gelatinisation. Materials covered a range of moisture contents from 3.6% to 18.8%, which corresponded to relative humidity values of 11% and 75%. Salt addition was up to 6.0% in formulations. Instrumental work was carried out with dynamic mechanical analysis in tension, modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and wide angle X-ray diffraction. Experimental conditions ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of sodium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Sodium ions interact with chemical moieties of the polysaccharide chain to alter considerably structural properties, as compared to the starch-water matrix.

  19. Terahertz spectral change associated with glass transition of poly-ε-caprolactone

    SciTech Connect

    Komatsu, Marina; Mizuno, Maya; Fukunaga, Kaori; Saito, Shingo; Ohki, Yoshimichi

    2015-04-07

    We measured absorption spectra of unidirectionally stretched poly-ε-caprolactone (PCL) film in a range from 0.3 to 3.6 THz at temperatures from 10 to 300 K. Several absorption peaks were observed, when the electric field of THz waves was set in directions parallel and perpendicular to the stretching direction. The absorption bandwidths became significantly broad at around 200 K and above at least in two specific peaks. This temperature is close to the glass transition temperature of PCL. Further, it is shown by quantum chemical calculations that all the peaks obtained experimentally originate in skeletal vibrations of PCL. Therefore, it has become clear that a specific feature appears in the THz absorption spectrum of PCL associated with its glass transition.

  20. Amorphous to amorphous insulator-metal transition in GeSe3:Ag glasses

    NASA Astrophysics Data System (ADS)

    Prasai, Kiran; Chen, Gang; Drabold, D. A.

    2017-06-01

    We study an insulator-metal transition in a ternary chalcogenide glass (GeSe3)1 -xAgx for x =0.15 and 0.25. The conducting phase of the glass is obtained by using gap sculpting [Prasai et al., Sci. Rep. 5, 15522 (2015), 10.1038/srep15522] and it is observed that the metallic and insulating phases have nearly identical density functional energies but have a conductivity contrast of ˜108 . As such, we demonstrate an example of polyamorphism for which energetically close phases exhibit dramatically different optical properties. The transition from insulator to metal involves growth of an Ag-rich phase accompanied by a depletion of tetrahedrally bonded Ge (Se1/2)4 in the host network. The relative fraction of the amorphous Ag2Se phase and GeSe2 phase is shown to be a critical determinant of dc conductivity.

  1. Phase transitions in the three-state Ising spin-glass model with finite connectivity.

    PubMed

    Erichsen, R; Theumann, W K

    2011-06-01

    The statistical mechanics of a two-state Ising spin-glass model with finite random connectivity, in which each site is connected to a finite number of other sites, is extended in this work within the replica technique to study the phase transitions in the three-state Ghatak-Sherrington (or random Blume-Capel) model of a spin glass with a crystal-field term. The replica symmetry ansatz for the order function is expressed in terms of a two-dimensional effective-field distribution, which is determined numerically by means of a population dynamics procedure. Phase diagrams are obtained exhibiting phase boundaries that have a reentrance with both a continuous and a genuine first-order transition with a discontinuity in the entropy. This may be seen as "inverse freezing," which has been studied extensively lately, as a process either with or without exchange of latent heat.

  2. A wuantitative structure-property relationship study of the glass transition temperature of OLED materials.

    PubMed

    Yin, ShiWei; Shuai, Z; Wang, Yilin

    2003-01-01

    Organic light-emitting-diodes (OLED) materials possess great potential applications. Stability and efficiency are the two major factors to be improved toward commercialization, especially the thermal stability, because in the working device, the organic molecular materials can have high temperature. One of the most important factors, which influences the stability, is the glass transition temperature (T(g)). We employed a QSPR (quantitative structure-properties relationship) approach to establish a theoretical model to predict the glass transition temperatures of organic molecular materials. A six-parameter correlation with the squared correlation coefficient R(2) = 0.9270 and the average absolute error 8.5 K was developed for a diverse set of 73 OLED materials. All descriptors were derived solely from the chemical structures of the organic compounds. A satisfactory average absolute error of 17.9 K for a test set of 15 OLED materials makes the model very useful for the prediction of the unknown OLED materials.

  3. Correlation between the glass-rubber transition and ionic conductivity in poly(3-hexylthiophene)

    NASA Astrophysics Data System (ADS)

    Lada, M.

    2008-10-01

    Using impedance spectroscopy and metal-insulator-semiconductor structures, the small-signal bulk conductivity of annealed poly(3-hexylthiophene) (P3HT) has been extracted in the temperature range of 150-420K. A faster-than-Arrhenius increase in the conductivity of P3HT observed near and above room temperature is shown to be a result of the glass-rubber transition and is closely related to the amorphous phase of the polymer. The super-Arrhenius conductivity can be modeled and interpreted as ionic, arising from the thermal motion of the polymer segments. In addition, a percolative conduction mechanism induced by the glass transition can phenomenologically model the conductivity increase.

  4. Glass transition accelerates the spreading of polar solvents on a soluble polymer.

    PubMed

    Dupas, Julien; Verneuil, Emilie; Van Landeghem, Maxime; Bresson, Bruno; Forny, Laurent; Ramaioli, Marco; Lequeux, Francois; Talini, Laurence

    2014-05-09

    We study the wetting of polymer layers by polar solvents. As previously observed, when a droplet of solvent spreads, both its contact angle and velocity decrease with time as a result of solvent transfers from the droplet to the substrate. We show that, when the polymer is initially glassy, the angle decreases steeply for a given value of the velocity, Ug. We demonstrate that those variations result from a plasticization, i.e., a glass transition, undergone by the polymer layer during spreading, owing to the increase of its solvent content. By analyzing previous predictions on the wetting of rigid and soft viscoelastic substrates, we relate Ug to the viscosity of the polymer gel close to the glass transition. Finally, we derive an analytical prediction for Ug based on existing predictions for the water transfer from the droplet to the substrate. Using polar solvents of different natures, we show that the experimental data compare well to the predicted expression for Ug.

  5. Role of branching architecture on the glass transition of hyperbranched polyethers.

    PubMed

    Zhu, Qi; Wu, Jieli; Tu, Chunlai; Shi, Yunfeng; He, Lin; Wang, Ruibin; Zhu, Xinyuan; Yan, Deyue

    2009-04-30

    The influence of branching architecture on the glass transition of hyperbranched polyethers has been investigated. For amorphous samples, the glass transition temperature (T(g)) first increases with the degree of branching (DB), passes through a maximum, and then decreases sharply. An attempt is made to explain this by the competition between the junction density and the free volume of terminal units. For the crystalline samples, the crystallization of polymer chains makes the relationship of DB and T(g) more complicated. By the introduction of branching architecture, the crystallization ability of the branched polymer is weakened gradually. When the samples are isothermally crystallized for a long time, the T(g) of polyethers decreases monotonically with DB.

  6. Dielectric spectroscopy for the determination of the glass transition temperature of pharmaceutical solid dispersions.

    PubMed

    O'Donnell, Kevin P; Woodward, W H Hunter

    2015-06-01

    The purpose of this study was to evaluate analytical techniques for the measurement of the glass transition temperature of HPMC and formulated solid dispersions thereof. Unmodified samples of various grades of HPMC and solid dispersions of HPMC and itraconazole produced by hot melt extrusion were analyzed by thermomechanical analysis, differential scanning calorimetry, thermally stimulated depolarization current and dielectric spectroscopy. It was found that dielectric spectroscopy offers the best accuracy and reproducibility for analysis of the base HPMC powders regardless of the substitution type or viscosity grade and that the obtained results were not frequency dependent. The results of dielectric measurements of solid dispersions prepared by hot melt extrusion were compared with predicted values of the Gordon-Taylor equation. It was found that time-temperature superposition effects and small molecule frequency dependence makes broadly applying determination of the glass transition temperature in drug dispersions by dielectric spectroscopy prohibitively difficult.

  7. Direct Observation of Percolation in the Yielding Transition of Colloidal Glasses

    NASA Astrophysics Data System (ADS)

    Ghosh, Antina; Budrikis, Zoe; Chikkadi, Vijayakumar; Sellerio, Alessandro L.; Zapperi, Stefano; Schall, Peter

    2017-04-01

    When strained beyond the linear regime, soft colloidal glasses yield to steady-state plastic flow in a way that is similar to the deformation of conventional amorphous solids. Because of the much larger size of the colloidal particles with respect to the atoms comprising an amorphous solid, colloidal glasses allow us to obtain microscopic insight into the nature of the yielding transition, as we illustrate here combining experiments, atomistic simulations, and mesoscopic modeling. Our results unanimously show growing clusters of nonaffine deformation percolating at yielding. In agreement with percolation theory, the spanning cluster is fractal with a fractal dimension df≃2 , and the correlation length diverges upon approaching the critical yield strain. These results indicate that percolation of highly nonaffine particles is the hallmark of the yielding transition in disordered glassy systems.

  8. Studies of Transitional Flow, Unsteady Separation Phenomena and Particle Induced Augmentation Heating on Ablated Nose Tips.

    DTIC Science & Technology

    1975-10-01

    63 29 Variation of Profile Shape with Time for Axisyinmetric Camphor Models 63 30 The Development of Ablated Nose Shapes Over Which Flow...ablation tests using camphor models and inferred from downrange observation of full scale flight missions. Regions of gross instability on nose...been verified in wind tunnel tests of camphor models where shapes similar to those shown on Figure 29 can be developed under transitional conditions

  9. Computational Investigation of Impact Energy Absorption Capability of Polyurea Coatings via Deformation-Induced Glass Transition

    DTIC Science & Technology

    2010-01-01

    homepage: www.e lsev ier .com/ locate /msea Computational investigation of impact energy absorption capability of polyurea coatings via deformation-induced...Keywords: Polyurea Computational analysis Glass transition Blast/impact energy absorption coating a b s t r a c t A number of experimental investigations...reported in the open literature have indicated that the applica- tion of polyurea coatings can substantially improve blast and ballistic impact

  10. Hard sphere-like glass transition in eye lens α-crystallin solutions

    PubMed Central

    Savin, Gabriela; Bucciarelli, Saskia; Dorsaz, Nicolas; Thurston, George M.; Stradner, Anna; Schurtenberger, Peter

    2014-01-01

    We study the equilibrium liquid structure and dynamics of dilute and concentrated bovine eye lens α-crystallin solutions, using small-angle X-ray scattering, static and dynamic light scattering, viscometry, molecular dynamics simulations, and mode-coupling theory. We find that a polydisperse Percus–Yevick hard-sphere liquid-structure model accurately reproduces both static light scattering data and small-angle X-ray scattering liquid structure data from α-crystallin solutions over an extended range of protein concentrations up to 290 mg/mL or 49% vol fraction and up to ca. 330 mg/mL for static light scattering. The measured dynamic light scattering and viscosity properties are also consistent with those of hard-sphere colloids and show power laws characteristic of an approach toward a glass transition at α-crystallin volume fractions near 58%. Dynamic light scattering at a volume fraction beyond the glass transition indicates formation of an arrested state. We further perform event-driven molecular dynamics simulations of polydisperse hard-sphere systems and use mode-coupling theory to compare the measured dynamic power laws with those of hard-sphere models. The static and dynamic data, simulations, and analysis show that aqueous eye lens α-crystallin solutions exhibit a glass transition at high concentrations that is similar to those found in hard-sphere colloidal systems. The α-crystallin glass transition could have implications for the molecular basis of presbyopia and the kinetics of molecular change during cataractogenesis. PMID:25385638

  11. Correlating Free-Volume Hole Distribution to the Glass Transition Temperature of Epoxy Polymers.

    PubMed

    Aramoon, Amin; Breitzman, Timothy D; Woodward, Christopher; El-Awady, Jaafar A

    2017-09-07

    A new algorithm is developed to quantify the free-volume hole distribution and its evolution in coarse-grained molecular dynamics simulations of polymeric networks. This is achieved by analyzing the geometry of the network rather than a voxelized image of the structure to accurately and efficiently find and quantify free-volume hole distributions within large scale simulations of polymer networks. The free-volume holes are quantified by fitting the largest ellipsoids and spheres in the free-volumes between polymer chains. The free-volume hole distributions calculated from this algorithm are shown to be in excellent agreement with those measured from positron annihilation lifetime spectroscopy (PALS) experiments at different temperature and pressures. Based on the results predicted using this algorithm, an evolution model is proposed for the thermal behavior of an individual free-volume hole. This model is calibrated such that the average radius of free-volumes holes mimics the one predicted from the simulations. The model is then employed to predict the glass-transition temperature of epoxy polymers with different degrees of cross-linking and lengths of prepolymers. Comparison between the predicted glass-transition temperatures and those measured from simulations or experiments implies that this model is capable of successfully predicting the glass-transition temperature of the material using only a PDF of the initial free-volume holes radii of each microstructure. This provides an effective approach for the optimized design of polymeric systems on the basis of the glass-transition temperature, degree of cross-linking, and average length of prepolymers.

  12. Dynamic and thermodynamic characteristics associated with the glass transition of amorphous trehalose-water mixtures.

    PubMed

    Weng, Lindong; Elliott, Gloria D

    2014-06-21

    The glass transition temperature Tg of biopreservative formulations is important for predicting the long-term storage of biological specimens. As a complementary tool to thermal analysis techniques, which are the mainstay for determining Tg, molecular dynamics simulations have been successfully applied to predict the Tg of several protectants and their mixtures with water. These molecular analyses, however, rarely focused on the glass transition behavior of aqueous trehalose solutions, a subject that has attracted wide scientific attention via experimental approaches. Important behavior, such as hydrogen-bonding dynamics and self-aggregation has yet to be explored in detail, particularly below, or in the vicinity of, Tg. Using molecular dynamics simulations of several dynamic and thermodynamic properties, this study reproduced the supplemented phase diagram of trehalose-water mixtures (i.e., Tg as a function of the solution composition) based on experimental data. The structure and dynamics of the hydrogen-bonding network in the trehalose-water systems were also analyzed. The hydrogen-bonding lifetime was determined to be an order of magnitude higher in the glassy state than in the liquid state, while the constitution of the hydrogen-bonding network exhibited no noticeable change through the glass transition. It was also found that trehalose molecules preferred to form small, scattered clusters above Tg, but self-aggregation was substantially increased below Tg. The average cluster size in the glassy state was observed to be dependent on the trehalose concentration. Our findings provided insights into the glass transition characteristics of aqueous trehalose solutions as they relate to biopreservation.

  13. Translation-rotation coupling, phase transitions, and elastic phenomena in orientationally disordered crystals

    NASA Astrophysics Data System (ADS)

    Lynden-Bell, R. M.; Michel, K. H.

    1994-07-01

    Many of the properties of orientationally disordered crystals are profoundly affected by the coupling (known as translation-rotation coupling) between translation displacements and molecular orientation. The consequences of translation-rotation coupling depend on molecular and crystal symmetry, and vary throughout the Brillouin zone. One result is an indirect coupling between the orientations of different molecules, which plays an important role in the order/disorder phase transition, especially in ionic orientationally disordered crystals. Translation-rotation coupling also leads to softening of elastic constants and affects phonon spectra. This article describes the theory of the coupling from the point of view of the microscopic Hamiltonian and the resulting Landau free energy. Considerable emphasis is placed on the restrictions due to symmetry as these are universal and can be used to help one's qualitative understanding of experimental observations. The application of the theory to phase transitions is described. The softening of elastic constants is discussed and shown to be universal. However, anomalies associated with the order/disorder phase transition are shown to be restricted to cases in which the symmetry of the order parameter satisfies certain conditions. Dynamic effects on phonon spectra are described and finally the recently observed dielectric behavior of ammonium compounds is discussed. Throughout the article examples from published experiments are used to illustrate the application of the theory including well known examples such as the alkali metal cyanides and more recently discovered orientationally disordered crystals such as the fullerite, C60.

  14. Viscoelastic processes in non-ergodic states (percolation and glass transitions) of attractive micellar systems

    NASA Astrophysics Data System (ADS)

    Mallamace, F.; Broccio, M.; Tartaglia, P.; Chen, W. R.; Faraone, A.; Chen, S. H.

    2003-12-01

    We report a set of viscoelastic measurements in aqueous solutions of a copolymer micellar system with attractive interactions, a system characterized by a percolation line (PT), and a structural arrest (SA) in the particle diffusion motions of a kinetic glass transition (KGT). We observe, in both transitions, dramatic variations in both the elastic (or storage G‧( ω)) and loss components ( G″( ω)) of the shear moduli. At the PT, rheological data are characterized by a scaling behavior, whereas at the SA G‧ and G″ develop a plateau and a marked minimum, respectively. These behaviors are described in the frame of percolation models and mode coupling theory (MCT).

  15. Optical transitions and frequency upconversion emission of Er 3+ions in novel lead-bismuthate glass

    NASA Astrophysics Data System (ADS)

    Sun, Hongtao; Dai, Shixun; Zhang, Debao; Xu, Shiqing; Zhang, Junjie; Hu, Lili; Jiang, Zhonghong

    2004-12-01

    Er 3+-doped strontiam lead bismuth glass for developing upconversion lasers has been fabricated and characterized. The Judd-Ofelt analysis was performed on the absorption spectrum and the transition probabilities, excited state lifetimes, and the fluorescence branching ratios were calculated and discussed. Under 975 nm excitation, intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H→4I, 4S→4I, and 4F→4I, respectively, were observed. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for the green and red emissions.

  16. Cubic to tetragonal phase transition of Tm{sup 3+} doped nanocrystals in oxyfluoride glass ceramics

    SciTech Connect

    Li, Yiming; Fu, Yuting; Shi, Yahui; Zhang, Xiaoyu; Yu, Hua E-mail: yuhua@nankai.edu.cn; Zhao, Lijuan E-mail: yuhua@nankai.edu.cn

    2016-02-15

    Tm{sup 3+} ions doped β-PbF{sub 2} nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm{sup 3+} doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an O{sub h} to D{sub 4h} site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm{sup 3+} doped nanocrystals at 800 nm was modulated by the phase transition of the surrounding crystal field.

  17. Transition to Glass: Pilot Training for High-Technology Transport Aircraft

    NASA Technical Reports Server (NTRS)

    Wiener, Earl L.; Chute, Rebecca D.; Moses, John H.

    1999-01-01

    This report examines the activities of a major commercial air carrier between 1993 and late 1996 as it acquired an advanced fleet of high-technology aircraft (Boeing 757). Previously, the airline's fleet consisted of traditional (non-glass) aircraft, and this report examines the transition from a traditional fleet to a glass one. A total of 150 pilots who were entering the B-757 transition training volunteered for the study, which consisted of three query phases: (1) first day of transition training, (2) 3 to 4 months after transition training, and (3) 12 to 14 months after initial operating experience. Of these initial 150 pilots, 99 completed all three phases of the study, with each phase consisting of probes on attitudes and experiences associated with their training and eventual transition to flying the line. In addition to the three questionnaires, 20 in-depth interviews were conducted. Although the primary focus of this study was on the flight training program, additional factors such as technical support, documentation, and training aids were investigated as well. The findings generally indicate that the pilot volunteers were highly motivated and very enthusiastic about their training program. In addition, the group had low levels of apprehension toward automation and expressed a high degree of satisfaction toward their training. However, there were some concerns expressed regarding the deficiencies in some of the training aids and lack of a free-play flight management system training device.

  18. Microscopic dynamics of the glass transition investigated by time-resolved fluorescence measurements of doped chromophores

    NASA Astrophysics Data System (ADS)

    Ye, Jing Yong; Hattori, Toshiaki; Nakatsuka, Hiroki; Maruyama, Yoshihiro; Ishikawa, Mitsuru

    1997-09-01

    The microscopic dynamics of several monomeric and polymeric glass-forming materials has been investigated by time-resolved fluorescence measurements of doped malachite green molecules in a wide temperature region. For monomers, 1-propanol, propylene glycol, and glycerol, and a polymer without side chains, poly- butadiene, the temperature dependence of nonradiative decay time of doped malachite green molecules behaves in a similar way through the glass-transition region. Besides a kink around the calorimetric glass-transition temperature Tg, another crossover at a critical temperature Tc about 30-50 K above Tg has been clearly observed. This experimental finding is in agreement with the prediction of the mode-coupling theory that a dynamical transition exists well above Tg. On the other hand, for the complex polymers with side chains, poly(vinyl acetate), poly(methyl acrylate), and poly(ethyl methacrylate), the crossover at Tg is less pronounced than those for the monomers and the polymer without side chains. Moreover, although we could not distinguish any singularities above Tg for these complex polymers, we observed another kink below Tg, which may be attributed to the side-chain motions.

  19. Influence of the glass transition on the secondary relaxation of an epoxy resin

    NASA Astrophysics Data System (ADS)

    Casalini, R.; Fioretto, D.; Livi, A.; Lucchesi, M.; Rolla, P. A.

    1997-08-01

    The dynamics of diglycidyl ether of bisphenol-A (DGEBA) was studied by employing broadband dielectric spectroscopy over a wide temperature range extending from below to above the glass-transition temperature. Dielectric spectra reveal the existence of two relaxation processes: the structural relaxation, slowing down for decreasing temperature and freezing at Tg, and a secondary process present in both liquid and glassy phase. Above the glass transition the temperature behavior of the structural relaxation time is properly described by a Vogel-Fulcher-Tamman equation with the singularity at T0=234 K. The analysis of the variation of the relaxation strength versus temperature of both processes clearly shows the onset of the structural relaxation at Ton~350 K. Below this temperature the two relaxations progressively separate their time scales and change their shapes. The occurrence of the glass-transition phenomenon is markedly evidenced by the changes of the relaxation strength and of the low-frequency slope of the secondary relaxation.

  20. Glass transition study in model food systems prepared with mixtures of fructose, glucose, and sucrose.

    PubMed

    Saavedra-Leos, M Z; Grajales-Lagunes, A; González-García, R; Toxqui-Terán, A; Pérez-García, S A; Abud-Archila, M A; Ruiz-Cabrera, M A

    2012-05-01

    The glass transition temperature of model food systems prepared with several glucose/fructose/sucrose mass fractions was studied using differential scanning calorimetry (DSC). A distance-based experimental design for mixtures of 3 components was used to establish the proportion of sugars of the model systems. Thus, 32 compositions including individual sugars and sugar mixtures, both binary and ternary were prepared and analyzed. Thermograms showing the complete process of heating-cooling-reheating were used to determine the precise glass transition temperature during cooling (T(g)(c)) or reheating (T(g)(H) in amorphous sugars. The Scheffe cubic model was applied to experimental results to determine the influence of sugar composition on the glass transition temperature (P < 0.05). The final model proved to be appropriate (R(2) > 0.97, CV < 9%, model significance <0.0001) to predict the T(g) values of any dry mixture of amorphous fructose, glucose, and sucrose. © 2012 Institute of Food Technologists®

  1. Reversibility and hysteresis of the sharp yielding transition of a colloidal glass under oscillatory shear.

    PubMed

    Dang, M T; Denisov, D; Struth, B; Zaccone, A; Schall, P

    2016-04-01

    The mechanical response of glasses remains challenging to understand. Recent results indicate that the oscillatory rheology of soft glasses is accompanied by a sharp non-equilibrium transition in the microscopic dynamics. Here, we use simultaneous x-ray scattering and rheology to investigate the reversibility and hysteresis of the sharp symmetry change from anisotropic solid to isotropic liquid dynamics observed in the oscillatory shear of colloidal glasses (D. Denisov, M.T. Dang, B. Struth, A. Zaccone, P. Schall, Sci. Rep. 5 14359 (2015)). We use strain sweeps with increasing and decreasing strain amplitude to show that, in analogy with equilibrium transitions, this sharp symmetry change is reversible and exhibits systematic frequency-dependent hysteresis. Using the non-affine response formalism of amorphous solids, we show that these hysteresis effects arise from frequency-dependent non-affine structural cage rearrangements at large strain. These results consolidate the first-order-like nature of the oscillatory shear transition and quantify related hysteresis effects both via measurements and theoretical modelling.

  2. Unveiling the Dependence of Glass Transitions on Mixing Thermodynamics in Miscible Systems

    NASA Astrophysics Data System (ADS)

    Tu, Wenkang; Wang, Yunxi; Li, Xin; Zhang, Peng; Tian, Yongjun; Jin, Shaohua; Wang, Li-Min

    2015-02-01

    The dependence of the glass transition in mixtures on mixing thermodynamics is examined by focusing on enthalpy of mixing, ΔHmix with the change in sign (positive vs. negative) and magnitude (small vs. large). The effects of positive and negative ΔHmix are demonstrated based on two isomeric systems of o- vs. m- methoxymethylbenzene (MMB) and o- vs. m- dibromobenzene (DBB) with comparably small absolute ΔHmix. Two opposite composition dependences of the glass transition temperature, Tg, are observed with the MMB mixtures showing a distinct negative deviation from the ideal mixing rule and the DBB mixtures having a marginally positive deviation. The system of 1, 2- propanediamine (12PDA) vs. propylene glycol (PG) with large and negative ΔHmix is compared with the systems of small ΔHmix, and a considerably positive Tg shift is seen. Models involving the properties of pure components such as Tg, glass transition heat capacity increment, ΔCp, and density, ρ, do not interpret the observed Tg shifts in the systems. In contrast, a linear correlation is revealed between ΔHmix and maximum Tg shifts.

  3. Development of Toroidal Magnetic Thermometry to Study New Phenomena Associated with the Superfluid Transition in Liquid HELIUM-4

    NASA Astrophysics Data System (ADS)

    Duncan, Robert Vance

    A new type of paramagnetic susceptibility thermometry called toroidal magnetic thermometry (TMT) has been developed. These TMT thermometers have a thermal resolution of five nanoKelvin near the ^4He superfluid transition temperature T_lambda = 2.172K, making TMT roughly a factor of fifty times better in resolution than conventional germanium resistance thermometry which is commercially available. The dramatic improvement in thermal resolution provided by TMT has been used to observe new phenomena associated with the superfluid transition in pure liquid ^4He. Such phenomena include a component of the thermal boundary (Kapitza) resistance R_{rm K} which is singular at the superfluid transition temperature T_lambda. In addition to the singularity, measurements of R _{rm K} exhibit a strong dependence on the heat current Q used to make the measurements for reduced temperature t equiv 1 - T/T_lambda<=ss than t_{rm c}(Q). This t_{rm c} was observed to be approximately proportional to Q. For t < t_{rm c} the initial value of the derivative dR_ {rm K}/dQ was observed to be approximately proportional to 1/t. In addition to the boundary effects described above, these TMT thermometers have been used to detect the depression of T_lambda by a heat current Q flowing through the liquid helium. Due to the ultrahigh resolution of the TMT thermometers this effect has been studied using values of Q < 10 muW/cm^2 where superfluid thermal gradients have been observed to be very small. When these values of Delta T_lambda(Q) were used to calculate the depression of the superfluid density Deltarho_{ rm s}(Q) the results agreed well with a prediction based on the theory of Ginzburg and Pitaevskii. The calibration of the TMT thermometers provide high-resolution measurements of the a.c. paramagnetic susceptibility of their magnetic salt: Copper ammonium bromide (CAB). These calibration parameters, together with power dissipation data near the CAB Curie temperature T_{rm c} = 1.795K, provide

  4. Investigating the Glass Transition Temperature of Water using a Variety of Models and Methods via Molecular Dynamics Simulation

    NASA Astrophysics Data System (ADS)

    Muryn, John; Leuty, Gary; Tsige, Mesfin

    2012-02-01

    In everyday life, we think of solid water existing as crystalline ice. The majority of water in the universe, however, exists as an amorphous solid or ``glassy'' form. This glassy form has garnered significant interest and sparked sizable debate in recent years over the nature and conditions surrounding the transition from liquid to amorphous solid, not the least of which centers on the determination of the glass transition temperature. Previous experimental studies have suggested a glass transition temperature below the temperature at which water undergoes homogeneous nucleation, thus making experimental determination of the glass transition temperature difficult because of the need to avoid ice formation. In this study, we have used molecular dynamics simulation to study the structure, order and dynamics of water molecules at small timescales and under rapid cooling conditions to elucidate the formation of the amorphous solid and better understand the glass transition. Constant-pressure and constant-volume simulations have been performed in order to examine convergence or divergence of water dynamics under differing conditions. In addition, the van der Waals energy of simulation systems has been examined in an attempt to identify the glass transition temperature in a way that, to our knowledge, has not previously been used. Results suggest a glass transition temperature higher than previous widely accepted values but comparable to more recent results.

  5. Unraveling wetting transition through surface textures with X-rays: Liquid meniscus penetration phenomena

    PubMed Central

    Antonini, C.; Lee, J. B.; Maitra, T.; Irvine, S.; Derome, D.; Tiwari, Manish K.; Carmeliet, J.; Poulikakos, D.

    2014-01-01

    In this report we show that synchrotron X-ray radiography is a powerful method to study liquid-air interface penetration through opaque microtextured surface roughness, leading to wetting transition. We investigate this wetting phenomenon in the context of sessile drop evaporation, and establish that liquid interface sinking into the surface texture is indeed dictated by the balance of capillary and Laplace pressures, where the intrinsically three-dimensional nature of the meniscus must be accounted for. Air bubble entrapment in the texture underneath impacting water drops is also visualized and the mechanisms of post-impact drop evaporation are discussed. PMID:24514762

  6. Unraveling wetting transition through surface textures with X-rays: liquid meniscus penetration phenomena.

    PubMed

    Antonini, C; Lee, J B; Maitra, T; Irvine, S; Derome, D; Tiwari, Manish K; Carmeliet, J; Poulikakos, D

    2014-02-11

    In this report we show that synchrotron X-ray radiography is a powerful method to study liquid-air interface penetration through opaque microtextured surface roughness, leading to wetting transition. We investigate this wetting phenomenon in the context of sessile drop evaporation, and establish that liquid interface sinking into the surface texture is indeed dictated by the balance of capillary and Laplace pressures, where the intrinsically three-dimensional nature of the meniscus must be accounted for. Air bubble entrapment in the texture underneath impacting water drops is also visualized and the mechanisms of post-impact drop evaporation are discussed.

  7. Low-density to high-density transition in Ce75Al23Si2 metallic glass.

    PubMed

    Zeng, Q S; Fang, Y Z; Lou, H B; Gong, Y; Wang, X D; Yang, K; Li, A G; Yan, S; Lathe, C; Wu, F M; Yu, X H; Jiang, J Z

    2010-09-22

    Using in situ high-pressure x-ray diffraction (XRD), we observed a pressure-induced polyamorphic transition from the low-density amorphous (LDA) state to the high-density amorphous (HDA) state in Ce(75)Al(23)Si(2) metallic glass at about 2 GPa and 300 K. The thermal stabilities of both LDA and HDA metallic glasses were further investigated using in situ high-temperature and high-pressure XRD, which revealed different pressure dependences of the onset crystallization temperature (T(x)) between them with a turning point at about 2 GPa. Compared with Ce(75)Al(25) metallic glass, minor Si doping shifts the onset polyamorphic transition pressure from 1.5 to 2 GPa and obviously stabilizes both LDA and HDA metallic glasses with higher T(x) and changes their slopes dT(x)/dP. The results obtained in this work reveal another polyamorphous metallic glass system by minor alloying (e.g. Si), which could modify the transition pressure and also properties of LDA and HDA metallic glasses. The minor alloying effect reported here is valuable for the development of more polyamorphous metallic glasses, even multicomponent bulk metallic glasses with modified properties, which will trigger more investigations in this field and improve our understanding of polyamorphism and metallic glasses.

  8. Optical transitions of Tm3+ in oxyfluoride glasses and compositional and thermal effect on upconversion luminescence of Tm3+/Yb3+-codoped oxyfluoride glasses.

    PubMed

    Feng, Li; Wu, Yinsu; Liu, Zhuo; Guo, Tao

    2014-01-24

    Optical properties of Tm(3+)-doped SiO2-BaF2-ZnF2 glasses have been investigated on the basis of the Judd-Ofelt theory. Judd-Ofelt intensity parameters, radiative transition probabilities, fluorescence branching ratios and radiative lifetimes have been calculated for different glass compositions. Upconversion emissions were observed in Tm(3+)/Yb(3+)-codoped SiO2-BaF2-ZnF2 glasses under 980 nm excitation. The effects of composition, concentration of the doping ions, temperature, and excitation pump power on the upconversion emissions were also systematically studied. Copyright © 2013 Elsevier B.V. All rights reserved.

  9. Glass transition in ferroic glass K x (ND4)1-x D2PO4: a complete x-ray diffraction line shape analysis

    NASA Astrophysics Data System (ADS)

    Ranjan Choudhury, Rajul; Chitra, R.; Jayakrishnan, V. B.

    2016-03-01

    Quenching of dynamic disorder in glassy systems is termed as the glass transition. Ferroic glasses belong to the class of paracrystalline materials having crystallographic order in-between that of a perfect crystal and amorphous material, a classic example of ferroic glass is the solid solution of ferroelectric deuterated potassium dihydrogen phosphate and antiferroelectric deuterated ammonium dihydrogen phosphate. Lowering temperature of this ferroic glass can lead to a glass transition to a quenched disordered state. The subtle atomic rearrangement that takes place at such a glass transition can be revealed by careful examination of the temperature induced changes occurring in the x-ray powder diffraction (XRD) patterns of these materials. Hence we report here results of a complete diffraction line shape analysis of the XRD patterns recorded at different temperatures from deuterated mixed crystals DK x A1-x DP with mixing concentration x ranging as 0 < x < 1. Changes observed in diffraction peak shapes have been explained on the basis of structural rearrangements induced by changing O-D-O hydrogen bond dynamics in these paracrystals.

  10. Ultraviolet and visible Brillouin scattering study of viscous relaxation in 3-methylpentane down to the glass transition

    NASA Astrophysics Data System (ADS)

    Benassi, P.; Nardone, M.; Giugni, A.

    2012-09-01

    Brillouin light scattering spectra from transverse and longitudinal acoustic waves in liquid and supercooled 3-methylpentane have been collected from room temperature down to 80 K, just above the glass transition. Spectra at different wave vectors have been obtained using 532 nm and 266 nm excitation. We found evidence of a shear relaxation with a characteristic time of 100 s at the glass transition which only partly accounts for the relaxation observed in the propagation and attenuation of the longitudinal modes. The inclusion of a relaxing bulk viscosity contribution with a relaxation time of the order of 102 ns at the glass transition is found to adequately reproduce the experimental data including transient grating data at a much lower frequency. A consistent picture of relaxed shear and bulk moduli as a function of temperature is derived. These two quantities are found to be related by a linear relation suggesting that a Cauchy-like relation holds also above the glass transition.

  11. Glass transition-related changes in molecular mobility below glass transition temperature of freeze-dried formulations, as measured by dielectric spectroscopy and solid state nuclear magnetic resonance.

    PubMed

    Yoshioka, Sumie; Aso, Yukio

    2005-02-01

    The purpose of this study was to explore why changes in the molecular mobility associated with glass transition, the timescale of which is on the order of 100 s, can be detected by measuring the nuclear magnetic resonance relaxation times that reflect molecular motions on the order of 10 kHz and 1 MHz. The molecular motions in freeze-dried dextran 40k, dextran 1k, isomaltotriose (IMT), and alpha-glucose comprising a common unit but with different glass transition temperatures, were investigated by dielectric spectroscopy (DES) in the frequency range of 0.01 Hz to 100 kHz and in the temperature range of -20 degrees to 200 degrees C, in order to compare with the molecular motions reflected in nuclear magnetic resonance relaxation times. The alpha-relaxation process for freeze-dried alpha-glucose was visualized by DES, whereas those for freeze-dried dextran 40k, dextran 1k, and IMT were too slow to be visualized by DES. The latter freeze-dried cakes exhibited quasi-dc polarization because of proton-hopping-like motion rather than alpha-relaxation process. The correlation time (tau(c)) for the backbone carbon of dextran 40k and IMT, calculated from the measured value of spin-lattice relaxation time in the rotating frame, was found to be close to the relaxation time of proton-hopping-like motion determined by DES (tau(DES)) at temperatures around glass transition temperature. The timescales of molecular motions reflected in the tau(c) and tau(DES) were significantly smaller than that of motions leading to molecular rearrangement (molecular rearrangement motions), which correspond to alpha-relaxation. However, the shapes of temperature dependence for the tau(c) and tau(DES) were similar to that of the calorimetrically determined relaxation time of molecular rearrangement motions. Results suggest that the molecular motions reflected in the tau(c) and tau(DES) are linked to molecular rearrangement motions, such that enhancement of molecular rearrangement motions enhances

  12. The peculiar behavior of the glass transition temperature of amorphous drug-polymer films coated on inert sugar spheres.

    PubMed

    Dereymaker, Aswin; Van Den Mooter, Guy

    2015-05-01

    Fluid bed coating has been proposed in the past as an alternative technology for manufacturing of drug-polymer amorphous solid dispersions, or so-called glass solutions. It has the advantage of being a one-step process, and thus omitting separate drying steps, addition of excipients, or manipulation of the dosage form. In search of an adequate sample preparation method for modulated differential scanning calorimetry analysis of beads coated with glass solutions, glass transition broadening and decrease of the glass transition temperature (Tg ) were observed with increasing particle size of crushed coated beads and crushed isolated films of indomethacin (INDO) and polyvinylpyrrolidone (PVP). Substituting INDO with naproxen gave comparable results. When ketoconazole was probed or the solvent in INDO-PVP films was switched to dichloromethane (DCM) or a methanol-DCM mixture, two distinct Tg regions were observed. Small particle sizes had a glass transition in the high Tg region, and large particle sizes had a glass transition in the low Tg region. This particle size-dependent glass transition was ascribed to different residual solvent amounts in the bulk and at the surface of the particles. A correlation was observed between the deviation of the Tg from that calculated from the Gordon-Taylor equation and the amount of residual solvent at the Tg of particles with different sizes. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

  13. Nd - Fe - Al, A SPIN GLASS TRANSITION IN A COLLECTION OF SUPERPARAMAGNETIC CLUSTERS.

    SciTech Connect

    MCCALLUM,R.W.KRAMER,M.J.DENNIS,K.W.LEWIS,L.H.

    2002-08-18

    In the Nd-Fe-A1 system, compositions in the range of Nd{sub 60}Fe{sub 30}Al{sub 10} have been reported to be ferromagnetic bulk metallic glasses with high coercivities. Careful examination of both the microstructure and magnetic properties of these materials shows this to be true only in the most general sense. The materials are shown to be nanocomposites, in the strictest sense, with characteristic structural length scales on the order of 1.2 nm. Magnetically, the materials are also composites exhibiting a number of magnetic transitions as a function of temperature. The temperature dependence of the magnetic properties will be discussed in terms of strongly-interacting superparamagnetic clusters residing in a paramagnetic matrix. The clusters exhibit a frequency-dependent blocking temperature as determined from AC susceptibility, that is inconsistent with simple superparamagnetic behavior but is consistent with a spin glass-type ordering of the clusters to form a cluster glass. For a temperature region extending approximately 100 K below the cluster glass ordering temperature, the materials exhibit low coercivity. Below this temperature regime significant coercivities develop. The energy barrier to magnetic reversal provided by the product of the cluster volume multiplied by the anisotropy energy is inconsistent with the values required to fit the superparamagnetic behavior above the spin glass transition in the framework of the random anisotropy model. Instead, the existence in this system of significant coercivity is associated with a change in the paramagnetic fraction of the sample consistent with antiferromagnetic ordering of part of the paramagnetic matrix. The remainder of the matrix material orders ferromagnetically at a lower temperature and the interaction between the antiferromagnetic clusters and the ferromagnetic matrix underlies the large coercivities observed at low temperatures.

  14. Thermodynamic aspects of the glass transition phenomenon. II. Molecular liquids with variable interactions

    NASA Astrophysics Data System (ADS)

    Alba-Simionesco, C.; Fan, J.; Angell, C. A.

    1999-03-01

    As a contribution to the understanding of the thermodynamics of the glass transition phenomenon a series of molecules having the same steric character, but differing in the strength and nature of intermolecular interactions, has been investigated. The series is based on systematic changes of substituents on disubstituted benzene ring compounds, the simplest example of which is meta-xylene. Meta-isomers are chosen in each instance because of their greater tendency to supercool. In particular, m-fluoroaniline cannot be crystallized at ambient pressure. The principal measurements performed were of heat capacity and enthalpy change, using the technique of differential scanning calorimetry, and these have been examined in the light of literature data on the liquid viscosities and some recent data for dielectric relaxation. As the strength of hydrogen-bonding interactions between the ring substituents on adjacent molecules increases, the glass transition temperature Tg increases by almost 100 degrees from the lowest value in the series, 122.5 K, for m-fluorotoluene. Empirical rules involving Tb/Tm and Tg/Tm are found wanting. The important thermodynamic characteristic of the glass transition, viz., the change in heat capacity at the glass transition, ΔCp, remains approximately constant until the -OH substituent is introduced, whereupon a new element appears. This is a specific component of ΔCp which appears at temperatures above an initially small jump at Tg. It is well accounted for by the addition of a two-state H-bond breaking component (with the usual H⋯-OH bond energy) to the total excess heat capacity. The liquid ground state (or Kauzmann) temperature TK assessed from thermodynamic data acquired in this study, falls 20%-30% below the glass transition temperature. From the limited transport data available, these liquids appear to be quite fragile in character implying that the phenyl group influence dominates the hydrogen bond factor which has often seemed

  15. A study of many-body phenomena in metal nanoclusters (Au, Cu) close to their transition to the nonmetallic state

    SciTech Connect

    Borman, V. D.; Borisyuk, P. V.; Lebid'ko, V. V.; Pushkin, M. A.; Tronin, V. N.; Troyan, V. I. Antonov, D. A.; Filatov, D. O.

    2006-02-15

    The results of a study of many-body phenomena in gold and copper nanoclusters are presented. The measured conductivity as a function of nanocluster height h was found to have a minimum at h {approx} 0.6 nm. Conductivity was local in character at nanocluster sizes l {<=} l{sub c} {approx} 2.5 nm. Changes in core hole screening and an anomalous increase in the Anderson singularity index {alpha} in gold and copper nanoclusters could be caused by changes in permittivity from metallic ({epsilon} {sup {yields}} {infinity}) to nonmetallic ({epsilon} {proportional_to} l{sup 2}). The many-body phenomenon characteristics observed in the X-ray photoelectron and tunnel spectra of gold and copper nanoclusters as the size of the nanoclusters changed led us to suggest changes in the band structure of the nanoclusters and, therefore, their possible transition from the metallic to nonmetallic state.

  16. Thermodynamic evidence for the Bose glass transition in twinnedYBa2Cu3O7-δcrystals

    DOE PAGES

    Pérez-Morelo, D. J.; Osquiguil, E.; Kolton, A. B.; ...

    2015-07-21

    We used a micromechanical torsional oscillator to measure the magnetic response of a twinned YBaBa2Cu3O7-δ single crystal disk near the Bose glass transition. We observe an anomaly in the temperature dependence of the magnetization consistent with the appearance of a magnetic shielding perpendicular to the correlated pinning of the twin boundaries. This effect is related to the thermodynamic transition from the vortex liquid phase to a Bose glass state.

  17. Implications of storage and handling conditions on glass transition and potential devitrification of oocytes and embryos.

    PubMed

    Sansinena, M; Santos, M V; Taminelli, G; Zaritky, N

    2014-08-01

    Devitrification, the process of crystallization of a formerly crystal-free, amorphous glass state, can lead to damage during the warming of cells. The objective of this study was to determine the glass transition temperature of a cryopreservation solution typically used in the vitrification, storage, and warming of mammalian oocytes and embryos using differential scanning calorimetry. A numerical model of the heat transfer process to analyze warming and devitrification thresholds for a common vitrification carrier (open-pulled straw) was conducted. The implications on specimen handling and storage inside the dewar in contact with nitrogen vapor phase at different temperatures were determined. The time required for initiation of devitrification of a vitrified sample was determined by mathematical modeling and compared with measured temperatures in the vapor phase of liquid nitrogen cryogenic dewars. Results indicated the glass transition ranged from -126 °C to -121 °C, and devitrification was initiated at -109 °C. Interestingly, samples entered rubbery state at -121 °C and therefore could potentially initiate devitrification above this value, with the consequent damaging effects to cell survival. Devitrification times were calculated considering an initial temperature of material immersed in liquid nitrogen (-196 °C), and two temperatures of liquid nitrogen vapors within the dewar (-50 °C and -70 °C) to which the sample could be exposed for a period of time, either during storage or upon its removal. The mathematical model indicated samples could reach glass transition temperatures and undergo devitrification in 30 seconds. Results of the present study indicate storage of vitrified oocytes and embryos in the liquid nitrogen vapor phase (as opposed to completely immersed in liquid nitrogen) poses the potential risk of devitrification. Because of the reduced time-handling period before samples reach critical rubbery and devitrification values, caution should be

  18. Dynamic phase transition phenomena and magnetization reversal process in uniaxial ferromagnetic nanowires

    NASA Astrophysics Data System (ADS)

    Yüksel, Yusuf

    2015-09-01

    By utilizing the Monte Carlo simulation technique with Metropolis algorithm, we have studied the dynamic phase transition properties such as dynamic hysteresis loops and frequency dispersion of their area in the presence of externally applied oscillating magnetic fields. Particular attention has been paid on the variation of the hysteresis loop area (HLA) curves and their maximal behavior at different temperature regimes. In order to understand the physical mechanism behind the maximum lossy point observed in HLA curves, time series of instantaneous magnetization, as well as micromagnetic domain structures have been provided. Most of the qualitative aspects of the results reported in the present work are shown to be not model-specific type but common phenomenon observed in dynamic magnetic systems.

  19. Investigation of laminar to turbulent transition phenomena effects on impingement heat transfer

    NASA Astrophysics Data System (ADS)

    Isman, Mustafa Kemal; Morris, Philip J.; Can, Muhiddin

    2016-10-01

    Turbulent impinging air flow is investigated numerically by using the ANSYS-CFX® code. All computations are performed by considering three-dimensional, steady, and incompressible flow. Three different Reynolds averaged Navier-Stokes (RANS) turbulence models and two Reynolds stress models (RSM's) are employed. Furthermore three different laminar to turbulent transition (LTT) models are employed with the shear stress transport (SST) and the baseline (BSL) models. Results show that predictions of the SST and two RSM's are very close each other and these models' results are in better agreement with the experimental data when all Reynolds numbers used in this study are considered. Secondary maxima in Nusselt number can be seen only if the LTT formula is employed with SST and BSL models.

  20. Phase transitions and reentrant phenomena in liquid crystals having both rigid and flexible intramolecular joints

    NASA Astrophysics Data System (ADS)

    Pyżuk, W.; Górecka, E.; Mieczkowski, J.; Przedmojski, J.

    1992-07-01

    Two series of liquid-crystalline compounds having three phenyl rings separated by flexible spacer —CH(CH{3})CH{2}—COO— and by rigid azo and azoxy group, were studied by DSC, optical and X-ray methods. For esters of dl-3-(4^{prime}-nitro)-phenylbutyric acid with 4^{prime}-alkoxy-phenylazo-phenol-4 having dodecyloxy or longer terminal chains, as well as for related azoxy compounds, a narrow (even below 5 K) reentrant or inverted nematic phase appearing between partly bilayer and monolayer smectics A was observed. For higher homologues of the azoxy series additional smectic phases appear, leading to the occurrence of new multicritical points, e.g. the critical end point Ad Cd N^re. On each of the lines, which separate nematic from smectic A phases, transitions are of weakly first or second-order and more than one tricritical point can occur. On the A{1} N/A{1} N^re line, a simple N A{1} tricritical point is observed at T_NI/T_AN = 0.834. The presence of further critical points depends on the components of the binary system involved. Four of the azoxy compounds studied undergo a second order phase transition between partly bilayer smectics, Ad and Cd. Such a transition is accompanied by a jumb in the specific heat, varying linearly with the length of the molecular tails. Various temperature dependences of the layer spacing in the Ad phase are observed for subsequent homologues from the azoxy series. Plusieurs cristaux liquides composés de trois groupements phényl séparés par un groupement —CH(CH{3})CH{2}—COO—, ainsi que par des groupements azo et azoxy, ont été examinés par AED, méthodes optiques et par rayons X. Pour des esters de l'acide dl-3-(4^{prime}-nitro)phénylbutyrique et de 4^{prime}-alkoxy-phénylazo-phénol-4 ayant comme terminaison une chaîne dodecyloxy ou bien plus longue, ainsi que pour des composés azoxy relatif, on observe (même au-dessous de 5 K) une étroite phase nématique réentrante ou inverse entre les phases smectiques

  1. Strain glass transition in a multifunctional β-type Ti alloy

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Gao, Jinghui; Wu, Haijun; Yang, Sen; Ding, Xiangdong; Wang, Dong; Ren, Xiaobing; Wang, Yunzhi; Song, Xiaoping; Gao, Jianrong

    2014-02-01

    Recently, a class of multifunctional Ti alloys called GUM metals attracts tremendous attentions for their superior mechanical behaviors (high strength, high ductility and superelasticity) and novel physical properties (Invar effect, Elinvar effect and low modulus). The Invar and Elinvar effects are known to originate from structural or magnetic transitions, but none of these transitions were found in the GUM metals. This challenges our fundamental understanding of their physical properties. In this study, we show that the typical GUM metal Ti-23Nb-0.7Ta-2Zr-1.2O (at%) alloy undergoes a strain glass transition, where martensitic nano-domains are frozen gradually over a broad temperature range by random point defects. These nano-domains develop strong texture after cold rolling, which causes the lattice elongation in the rolling direction associated with the transition upon cooling and leads to its Invar effect. Moreover, its Elinvar effect and low modulus can also be explained by the nano-domain structure of strain glass.

  2. Single-frequency dielectric relaxation used to characterize the glass transition time of polydextrose

    NASA Astrophysics Data System (ADS)

    Buehler, Martin G.; Campbell, Zachary J.; Carter, Brady P.

    2017-02-01

    Dielectric relaxation methods are applicable to powdery materials such as carbohydrates. These materials have relaxations that occur in the milli-Hz range while samples are held at fixed temperatures and fixed water activities, a w, (relativity humidity). Under proper conditions these materials undergo physical changes where the initially glassy powder transitions to an amorphous equilibrium state at the glass transition temperature, T g. Determining this transition involves characterizing the boundary curve (T g versus a w) which determines T g and a w conditions where materials are stable with long-shelf life or unstable with very a short shelf-life. This paper serves to illustrate multiple methodologies which can be used to characterize glass transition from frequency-spectra. Three methodologies are described: peak-broadening, peak-shift, and single-frequency. The new single frequency method not only provides results that identical to those of the peak-shift method but increases the data acquisition speeds by a factor of 5. This method is illustrated on polydextrose, a common sugar substitute. The information gathered can then be used to construct the boundary curve which is used to characterize the shelf-life of a material at various conditions.

  3. Glass Transition and Re-entrant Melting in a Polydisperse Hard-Sphere Fluid

    NASA Astrophysics Data System (ADS)

    Tokuyama, Michio; Terada, Yayoi

    2006-05-01

    Extensive molecular dynamics simulations are performed for a hard-sphere fluid at 6% polydispersity. The simulation results are then analyzed based on the mean-field theory proposed recently by Tokuyama (Physica A 364, 23-62 (2006)). The phase diagram and the dynamic behavior are investigated fully in each phase. It is then found that as the volume fraction φ is increased, a supercooled liquid phase appears at the supercooled point φβ (≃ 0.5524) and a transition from supercooled liquid to crystal then occurs at the melting volume fraction φm(1) (≃ 0.5625). As φ is further increased, a transition from crystal to supercooled liquid (re-entrant melting) is also observed at the second melting volume fraction φm(2) (≃ 0.5770) within a waiting time tw = 7 × 104t0, where t0 is a time for a particle to move over a distance of a particle radius with an average velocity. The glass transition is thus predicted to occur at the glass transition volume fraction φg (≃ 0.6005). The various aspects obtained in our study is quite similar to those in the experiment for the suspension of hard spheres, including the logarithmic growth of the mean-square displacement in fast-β stage, the non-singular behavior of the long-time self-diffusion coefficient, and the non divergence of any characteristic times, such as the α- and β-relaxation times.

  4. Quantum percolation phase transition and magnetoelectric dipole glass in hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Vojta, T.; Jones, A. T.; Guo, W.; Oliveira, J.; Morrison, F. D.; Lindfield, N.; Baggio Saitovitch, E.; Watts, B. E.; Scott, J. F.

    2017-07-01

    Hexagonal ferrites not only have enormous commercial impact (£2 billion/year in sales) due to applications that include ultrahigh-density memories, credit-card stripes, magnetic bar codes, small motors, and low-loss microwave devices, they also have fascinating magnetic and ferroelectric quantum properties at low temperatures. Here we report the results of tuning the magnetic ordering temperature in PbF e12 -xG axO19 to zero by chemical substitution x . The phase transition boundary is found to vary as TN˜(1-x /xc ) 2 /3 with xc very close to the calculated spin percolation threshold, which we determine by Monte Carlo simulations, indicating that the zero-temperature phase transition is geometrically driven. We find that this produces a form of compositionally tuned, insulating, ferrimagnetic quantum criticality. Close to the zero-temperature phase transition, we observe the emergence of an electric dipole glass induced by magnetoelectric coupling. The strong frequency behavior of the glass freezing temperature Tm has a Vogel-Fulcher dependence with Tm finite, or suppressed below zero in the zero-frequency limit, depending on composition x . These quantum-mechanical properties, along with the multiplicity of low-lying modes near the zero-temperature phase transition, are likely to greatly extend applications of hexaferrites into the realm of quantum and cryogenic technologies.

  5. Continuous Structural Transition in Glass-Forming Molten Titanate BaTi2O5

    DOE PAGES

    Alderman, O. L. G.; Benmore, C. J.; Tamalonis, A.; ...

    2016-11-01

    The structure of the model titanate glass former BaTi2O5 has been studied over a wide temperature (T) range in the molten, supercooled, and glassy states under conditions of aerodynamic levitation. Both high-energy X-ray diffraction and Ti K-edge X-ray absorption spectroscopy reveal a continuous structural transition involving reduction of the cation–oxygen (and oxygen–cation) average coordination numbers and bond lengths with increasing T. Ti–O coordination in the moderately supercooled and equilibrium melt follows a linear trend nTiO = 5.4(1) – [3.5(7) × 10–4]T [K] (1300 ≤ T ≤ 1830 K, Tg = 960 K, Tm = 1660 K). Comparison to the melt-quenchedmore » glass implies an increase in ∂nTiO/∂T at lower T, as Tg is approached from above. Both Ba–O coordination and bond length also decrease at higher T, and the role of Ba addition is to reduce nTiO below its value in pure molten TiO2, which is related to the presence of density maxima in molten BaO-TiO2. Density measurements made by imaging of the levitated melt yielded ρ(T) = 4.82(55) – 0.0004(3)T in units of K and g cm–3. While BaTi2O5 glass likely consists of a fully connected Ti–O network, free of nonbridging oxygen (NBO) [OTi1] and with at least 13(4)% [OTi3] triclusters, the 1835(40) K equilibrium melt contains at least 10(4)% NBO along with 90(4)% bridging oxygen [OTi2]. The results highlight the fact that glasses can be considered as structural analogues of melts only for those melts deeply supercooled into the glass transition region. The results imply possible fictive T dependence of titanate glass structure, suggesting applications as, e.g., laser written waveguides with large refractive indices and refractive index contrasts. Furthermore, the temperature-dependent structure further implies a super-Arrhenian melt viscosity with consequences for glass manufacture, titanate-rich slags produced in iron smelting, TiO2-bearing magmas, and by analogy silicate melts at high pressures, as

  6. Correlation between physical properties and ultrasonic relaxation parameters in transition metal tellurite glasses

    NASA Astrophysics Data System (ADS)

    Abd El-Moneim, A.

    2003-07-01

    The correlation between activation energy of ultrasonic relaxation process through the temperature range from 140 to 300 K and some physical properties has been investigated in pure TeO 2 and transition metal TeO 2-V 2O 5 and TeO 2-MoO 3 glasses according to Bridge and Patel's theory. The oxygen density (loss centers), number of two-well systems, hopping distance and mechanical relaxation time have been calculated in these glasses from the data of density, bulk modulus and stretching force constant of the glass. It has been found that the acoustic activation energy increased linearly with both the oxygen density and the number of two-well systems. The correlation between the acoustic activation energy and bulk modulus was achieved through the stretching force constant of the network and other structural parameters. Moreover, the experimental values of activation energy (V) agree well with those calculated from an empirical equation presented in this study in the form V=2.9×10 -7 F( F/ K) 3.37, where F is the stretching force constant of the glass and K is the experimental bulk modulus.

  7. Polymer glass transition occurs at the marginal rigidity point with connectivity z* = 4.

    PubMed

    Lappala, Anna; Zaccone, Alessio; Terentjev, Eugene M

    2016-09-21

    We re-examine the physical origin of the polymer glass transition from the point of view of marginal rigidity, which is achieved at a certain average number of mechanically active intermolecular contacts per monomer. In the case of polymer chains in a melt/poor solvent, each monomer has two neighbors bound by covalent bonds and also a number of central-force contacts modelled by the Lennard-Jones (LJ) potential. We find that when the average number of contacts per monomer (covalent and non-covalent) exceeds the critical value z* ≈ 4, the system becomes solid and the dynamics arrested - a state that we declare the glass. Coarse-grained Brownian dynamics simulations show that at sufficient strength of LJ attraction (which effectively represents the depth of quenching, or the quality of solvent) the polymer globule indeed crosses the threshold of z*, and becomes a glass with a finite zero-frequency shear modulus, G∝ (z-z*). We verify this by showing the distinction between the 'liquid' polymer droplet at z < z*, which changes shape and adopts the spherical conformation in equilibrium, and the glassy 'solid' droplet at z > z*, which retains its shape frozen at the moment of z* crossover. These results provide a robust microscopic criterion to tell the liquid apart from the glass for the linear polymers.

  8. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

    NASA Astrophysics Data System (ADS)

    Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep

    2016-06-01

    High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

  9. Rigidity transitions in glasses driven by changes in network dimensionality and structural groupings

    NASA Astrophysics Data System (ADS)

    Vignarooban, K.; Boolchand, P.; Micoulaut, M.; Malki, M.; Bresser, W. J.

    2014-12-01

    Calorimetric, Raman and electrical conductivity properties of alkali borates {(100-x)}\\text{B}_2\\text{O}_3\\text-x\\text{M}_2\\text{O} (\\text{M}=\\text{Li} , Na) are studied as a function of composition (x) and these show the presence of stiffness transitions and an intermediate phase which are driven by a combination of network dimensionality change and usual topological constraint changes. This picture is confirmed by a detailed Raman analysis showing that specific modes of molecular structural groupings dominate the network structure in the intermediate phase. Their evolution shows a one-to-one correspondance with the observed non-reversing heat flow at the glass transition, and are correlated with thresholds in ionic conductivity that allows identifying a flexible phase at high alkali content, whereas the mildly stressed-rigid \\text{B}_2\\text{O}3 -rich glasses are driven by the conversion of planar 2D boroxol ring structures into the 3D structural groupings. These findings deeply modify the usual picture of these archetypal glasses, and reveal the very first example of the onset of rigidity tuned by network dimensional conversion.

  10. Polyamorphic phase transition of Yb-based metallic glass at high pressure

    NASA Astrophysics Data System (ADS)

    li, L.; Li, R.; Liu, H.; Chupas, P.

    2013-12-01

    A family of Yb-based bulk metallic glasses (BMG) has been fabricated based on strong liquid characteristic and excellent glass-forming ability. Using a diamond anvil cell with high-energy synchrotron X-ray, the total scattering of metallic glass Yb-Mg-Zn was studied at pressure up to 30GPa in a hydrostatic isopropanol pressure-medium. The local structure was investigated through direct Fourier transformation of the structure factor [S(Q)], pair distribution function (PDF) [G(r)] with background correction. Polyamorphic phase transition is achieved because smaller atoms are extruded into the clearance of the larger rare earth atoms and 4f electrons delocalized. Phase transition from a low-density state to a high-density state occurs, smaller atoms can be extruded is one of two reasons for the high compressibility of rare earth BMG. The second reason is the delocalization of 4f electrons, which can induce the volume collapse of rare earth atoms.

  11. Theory of activated dynamics and glass transition of hard colloids in two dimensions.

    PubMed

    Zhang, Bo-kai; Li, Hui-shu; Tian, Wen-de; Chen, Kang; Ma, Yu-qiang

    2014-03-07

    The microscopic nonlinear Langevin equation theory is applied to study the localization and activated hopping of two-dimensional hard disks in the deeply supercooled and glass states. Quantitative comparisons of dynamic characteristic length scales, barrier, and their dependence on the reduced packing fraction are presented between hard-disk and hard-sphere suspensions. The dynamic barrier of hard disks emerges at higher absolute and reduced packing fractions and correspondingly, the crossover size of the dynamic cage which correlates to the Lindemann length for melting is smaller. The localization lengths of both hard disks and spheres decrease exponentially with packing fraction. Larger localization length of hard disks than that of hard spheres is found at the same reduced packing fraction. The relaxation time of hard disks rises dramatically above the reduced packing fraction of 0.88, which leads to lower reduced packing fraction at the kinetic glass transition than that of hard spheres. The present work provides a foundation for the subsequent study of the glass transition of binary or polydisperse mixtures of hard disks, normally adopted in experiments and simulations to avoid crystallization, and further, the rheology and mechanical response of the two-dimensional glassy colloidal systems.

  12. Glass phase and other multiple liquid-to-liquid transitions resulting from two-liquid phase competition

    NASA Astrophysics Data System (ADS)

    Tournier, Robert F.

    2016-11-01

    Melt supercooling leads to glass formation. Liquid-to-liquid phase transitions are observed depending on thermal paths. Viscosity, density and surface tension thermal dependences measured at heating and subsequent cooling show hysteresis below a branching temperature and result from the competition of two-liquid phases separated by an enthalpy difference depending on temperature. The nucleation classical equation of these phases is completed by this enthalpy saving existing at all temperatures. The glass phase thermodynamic parameters and their thermal variation have already been determined in such a two-liquid model. They are used at high temperatures to predict liquid-to-liquid transitions in some metallic glass-forming melts.

  13. Ising spin-glass transition in a magnetic field outside the limit of validity of mean-field theory.

    PubMed

    Leuzzi, L; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, J J

    2009-12-31

    The spin-glass transition in a magnetic field is studied both in and out of the limit of validity of mean-field theory on a diluted one dimensional chain of Ising spins where exchange bonds occur with a probability decaying as the inverse power of the distance. Varying the power in this long-range model corresponds, in a one-to-one relationship, to changing the dimension in spin-glass short-range models. Evidence for a spin-glass transition in a magnetic field is found also for systems whose equivalent dimension is below the upper critical dimension in a zero magnetic field.

  14. Response of water to electric fields at temperatures below the glass transition: A molecular dynamics analysis

    SciTech Connect

    Hu, Xiaohu; Elghobashi-Meinhardt, Nadia; Gembris, Daniel; Smith, Jeremy C

    2011-01-01

    The electric field dependence of the structure and dynamics of water at 77 K, i.e., below the glass transition temperature (136 K), is investigated using molecular dynamics simulations. Transitions are found at two critical field strengths, denoted E1 and E2. The transition around E1 3.5 V/nm is characterized by the onset of significant structural disorder, a rapid increase in the orientational polarization, and a maximum in the dynamical fluctuations. At E2 40 V/nm, the system crystallizes in discrete steps into a body-centered-cubic unit cell that minimizes the potential energy by simultaneous superpolarization of the water molecular dipoles and maximization of the intermolecular hydrogen bonds. The stepwise and discontinuous increase of the orientational polarization with the increasing electric field indicates that the dipole relaxation in the electric field is highly cooperative.

  15. Phase Transition for Quenched Coupled Replicas in a Plaquette Spin Model of Glasses

    NASA Astrophysics Data System (ADS)

    Jack, Robert L.; Garrahan, Juan P.

    2016-02-01

    We study a three-dimensional plaquette spin model whose low temperature dynamics is glassy, due to localized defects and effective kinetic constraints. The thermodynamics of this system is smooth at all temperatures. We show that coupling it to a second system with a fixed (quenched) configuration leads to a phase transition, at finite coupling. The order parameter is the overlap between the copies, and the transition is between phases of low and high overlap. We find critical points whose properties are consistent with random-field Ising universality. We analyze the interfacial free energy cost between the high- and low-overlap states that coexist at (and below) the critical point, and we use this cost as the basis for a finite-size scaling analysis. We discuss these results in the context of mean-field and dynamical facilitation theories of the glass transition.

  16. Confinement effects on glass transition temperature, transition breadth, and expansivity: Comparison of ellipsometry and fluorescence measurements on polystyrene films

    NASA Astrophysics Data System (ADS)

    Kim, S.; Hewlett, S. A.; Roth, C. B.; Torkelson, J. M.

    2009-09-01

    Using ellipsometry, we characterized the nanoconfinement effect on the glass transition temperature (T gof supported polystyrene (PS) films employing two methods: the intersection of fits to the temperature (Tdependences of rubbery- and glassy-state thicknesses, and the transition mid-point between rubbery- and glassy-state expansivities. The results demonstrate a strong effect of thickness: ensuremath Tg(bulk)-Tg(23{ nm})= 10 circ C. The T -range needed for accurate measurement increases significantly with decreasing thickness, an effect that arises from the broadening of the transition with confinement and a region below T g where expansivity slowly decreases with decreasing T . As determined from expansivities, the T g breadth triples in going from bulk films to a 21-nm-thick film; this broadening of the transition may be a more dramatic effect of confinement than the T g reduction itself. In contrast, there is little effect of confinement on the rubbery- and glassy-state expansivities. Compared with ellipsometry, T g ’s from fluorescence agree well in bulk films but yield lower values in nanoconfined films: T g(bulk) - T g(23 nm) = 15° C via fluorescence. This small difference in the T g confinement effect reflects differences in how fluorescence and ellipsometry report “average T g ” with confinement. With decreasing nanoscale thickness, fluorescence may slightly overweight the contribution of the free-surface layer while ellipsometry may evenly weight or underweight its contribution. in here

  17. Upper-nose temper phenomena and transition behavior of fracture toughness of 2. 25Cr-1Mo pressure vessel steel

    SciTech Connect

    Holzmann, M.; Man, J.; Vlach, B. . Academy of Sciences)

    1993-12-15

    A non-reversible upper-nose temper embrittlement (UNTE) which is characterized by transcrystalline cleavage could occur in low alloy steels when tempered or post-weld heat treated at temperatures ranging between 600 C to A[sub c1] for longer-time period. The deterioration of mechanical properties, in particular toughness, associated with this process, is a very relevant problem for fabricators of large components in petrochemical and power industry. One must be very careful when evaluating the embrittlement of the structure itself, using results of the Charpy test. The authors of the present work have reported in a recent paper that the cleavage fracture stress [sigma][sub CF], due to structural changes during temper treatment, has fallen steadily from the very beginning of tempering and a model has been suggested, explaining the transition behavior in the Charpy test. Even though the Charpy tests provide valuable information regarding impact toughness properties, the fracture toughness is a more exact material characteristic defining the fracture resistance properties. Therefore, the fracture toughness temperature curves, measured for a variety of tempered conditions, aim to reveal to what extent UNTE phenomena can influence the level and transition behavior of this material characteristic. Some representative results are given in the present paper.

  18. Two glass transitions of polyurea networks: effect of the segmental molecular weight.

    PubMed

    Reinecker, Marius; Soprunyuk, Viktor; Fally, Martin; Sánchez-Ferrer, Antoni; Schranz, Wilfried

    2014-08-21

    Polymer-nanoparticle composites (PNCs) play an increasing role in technology. Inorganic or organic nanoparticles are usually incorporated into a polymer matrix to improve material properties. Polyurea is a spontaneously occurring PNC, exhibiting a phase segregated structure with hard nanodomains embedded in a soft (elastically compliant) matrix. This system shows two glass transitions at Tg1 and Tg2. It has been argued that they are related to the freezing of motion of molecular segments in the soft matrix (usual polymer α-glass transition at Tg1) and to regions of restricted mobility near the hard nanodomains (α'-process) at Tg2, respectively. We present detailed dynamic mechanical analysis (DMA) measurements for polyurea networks with different segmental lengths l(c) (2.5, 12.1, 24.5 nm) of the polymer chains, i.e. different volume fractions ϕ(x) (0.39, 0.12, 0.07) of the hard domains. The two glass transitions show up in two distinct peaks in tan δ at Tα and Tα'. Analysing the data using a Havriliak-Negami term for the α- and α'-relaxation, as well as Vogel-Fulcher dependencies for the corresponding relaxation times, it is found that the α-glass transition at Tg1 increases strongly (up to ΔT = 70 K) with increasing ϕ(x), whereas the α'-transition at Tg2 remains unchanged. At ϕ(x)(c) ≈ 0.19 the two curves intersect, i.e. Tg1 = Tg2. This value of ϕ(x)(c) is very close to the percolation threshold of randomly oriented overlapping ellipsoids of revolution with an aspect ratio of about 1 : 4-1 : 5. We therefore conclude that around 19% of the hard nanodomains polyurea changes from a system of hard nanoparticles embedded in a soft matrix (ϕ(x) ≤ ϕ(x)(c)) to a system of soft domains confined in a network of percolated hard domains at ϕ(x) ≥ ϕ(x)(c).

  19. Crystallization at the glass transition in supercooled thin films of methanol

    NASA Astrophysics Data System (ADS)

    Dounce, Susan M.; Mundy, Julia; Dai, Hai-Lung

    2007-05-01

    The stability of an amorphous material depends on how fast and by what mechanism crystallization occurs. Based on crystallization rate measurements through optical reflectivity changes in supercooled methanol thin films, it is observed for the first time that there is a definitive and detectable change of the crystallization mechanism at the glass transition temperature Tg. For methanol glasses below Tg=103.4K, crystallization occurs as an interface controlled, one-dimension process at frozen-in embryo sites, while in the deep supercooled liquid phase above Tg crystallization is diffusion controlled in two dimensions with a constant nucleation rate and an activation energy of 107.8(±4.7)kJ/mol.

  20. Glass Transitions in Monodisperse Cluster-Forming Ensembles: Vortex Matter in Type-1.5 Superconductors

    NASA Astrophysics Data System (ADS)

    Díaz-Méndez, Rogelio; Mezzacapo, Fabio; Lechner, Wolfgang; Cinti, Fabio; Babaev, Egor; Pupillo, Guido

    2017-02-01

    At low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster crystal. In the present Letter, we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multiscale intervortex forces. We find that, for small temperatures following a quench, the suppression of the thermally activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in terms of an "effective polydispersity" induced by multiscale interactions. This demonstrates that a vortex glass can form in clean systems of thin films of "type-1.5" superconductors. An additional setup to study this physics can be layered superconducting systems, where the shape of the effective vortex-vortex interactions can be engineered.

  1. Relaxation map of a 100% green thermoplastic film. Glass transition and fragility

    NASA Astrophysics Data System (ADS)

    Saiter, J. M.; Dobircau, L.; Saiah, R.; Sreekumar, P. A.; Galandon, A.; Gattin, R.; Leblanc, N.; Adhikari, R.

    2010-02-01

    A 100% green thermoplastic obtained by extrusion of a mixture of wheat flour and plasticizers has been realized. The existence of two vitreous phases in this 100% green thermoplastic film has been pointed out by means of calorimetric measurements ( T g=-56 °C and T g=10 °C) and confirmed by electron microscopy. The molecular dynamics have been investigated by means of DMA measurements for temperature domains in the vicinity of the glass transition of each phase. We show that each phase exhibits a molecular dynamic characteristic of a fragile glass liquid former. The size of the cooperative domain engaged in the relaxation processes have also been estimated and we show that this new green thermoplastic exhibits relaxation mechanisms as expected for a conventional thermoplastic, as for instance a PMMA.

  2. Disorder-assisted melting and the glass transition in amorphous solids

    NASA Astrophysics Data System (ADS)

    Zaccone, Alessio; Terentjev, Eugene

    2013-03-01

    The mechanical response of solids depends on temperature because the way atoms and molecules respond collectively to deformation is affected at various levels by thermal motion. This is a fundamental problem of solid state science and plays a crucial role in metallurgy, aerospace engineering, energy. In disordered solids (glass, amorphous semiconductors, ceramics, metallic glass, polymers) the vanishing of rigidity as a function of temperature is not well understood because continuum elasticity is inapplicable due to the disorder leading to nontrivial (nonaffine) components in the atomic displacements. Our theory explains the basic mechanism of the melting transition of amorphous solids in terms of the lattice energy lost to nonaffine motion, compared to which thermal vibrations turn out to play a negligible role. The theory is in good agreement with data on melting of amorphous polymers (where no alternative theory can be found in the literature) and offers new opportunities in materials science.

  3. Glass Transitions in Monodisperse Cluster-Forming Ensembles: Vortex Matter in Type-1.5 Superconductors.

    PubMed

    Díaz-Méndez, Rogelio; Mezzacapo, Fabio; Lechner, Wolfgang; Cinti, Fabio; Babaev, Egor; Pupillo, Guido

    2017-02-10

    At low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster crystal. In the present Letter, we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multiscale intervortex forces. We find that, for small temperatures following a quench, the suppression of the thermally activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in terms of an "effective polydispersity" induced by multiscale interactions. This demonstrates that a vortex glass can form in clean systems of thin films of "type-1.5" superconductors. An additional setup to study this physics can be layered superconducting systems, where the shape of the effective vortex-vortex interactions can be engineered.

  4. On the glass transition of the one-component metallic melts

    NASA Astrophysics Data System (ADS)

    Fedorchenko, A. I.

    2017-10-01

    In this paper, the conditions for one-component metallic melts vitrification by quenching from a liquid state were formulated. It is shown that the tendency to the glass formation drastically increases with the temperature of melting. The maximum glass layer thickness and the associated cooling rates along with the vitrification temperatures was determined for Al, Cu, and Ni melts deposited on the Cu substrate. The results are in agreement with the available experimental data. Based on analytical solution of the impinging droplet solidification, the numerical value of the early-introduced asymptotic Ω criterion, which separates equilibrium and non-equilibrium phase transitions, was determined. Good agreement between the calculated and experimental values of the thickness of the splats shows that Ω criterion indeed predicts a priori a scenario of solidification.

  5. Spin-glass transition in bond-disordered Heisenberg antiferromagnets coupled with local lattice distortions on a pyrochlore lattice.

    PubMed

    Shinaoka, Hiroshi; Tomita, Yusuke; Motome, Yukitoshi

    2011-07-22

    Motivated by puzzling characteristics of spin-glass transitions widely observed in pyrochlore-based frustrated materials, we investigate the effects of coupling to local lattice distortions in a bond-disordered antiferromagnet on the pyrochlore lattice by extensive Monte Carlo simulations. We show that the spin-glass transition temperature T(f) is largely enhanced by the spin-lattice coupling and, furthermore, becomes almost independent of Δ in a wide range of the disorder strength Δ. The critical property of the spin-glass transition is indistinguishable from that of the canonical Heisenberg spin glass in the entire range of Δ. These peculiar behaviors are ascribed to a modification of the degenerate manifold from a continuous to semidiscrete one by spin-lattice coupling.

  6. Thermoelastic Model for Impulsive Stimulated Scattering Monitoring the Evolution from Capillary to Rayleigh Type Wave Propagation on the Surface of Viscoelastic Materials Throughout the Glass Transition

    NASA Astrophysics Data System (ADS)

    Sermeus, J.; Matsuda, O.; Salenbien, R.; Verstraeten, B.; Fivez, J.; Glorieux, C.

    2012-11-01

    In recent decades, the impulsive stimulated scattering (ISS) method, which is based on photothermal and photoacoustic phenomena, has been successfully used to simultaneously investigate the thermal and elastic properties in a four-wave mixing configuration, both in transmission in semitransparent materials and on reflecting surfaces of solids. In this report, an extension of the technique is proposed to study a laser-induced thermoelastic response at the free surface of glass-forming liquids. The employed all-optical configuration allows extraction of information about the acoustic shear modulus in the MHz frequency range, and hence is complementary to the classical ISS configuration in the transmission mode, which is suitable to study the relaxation of the longitudinal acoustic modulus, and to another earlier reported ISS configuration, which is exciting and probing laser-induced thermoelastic phenomena at a liquid-solid interface. A theoretical model is presented and numerically illustrated for the glass transition of glycerol, and experimentally validated for water at room temperature.

  7. 93 Nb NMR investigation of vortex- glass transition in layered NbSe2

    NASA Astrophysics Data System (ADS)

    Wilson, Douglas; Saraswat, Garima; Shirage, Parasharam; Kuhns, Philip; Hoch, Michael J. R.; Reyes, Arneil

    We report a detailed low temperature investigation of vortex glass transition in layered superconducting compound NbSe2 using 93Nb NMR at fields below Hc2. Preliminary measurements show that spin-lattice relaxation rate 1/T1 demonstrates a classic Korringa behavior 1/T1~ T above the superconducting transition Tc , consistent with previous measurements on this compound. However, for field H perpendicular to the layers, we observed that 1/T1 exhibits an anomalous plateau between Tc (H = 0) and Tc (H) and a suppression of the superconducting enhancement expected below Tc. Instead, a power law behavior, 1/T1 ~T 1 . 2 below Tc down to 360mK was observed which suggests a strong anisotropy in the low energy excitations. However, the possibility of enhancement in 1/T1 due to vortex fluctuations which competes with electronic mechanisms cannot be excluded. The implications of these results with regards to vortex-glass transition will be discussed. This work was performed at the National High Magnetic Field Laboratory, which is supported by NSF DMR-1157490 and the State of Florida.

  8. Gelation and glass transition of particles with short-range attraction induced by adsorbing microgel

    NASA Astrophysics Data System (ADS)

    Yuan, Guangcui; Luo, Junhua; Han, Charles C.

    2015-03-01

    Mixed suspensions of large hard polystyrene microsphere and small poly(N-isopropylacrylamide) microgel is used as model systems to investigate the static and viscoelastic properties of suspensions which go through liquid to gel and to glass transitions. The microgels cause short-range attraction between microspheres through bridging and depletion mechanism whose strength can be tuned by the microgel concentration. Baxter's sticky hard-sphere model is used to extract the effective inter-microsphere interaction introduced by bridging or depletion of microgels despite the fact that the physical mechanisms of bridging attraction and depletion attraction are different at a molecular level. A new state diagram of gelation and even of glass transition was constructed by taking the bridges as a short-ranged attractive interaction With the help of the well-defined bridging bonds, some controversies regarding to the interference between two origins for ergodic to\\ non-ergodic transition in condensed system, i.e. cage effect and bond effect, were clarified. This work is supported by the National Basic Research Program of China (973 Program, 2012CB821503).

  9. Effects of temperature and pressure on the glass transitions of plastic bonded explosives

    SciTech Connect

    Campbell, M.S.; Garcia, D.; Idar, D.

    1998-12-31

    Various plastic bonded explosives (PBXs) contain about 5-wt% polymer, plasticizer, and stabilizer as binder. The glass-transition temperature (T{sub g}) determines, in part, if the binder will reduce or increase the sensitivity of the PBX to impact. A soft binder reduces the impact sensitivity; however, too soft a binder compromises the mechanical strength below that desirable for dimensional stability. Glass transitions were measured by temperature modulated DSC for PBXs before and after pressing. Pressing temperature was 90 C. The T{sub g} of Estane, a polyester/polyurethane used in some PBX binders, was investigated. Only small changes were observed in the low temperature T{sub g} of the soft segments but larger changes were seen in the higher temperature transitions due to the relaxation of the hard segments. The T{sub g} of Kel F 800, a binder used in insensitive PBX 9502, was observed near ambient temperature. The PBX 9502 had a lower T{sub g} than the neat polymer. Mechanical strength will be measured for the samples.

  10. Lattice model of glasses

    NASA Astrophysics Data System (ADS)

    Cellai, Davide; Fima, Andrzej Z.; Lawlor, Aonghus; Dawson, Kenneth A.

    2011-03-01

    Glass-forming liquids have been extensively studied in recent decades, but there is still no theory that fully describes these systems, and the diversity of treatments is in itself a barrier to understanding. Here we introduce a new simple model that (possessing both liquid-crystal and glass transition) unifies different approaches, producing most of the phenomena associated with real glasses, without loss of the simplicity that theorists require. Within the model we calculate energy relaxation, nonexponential slowing phenomena, the Kauzmann temperature, and other classical signatures. Moreover, the model reproduces a subdiffusive exponent observed in experiments of dense systems. The simplicity of the model allows us to identify the microscopic origin of glassification, leaving open the possibility for theorists to make further progress.

  11. Lattice model of glasses.

    PubMed

    Cellai, Davide; Fima, Andrzej Z; Lawlor, Aonghus; Dawson, Kenneth A

    2011-03-21

    Glass-forming liquids have been extensively studied in recent decades, but there is still no theory that fully describes these systems, and the diversity of treatments is in itself a barrier to understanding. Here we introduce a new simple model that (possessing both liquid-crystal and glass transition) unifies different approaches, producing most of the phenomena associated with real glasses, without loss of the simplicity that theorists require. Within the model we calculate energy relaxation, nonexponential slowing phenomena, the Kauzmann temperature, and other classical signatures. Moreover, the model reproduces a subdiffusive exponent observed in experiments of dense systems. The simplicity of the model allows us to identify the microscopic origin of glassification, leaving open the possibility for theorists to make further progress.

  12. Continuous Structural Transition in Glass-Forming Molten Titanate BaTi 2 O 5

    DOE PAGES

    Alderman, O. L. G.; Benmore, C. J.; Tamalonis, A.; ...

    2016-12-01

    The structure of the model titanate glass former BaTi2O5 has been studied over a wide temperature (T) range in the molten, supercooled, and glassy states under conditions of aerodynamic levitation. Both high-energy X-ray diffraction and Ti K-edge X-ray absorption spectroscopy reveal a continuous structural transition involving reduction of the cation-oxygen (and oxygen-cation) average coordination numbers and bond lengths with increasing T. Ti-0 coordination in the moderately supercooled and equilibrium melt follows a linear trend n(Tio) = 5.4(1)- [3.5(7) x 10(-4)]T [K] (1300 <= T <= 1830 K, T-g = 960 K, T-m = 1660 K). Comparison to the melt-quenched glassmore » implies an increase in partial derivative n(Tio)/partial derivative T at lower T, as T-g is approached from above. Both Ba-0 coordination and bond length also decrease at higher T, and the role of Ba addition is to reduce n(Tio) below its value in pure molten TiO2, which is related to the presence of density maxima in molten BaO-TiO2. Density measurements made by imaging of the levitated melt yielded rho(T) = 4.82(55)- 0.0004(3)T in units of K and g cm(-3). While BaTi2O5 glass likely consists of a fully connected Ti-0 network, free of nonbridging oxygen (NBO) [OTi1 and with at least 13(4)% [OTi3] triclusters, the 1835(40) K equilibrium melt contains at least 10(4)% NBO along with 90(4)% bridging oxygen [OTi2]. The results highlight the fact that glasses can be considered as structural analogues of melts only for those melts deeply supercooled into the glass transition region. The results imply possible fictive T dependence of titanate glass structure, suggesting applications as, e.g., laser written waveguides with large refractive indices and refractive index contrasts. The temperature-dependent structure further implies a super-Arrhenian melt viscosity with consequences for glass manufacture, titanate-rich slags produced in iron smelting, TiO2-bearing magmas, and by analogy silicate melts at high

  13. Flory Model of Polymer Crystallization, Kauzmann Paradox and Gibbs-DiMarzio Theory of Glass Transition

    NASA Astrophysics Data System (ADS)

    Corsi, A.; Gujrati, P. D.

    2000-03-01

    The Flory model of crystallization of polymers is well known and forms the cornerstone of the Gibbs-DiMarzio theory of glass transition. The model has no known exact solution and the original calculation [1] was shown to be incorrect [2]. Still it is interesting to know the order of the phase transition, if it has one. We have studied the thermodynamics of the model in the limit of infinite molecular weight. We have solved it exactly on a recursive lattice with coordination number q=4, relevant for a tetrahedral lattice. Our results show that there is a continuous, i.e. a second-order, transition at which the entropy of the system is continuous. It is finite at all temperatures and approaches 0 as T goes to 0 so that the system is never completely ordered except at T=0. As the temperature is raised above T=0 the system begins to disorder with a degree of disorder that depends on T, which is in accordance with the analysis of Gujrati and Goldstein [2]. Since there is no first order transition there is no Kauzmann paradox. Similarly there is no possible metastable extension in the model which is central to the Gibbs-DiMarzio conjecture for an ideal glass transition. Thus, our solution does not justify their conjecture. [1] P.J. Flory, Proc. R. Soc. London Ser., A234, 60 (1956) [2] P.D. Gujrati, J. Phys. A: Math. Gen., 13, L437 (1980), P.D. Gujrati, M. Goldstein, J. Chem. Phys., 74(4), 2596 (1981)

  14. Differential scanning calorimetry study of glass transition in frozen starch gels.

    PubMed

    Tananuwong, Kanitha; Reid, David S

    2004-06-30

    The effects of initial water content, maximum heating temperature, amylopectin crystallinity type, and annealing on the glass transition of starch gels were studied by differential scanning calorimetry (DSC). The glass transition temperatures of the frozen gels measured as the onset (T(g,onset)) or midpoint temperature (T(g,midpoint)), heat capacity change during the glass transition (deltaC(p)), unfrozen water of starch gels, and additional unfrozen water (AUW) arising from gelatinization were reported. The results show that T(g,onset) and T(g,midpoint) of the partially gelatinized gels are independent of the initial water content, while both of the T(g) values of the fully gelatinized gel increase as the initial water content increases. These observations might result from the difference in the level of structural disruption associated with different heating conditions, resulting in different gel structures as well as different concentrations of the sub-T(g) unfrozen matrix. The amylopectin crystallinity type does not greatly affect T(g,onset) and T(g,midpoint) of the gels. Annealing at a temperature near T(g,onset) increases both T(g,onset) and T(g,midpoint) of the gels, possibly due to an increase in the extent of the freeze concentration as evidenced by a decrease in AUW. Annealing results in an increase in the deltaC(p) value of the gels, presumably due to structural relaxation. A devitrification exotherm may be related to AUW. The annealing process decreases AUW, thus also decreasing the size of the exotherm.

  15. The Nonequilibrium Phase and Glass Transition Behavior of β-Lactoglobulin

    PubMed Central

    Parker, Roger; Noel, Timothy R.; Brownsey, Geoffrey J.; Laos, Katrin; Ring, Stephen G.

    2005-01-01

    Concentrated solutions of bovine β-lactoglobulin were studied using osmotic stress and rheological techniques. At pH 6.0 and 8.0, the osmotic pressure was largely independent of NaCl concentration and could be described by a hard sphere equation of state. At pH 5.1, close to the isoelectric point, the osmotic pressure was lower at the lower NaCl concentrations (0 mM, 100 mM) and was fitted by an adhesive hard sphere model. Liquid-liquid phase separation was observed at pH 5.1 at ionic strengths of 13 mM and below. Comparison of the liquid-liquid and literature solid-liquid coexistence curves showed these solutions to be supersaturated and the phase separation to be nonequilibrium in nature. In steady shear, the zero shear viscosity of concentrated solutions at pH 5.1 was observed at shear rates above 50 s−1. With increasing concentration, the solution viscosity showed a progressive increase, a behavior interpreted as the approach to a colloidlike glass transition at ∼60% w/w. In oscillatory shear experiments, the storage modulus crossed the loss modulus at concentrations of 54% w/w, an indication of the approaching glass transition. Comparison of the viscous behavior with predictions from the Krieger-Dougherty equation indicates the hydrodynamic size of the protein decreases with increasing concentration, resulting in a slower approach to the glass transition than a hard sphere system. PMID:15923230

  16. Glass transition of polymers in bulk, confined geometries, and near interfaces

    NASA Astrophysics Data System (ADS)

    Napolitano, Simone; Glynos, Emmanouil; Tito, Nicholas B.

    2017-03-01

    When cooled or pressurized, polymer melts exhibit a tremendous reduction in molecular mobility. If the process is performed at a constant rate, the structural relaxation time of the liquid eventually exceeds the time allowed for equilibration. This brings the system out of equilibrium, and the liquid is operationally defined as a glass—a solid lacking long-range order. Despite almost 100 years of research on the (liquid/)glass transition, it is not yet clear which molecular mechanisms are responsible for the unique slow-down in molecular dynamics. In this review, we first introduce the reader to experimental methodologies, theories, and simulations of glassy polymer dynamics and vitrification. We then analyse the impact of connectivity, structure, and chain environment on molecular motion at the length scale of a few monomers, as well as how macromolecular architecture affects the glass transition of non-linear polymers. We then discuss a revised picture of nanoconfinement, going beyond a simple picture based on interfacial interactions and surface/volume ratio. Analysis of a large body of experimental evidence, results from molecular simulations, and predictions from theory supports, instead, a more complex framework where other parameters are relevant. We focus discussion specifically on local order, free volume, irreversible chain adsorption, the Debye–Waller factor of confined and confining media, chain rigidity, and the absolute value of the vitrification temperature. We end by highlighting the molecular origin of distributions in relaxation times and glass transition temperatures which exceed, by far, the size of a chain. Fast relaxation modes, almost universally present at the free surface between polymer and air, are also remarked upon. These modes relax at rates far larger than those characteristic of glassy dynamics in bulk. We speculate on how these may be a signature of unique relaxation processes occurring in confined or heterogeneous polymeric

  17. Protein thermal denaturation and matrix glass transition in different protein-trehalose-water systems.

    PubMed

    Bellavia, Giuseppe; Giuffrida, Sergio; Cottone, Grazia; Cupane, Antonio; Cordone, Lorenzo

    2011-05-19

    Biopreservation by saccharides is a widely studied issue due to its scientific and technological importance; in particular, ternary amorphous protein-saccharide-water systems are extensively exploited to model the characteristics of the in vivo biopreservation process. We present here a differential scanning calorimetry (DSC) study on amorphous trehalose-water systems with embedded different proteins (myoglobin, lysozyme, BSA, hemoglobin), which differ for charge, surface, and volume properties. In our study, the protein/trehalose molar ratio is kept constant at 1/40, while the water/sugar molar ratio is varied between 2 and 300; results are compared with those obtained for binary trehalose-water systems. DSC upscans offer the possibility of investigating, in the same measurement, the thermodynamic properties of the matrix (glass transition, T(g)) and the functional properties of the encapsulated protein (thermal denaturation, T(den)). At high-to-intermediate hydration, the presence of the proteins increases the glass transition temperature of the encapsulating matrix. The effect mainly depends on size properties, and it can be ascribed to confinement exerted by the protein on the trehalose-water solvent. Conversely, at low hydration, lower T(g) values are measured in the presence of proteins: the lack of water promotes sugar-protein interactions, thus weakening the confinement effect and softening the matrix with respect to the binary system. A parallel T(den) increase is also observed; remarkably, this stabilization can reach ∼70 K at low hydration, a finding potentially of high biotechnological relevance. A linear relationship between T(g) and T(den) is also observed, in line with previous results; this finding suggests that collective water-trehalose interactions, responsible for the glass transition, also influence the protein denaturation. © 2011 American Chemical Society

  18. Predict the glass transition temperature of glycerol-water binary cryoprotectant by molecular dynamic simulation.

    PubMed

    Li, Dai-Xi; Liu, Bao-Lin; Liu, Yi-shu; Chen, Cheng-lung

    2008-04-01

    Vitrification is proposed to be the best way for the cryopreservation of organs. The glass transition temperature (T(g)) of vitrification solutions is a critical parameter of fundamental importance for cryopreservation by vitrification. The instruments that can detect the thermodynamic, mechanical and dielectric changes of a substance may be used to determine the glass transition temperature. T(g) is usually measured by using differential scanning calorimetry (DSC). In this study, the T(g) of the glycerol-aqueous solution (60%, wt/%) was determined by isothermal-isobaric molecular dynamic simulation (NPT-MD). The software package Discover in Material Studio with the Polymer Consortium Force Field (PCFF) was used for the simulation. The state parameters of heat capacity at constant pressure (C(p)), density (rho), amorphous cell volume (V(cell)) and specific volume (V(specific)) and radial distribution function (rdf) were obtained by NPT-MD in the temperature range of 90-270K. These parameters showed a discontinuity at a specific temperature in the plot of state parameter versus temperature. The temperature at the discontinuity is taken as the simulated T(g) value for glycerol-water binary solution. The T(g) values determined by simulation method were compared with the values in the literatures. The simulation values of T(g) (160.06-167.51K) agree well with the DSC results (163.60-167.10K) and the DMA results (159.00K). We drew the conclusion that molecular dynamic simulation (MDS) is a potential method for investigating the glass transition temperature (T(g)) of glycerol-water binary cryoprotectants and may be used for other vitrification solutions.

  19. Interfacial and topological effects on the glass transition in free-standing polystyrene films

    NASA Astrophysics Data System (ADS)

    Lyulin, Alexey V.; Balabaev, Nikolay K.; Baljon, Arlette R. C.; Mendoza, Gerardo; Frank, Curtis W.; Yoon, Do Y.

    2017-05-01

    United-atom molecular-dynamics computer simulations of atactic polystyrene (PS) were performed for the bulk and free-standing films of 2 nm-20 nm thickness, for both linear and cyclic polymers comprised of 80 monomers. Simulated volumetric glass-transition temperatures (Tg) show a strong dependence on the film thickness below 10 nm. The glass-transition temperature of linear PS is 13% lower than that of the bulk for 2.5 nm-thick films, as compared to less than 1% lower for 20 nm films. Our studies reveal that the fraction of the chain-end groups is larger in the interfacial layer with its outermost region approximately 1 nm below the surface than it is in the bulk. The enhanced population of the end groups is expected to result in a more mobile interfacial layer and the consequent dependence of Tg on the film thickness. In addition, the simulations show an enrichment of backbone aliphatic carbons and concomitant deficit of phenyl aromatic carbons in the interfacial film layer. This deficit would weaken the strong phenyl-phenyl aromatic (π -π ) interactions and, hence, lead to a lower film-averaged Tg in thin films, as compared to the bulk sample. To investigate the relative importance of the two possible mechanisms (increased chain ends at the surface or weakened π -π interactions in the interfacial region), the data for linear PS are compared with those for cyclic PS. For the cyclic PS, the reduction of the glass-transition temperature is also significant in thin films, albeit not as much as for linear PS. Moreover, the deficit of phenyl carbons in the film interface is comparable to that observed for linear PS. Therefore, chain-end effects alone cannot explain the observed pronounced Tg dependence on the thickness of thin PS films; the weakened phenyl-phenyl interactions in the interfacial region seems to be an important cause as well.

  20. Surfactant Induced Interfacial Anchoring Transitions in Nematic Liquid Crystal Droplets on Glass Surfaces

    NASA Astrophysics Data System (ADS)

    Kulkarni, Siddharth; Thareja, Prachi

    The interfacial adsorption of surfactants at planar nematic liquid crystal (NLC)-water interface induces an ordering transition from a tilted to perpendicular anchoring with the increase in surfactant concentration at CN=C/Ccmc≪1, where Ccmc is the Critical Micelle Concentration of surfactants in water. In this study, we show that depending upon the surfactant structure a tilted to perpendicular NLC anchoring transition is observed at C/Ccmc≥1 in 5CB droplets of size 50-70μm. Micrometer sized 5CB droplets are deposited on glass surfaces using flow coating of 5CB-in-ethanol solutions. When placed on 5CB drop decorated glass surfaces, the aqueous surfactant solutions of aliphatic chain surfactants (SDS, CTAB and CPBr) at CN<1, result in an optical transition to a bright-cross texture attributed to the tilted anchoring of 5CB molecules at 5CB-water interface. At C/Ccmc≥1, perpendicular anchoring of 5CB molecules at 5CB-water interface results in a droplet texture with a hedgehog defect. In contrast, aqueous solutions of SDBS lead to 5CB droplets with a bright-cross texture regardless of the surfactant concentration in the aqueous phase. These results indicate that the orientation of 5CB molecules is independent of the nature of the surfactant headgroup. In addition, 5CB droplet decorated OTS treated glass substrates show a hedgehog texture which disappears completely on exposure to organic vapors with the response time-dependent on the polarity of the vapor molecules.

  1. Ductile to brittle transition in dynamic fracture of brittle bulk metallic glass

    SciTech Connect

    Wang, G.; Han, Y. N.; Han, B. S.; Wang, W. H.; Xu, X. H.; Ke, F. J.

    2008-05-01

    We report an unusual transition from a locally ductile to a pure brittle fracture in the dynamic fracture of brittle Mg{sub 65}Cu{sub 20}Gd{sub 10} bulk metallic glass. The fractographic evolution from a dimple structure to a periodic corrugation pattern and then to the mirror zone along the crack propagation direction during the dynamic fracture process is discussed within the framework of the meniscus instability of the fracture process zone. This work might provide an important clue in understanding of the energy dissipation mechanism for dynamic crack propagation in brittle glassy materials.

  2. Use of glass transition temperature for stabilization of board's cracks of Eucalyptus grandis.

    PubMed

    Calonego, Fred W; Severo, Elias T D; Cunha, Antonio R; Gaia, Daiane C

    2010-09-01

    The Eucalyptus grandis logs temperatures were determined and correlated with the board's cracks during steaming. Thermocouples were inserted in the logs center, registering their temperatures during steaming at 90°C. The logs were sawed and the board's cracks measured. It was concluded that: (1) the logistic S-shaped curve explains the logs temperature variation; (2) the logs with diameter of 20 to <25, 25 to <30 and 30 to <35 cm presented, respectively, 84.2°C, 73.1°C and 45.8°C in the steaming; and (3) the cracks lengths significantly decreased in logs that reached the glass transition temperature.

  3. Deviations of the glass transition temperature in amorphous conjugated polymer thin films

    NASA Astrophysics Data System (ADS)

    Liu, Dan; Osuna Orozco, Rodrigo; Wang, Tao

    2013-08-01

    The deviations of the glass transition temperature (Tg) in thin films of an amorphous conjugated polymer poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) are reported. Monotonic and nonmonotonic Tg deviations are observed in TFB thin films supported on Si-SiOx and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), respectively. A three-layer model is developed to fit both monotonic and nonmonotonic Tg deviations in these films. A 5-nm PEDOT:PSS capping layer was not found to be effective to remove the free-surface effect in Si-SiOx supported TFB films.

  4. Predicting the glass transition temperature as function of crosslink density and polymer interactions in rubber compounds

    NASA Astrophysics Data System (ADS)

    D'Escamard, Gabriella; De Rosa, Claudio; Auriemma, Finizia

    2016-05-01

    Crosslink sulfur density in rubber compounds and interactions in polymer blends are two of the composition elements that affect the rubber compound properties and glass transition temperature (Tg), which is a marker of polymer properties related to its applications. Natural rubber (NR), butadiene rubber (BR) and styrene-butadiene rubber (SBR) compounds were investigated using calorimetry (DSC) and dynamic mechanical analysis (DMA). The results indicate that the Di Marzio's and Schneider's Models predict with accuracy the dependence of Tg on crosslink density and composition in miscible blends, respectively, and that the two model may represent the base to study the relevant "in service" properties of real rubber compounds.

  5. Acoustic and thermal anomalies in a liquid-glass transition of racemic S(+)-R(-) ketoprofen

    NASA Astrophysics Data System (ADS)

    Shibata, Tomohiko; Takayama, Haruki; Kim, Tae Hyun; Kojima, Seiji

    2014-01-01

    Acoustic and thermal properties of pharmaceutical racemic S(+)-R(-) ketoprofen were investigated in wide temperature range including glassy, supercooled liquid and liquid states by Brillouin scattering and temperature modulated DSC. Sound velocity and acoustic attenuation exhibited clear changes at 265 K indicating a liquid-glass transition and showed the typical structural relaxation above Tg. The high value of the fragility index m = 71 was determined by the dispersion of the complex heat capacity. New relaxation map was suggested in combination with previous study of dielectric measurement.

  6. Influence of the glass transition on the liquid-gas spinodal decomposition.

    PubMed

    Testard, Vincent; Berthier, Ludovic; Kob, Walter

    2011-03-25

    We use large-scale molecular dynamics simulations to study the kinetics of the liquid-gas phase separation if the temperature is lowered across the glass transition of the dense phase. We observe a gradual change from phase separated systems at high temperatures to nonequilibrium, gel-like structures that evolve very slowly at low temperatures. The microscopic mechanisms responsible for the coarsening strongly depend on temperature, and change from diffusive motion at high temperature to a strongly intermittent, heterogeneous, and thermally activated dynamics at low temperature, leading to logarithmically slow growth of the typical domain size.

  7. Modified thiol-ene networks: Tuning the glass transition temperature and energy damping capabilities

    NASA Astrophysics Data System (ADS)

    Sun, Ning; Rafailovich, Miriam; Gersappe, Dilip

    2013-03-01

    Utilizing thiol-ene `click' reactions, it is possible to produce thermoset networks that are highly homogeneous and thus exhibit enhanced energy damping capabilities. This talk will present recent results in the characterization and impact testing of modified thiol-ene networks with tunable physical properties. In particular, we synthesize ternary networks containing (1) bulky side-chain substituents, (2) isocyanate functionality, or (3) dual thiol components to improve control over the glass transition temperature and strain at break. In addition, we present results in the high-impact compression testing to demonstrate the energy damping capabilities of these materials.

  8. Study of L-ascorbic acid (vitamin C)/H 2O mixture across glass transition

    NASA Astrophysics Data System (ADS)

    Migliardo, F.; Branca, C.; Faraone, A.; Magazù, S.; Migliardo, P.

    2001-07-01

    In this paper, we report quasi elastic neutron scattering (QENS) spectra of vitamin C aqueous solutions, obtained using MIBEMOL spectrometer (LLB). The main purpose of this work is to characterize the relaxational and vibrational properties of the Vitamin C/H 2O system below and above the glass transition temperature by analysing the low-frequency neutron scattering spectra. The determination of the relative weight of vibrational over relaxational contributions allows to get information on the fragility degree of this peculiar hydrogen-bond system.

  9. Random pinning glass transition: hallmarks, mean-field theory and renormalization group analysis.

    PubMed

    Cammarota, Chiara; Biroli, Giulio

    2013-03-28

    We present a detailed analysis of glass transitions induced by pinning particles at random from an equilibrium configuration. We first develop a mean-field analysis based on the study of p-spin spherical disordered models and then obtain the three-dimensional critical behavior by the Migdal-Kadanoff real space renormalization group method. We unveil the important physical differences with the case in which particles are pinned from a random (or very high temperature) configuration. We contrast the pinning particles approach to the ones based on biasing dynamical trajectories with respect to their activity and on coupling to equilibrium configurations. Finally, we discuss numerical and experimental tests.

  10. Fluctuation phenomena

    SciTech Connect

    Montroll, E.W.; Lebowitz, J.L.

    1986-01-01

    Fluctuation phenomena are the ''tip of the iceberg'' revealing the existence, behind even the most quiescent appearing macroscopic states, of an underlying world of agitated, ever-changing microscopic processes. While the presence of these fluctuations can be ignored in some cases, e.g. if one is satisfied with purely thermostatic description of systems in equilibrium, they are central to the understanding of other phenomena, e.g. the nucleation of a new phase following the quenching of a system into the co-existence region. This volume contains a collection of review articles, written by experts in the field, on the subject of fluctuation phenomena. Some of the articles are of a very general nature discussing the modern mathematical formulation of the problems involved, while other articles deal with specific topics such as kinetics of phase transitions and conductivity in solids. The juxtaposition of the variety of physical situations in which fluctuation phenomena play an important role is novel and should give the reader an insight into this subject.

  11. A phenomenological molecular model for yielding and brittle-ductile transition of polymer glasses.

    PubMed

    Wang, Shi-Qing; Cheng, Shiwang; Lin, Panpan; Li, Xiaoxiao

    2014-09-07

    This work formulates, at a molecular level, a phenomenological theoretical description of the brittle-ductile transition (BDT) in tensile extension, exhibited by all polymeric glasses of high molecular weight (MW). The starting point is our perception of a polymer glass (under large deformation) as a structural hybrid, consisting of a primary structure due to the van der Waals bonding and a chain network whose junctions are made of pairs of hairpins and function like chemical crosslinks due to the intermolecular uncrossability. During extension, load-bearing strands (LBSs) emerge between the junctions in the affinely strained chain network. Above the BDT, i.e., at "warmer" temperatures where the glass is less vitreous, the influence of the chain network reaches out everywhere by activating all segments populated transversely between LBSs, starting from those adjacent to LBSs. It is the chain network that drives the primary structure to undergo yielding and plastic flow. Below the BDT, the glassy state is too vitreous to yield before the chain network suffers a structural breakdown. Thus, brittle failure becomes inevitable. For any given polymer glass of high MW, there is one temperature TBD or a very narrow range of temperature where the yielding of the glass barely takes place as the chain network also reaches the point of a structural failure. This is the point of the BDT. A theoretical analysis of the available experimental data reveals that (a) chain pullout occurs at the BDT when the chain tension builds up to reach a critical value f(cp) during tensile extension; (b) the limiting value of f(cp), extrapolated to far below the glass transition temperature T(g), is of a universal magnitude around 0.2-0.3 nN, for all eight polymers examined in this work; (c) pressurization, which is known [K. Matsushige, S. V. Radcliffe, and E. Baer, J. Appl. Polym. Sci. 20, 1853 (1976)] to make brittle polystyrene (PS) and poly(methyl methacrylate) (PMMA) ductile at room

  12. A phenomenological molecular model for yielding and brittle-ductile transition of polymer glasses

    NASA Astrophysics Data System (ADS)

    Wang, Shi-Qing; Cheng, Shiwang; Lin, Panpan; Li, Xiaoxiao

    2014-09-01

    This work formulates, at a molecular level, a phenomenological theoretical description of the brittle-ductile transition (BDT) in tensile extension, exhibited by all polymeric glasses of high molecular weight (MW). The starting point is our perception of a polymer glass (under large deformation) as a structural hybrid, consisting of a primary structure due to the van der Waals bonding and a chain network whose junctions are made of pairs of hairpins and function like chemical crosslinks due to the intermolecular uncrossability. During extension, load-bearing strands (LBSs) emerge between the junctions in the affinely strained chain network. Above the BDT, i.e., at "warmer" temperatures where the glass is less vitreous, the influence of the chain network reaches out everywhere by activating all segments populated transversely between LBSs, starting from those adjacent to LBSs. It is the chain network that drives the primary structure to undergo yielding and plastic flow. Below the BDT, the glassy state is too vitreous to yield before the chain network suffers a structural breakdown. Thus, brittle failure becomes inevitable. For any given polymer glass of high MW, there is one temperature TBD or a very narrow range of temperature where the yielding of the glass barely takes place as the chain network also reaches the point of a structural failure. This is the point of the BDT. A theoretical analysis of the available experimental data reveals that (a) chain pullout occurs at the BDT when the chain tension builds up to reach a critical value fcp during tensile extension; (b) the limiting value of fcp, extrapolated to far below the glass transition temperature Tg, is of a universal magnitude around 0.2-0.3 nN, for all eight polymers examined in this work; (c) pressurization, which is known [K. Matsushige, S. V. Radcliffe, and E. Baer, J. Appl. Polym. Sci. 20, 1853 (1976)] to make brittle polystyrene (PS) and poly(methyl methacrylate) (PMMA) ductile at room temperature

  13. Spectroscopic cell for fast pressure jumps across the glass transition line

    NASA Astrophysics Data System (ADS)

    Di Leonardo, R.; Scopigno, T.; Ruocco, G.; Buontempo, U.

    2004-08-01

    We present an experimental protocol for the spectroscopic study of the dynamics of glasses in the aging regime induced by sudden pressure jumps (crunches) across the glass transition line. The sample, initially in the liquid state, is suddenly brought in the glassy state, and therefore out of equilibrium, in a four-window optical crunch cell which is able to perform pressure jumps of 3 Kbar in a time interval of ≈10 ms. The main advantages of this setup with respect to previous pressure-jump systems is that the pressure jump is induced through a pressure transmitting fluid mechanically coupled to the sample stage through a deformable membrane, thus avoiding any flow of the sample itself in the pressure network and allowing us to deal with highly viscous materials. The dynamics of the sample during the aging regime is investigated by Brillouin light scattering. For this purpose the crunch cell is used in conjunction with a high resolution double monochromator equipped with a charge-coupled device detector. This system is able to record a full spectrum of a typical glass forming material in a single 1 s shot. As an example we present the study of the evolution toward equilibrium of the infinite frequency longitudinal elastic modulus (M∞) of low molecular weight polymer [Poly(bisphenol A-co-epichlorohydrin), glycidyl end capped]. The observed time evolution of M∞, well represented by a single stretched exponential, is interpreted within the framework of the Tool-Narayanaswamy theory.

  14. Electrical Conductivity, Relaxation and the Glass Transition: A New Look at a Familiar Phenomenon

    NASA Technical Reports Server (NTRS)

    Angel, Paul W.; Cooper, Alfred R.; DeGuire, Mark R.

    1996-01-01

    Annealed samples from a single melt of a 10 mol% K2O-90SiO2 glass were reheated to temperatures ranging from 450 to 800 C, held isothermally for 20 min, and then quenched in either air or a silicon oil bath. The complex impedance of both the annealed and quenched samples was measured as a function of temperature from 120 to 250 C using ac impedance spectroscopy from 1 Hz to 1 MHz. The dc conductivity, sigma(sub dc), was measured from the low frequency intercept of depressed semicircle fits to the complex impedance data. When the sigma(sub dc) at 150 C was plotted against soak temperature, the results fell into three separate regions that are explained in terms of the glass structural relaxation time, tau(sub S). This sigma(sub dc) plot provides a new way to look the glass transition range, Delta T(sub r). In addition, sigma(sub dc) was measured for different soak times at 550 C, from which an average relaxation time of 7.3 min was calculated. It was found that the size and position of the Delta T(sub r) is controlled by both the soak time and cooling rate.

  15. Short time dynamics determine glass forming ability in a glass transition two-level model: A stochastic approach using Kramers' escape formula

    NASA Astrophysics Data System (ADS)

    Toledo-Marín, J. Quetzalcóatl; Naumis, Gerardo G.

    2017-03-01

    The relationship between short and long time relaxation dynamics is obtained for a simple solvable two-level energy landscape model of a glass. This is done through means of the Kramers' transition theory, which arises in a very natural manner to calculate transition rates between wells. Then the corresponding stochastic master equation is analytically solved to find the population of metastable states. A relation between the cooling rate, the characteristic relaxation time, and the population of metastable states is found from the solution of such equation. From this, a relationship between the relaxation times and the frequency of oscillation at the metastable states, i.e., the short time dynamics, is obtained. Since the model is able to capture either a glass transition or a crystallization depending on the cooling rate, this gives a conceptual framework in which to discuss some aspects of rigidity theory, for example.

  16. Understanding the physical stability of freeze dried dosage forms from the glass transition temperature of the amorphous components.

    PubMed

    Fitzpatrick, Shaun; Saklatvala, Robert

    2003-12-01

    Modulated differential scanning calorimetry has been applied to understanding the long-term physical stability of freeze-dried units. It is known that these units are liable to contract on exposure to elevated temperature or humidity. The contraction occurs when the storage temperature is above the glass transition temperature of the amorphous components in the system. The effect of moisture content on the glass transition temperature of the amorphous components in the system has been studied. By combining this information with the moisture sorption isotherm it has been demonstrated that it is possible to predict the temperature and humidity conditions that will induce contraction of the unit. The magnitude of the glass transition temperature is composed of the contribution of each of the amorphous components in the system. It is proposed that it should be possible to develop a more robust system by the rational selection of excipients that increase the glass transition temperature or by modification of the processing conditions to promote crystallization of components that would otherwise depress the glass transition temperature.

  17. Calorimetric and Neutron Scattering Studies on Glass Transitions and Ionic Diffusions in Imidazolium-based Ionic Liquids

    NASA Astrophysics Data System (ADS)

    Yamamuro, O.; Kofu, M.

    2017-05-01

    Glass transition is one of the central research issues of ionic liquids (ILs). In particular, the most typical ILs, imidazolium-basedones (ImILs) are readily supercooled and exhibit glass transitions below room temperature. We have measured the heat capacities of several ImILs, encoded as CnmimX (n: alkyl carbon number, n = 2-8, X: anion, X = Cl, I, FeCl4, TFSI) using an adiabatic calorimeter. We found that most of ImILs exhibit glass transitions with large Cp jumps in a temperature range between 170 K and 230 K. The large Cp jumps reflect that these ILs are fragile liquids that exhibit large structural change depending on temperature near the glass transition temperature T g. It is also revealed that T g does not depend much on n but on the anion radius. We have investigated the dynamics of CnmimX (n = 2-8, X = Cl, NO3, PF6, TF, FSI, TFSI) by means of a quasielastic neutron scattering (QENS) technique. It was clarified that the ionic diffusion is directly associated with the viscosity and glass transition. The activation energy ΔE a of the ionic diffusion increases with decreasing anion size but remains almost unchanged with n as found for T g. These systematic change of T g and ΔE a can be explained well by taking account the nano-domain structure which is the most characteristic feature of ImILs.

  18. Reversing and nonreversing heat capacity of poly(lactic acid) in the glass transition region by TMDSC

    SciTech Connect

    Pyda, Marek {nmn}; Wunderlich, Bernhard {nmn}

    2005-11-01

    A study of the glass transition of an amorphous and a semicrystalline poly(lactic acid) (PLA) is performed with adiabatic calorimetry, differential scanning calorimetry (DSC), and temperature-modulated DSC (TMDSC). The reversing, total, and nonreversing apparent heat capacities of samples with different contents of L- and D-lactic acid and with various thermal histories were evaluated. Different modes of TMDSC analyses of amorphous and semicrystalline PLA were compared to the total heat capacity from standard DSC. The enthalpy relaxation and the cold crystallization in the glass transition region are largely irreversible. The melting is largely irreversible, but a 100% reversing fraction is observed at low temperatures from 375 to 420 K, which becomes small inside the major melting peak at about 440 K. From the TMDSC of amorphous PLA, the combined information on endothermic and exothermic enthalpy relaxation and glass transition were deconvoluted into the reversing and nonreversing components. The glass transition temperature from the reversing heat capacity and the enthalpy relaxation peaks from the nonreversing component shift to higher temperature for increasingly annealed PLA. The relaxation times for aging decrease on cooling until the glass transition is reached and then increase. This behavior is linked to cooperativity. All quantitative thermal analyses are based on the heat capacity of the solid and liquid, evaluated earlier with the advanced thermal analysis system (ATHAS).

  19. Pseudogap Phenomena Near the BKT Transition of a Two-Dimensional Ultracold Fermi Gas in the Crossover Region

    NASA Astrophysics Data System (ADS)

    Matsumoto, M.; Hanai, R.; Inotani, D.; Ohashi, Y.

    2017-06-01

    We investigate strong-coupling properties of a two-dimensional ultracold Fermi gas in the normal phase. In the three-dimensional case, it has been shown that the so-called pseudogap phenomena can be well described by a (non-self-consistent) T-matrix approximation (TMA). In the two-dimensional case, while this strong-coupling theory can explain the pseudogap phenomenon in the strong-coupling regime, it unphysically gives large pseudogap size in the crossover region, as well as in the weak-coupling regime. We show that this difficulty can be overcome when one improves TMA to include higher-order pairing fluctuations within the framework of a self-consistent T-matrix approximation (SCTMA). The essence of this improvement is also explained. Since the observation of the BKT transition has recently been reported in a two-dimensional ^6{Li} Fermi gas, our results would be useful for the study of strong-coupling physics associated with this quasi-long-range order.

  20. Glass transition of adsorbed stereoregular PPMA by inverse gas chromatography at infinite dilution

    NASA Astrophysics Data System (ADS)

    Hamieh, T.; Rezzaki, M.; Grohens, Y.; Schultz, J.

    1998-10-01

    In this paper, we used inverse gas chromatography (IGC) at infinite dilution that proved to be a powerful technique to determine glass transition and other transitions of PMMA adsorbed on α-alumina. We highlighted the glass transition temperature of the system PMMA/α-Al2O3 with defined polymer tacticity at various covered surface fractions. Thus, the Tg of the adsorbed isotactic PMMA increases strongly as compared to the bulk value. The study of the physical chemical properties of PMMA/α-alumina revealed an important difference in the acidic and basic behaviour, in Lewis terms, of aluminium oxide covered by various concentrations of PMMA. It appears that there is a stabilisation of the physical chemical properties of PMMA/α-Al2O3 for a surface coverage above 50%. This study also highlighted an important effect of the tacticity of the polymer on the acid-base character of the system PMMA/Al2O3. Dans cet article, nous montrons que la chromatographie gazeuse inverse (CGI) à dilution infinie se révèle être une technique très intéressante pour la détermination de la transition vitreuse de polymères stéréoréguliers adsorbés sur des substrats solides tels que l'alumine. Nous avons mis en évidence des transitions attribuées aux phénomènes de relaxation béta, transition vitreuse et autres transitions des systèmes PMMA/Al2O3 de tacticité définie à différents taux de recouvrement. Ainsi, la Tg du PMMA isotactique adsorbé augmente de façon significative par rapport a celle du polymère massique. L'étude des propriétés physico-chimiques du système PMMA/Al2O3, révèle une différence importante dans le comportement acido-basique, au sens de Lewis, de l'alumine pour de taux de recouvrement en PMMA variables. Il apparaît qu'il y a stabilisation des propriétés physico-chimiques de PMMA/Al2O3 pour un taux de recouvrement en PMMA supérieur à 50 %. Cette étude a montré également une influence importante de la tacticité du polymère sur le

  1. Glass transition dynamics and conductivity scaling in ionic deep eutectic solvents: The case of (acetamide + lithium nitrate/sodium thiocyanate) melts

    NASA Astrophysics Data System (ADS)

    Tripathy, Satya N.; Wojnarowska, Zaneta; Knapik, Justyna; Shirota, Hideaki; Biswas, Ranjit; Paluch, Marian

    2015-05-01

    A detailed investigation on the molecular dynamics of ionic deep eutectic solvents (acetamide + lithium nitrate/sodium thiocyanate) is reported. The study was carried out employing dielectric relaxation spectroscopy covering seven decades in frequency (10-1-106 Hz) and in a wide temperature range from 373 K down to 173 K, accessing the dynamic observables both in liquid and glassy state. The dielectric response of the ionic system has been presented in the dynamic window of modulus formalism to understand the conductivity relaxation and its possible connection to the origin of localized motion. Two secondary relaxation processes appear below glass transition temperature. Our findings provide suitable interpretation on the nature of secondary Johari-Goldstein process describing the ion translation and orientation of dipoles in a combined approach using Ngai's coupling model. A nearly constant loss feature is witnessed at shorter times/lower temperatures. We also discuss the ac conductivity scaling behavior using Summerfield approach and random free energy barrier model which establish the time-temperature superposition principle. These experimental observations have fundamental importance on theoretical elucidation of the conductivity relaxation and glass transition phenomena in molten ionic conductors.

  2. Glass transition dynamics and conductivity scaling in ionic deep eutectic solvents: The case of (acetamide + lithium nitrate/sodium thiocyanate) melts

    SciTech Connect

    Tripathy, Satya N. Wojnarowska, Zaneta; Knapik, Justyna; Paluch, Marian; Shirota, Hideaki; Biswas, Ranjit

    2015-05-14

    A detailed investigation on the molecular dynamics of ionic deep eutectic solvents (acetamide + lithium nitrate/sodium thiocyanate) is reported. The study was carried out employing dielectric relaxation spectroscopy covering seven decades in frequency (10{sup −1}-10{sup 6} Hz) and in a wide temperature range from 373 K down to 173 K, accessing the dynamic observables both in liquid and glassy state. The dielectric response of the ionic system has been presented in the dynamic window of modulus formalism to understand the conductivity relaxation and its possible connection to the origin of localized motion. Two secondary relaxation processes appear below glass transition temperature. Our findings provide suitable interpretation on the nature of secondary Johari-Goldstein process describing the ion translation and orientation of dipoles in a combined approach using Ngai’s coupling model. A nearly constant loss feature is witnessed at shorter times/lower temperatures. We also discuss the ac conductivity scaling behavior using Summerfield approach and random free energy barrier model which establish the time-temperature superposition principle. These experimental observations have fundamental importance on theoretical elucidation of the conductivity relaxation and glass transition phenomena in molten ionic conductors.

  3. High-temperature tolerance in anhydrobiotic tardigrades is limited by glass transition.

    PubMed

    Hengherr, S; Worland, M R; Reuner, A; Brümmer, F; Schill, R O

    2009-01-01

    Survival in microhabitats that experience extreme fluctuations in water availability and temperature requires special adaptations. To withstand such environmental conditions, tardigrades, as well as some nematodes and rotifers, enter a completely desiccated state known as anhydrobiosis. We examined the effects of high temperatures on fully desiccated (anhydrobiotic) tardigrades. Nine species from the classes Heterotardigrada and Eutardigrada were exposed to temperatures of up to 110 degrees C for 1 h. Exposure to temperatures of up to 80 degrees C resulted in a moderate decrease in survival. Exposure to temperatures above this resulted in a sharp decrease in survival, with no animals of the families Macrobiotidae and Echiniscidae surviving 100 degrees C. However, Milnesium tardigradum (Milnesidae) showed survival of >90% after exposure to 100 degrees C; temperatures above this resulted in a steep decrease in survival. Vitrification is assumed to play a major role in the survival of anhydrobiotic organisms during exposure to extreme temperatures, and consequently, the glass-transition temperature (T(g)) is critical to high-temperature tolerance. In this study, we provide the first evidence of the presence of a glass transition during heating in an anhydrobiotic tardigrade through the use of differential scanning calorimetry.

  4. Relaxation transition in glass-forming polybutadiene as revealed by nuclear resonance X-ray scattering.

    PubMed

    Kanaya, Toshiji; Inoue, Rintaro; Saito, Makina; Seto, Makoto; Yoda, Yoshitaka

    2014-04-14

    We investigated the arrest mechanism of molecular motions in a glass forming polybutadiene near the glass transition using a new nuclear resonance synchrotron X-ray scattering technique to cover a wide time range (10(-9) to 10(-5) s) and a scattering vector Q range (9.6-40 nm(-1)), which have never been accessed by other methods. Owing to the wide time and Q ranges it was found for the first time that a transition of the α-process to the slow β-process (or the Johari-Goldstein process) was observed in a Q range higher than the first peak in the structure factor S(Q) at the critical temperature T(c) in the mode coupling theory. The results suggest the important roles of hopping motions below T(c), which was predicted by the recent extended mode coupling theory and the cooperative motions due to the strong correlation at the first peak in S(Q) in the arrest mechanism.

  5. Relaxation transition in glass-forming polybutadiene as revealed by nuclear resonance X-ray scattering

    NASA Astrophysics Data System (ADS)

    Kanaya, Toshiji; Inoue, Rintaro; Saito, Makina; Seto, Makoto; Yoda, Yoshitaka

    2014-04-01

    We investigated the arrest mechanism of molecular motions in a glass forming polybutadiene near the glass transition using a new nuclear resonance synchrotron X-ray scattering technique to cover a wide time range (10-9 to 10-5 s) and a scattering vector Q range (9.6-40 nm-1), which have never been accessed by other methods. Owing to the wide time and Q ranges it was found for the first time that a transition of the α-process to the slow β-process (or the Johari-Goldstein process) was observed in a Q range higher than the first peak in the structure factor S(Q) at the critical temperature Tc in the mode coupling theory. The results suggest the important roles of hopping motions below Tc, which was predicted by the recent extended mode coupling theory and the cooperative motions due to the strong correlation at the first peak in S(Q) in the arrest mechanism.

  6. Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature.

    PubMed

    Chremos, Alexandros; Glynos, Emmanouil; Green, Peter F

    2015-01-28

    Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties.

  7. On the Glass Transition in Polystyrene-TiO2 Nanocomposites

    NASA Astrophysics Data System (ADS)

    Alarcon, Jorge; Chipara, Dorina M.; Lozano, Karen; Chipara, Mircea; Chipara, Alin Cristian; Vajtai, Robert; Ajayan, Pullickel M.; University of Texas-Pan American Collaboration; Rice University Collaboration

    2014-03-01

    Nanocomposites of atactic polystyrene (PS) filled with TiO2 nanoparticles of about 15 nm have been prepared. A dilute solution of PS in a good solvent (chlorophorm) has been prepared by stirring the components at room temperature for 24 h at 500 rotations per minute. The solution was then sonicated for 5 minutes by using a high power sonicator. TiO2 nanoparticles were added in the sonicating bath and the sonication continued for 1 hour in order to achieve an uniform dispersion on nanoparticles. Then, a non solvent (distilled water) has been suddenly added under sonication. The sonication continued for about 30 minutes. After 30 minutes, the polymer nanocomposite was isolated from the liquid mixture by filtration. The residual amount of solvent and water was removed by placing the nanocomposites into a vacuum oven at 100 C for 12 hours. The complete removel of water and solvent was confirmed by TGA. The as obtained samples were measured by Differential Scanning Calorimetry and the effect of TiO2 on the glass transition temperature was investigated. The effect of TiO2 on the glass transition of PS is discussed.

  8. Impact of caramelization on the glass transition temperature of several caramelized sugars. Part I: Chemical analyses.

    PubMed

    Jiang, Bin; Liu, Yeting; Bhandari, Bhesh; Zhou, Weibiao

    2008-07-09

    This study aims to investigate the relationship between caramelization of several sugars including fructose, glucose, and sucrose and their glass transition temperature (Tg). Differential scanning calorimetry (DSC) was used for creating caramelized sugar samples as well as determining their glass transition temperature, which was found to decrease first and then increase as the holding time at the highest temperature increased. The extent of caramelization was quantified by UV-vis absorbance measurement and high-performance liquid chromatography analysis. Results showed that the amount of small molecules from the degradation of sugar increased very fast at the beginning of heating, and this increase slowed down in the later stage of caramelization. On the other hand, there was a lag phase in the formation of large molecules from the degradation of sugar at the beginning of heating, followed by a fast increase in the later stage of caramelization. The obtained results clearly indicate the impact of melting condition on the T g of sugars through formation of intermediates and end products of caramelization. Generally, when the heating condition is relatively mild, small molecules are formed first by decomposition of the sugar, which leads to a decrease of the overall Tg, and as the heating time becomes longer and/or the heating condition becomes more severe, polymerization takes over and more large molecules are formed, which results in an increase of the overall Tg. Mathematical modeling of the relationship will be presented as part II of the study in a separate paper.

  9. Glass transition and water effects on sucrose inversion by invertase in a lactose-sucrose system.

    PubMed

    Kouassi, K; Roos, Y H

    2000-06-01

    Enzymatic changes are often detrimental to quality of low-moisture foods. In the present study, effects of glass transition and water on sucrose inversion in a lactose-sucrose food model were investigated. Amorphous samples were produced by freeze-drying lactose-sucrose (2:1)-invertase (20 mg invertase/49.4 g of carbohydrate) dissolved in distilled water. Sorption isotherms were determined gravimetrically at 24 degrees C. Sucrose hydrolysis was determined by monitoring glucose content using a test kit and the amounts of fructose, glucose, and sucrose using HPLC. The glass transition temperatures, T(g), at various water contents were measured using differential scanning calorimetry (DSC). The BET and the GAB sorption models were fitted to experimental data up to a(w) 0.444 and 0.538, respectively. Water sorption and DSC results suggested time-dependent crystallization of sugars at a(w) 0.444 and above. Significant sucrose hydrolysis occurred only above T(g), concomitantly with crystallization. Sucrose hydrolysis and crystallization were not likely in glassy materials.

  10. Interparticle interactions mediated superspin glass to superferromagnetic transition in Ni-bacterial cellulose aerogel nanocomposites

    NASA Astrophysics Data System (ADS)

    Thiruvengadam, V.; Vitta, Satish

    2016-06-01

    The interparticle interactions in the magnetic nanocomposites play a dominant role in controlling phase transitions: superparamagnetic to superspin glass and to superferromagnetic. These interactions can be tuned by controlling the size and number density of nanoparticles. The aerogel composites, 0.3Ni-BC and 0.7Ni-BC, consisting of Ni nanoparticles distributed in the bacterial cellulose have been used as a model system to study these interactions. Contrary to conventional approach, size of Ni-nanoparticles is not controlled and allowed to form naturally in bacterial cellulose template. The uncontrolled growth of Ni results in the formation of nanoparticles with 3 different size distributions - <10 nm particles along the length of fibrils, 50 nm particles in the intermediate spaces between the fibrils, and >100 nm particles in voids formed by reticulate structure. At room temperature, the composites exhibit a weakly ferromagnetic behaviour with a coercivity of 40 Oe, which increases to 160 Oe at 10 K. The transition from weakly ferromagnetic state to superferromagnetic state at low temperatures is mediated by the superspin glass state at intermediate temperatures via the interparticle interactions aided by nanoparticles present along the length of fibres. A temperature dependent microstructural model has been developed to understand the magnetic behaviour of nanocomposite aerogels.

  11. In-Situ Phase Transition Control in the Supercooled State for Robust Active Glass Fiber.

    PubMed

    Lv, Shichao; Cao, Maoqing; Li, Chaoyu; Li, Jiang; Qiu, Jianrong; Zhou, Shifeng

    2017-06-21

    The construction of a dopant-activated photonic composite is of great technological importance for various applications, including smart lighting, optical amplification, laser, and optical detection. The bonding arrangement around the introduced dopants largely determines the properties, yet it remains a daunting challenge to manipulate the local state of the matrix (i.e., phase) inside the transparent composite in a controllable manner. Here we demonstrate that the relaxation of the supercooled state enables in-situ phase transition control in glass. Benefiting from the unique local atom arrangement manner, the strategy offers the possibility for simultaneously tuning the chemical environment of the incorporated dopant and engineering the dopant-host interaction. This allows us to effectively activate the dopant with high efficiency (calculated as ∼100%) and profoundly enhance the dopant-host energy-exchange interaction. Our results highlight that the in-situ phase transition control in glass may provide new opportunities for fabrication of unusual photonic materials with intense broadband emission at ∼1100 nm and development of the robust optical detection unit with high compactness and broadband photon-harvesting capability (from X-ray to ultraviolet light).

  12. Glass transitions and physical aging of cassava starch - corn oil blends.

    PubMed

    Pérez, Adriana; Sandoval, Aleida J; Cova, Aura; Müller, Alejandro J

    2014-05-25

    Glass transition temperatures and physical aging of amorphous cassava starch and their blends with corn oil were assessed by differential scanning calorimetry (DSC). Two enthalpic relaxation endotherms, well separated in temperature values, were exhibited by neat amorphous cassava starch with 10.6% moisture content, evidencing two amorphous regions within the starch with different degrees of mobility. The phase segregation of these two amorphous regions was favored by added corn oil at low moisture contents during storage. The presence of amylose-lipid complexes in this matrix, may also affect the molecular dynamics of these two amorphous regions at low moisture contents. Increasing moisture content, leads to a homogeneous amorphous phase, with an aging process characterized by a single enthalpic relaxation peak. In all cases, after deleting the thermal history of the samples only one glass transition temperature was detected (during DSC second heating runs) indicating that a single homogeneous amorphous phase was attained after erasing the effects of physical aging. Trends of the enthalpic relaxation parameters were also different at the two moisture contents considered in this work. Copyright © 2014 Elsevier Ltd. All rights reserved.

  13. Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature

    NASA Astrophysics Data System (ADS)

    Chremos, Alexandros; Glynos, Emmanouil; Green, Peter F.

    2015-01-01

    Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties.

  14. Calcium chloride effects on the glass transition of condensed systems of potato starch.

    PubMed

    Chuang, Lillian; Panyoyai, Naksit; Katopo, Lita; Shanks, Robert; Kasapis, Stefan

    2016-05-15

    The effect of calcium chloride on the structural properties of condensed potato starch undergoing a thermally induced glass transition has been studied using dynamic mechanical analysis and modulated differential scanning calorimetry. Extensive starch gelatinisation was obtained by hot pressing at 120°C for 7 min producing materials that covered a range of moisture contents from 3.7% w/w (11% relative humidity) to 18.8% w/w (75% relative humidity). FTIR, ESEM and WAXD were also performed in order to elucidate the manner by which salt addition affects the molecular interactions and morphology of condensed starch. Experimental protocol ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of calcium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Highly reactive calcium ions form a direct interaction with starch to alter considerably its structural properties via an anti-plasticizing effect, as compared to the polymer-water matrix.

  15. Glass transition temperature and thermal stability of ZnS/PMMA nanocomposites

    NASA Astrophysics Data System (ADS)

    Agrawal, Sonalika; Patidar, Dinesh; Saxena, N. S.

    2011-11-01

    In this article, ZnS nanoparticles were prepared by wet chemical precipitation method using zinc sulphate (ZnSO4), sodium sulphide (Na2S) and thio-glycerol. These nanoparticles were characterized through X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The solution-based processing was used to prepare Poly methyl methacrylate (PMMA) nanocomposites with different weight percents (0, 2, 4, 6 and 8) of ZnS nanoparticles. The obtained ZnS/PMMA nanocomposites were characterized through XRD, scanning electron microscope and TEM measurements. The dynamic mechanical analyzer was used to obtain the storage modulus and glass transition temperature (T g) of the nanocomposites. The apparent activation energy of the glass transition region was also determined using the Vogel-Fulcher-Tammann equation. The results indicated that the thermal stability of ZnS/PMMA nanocomposites was higher than PMMA and 6 wt. % of ZnS nanoparticles in PMMA matrix showed the maximum activation energy, which indicated that this nanocomposite had higher thermal stability than other composites.

  16. Determination of Material Properties Near the Glass Transition Temperature for an Isogrid Boom

    NASA Technical Reports Server (NTRS)

    Blandino, Joseph R.; Woods-Vedeler, Jessica A. (Technical Monitor)

    2002-01-01

    Experiments were performed and results obtained to determine the temperature dependence of the modulus of elasticity for a thermoplastic isogrid tube. The isogrid tube was subjected to axial tensile loads of 0-100 lbf and strain was measured at room and elevated temperatures of 100, 120, 140, 160, 180, 190, and 200 F. These were based on tube manufacturer specifying an incorrect glass transition temperature of 210 F. Two protocols were used. For the first protocol the tube was brought to temperature and a tensile test performed. The tube was allowed to cool between tests. For the second protocol the tube was ramped to the desired test temperature and held. A tensile test was performed and the tube temperature ramped to the next test temperature. The second protocol spanned the entire test range. The strain rate was constant at 0.008 in/min. Room temperature tests resulted in the determination of an average modulus of 2.34 x 106 Psi. The modulus decreased above 100 F. At 140 F the modulus had decreased by 7.26%. The two test protocols showed good agreement below 160 F. At this point the glass transition temperature had been exceeded. The two protocols were not repeated because the tube failed.

  17. The effect of water on the glass transition of human hair.

    PubMed

    Wortmann, F-J; Stapels, M; Elliott, R; Chandra, L

    2006-04-05

    The glass transition of human hair and its dependence on water content were determined by means of differential scanning calorimetry (DSC). The relationship between the data is suitably described by the Fox equation, yielding for human hair a glass transition temperature of T(g) = 144 degrees C, which is substantially lower than that for wool (174 degrees C). This effect is attributed to a higher fraction of hydrophobic proteins in the matrix of human hair, which acts as an internal plasticizer. The applicability of the Fox equation for hair as well as for wool implies that water is homogeneously distributed in alpha-keratins, despite their complex morphological, semicrystalline structure. To investigate this aspect, hair was rendered amorphous by thermal denaturation. For the amorphous hair neither the water content nor T(g) were changed compared to the native state. These results provide strong support for the theory of a quasi-homogeneous distribution of water within alpha-keratins. Copyright 2005 Wiley Periodicals, Inc.

  18. Glass transition dynamics and boiling temperatures of molecular liquids and their isomers.

    PubMed

    Wang, Li-Min; Richert, Ranko

    2007-03-29

    The relation between a dynamic and a thermodynamic temperature, glass transition Tg and boiling point Tb, is investigated for various glass-forming liquids, with emphasis on monohydroxy alcohols. As is well known, Tb and Tg are positively correlated across a large variety of liquids. However, we found that the same quantities show a negative correlation within an isomeric series, i.e., Tb decreases with increasing Tg for different isomers of the same chemical formula. For the alcohol series, CnH2n+1OH with 3 < or = n < or = 10, a master curve of the negative Tg - Tb correlation is obtained if the temperatures are normalized to the respective values of the n-alkanols. This Tg - Tb dependence of isomeric liquids is linked to entropic effects and responsible for much of the scatter of the correlation observed for a large number of molecular organic glass-formers with 45 < Tg < 250 K. Dielectric relaxation is measured for three groups of isomers: (a) 3-methoxyl-1-butanol and 2-iso-propoxyethanol, (b) 1,4-, 1,2-, and 2,4-pentanediol, and (c) di-n- and di-iso-butyl phthalate. Two key parameters of the dynamics, fragility m and stretching exponent beta, are found to be indistinguishable within isomers of moderately different Tgs. Larger fragility differences are readily expected with pronounced structural change, but no systematic trend is observed within an isomer series. The results provide a useful tool for assessing Tg, m, and beta for marginal glass formers on the basis of their isomers.

  19. On the theoretical determination of the Prigogine-Defay ratio in glass transition.

    PubMed

    Tropin, Timur V; Schmelzer, Jürn W P; Gutzow, Ivan; Schick, Christoph

    2012-03-28

    In a recent analysis [J. W. P. Schmelzer and I. Gutzow, J. Chem. Phys. 125, 184511 (2006)] it was shown for the first time that--in contrast to earlier belief arising from the works of Prigogine and Defay [Chemical Thermodynamics (Longman, London, 1954), Chap. 19; The first French edition of this book was published in 1950] and Davies and Jones [Adv. Phys. 2, 370 (1953); and Proc. R. Soc. London, Ser. A 217, 26 (1953)]--a satisfactory theoretical interpretation of the experimentally observed values of the so-called Prigogine-Defay ratio Π, being a combination of jumps of thermodynamic coefficients at glass transition, can be given employing only one structural order parameter. According to this analysis, this ratio has to be, in full agreement with experimental findings, larger than one (Π > 1). Its particular value depends both on the thermodynamic properties of the system under consideration and on cooling and heating rates. Based on above-mentioned analysis, latter dependence on cooling rates has been studied in detail in another own preceding paper [T. V. Tropin, J. W. P. Schmelzer, and C. Schick, J. Non-Cryst. Solids 357, 1303 (2011)]. In the present analysis, an alternative general method of determination of the Prigogine-Defay ratio is outlined, allowing one to determine this ratio having at ones disposal the generalized equation of state of the glass-forming melts under consideration and, in particular, the knowledge of the equilibrium properties of the melts in the glass transformation range. Employing, as an illustration of the method, a particular model for the description of glass-forming melts, theoretical estimates are given for this ratio being, again, in good agreement with experimental data.

  20. On the theoretical determination of the Prigogine-Defay ratio in glass transition

    NASA Astrophysics Data System (ADS)

    Tropin, Timur V.; Schmelzer, Jürn W. P.; Gutzow, Ivan; Schick, Christoph

    2012-03-01

    In a recent analysis [J. W. P. Schmelzer and I. Gutzow, J. Chem. Phys. 125, 184511 (2006), 10.1063/1.2374894] it was shown for the first time that - in contrast to earlier belief arising from the works of Prigogine and Defay [Chemical Thermodynamics (Longman, London, 1954), Chap. 19; The first French edition of this book was published in 1950] and Davies and Jones [Adv. Phys. 2, 370 (1953), 10.1080/00018735300101252; Davies and Jones Proc. R. Soc. London, Ser. A 217, 26 (1953), 10.1098/rspa.1953.0044] - a satisfactory theoretical interpretation of the experimentally observed values of the so-called Prigogine-Defay ratio Π, being a combination of jumps of thermodynamic coefficients at glass transition, can be given employing only one structural order parameter. According to this analysis, this ratio has to be, in full agreement with experimental findings, larger than one (Π > 1). Its particular value depends both on the thermodynamic properties of the system under consideration and on cooling and heating rates. Based on above-mentioned analysis, latter dependence on cooling rates has been studied in detail in another own preceding paper [T. V. Tropin, J. W. P. Schmelzer, and C. Schick, J. Non-Cryst. Solids 357, 1303 (2011), 10.1016/j.jnoncrysol.2010.12.005]. In the present analysis, an alternative general method of determination of the Prigogine-Defay ratio is outlined, allowing one to determine this ratio having at ones disposal the generalized equation of state of the glass-forming melts under consideration and, in particular, the knowledge of the equilibrium properties of the melts in the glass transformation range. Employing, as an illustration of the method, a particular model for the description of glass-forming melts, theoretical estimates are given for this ratio being, again, in good agreement with experimental data.

  1. Excess of low frequency vibrational modes and glass transition: a molecular dynamics study for soft spheres at constant pressure.

    PubMed

    Flores-Ruiz, Hugo M; Naumis, Gerardo G

    2009-10-21

    Using molecular dynamics at constant pressure, the relationship between the excess of low frequency vibrational modes (known as the boson peak) and the glass transition is investigated for a truncated Lennard-Jones potential. It is observed that the quadratic mean displacement is enhanced by such modes, as predicted using a harmonic Hamiltonian for metastable states. As a result, glasses loose mechanical stability at lower temperatures than the corresponding crystal, since the Lindemann criteria are observed, as is also deduced from density functional theory. Finally, we found that the average force and elastic constant are reduced in the glass due to such excess of modes. The ratio between average elastic constants can be approximated using the 2/3 rule between melting and glass transition temperatures.

  2. Glass Transition and Molecular Mobility in Styrene-Butadiene Rubber Modified Asphalt.

    PubMed

    Khabaz, Fardin; Khare, Rajesh

    2015-11-05

    Asphalt, a soft matter consisting of more than a thousand chemical species, is of vital importance for the transportation infrastructure, yet it poses significant challenges for microscopic theory and modeling approaches due to its multicomponent nature. Polymeric additives can potentially enhance the thermo-mechanical properties of asphalt, thus helping reduce the road repair costs; rational design of such systems requires knowledge of the molecular structure and dynamics of these systems. We have used molecular dynamics (MD) simulations to investigate the volumetric, structural, and dynamic properties of the neat asphalt as well as styrene-butadiene rubber (SBR) modified asphalt systems. The volume-temperature behavior of the asphalt systems exhibited a glass transition phenomenon, akin to that observed in experiments. The glass transition temperature, room temperature density, and coefficient of volume thermal expansion of the neat asphalt systems so evaluated were in agreement with experimental data when the effect of the high cooling rate used in simulations was accounted for. While the volumetric properties of SBR modified asphalt were found to be insensitive to the presence of the SBR additive, the addition of SBR led to an increase in the aggregation of asphaltene molecules. Furthermore, addition of SBR caused a reduction in the mobility of the constituent molecules of asphalt, with the reduction being more significant for the larger constituent molecules. Similar to other glass forming liquids, the reciprocal of the diffusion coefficient of the selected molecules was observed to follow the Vogel-Fulcher-Tammann (VFT) behavior as a function of temperature. These results suggest the potential for using polymeric additives for enhancing the dynamic mechanical properties of asphalt without affecting its volumetric properties.

  3. Glass transition of aqueous solutions involving annealing-induced ice recrystallization resolves liquid-liquid transition puzzle of water.

    PubMed

    Zhao, Li-Shan; Cao, Ze-Xian; Wang, Qiang

    2015-10-27

    Liquid-liquid transition of water is an important concept in condensed-matter physics. Recently, it was claimed to have been confirmed in aqueous solutions based on annealing-induced upshift of glass-liquid transition temperature, T(g) . Here we report a universal water-content, X(aqu) , dependence of T(g) for aqueous solutions. Solutions with X(aqu)>X(cr)(aqu)vitrify/devitrify at a constant temperature, ~T(g) , referring to freeze-concentrated phase with X(aqu)left behind ice crystallization. Those solutions with X(aqu)

  4. Glass transition of aqueous solutions involving annealing-induced ice recrystallization resolves liquid-liquid transition puzzle of water

    PubMed Central

    Zhao, Li-Shan; Cao, Ze-Xian; Wang, Qiang

    2015-01-01

    Liquid-liquid transition of water is an important concept in condensed-matter physics. Recently, it was claimed to have been confirmed in aqueous solutions based on annealing-induced upshift of glass-liquid transition temperature, . Here we report a universal water-content, , dependence of for aqueous solutions. Solutions with vitrify/devitrify at a constant temperature, , referring to freeze-concentrated phase with left behind ice crystallization. Those solutions with totally vitrify at under conventional cooling/heating process though, of the samples annealed at temperatures   to effectively evoke ice recrystallization is stabilized at . Experiments on aqueous glycerol and 1,2,4-butanetriol solutions in literature were repeated, and the same samples subject to other annealing treatments equally reproduce the result. The upshift of by annealing is attributable to freeze-concentrated phase of solutions instead of ‘liquid II phase of water’. Our work also provides a reliable method to determine hydration formula and to scrutinize solute-solvent interaction in solution. PMID:26503911

  5. Fluid to soft-glass transition in a quasi-2D system: thermodynamic and rheological evidences for a Langmuir monolayer.

    PubMed

    Maestro, Armando; Guzmán, Eduardo; Chuliá, Raquel; Ortega, Francisco; Rubio, Ramón G; Miller, Reinhard

    2011-05-28

    We report an experimental study that points out the existence of a fluid to soft-glass transition in Langmuir polymer monolayers of poly(methyl methacrylate) (PMMA), for which the water/air interface behaves as a poor-solvent. The temperature dependence of surface pressure vs. surface area equilibrium isotherms shows a glass-like transition temperature at T(g,2D)≈ 298 K, significantly lower than the value for bulk PMMA (T(g,bulk)≈ 378 K). The plot of the film thickness h vs. temperature shows a sharp change of slope at about the same temperature, 298 K, which is a typical hallmark of a glass transition in thin polymer films [J. L. Keddie, R. A. L. Jones, R. A. Cory, Europhys. Lett., 1996, 27, 59-64]. Furthermore, slightly above T(g,2D), the temperature dependence of the dilational viscosity does not follow an Arrhenius law, but instead can be described by a Vogel-Fulcher-Tamman equation with parameters that are typical of a fragile glass. Not only the qualitative behavior of three distinct equilibrium and dynamic properties, but also the quantitative agreement of the values of T(g) obtained, are a strong evidence of the existence of a fluid to soft-glass transition in this quasi-2D system.

  6. An Experimental Investigation into Failure and Localization Phenomena in the Extension to Shear Fracture Transition in Rock

    NASA Astrophysics Data System (ADS)

    Choens, R. C., II; Chester, F. M.; Bauer, S. J.; Flint, G. M.

    2014-12-01

    Fluid-pressure assisted fracturing can produce mesh and other large, interconnected and complex networks consisting of both extension and shear fractures in various metamorphic, magmatic and tectonic systems. Presently, rock failure criteria for tensile and low-mean compressive stress conditions is poorly defined, although there is accumulating evidence that the transition from extension to shear fracture with increasing mean stress is continuous. We report on the results of experiments designed to document failure criteria, fracture mode, and localization phenomena for several rock types (sandstone, limestone, chalk and marble). Experiments were conducted in triaxial extension using a necked (dogbone) geometry to achieve mixed tension and compression stress states with local component-strain measurements in the failure region. The failure envelope for all rock types is similar, but are poorly described using Griffith or modified Griffith (Coulomb or other) failure criteria. Notably, the mode of fracture changes systematically from pure extension to shear with increase in compressive mean stress and display a continuous change in fracture orientation with respect to principal stress axes. Differential stress and inelastic strain show a systematic increase with increasing mean stress, whereas the axial stress decreases before increasing with increasing mean stress. The stress and strain data are used to analyze elastic and plastic strains leading to failure and compare the experimental results to predictions for localization using constitutive models incorporating on bifurcation theory. Although models are able to describe the stability behavior and onset of localization qualitatively, the models are unable to predict fracture type or orientation. Constitutive models using single or multiple yield surfaces are unable to predict the experimental results, reflecting the difficulty in capturing the changing micromechanisms from extension to shear failure. Sandia

  7. Glass transition and relaxation dynamics of propylene glycol-water solutions confined in clay

    NASA Astrophysics Data System (ADS)

    Elamin, Khalid; Björklund, Jimmy; Nyhlén, Fredrik; Yttergren, Madeleine; Mârtensson, Lena; Swenson, Jan

    2014-07-01

    The molecular dynamics of aqueous solutions of propylene glycol (PG) and propylene glycol methylether (PGME) confined in a two-dimensional layer-structured Na-vermiculite clay has been studied by broadband dielectric spectroscopy and differential scanning calorimetry. As typical for liquids in confined geometries the intensity of the cooperative α-relaxation becomes considerably more suppressed than the more local β-like relaxation processes. In fact, at high water contents the calorimetric glass transition and related structural α-relaxation cannot even be observed, due to the confinement. Thus, the intensity of the viscosity related α-relaxation is dramatically reduced, but its time scale as well as the related glass transition temperature Tg are for both systems only weakly influenced by the confinement. In the case of the PGME-water solutions it is an important finding since in the corresponding bulk system a pronounced non-monotonic concentration dependence of the glass transition related dynamics has been observed due to the growth of hydrogen bonded relaxing entities of water bridging between PGME molecules [J. Sjöström, J. Mattsson, R. Bergman, and J. Swenson, Phys. Chem. B 115, 10013 (2011)]. The present results suggest that the same type of structural entities are formed in the quasi-two-dimensional space between the clay platelets. It is also observed that the main water relaxation cannot be distinguished from the β-relaxation of PG or PGME in the concentration range up to intermediate water contents. This suggests that these two processes are coupled and that the water molecules affect the time scale of the β-relaxation. However, this is most likely true also for the corresponding bulk solutions, which exhibit similar time scales of this combined relaxation process below Tg. Finally, it is found that at higher water contents the water relaxation does not merge with, or follow, the α-relaxation above Tg, but instead crosses the

  8. Glass transition in thaumatin crystals revealed through temperature-dependent radiation-sensitivity measurements

    SciTech Connect

    Warkentin, Matthew Thorne, Robert E.

    2010-10-01

    Radiation damage to protein crystals exhibits two regimes of temperature-activated behavior between T = 300 and 100 K, with a crossover at the protein glass transition near 200 K. These results have implications for mechanistic studies of proteins and for structure determination when cooling to T = 100 K creates excessive disorder. The temperature-dependence of radiation damage to thaumatin crystals between T = 300 and 100 K is reported. The amount of damage for a given dose decreases sharply as the temperature decreases from 300 to 220 K and then decreases more gradually on further cooling below the protein-solvent glass transition. Two regimes of temperature-activated behavior were observed. At temperatures above ∼200 K the activation energy of 18.0 kJ mol{sup −1} indicates that radiation damage is dominated by diffusive motions in the protein and solvent. At temperatures below ∼200 K the activation energy is only 1.00 kJ mol{sup −1}, which is of the order of the thermal energy. Similar activation energies describe the temperature-dependence of radiation damage to a variety of solvent-free small-molecule organic crystals over the temperature range T = 300–80 K. It is suggested that radiation damage in this regime is vibrationally assisted and that the freezing-out of amino-acid scale vibrations contributes to the very weak temperature-dependence of radiation damage below ∼80 K. Analysis using the radiation-damage model of Blake and Phillips [Blake & Phillips (1962 ▶), Biological Effects of Ionizing Radiation at the Molecular Level, pp. 183–191] indicates that large-scale conformational and molecular motions are frozen out below T = 200 K but become increasingly prevalent and make an increasing contribution to damage at higher temperatures. Possible alternative mechanisms for radiation damage involving the formation of hydrogen-gas bubbles are discussed and discounted. These results have implications for mechanistic studies of proteins and for

  9. Ab initio molecular-dynamics study of pressure-induced glass-to-crystal transitions in the sodium system

    NASA Astrophysics Data System (ADS)

    Aoki, Masaru I.; Tsumuraya, Kazuo

    1997-08-01

    We study pressure-induced glass-to-crystal transitions in the sodium system. We apply an order-N ab initio molecular-dynamics (MD) method to study the transition. We use an isothermal-isobaric condition with an orbital-free density functional. The system contains 128 atoms in a supercell. We simulate the system at temperatures higher and lower than the glass-transition temperature Tg=120 K. At 50 K the pressure enhances the onset of crystallization from the glass. The system crystallizes at pressures greater than 2.75 GPa during which the crystalline atoms appear after the complete annihilation of the icosahedral clusters. At 290 K the system crystallizes at 10-3 GPa, during which the atoms appear before the annihilation of the clusters. The application of 1 GPa at this temperature retards the crystallization which is consistent with experiments on metallic glasses. Crystallization occurs after the clusters annihilate completely which is the same feature as the transitions at 50 K. The existence of the clusters disturbs the crystallization at high pressures irrespective of temperature. The icosahedral clusters are unstable and transform to other clusters at high pressures, although the clusters are elastically stable and the hardest within +/-0.07 GPa at 0 K [Masaru I. Aoki and Kazuo Tsumuraya, J. Chem. Phys. 104, 6719 (1996)]. The MD methods with the empirical pair potential is found to be insufficient to simulate the transition in this system.

  10. Experimental evidence for an absorbing phase transition underlying yielding of a soft glass

    NASA Astrophysics Data System (ADS)

    Nagamanasa, K. Hima; Gokhale, Shreyas; Sood, A. K.; Ganapathy, Rajesh

    2014-03-01

    A characteristic feature of solids ranging from foams to atomic crystals is the existence of a yield point, which marks the threshold stress beyond which a material undergoes plastic deformation. In hard materials, it is well-known that local yield events occur collectively in the form of intermittent avalanches. The avalanche size distributions exhibit power-law scaling indicating the presence of self-organized criticality. These observations led to predictions of a non-equilibrium phase transition at the yield point. By contrast, for soft solids like gels and dense suspensions, no such predictions exist. In the present work, by combining particle scale imaging with bulk rheology, we provide a direct evidence for a non-equilibrium phase transition governing yielding of an archetypal soft solid - a colloidal glass. The order parameter and the relaxation time exponents revealed that yielding is an absorbing phase transition that belongs to the conserved directed percolation universality class. We also identified a growing length scale associated with clusters of particles with high Debye-Waller factor. Our findings highlight the importance of correlations between local yield events and may well stimulate the development of a unified description of yielding of soft solids.

  11. Yielding of glass under shear: A directed percolation transition precedes shear-band formation

    NASA Astrophysics Data System (ADS)

    Shrivastav, Gaurav Prakash; Chaudhuri, Pinaki; Horbach, Jürgen

    2016-10-01

    Under external mechanical loading, glassy materials, ranging from soft matter systems to metallic alloys, often respond via formation of inhomogeneous flow patterns, during yielding. These inhomogeneities can be precursors to catastrophic failure, implying that a better understanding of their underlying mechanisms could lead to the design of smarter materials. Here, extensive molecular dynamics simulations are used to reveal the emergence of heterogeneous dynamics in a binary Lennard-Jones glass, subjected to a constant strain rate. At a critical strain, this system exhibits for all considered strain rates a transition towards the formation of a percolating cluster of mobile regions. We give evidence that this transition belongs to the universality class of directed percolation. Only at low shear rates, the percolating cluster subsequently evolves into a transient (but long-lived) shear band with a diffusive growth of its width. Finally, the steady state with a homogeneous flow pattern is reached. In the steady state, percolation transitions also do occur constantly, albeit over smaller strain intervals, to maintain the stationary plastic flow in the system.

  12. Thermodynamic behaviour of gliadins mixture and the glass-softening transition of its dried state.

    PubMed

    Ferrari, C; Johari, G P

    1997-10-01

    The glass-softening transition of a mixture of gliadins extracted from wheat flour has been studied in its dry state by differential scanning calorimetry (DSC). Further, the rate of removal of its water vapours on its evaporation from a gliadins mixture containing different amounts of water has been investigated, and through this the presence of any exothermic effect that could be attributed to polymerization of gliadins has been examined. The heat absorbed in this evaporation is comparable with the heat of evaporation of pure water measured in a separate experiment in identical conditions. This showed that the gliadins mixture did not polymerize on heating up to 473 K in the presence of moisture. In this respect the behaviour of the gliadins mixture differs remarkably from that of gluten studied before (J Phys Chem 1996:100:19692). The effects of purge gas, helium and argon, on the calorimetric effects during the evaporation of water have been studied. A restudy of gluten shows that helium decreases substantially the endothermic signal in the DSC measurements, and thereby reveals the exothermic effects of polymerization in gluten, but argon does not do so. The structural relaxation time, t, of dry gliadins mixtures at different temperatures has been calculated from an analysis of its glass-softening endotherm. The temperature at which t = 1 ks is 452 K, and the Tg, obtained by the usual method of intersection of the straight lines drawn, is 443 K, 7 K higher than for the polymerized dry gluten, the distribution of relaxation time parameter is 0.25, and increase in the heat capacity in this range is 0.21 J/g K. Physical ageing effects are considerable in the gliadins mixture, which alters the glass-softening endotherm but not the structural relaxation time or its distribution.

  13. How melt stretching affect the brittle-ductile transition temperature of polymer glasses

    NASA Astrophysics Data System (ADS)

    Cheng, Shiwang; Wang, Shi-Qing

    2013-03-01

    Upon increasing temperature a brittle polymer glass can turn ductile. PMMA is a good example. For a while this brittle-ductile transition (BDT) was thought to be determined by the emergence of a secondary relaxation....1-3 On the other hand, it has been known for a long time...4-6 that predeformation in the melt state (e.g., melt stretching) can also make brittle glasses behave in a ductile manner. This transformation has recently received a satisfactory explanation based on a picture of structural hybrid for polymer glasses....7 It appears that BDT is dictated by the relative mechanical characteristics of the primary structure (due to the van der Waals bonds) and the chain network. The present work, based on conventional Instron tensile extension tests and DMA tests, shows that melt stretching does not alter the secondary relaxation behavior of PMMA and PC yet can turn them the brittle PMMA ductile and the ductile PC brittle. Moreover, sufficient melt stretching makes the brittle PS ductile although it does not produce any secondary relaxation process..1. Monnerie, L.; Laupretre, F.; Halary, J. L. Adv. Polym. Sci2005, 187, 35-213. 2. Monnerie, L.; Halary, J. L.; Kausch, H. Adv. Polym. Sci2005, 187, 215-364. 3. Wu, S. J. Appl. Polym. Sci.1992, 46, (4), 619-624. 4. Vincent, P. I. Polymer1960, 1, (0), 425-444. 5. Harris, J. S.; Ward, I. M. J. Mater. Sci.1970, 5, (7), 573-579. 6. Ender, D. H.; Andrews, R. D. J. Appl. Phys.1965, 36, (10), 3057-3062. 7. Zartman, G. D.; Cheng, S.; Li, X.; Lin, F.; Becker, M. L.; Wang, S.-Q. Macromolecules2012, 45, (16), 6719-6732.

  14. A direct test of the correlation between elastic parameters and fragility of ten glass formers and their relationship to elastic models of the glass transition

    NASA Astrophysics Data System (ADS)

    Torchinsky, Darius H.; Johnson, Jeremy A.; Nelson, Keith A.

    2009-02-01

    We present an impulsive stimulated scattering test of the "shoving model" of the glass transition and of the correlation between the fragility index and the ratio of instantaneous elastic moduli of eight supercooled liquids. Samples of triphenyl phosphite, DC704 (tetramethyl tetraphenyl trisiloxane), m-fluoroaniline, Ca(NO3)2ṡ4H2O, diethyl phthalate, propylene carbonate, m-toluidine, phenyl salicylate (salol), 2-benzylphenol, and Santovac 5 (5-phenyl 4-ether), were cooled to their respective glass transition temperatures and the elastic moduli directly measured at the highest accessible shear frequencies. The shear modulus was then measured every 2 K as deeply as permitted into the liquid state for all liquids except propylene carbonate. Our results, in conjunction with dynamical relaxation data for these liquids obtained from the literature, lend credence to the notion that the dynamics of the glass transition are governed by the evolution of the shear modulus but do not suggest a strong correlation between the fragility index and the ratio of the elastic moduli.

  15. Retrogradation of Waxy Rice Starch Gel in the Vicinity of the Glass Transition Temperature

    PubMed Central

    Charoenrein, Sanguansri; Udomrati, Sunsanee

    2013-01-01

    The retrogradation rate of waxy rice starch gel was investigated during storage at temperatures in the vicinity of the glass transition temperature of a maximally concentrated system (Tg′), as it was hypothesized that such temperatures might cause different effects on retrogradation. The Tg′ value of fully gelatinized waxy rice starch gel with 50% water content and the enthalpy of melting retrograded amylopectin in the gels were investigated using differential scanning calorimetry. Starch gels were frozen to −30°C and stored at 4, 0, −3, −5, and −8°C for 5 days. The results indicated that the Tg′ value of gelatinized starch gel annealed at −7°C for 15 min was −3.5°C. Waxy rice starch gels retrograded significantly when stored at 4°C with a decrease in the enthalpy of melting retrograded starch in samples stored for 5 days at −3, −5, and −8°C, respectively, perhaps due to the more rigid glass matrix and less molecular mobility facilitating starch chain recrystallization at temperatures below Tg′. This suggests that retardation of retrogradation of waxy rice starch gel can be achieved at temperature below Tg′. PMID:26904602

  16. Transition from stress-driven to thermally activated stress relaxation in metallic glasses

    NASA Astrophysics Data System (ADS)

    Qiao, J. C.; Wang, Yun-Jiang; Zhao, L. Z.; Dai, L. H.; Crespo, D.; Pelletier, J. M.; Keer, L. M.; Yao, Y.

    2016-09-01

    The short-range ordered but long-range disordered structure of metallic glasses yields strong structural and dynamic heterogeneities. Stress relaxation is a technique to trace the evolution of stress in response to a fixed strain, which reflects the dynamic features phenomenologically described by the Kohlrausch-Williams-Watts (KWW) equation. The KWW equation describes a broad distribution of relaxation times with a small number of empirical parameters, but it does not arise from a particular physically motivated mechanistic picture. Here we report an anomalous two-stage stress relaxation behavior in a Cu46Zr46Al8 metallic glass over a wide temperature range and generalize the findings in other compositions. Thermodynamic analysis identifies two categories of processes: a fast stress-driven event with large activation volume and a slow thermally activated event with small activation volume, which synthetically dominates the stress relaxation dynamics. Discrete analyses rationalize the transition mechanism induced by stress and explain the anomalous variation of the KWW characteristic time with temperature. Atomistic simulations reveal that the stress-driven event involves virtually instantaneous short-range atomic rearrangement, while the thermally activated event is the percolation of the fast event accommodated by the long-range atomic diffusion. The insights may clarify the underlying physical mechanisms behind the phenomenological description and shed light on correlating the hierarchical dynamics and structural heterogeneity of amorphous solids.

  17. The relationship between the glass transition temperature and water vapor absorption by poly(vinylpyrrolidone)

    PubMed

    Oksanen, C A; Zografi, G

    1990-06-01

    Water associated with amorphous solids is known to affect significantly the physical and chemical properties of dosage form ingredients. An analysis of water vapor absorption isotherms of poly(vinylpyrrolidone) measured in this and other laboratories, over the range -40 to 60 degrees C, along with the measurement of the glass transition temperature of poly(vinylpyrrolidone) as a function of water content is reported. It is observed that the amount of water vapor absorbed at a particular relative humidity increases with decreasing temperature, along with a significant change in the shape of the isotherm. It is also shown that at any temperature, along with a significant change in the shape of the isotherm. It is also shown that at any temperature the state of the solid changes from a highly viscous glass to a much less viscous rubber in the region where absorbed water appears to enter into a "solvent-like" state. Further, the apparent "tightly bound" state, observed at low relative humidities, appears to exist when the polymer enters into a very viscous glassy state. It is concluded that the apparent states of water and polymer are interrelated in a dynamic manner and, therefore, that they cannot be uncoupled by simple thermodynamic analyses based only on a water-binding model.

  18. A novel difference between strong liquids and fragile liquids in their dynamics near the glass transition

    NASA Astrophysics Data System (ADS)

    Tokuyama, Michio; Enda, Shohei; Kawamura, Junichi

    2016-01-01

    The systematic method to explore how the dynamics of strong liquids (S) is different from that of fragile liquids (F) near the glass transition is proposed from a unified point of view discussed recently by Tokuyama. The extensive molecular-dynamics simulations are performed on different glass-forming materials. The simulation results for the mean- nth displacement Mn(t) are then analyzed from the unified point of view, where n is an even number. Thus, it is first shown that in each type of liquids there exists a master curve Hn(α) as Mn(t) =RnHn(α) (vth t / R ; D / Rvth) onto which any simulation results collapse at the same value of D / Rvth, where R is a characteristic length such as an interatomic distance, D a long-time self-diffusion coefficient, vth a thermal velocity, and α = F and S. The master curves Hn(F) and Hn(S) are then shown not to coincide with each other in the so-called cage region even at the same value of D / Rvth. Thus, it is emphasized that the dynamics of strong liquids is quite different from that of fragile liquids.

  19. Luminescence properties of rare earth and transition metal ions doped potassium lead borophosphate glass

    NASA Astrophysics Data System (ADS)

    Leong, P. M.; Eeu, T. Y.; Leow, T. Q.; Hussin, R.; Ibrahim, Z.

    2013-05-01

    A series of potassium lead borophosphate glass doped with rare earth and transition metal ions were fabricated using melt-quenching method without annealing process. With the composition of glass 0.15K2O-0.15PbO-0.35B2O3-0.5P2O5 as host doped with 0.01 mole % of neodymium oxide, iron oxide, yttrium oxide, and titanium oxide as activator and different composition were used to investigate the luminescence effect by using Photoluminescence Spectroscopy and UV-Vis (Ultraviolet-Visible) spectrophotometer. By exciting the samples at different wavelength (200-900 nm), the excitation and emission profile were obtained and analyzed to study the energy transfer process. By referring to the spectra obtained, selected samples were also codoped among each other to obtain desired luminescence properties. UV-Visible spectroscopy results revealed the absorption and transmission wavelength of samples for targeted application as a selected band filter. Physical properties such as chemical stability and color of the samples were also recorded to correlate with PL and UV-Vis result. Certain rare earth activated samples displayed slight coloring under the visible wavelength especially Nd2+ ions doped samples displayed slight purplish.

  20. A novel method to measure the glass and melting transitions of pharmaceutical powders.

    PubMed

    Abiad, Mohamad G; Gonzalez, David C; Mert, Behic; Campanella, Osvaldo H; Carvajal, M Teresa

    2010-08-30

    A method to measure thermo-mechanical properties of pharmaceutical and polymeric powders was developed. The measurements are conducted by characterizing the material's response to applied acoustic waves. Measurements were performed using griseofulvin, felodipine and indomethacin as model drugs and polyethylene oxide (MW=200,000, 900,000, 2,000,000Da) as model polymers. The method employed measures the mechanical impedance enabled the calculation of the powder rheological and thermo-mechanical properties. Measurements attained with this new technique are compared with measurements made using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The new method detects the melting and glass transitions events while providing complementary information to that provided by DSC and DMA.

  1. High-dimensional surprises neat the glass and the jamming transitions

    NASA Astrophysics Data System (ADS)

    Charbonneau, Patrick

    2013-03-01

    The glass problem is notoriously hard and controversial. Even at the mean-field level, there is little agreement about how a fluid turns sluggish while exhibiting but unremarkable structural changes. It is clear, however, that the process involves self-caging, which provides an order parameter for the transition. It is also broadly assumed that this cage should have a Gaussian shape in the mean-field limit. Here we show that this ansatz does not hold, and explore its consequences. Non-Gaussian caging, for instance, persists all the way to the jamming limit of infinitely compressed hard spheres, which affects mechanical stability. We thus obtain new scaling relations, and establish clear mileposts for the emergence of a mean-field theory of jamming.

  2. Glass transition of polystyrene (PS) studied by Raman spectroscopic investigation of its phenyl functional groups

    NASA Astrophysics Data System (ADS)

    Bertoldo Menezes, D.; Reyer, A.; Marletta, A.; Musso, M.

    2017-01-01

    In polymeric materials the glass transition (GT) is a well-known and very important relaxation process related to movements of functional groups in the polymeric chain. In this work, we show the potential of Raman spectroscopy for exploring the GT process in the polymer polystyrene. We collected Raman spectra during a step-by-step heating process of the sample, which allowed us to collect signatures of the GT process from peak parameters of specific vibrational modes, and to verify the GT temperature. Results of the latter were in accordance with published values obtained via other methods. We identified the aromatic ring vibrational modes of the phenyl functional groups to be those which, due to steric hindrance, suffer the largest influence during the GT process. This confirms that Raman spectroscopy can be used as a complementary technique to perform GT investigations in polymeric materials due to its sensitivity to small intermolecular changes affecting vibrational properties of relevant functional side groups.

  3. Fast dynamics in poly(vinyl chloride) below the glass transition: self and pair correlation functions

    NASA Astrophysics Data System (ADS)

    Moral, A.; Arbe, A.; Colmenero, J.

    2000-03-01

    In a previous work the incoherent scattering function of poly(vinyl chloride) (PVC) in the microscopic time range was successfully described in the frame of a model which assumes harmonic vibrations coexisting with relaxational contributions controlled by C-C torsional barriers. In the same frame the behaviour of the coherent scattering function well above the glass transition temperature Tg could also be interpreted. In this work, we investigate the applicability of such a model to coherent scattering of PVC below and around Tg. Within the experimental accuracy, the data can be well described starting from the results independently obtained from the study of the incoherent function. This gives additional support to the ideas involved in the proposed model.

  4. Glass transition temperature of PIB, PDMS and PMMA from small-time simulations

    NASA Astrophysics Data System (ADS)

    Duki, Solomon; Tsige, Mesfin; Taylor, Philip

    2009-03-01

    We have applied some new techniques to obtain predictions of the glass transition temperatures Tg of poly(isobutylene), poly(dimethyl-siloxane), and poly(methyl methacrylate) from small-time atomistic molecular dynamics simulations. The different fragilities of these materials are reflected in the results of the simulations. One approach involved measurement of the apparent softening of the ``cage'' in which a monomer is bound, while another involved studying autocorrelation of a convolution of the velocity with a smoothing function in order to detect the frequency of escapes from the ``cage.'' To check the accuracy of the short-time methods, the Tg of the polymers was also found using conventional diffusion simulations in which the rate of increase of the root mean squared displacement of an atom, monomer, or molecule is measured at very long times. The economical short-time simulations yielded results for Tg that were identical to those of the computer-intensive long-time simulations.

  5. Glass and Jamming Transitions: From Exact Results to Finite-Dimensional Descriptions

    NASA Astrophysics Data System (ADS)

    Charbonneau, Patrick; Kurchan, Jorge; Parisi, Giorgio; Urbani, Pierfrancesco; Zamponi, Francesco

    2017-03-01

    Despite decades of work, gaining a first-principles understanding of amorphous materials remains an extremely challenging problem. However, recent theoretical breakthroughs have led to the formulation of an exact solution of a microscopic glass-forming model in the mean-field limit of infinite spatial dimension. Numerical simulations have remarkably confirmed the dimensional robustness of some of the predictions. This review describes these latest advances. More specifically, we consider the dynamical and thermodynamic descriptions of hard spheres around the dynamical, Gardner, and jamming transitions. Comparing mean-field predictions with the finite-dimensional simulations, we identify robust aspects of the theory and uncover its more sensitive features. We conclude with a brief overview of ongoing research.

  6. Coupled effects of substrate adhesion and intermolecular forces on polymer thin film glass-transition behavior.

    PubMed

    Xia, Wenjie; Keten, Sinan

    2013-10-15

    Intermolecular noncovalent forces between polymer chains influence the mobility and glass-transition temperature (Tg), where weaker interchain interactions, all else being the same, typically results in lower bulk polymer Tg. Using molecular dynamics simulations, here we show that this relation can become invalid for supported ultrathin films when the substrate-polymer interaction is extremely strong and the polymer-polymer interactions are much weaker. This contrasting trend is found to be due to a more pronounced substrate-induced appreciation of the film Tg for polymers with weaker intermolecular interactions and low bulk Tg. We show that optimizing this coupling between substrate adhesion and bulk Tg maximizes thin film Tg, paving the way for tuning film properties through interface nanoengineering.

  7. Possible crossover to percolation scenario near superfluid-Bose-glass transition

    NASA Astrophysics Data System (ADS)

    Syromyatnikov, A. V.; Sizanov, A. V.

    2017-10-01

    We discuss magnetically ordered (;superfluid;) phase near quantum transition to Bose-glass phase in a simple modeling system, Heisenberg antiferromagnet in spatial dimension d > 2 in external magnetic field with disorder in exchange coupling constants. Our analytical consideration is based on hydrodynamic description of long-wavelength excitations and it is valid in the entire critical region near the quantum critical point (QCP). We demonstrate that the system behaves in full agreement with predictions by Fisher et al. (Phys. Rev. B 40, 546 (1989)) in close vicinity of QCP. On the other hand, we show that many recent experimental and numerical results obtained in various 3D systems can be described by our formulas using percolation critical exponents. Then, it is a possibility that a percolation critical regime arises in the ordered phase in some 3D systems not very close to QCP.

  8. Organotin piezo- and pyroelectric polymer films. [Synthesis, glass transition, and piezo- and pyroelectric activity

    SciTech Connect

    Liepins, R.; Timmons, M.L.; Morosoff, N.; Surles, J.

    1983-01-01

    The synthesis of a new class of piezo- and pyroelectrically active materials of various co- and terpolymers of tributylin methacrylate (TBTM) and trimethyltin methacrylate (TMTM) is described. A description of sample preparation, poling techniques, and measurement system is given in some detail. Films of the various polymer compositions were evaluated for tin current, glass transition temperature (Tg), crystallinity or ordering of the amorphous phase and piezo- and pytoelectric activity. Experimental results on 25 to 30 mol% TBTM/methyl methacrylate copolymers, which possessed good piezoelectric activity, antifouling properties and paint-formulation characteristics, are discussed in detail. Solvent-induced orientation effects that lead to piezoelectric activity in amorphous, unpoled, polymers are also described.

  9. Heat capacity in the glass transition range modeled on the basis of heterogeneous dynamics.

    PubMed

    Richert, Ranko

    2011-04-14

    A heterogeneous version of the Tool-Narayanaswamy-Moynihan (TNM) model is proposed, in which enthalpy relaxation is heterogeneous in the sense that the overall nonexponential relaxation originates from the superposition of independently and exponentially relaxing domains with individual time constants. Analogous to rate exchange at a constant temperature, there is only a single fictive temperature that controls the rate at which all time constants can change considerably during a temperature scan. The model is shown to be consistent with differential scanning calorimetry (DSC) data taken across the glass transition of polystyrene, propylene carbonate, and glycerol. In contrast to the standard homogeneous TNM model, the heterogeneous counterpart fits DSC up-scans for As(2)Se(3) for cooling rates of 0.31, 2.5, and 20 K∕min with a common set of parameters.

  10. Glass transition and degree of conversion of a light-cured orthodontic composite.

    PubMed

    Sostena, Michela M D S; Nogueira, Renata A; Grandini, Carlos R; Moraes, João Carlos Silos

    2009-01-01

    This study evaluated the glass transition temperature (Tg) and degree of conversion (DC) of a light-cured (Fill Magic) versus a chemically cured (Concise) orthodontic composite. Anelastic relaxation spectroscopy was used for the first time to determine the Tg of a dental composite, while the DC was evaluated by infrared spectroscopy. The light-cured composite specimens were irradiated with a commercial LED light-curing unit using different exposure times (40, 90 and 120 s). Fill Magic presented lower Tg than Concise (35-84 masculineC versus 135 masculineC), but reached a higher DC. The results of this study suggest that Fill Magic has lower Tg than Concise due to its higher organic phase content, and that when this light-cured composite is used to bond orthodontic brackets, a minimum energy density of 7.8 J/cm(2) is necessary to reach adequate conversion level and obtain satisfactory adhesion.

  11. Heat capacity in the glass transition range modeled on the basis of heterogeneous dynamics

    NASA Astrophysics Data System (ADS)

    Richert, Ranko

    2011-04-01

    A heterogeneous version of the Tool-Narayanaswamy-Moynihan (TNM) model is proposed, in which enthalpy relaxation is heterogeneous in the sense that the overall nonexponential relaxation originates from the superposition of independently and exponentially relaxing domains with individual time constants. Analogous to rate exchange at a constant temperature, there is only a single fictive temperature that controls the rate at which all time constants can change considerably during a temperature scan. The model is shown to be consistent with differential scanning calorimetry (DSC) data taken across the glass transition of polystyrene, propylene carbonate, and glycerol. In contrast to the standard homogeneous TNM model, the heterogeneous counterpart fits DSC up-scans for As2Se3 for cooling rates of 0.31, 2.5, and 20 K/min with a common set of parameters.

  12. Relaxation processes and glass transition in confined 1,4-polybutadiene films: A Molecular Dynamics study

    NASA Astrophysics Data System (ADS)

    Paul, Wolfgang; Solar, Mathieu

    We will present results from Molecular Dynamics simulations of a chemically realistic model of 1,4-polybutadiene (PB) chains confined by graphite walls. Relaxation processes in this system are heterogeneous and anisotropic. We will present evidence for a slow additional relaxation process related to chain desorption from the walls. We also study the structural relaxation resolved with respect to the distance from the graphite walls and show the influence of structural changes on the relaxation behavior. The temperature dependence of the dielectric relaxation in layers of different thickness near the walls shows no indication of a shift of Tg as a function of thickness when analyzed with a Vogel-Fulcher fit. We explain this by the importance of intramolecular dihedral barriers for the glass transition in PB which dominate over the density changes next to a wall except for a 1 nm thick layer directly at the wall.

  13. Critical test of the mode-coupling theory of the glass transition.

    PubMed

    Berthier, Ludovic; Tarjus, Gilles

    2010-09-01

    In its common implementation, the mode-coupling theory of the glass transition predicts the time evolution of the intermediate scattering functions in viscous liquids on the sole basis of the structural information encoded in two-point density correlations. We provide a critical test of this property and show that the theory fails to describe the strong differences of dynamical behavior seen in two model liquids characterized by very similar pair-correlation functions. Because we use "exact" static information provided by numerical simulations, our results are a direct indication that some important information about the dynamics of viscous liquids is not captured by pair correlations and is thus not described by the mode-coupling theory, even in the temperature regime where the theory is usually applied.

  14. Two Simultaneous Mechanisms Causing Glass Transition Temperature Reductions in High Molecular Weight Freestanding Polymer Films as Measured by Transmission Ellipsometry

    NASA Astrophysics Data System (ADS)

    Pye, Justin E.; Roth, Connie B.

    2011-12-01

    We study the glass transition in confined polymer films and present the first experimental evidence indicating that two separate mechanisms can act simultaneously on the film to propagate enhanced mobility from the free surface into the material. Using transmission ellipsometry, we have measured the thermal expansion of ultrathin, high molecular-weight (MW), freestanding polystyrene films over an extended temperature range. For two different MWs, we observed two distinct reduced glass transition temperatures (Tg’s), separated by up to 60 K, within single films with thicknesses h less than 70 nm. The lower transition follows the expected MW dependent, linear Tg(h) behavior previously seen in high MW freestanding films. We also observe a much stronger upper transition with no MW dependence that exhibits the same Tg(h) dependence as supported and low MW freestanding polymer films.

  15. Structural evolution during fragile-to-strong transition in CuZr(Al) glass-forming liquids.

    PubMed

    Zhou, Chao; Hu, Lina; Sun, Qijing; Zheng, Haijiao; Zhang, Chunzhi; Yue, Yuanzheng

    2015-02-14

    In the present work, we show experimental evidence for the dynamic fragile-to-strong (F-S) transition in a series of CuZr(Al) glass-forming liquids (GFLs). A detailed analysis of the dynamics of 98 glass-forming liquids indicates that the F-S transition occurs around Tf-s ≈ 1.36 Tg. Using the hyperquenching-annealing-x-ray scattering approach, we have observed a three-stage evolution pattern of medium-range ordering (MRO) structures during the F-S transition, indicating a dramatic change of the MRO clusters around Tf-s upon cooling. The F-S transition in CuZr(Al) GFLs is attributed to the competition among the MRO clusters composed of different locally ordering configurations. A phenomenological scenario has been proposed to explain the structural evolution from the fragile to the strong phase in the CuZr(Al) GFLs.

  16. Universal behavior of the osmotically compressed cell and its analogy to the colloidal glass transition.

    PubMed

    Zhou, E H; Trepat, X; Park, C Y; Lenormand, G; Oliver, M N; Mijailovich, S M; Hardin, C; Weitz, D A; Butler, J P; Fredberg, J J

    2009-06-30

    Mechanical robustness of the cell under different modes of stress and deformation is essential to its survival and function. Under tension, mechanical rigidity is provided by the cytoskeletal network; with increasing stress, this network stiffens, providing increased resistance to deformation. However, a cell must also resist compression, which will inevitably occur whenever cell volume is decreased during such biologically important processes as anhydrobiosis and apoptosis. Under compression, individual filaments can buckle, thereby reducing the stiffness and weakening the cytoskeletal network. However, the intracellular space is crowded with macromolecules and organelles that can resist compression. A simple picture describing their behavior is that of colloidal particles; colloids exhibit a sharp increase in viscosity with increasing volume fraction, ultimately undergoing a glass transition and becoming a solid. We investigate the consequences of these 2 competing effects and show that as a cell is compressed by hyperosmotic stress it becomes progressively more rigid. Although this stiffening behavior depends somewhat on cell type, starting conditions, molecular motors, and cytoskeletal contributions, its dependence on solid volume fraction is exponential in every instance. This universal behavior suggests that compression-induced weakening of the network is overwhelmed by crowding-induced stiffening of the cytoplasm. We also show that compression dramatically slows intracellular relaxation processes. The increase in stiffness, combined with the slowing of relaxation processes, is reminiscent of a glass transition of colloidal suspensions, but only when comprised of deformable particles. Our work provides a means to probe the physical nature of the cytoplasm under compression, and leads to results that are universal across cell type.

  17. Modeling the glass transition of amorphous networks for shape-memory behavior

    NASA Astrophysics Data System (ADS)

    Xiao, Rui; Choi, Jinwoo; Lakhera, Nishant; Yakacki, Christopher M.; Frick, Carl P.; Nguyen, Thao D.

    2013-07-01

    In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks. The model used multiple discrete relaxation processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow. A non-equilibrium thermodynamic framework based on the fictive temperature was introduced to demonstrate the thermodynamic consistency of the constitutive theory. Experimental and theoretical methods were developed to determine the parameters describing the distribution of stress and structural relaxation times and the dependence of the relaxation times on temperature, structure, and driving stress. The model was applied to study the effects of deformation temperatures and physical aging on the shape-memory behavior of amorphous networks. The model was able to reproduce important features of the partially constrained recovery response observed in experiments. Specifically, the model demonstrated a strain-recovery overshoot for cases programmed below Tg and subjected to a constant mechanical load. This phenomenon was not observed for materials programmed above Tg. Physical aging, in which the material was annealed for an extended period of time below Tg, shifted the activation of strain recovery to higher temperatures and increased significantly the initial recovery rate. For fixed-strain recovery, the model showed a larger overshoot in the stress response for cases programmed below Tg, which was consistent with previous experimental observations. Altogether, this work demonstrates how an understanding of the time-dependent behaviors of the glass transition can be used to tailor the temperature and deformation history of the shape-memory programming process to achieve more complex shape recovery pathways, faster recovery responses, and larger activation stresses.

  18. Glass transition of partially crystallized gelatin-water mixtures studied by broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Sasaki, Kaito; Kita, Rio; Shinyashiki, Naoki; Yagihara, Shin

    2014-03-01

    The glass transition of partially crystallized gelatin-water mixtures was investigated for gelatin concentrations of 40 and 20 wt. % by broadband dielectric spectroscopy (BDS) in wide frequency (10 mHz-50 GHz) and temperature (113-298 K) ranges. Three dielectric relaxation processes were clearly observed. The origin of each relaxation process was the same as that observed for partially crystallized bovine serum albumin (BSA)-water mixtures [N. Shinyashiki et al., J. Phys. Chem. B 113, 14448 (2009)]. The relaxation process at the highest frequency is originated from uncrystallized water (UCW) in the hydration shell of gelatin. Its relaxation time is almost the same as that of water in uncrystallized system; water in various binary aqueous mixtures and confined water in nanoscale region. The relaxation process at the intermediate frequency is originated from ice, and its relaxation time and strength were similar to those for the relaxation of pure ice, particularly above 240 K. The glass transition temperature Tg, is defined by BDS measurement as the temperature at which dielectric relaxation time τ, is 100-1000 s. The relaxation process at the lowest frequency, Tg is approximately 200 K, is originated from the cooperative motion of water and gelatin. This relaxation is strong and has a similar relaxation strength to that of hydrated BSA. At Tg for the relaxation process involving the cooperative motion of gelatin and water, the temperature dependence of the relaxation process of UCW crosses over from Vogel-Fulcher behavior to Arrhenius behavior with decreasing temperature. A characteristic property of the gelatin-water mixture is a change in the temperature dependence of the relaxation time of the relaxation processes of hydrated gelatin at approximately 260 K.

  19. Glass transition in thaumatin crystals revealed through temperature-dependent radiation-sensitivity measurements.

    PubMed

    Warkentin, Matthew; Thorne, Robert E

    2010-10-01

    The temperature-dependence of radiation damage to thaumatin crystals between T = 300 and 100 K is reported. The amount of damage for a given dose decreases sharply as the temperature decreases from 300 to 220 K and then decreases more gradually on further cooling below the protein-solvent glass transition. Two regimes of temperature-activated behavior were observed. At temperatures above ∼200 K the activation energy of 18.0 kJ mol(-1) indicates that radiation damage is dominated by diffusive motions in the protein and solvent. At temperatures below ∼200 K the activation energy is only 1.00 kJ mol(-1), which is of the order of the thermal energy. Similar activation energies describe the temperature-dependence of radiation damage to a variety of solvent-free small-molecule organic crystals over the temperature range T = 300-80 K. It is suggested that radiation damage in this regime is vibrationally assisted and that the freezing-out of amino-acid scale vibrations contributes to the very weak temperature-dependence of radiation damage below ∼80 K. Analysis using the radiation-damage model of Blake and Phillips [Blake & Phillips (1962), Biological Effects of Ionizing Radiation at the Molecular Level, pp. 183-191] indicates that large-scale conformational and molecular motions are frozen out below T = 200 K but become increasingly prevalent and make an increasing contribution to damage at higher temperatures. Possible alternative mechanisms for radiation damage involving the formation of hydrogen-gas bubbles are discussed and discounted. These results have implications for mechanistic studies of proteins and for studies of the protein glass transition. They also suggest that data collection at T ≃ 220 K may provide a viable alternative for structure determination when cooling-induced disorder at T = 100 is excessive.

  20. Glass transition measurements in mixed organic and organic/inorganic aerosol particles

    NASA Astrophysics Data System (ADS)

    Dette, Hans Peter; Qi, Mian; Schröder, David; Godt, Adelheid; Koop, Thomas

    2014-05-01

    The recent proposal of a semi-solid or glassy state of secondary organic aerosol (SOA) particles has sparked intense research in that area. In particular, potential effects of a glassy aerosol state such as incomplete gas-to-particle partitioning of semi-volatile organics, inhibited chemical reactions and water uptake, and the potential to act as heterogeneous ice nuclei have been identified so far. Many of these studies use well-studied proxies for oxidized organics such as sugars or other polyols. There are, however, few measurements on compounds that do exist in atmospheric aerosol particles. Here, we have performed studies on the phase state of organics that actually occur in natural SOA particles arising from the oxidation of alpha-pinene emitted in boreal forests. We have investigated the two marker compounds pinonic acid and 3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA) and their mixtures. 3-MBCTA was synthesized from methyl isobutyrate and dimethyl maleate in two steps. In order to transfer these substances into a glassy state we have developed a novel aerosol spray drying technique. Dilute solutions of the relevant organics are atomized into aerosol particles which are dried subsequently by diffusion drying. The dried aerosol particles are then recollected in an impactor and studied by means of differential scanning calorimetry (DSC), which provides unambiguous information on the aerosols' phase state, i.e. whether the particles are crystalline or glassy. In the latter case DSC is used to determine the glass transition temperature Tg of the investigated samples. Using the above setup we were able to determine Tg of various mixtures of organic aerosol compounds as a function of their dry mass fraction, thus allowing to infer a relation between Tg and the O:C ratio of the aerosols. Moreover, we also studied the glass transition behavior of mixed organic/inorganic aerosol particles, including the effects of liquid-liquid phase separation upon drying.