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Sample records for glass transition region

  1. 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).

  2. 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. PMID:24101518

  3. A review of the slow relaxation processes in the glass-rubber transition region of amorphous polymers

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; He, Xianru; Huang, Guangsu

    2015-09-01

    This article is a review that introduces several articles about slow relaxation processes, also known as slower segmental dynamics. According to the literature, the coupling effect and free volume holes are two important elements for slower micro-dynamics. In addition, the slower processes of many-body systems (blend and diluted systems) are summarised. A good numerical method for detecting multiple modes in the glass-rubber transition region is introduced.

  4. Dielectric determination of the glass transition temperature (T sub g)

    NASA Technical Reports Server (NTRS)

    Ries, Heidi R.

    1990-01-01

    The objective is to determine the glass transition temperature of a polymer using a dielectric dissipation technique. A peak in the dissipation factor versus temperature curve is expected near the glass transition temperature T sub g. It should be noted that the glass transition is gradual rather than abrupt, so that the glass transition temperature T sub g is not clearly identifiable. In this case, the glass transition temperature is defined to be the temperature at the intersection point of the tangent lines to the dissipation factor versus temperature curve above and below the transition region, as illustrated.

  5. Modification of the mechanical behavior in the glass transition region of poly(lactic acid) (PLA) through catalyzed reactive extrusion with poly(carbonate) (PC)

    NASA Astrophysics Data System (ADS)

    Phuong, Vu Thanh; Coltelli, Maria-Beatrice; Anguillesi, Irene; Cinelli, Patrizia; Lazzeri, Andrea

    2014-05-01

    In order to improve the thermal stability of PLA based materials the strategy of blending it with poly(carbonate) of bisphenol A (PC), having a higher glass transition temperature, was followed and PLA/PC blends with different compositions, obtained also in the presence of an interchange reaction catalyst, Tetrabutylammonium tetraphenylborate (TBATPB) and triacetin were prepared by melt extrusion. The dynamical mechanical characterization showed an interesting change of the storage modulus behavior in the PLA glass transition region, evident exclusively in the catalyzed blends. In particular, a new peak in the Tanδ trend at a temperature in between the one of PLA and the one of PC was observed only in the blends obtained in the presence of triacetin and TBATPB. The height and maximum temperature of the peak was different after the annealing of samples at 80°C. The data, showing an interesting improvement of thermal stability above the PLA glass transition, were explained keeping into account the formation of PLA-PC copolymer during the reactive extrusion. Furthermore, the glass transition temperature of the copolymer as a function of composition was studied and the obtained trend was discussed by comparing with literature models developed for copolymers.

  6. Modeling the "glass" transition in proteins.

    PubMed

    Sitnitsky, A E

    2002-02-01

    A model of a protein as a disordered system of identical spherical particles (which imitate protein side chains) interacting with each other via a repulsive soft sphere potential U(r) infinity r(-beta) is constructed. The particles undergo the conformational motion (CM) within their own harmonic conformational potentials around some mean equilibrium positions ascribed by the tertiary structure of the protein. A first principles calculation of the positional correlation functions for the CM is carried out. The general analysis is exemplified by the case in which the mean equilibrium positions of the particles form a cubic tightly-packed (face- centered) lattice (each particle has 12 nearest neighbors) with the step b(hydr) =6.6 A (the average distance between the centers of mass of hydrated protein subunits). The model yields dramatic slowing down of the relaxation with the decrease of temperature followed by a sharp glass transition at some crossover temperature T(c) < 200 K. At the transition the liquid-like dynamic behavior (the correlation functions tend to zero with time) is altered by the glass-like one (the correlation functions tend with time to some non-zero limit). In the liquid-like region above the crossover temperature the relaxation exhibits distinct alpha-process following the beta-one. The glass transition results from the interaction of the particles. Thus the model suggests that namely direct interactions of the fragments of protein structure rather than protein-solvent interactions are the origin of the phenomenon of the glass transition. The known increase of T(c) up to 300 K at dehydration of the protein is attributed to the known concomitant compression of the globule upon drying by about 4-6% so that positions of individual atoms displace by about 0.6 A (modeled by the decrease of the step of the lattice b by 0.6 A so that b(dehydr)=6 A). The model suggests that the solvent influences the phenomenon of the glass transition indirectly

  7. Glass transition and stable glass formation of tetrachloromethane

    NASA Astrophysics Data System (ADS)

    Chua, Y. Z.; Tylinski, M.; Tatsumi, S.; Ediger, M. D.; Schick, C.

    2016-06-01

    Physical vapor deposition (PVD) has been used to prepare organic glasses with very high kinetic stability and it has been suggested that molecular anisotropy is a prerequisite for stable glass formation. Here we use PVD to prepare glasses of tetrachloromethane, a simple organic molecule with a nearly isotropic molecular structure. In situ AC nanocalorimetry was used to characterize the vapor-deposited glasses. Glasses of high kinetic stability were produced by deposition near 0.8 Tg. The isothermal transformation of the vapor-deposited glasses into the supercooled liquid state gave further evidence that tetrachloromethane forms glasses with high kinetic stability, with the transformation time exceeding the structural relaxation time of the supercooled liquid by a factor of 103. The glass transition temperature of liquid-cooled tetrachloromethane is determined as Tg ≈ 78 K, which is different from previously reported values. The frequency dependence of the glass transition was also determined and the fragility was estimated as m ≈ 118. The successful formation of PVD glasses of tetrachloromethane which have high kinetic stability argues that molecular asymmetry is not a prerequisite for stable glass formation.

  8. Electron anions and the glass transition temperature.

    PubMed

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

    2016-09-01

    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

  9. Glass/Jamming Transition in Colloidal Aggregation

    NASA Technical Reports Server (NTRS)

    Segre, Philip N.; Prasad, Vikram; Weitz, David A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    We have studied colloidal aggregation in a model colloid plus polymer system with short-range attractive interactions. By varying the colloid concentration and the strength of the attraction, we explored regions where the equilibrium phase is expected to consist of colloidal crystallites in coexistance with colloidal gas (i.e. monomers). This occurs for moderate values of the potential depth, U approximately equal to 2-5 kT. Crystallization was not always observed. Rather, over an extended sub-region two new metastable phases appear, one fluid-like and one solid-like. These were examined in detail with light scattering and microscopy techniques. Both phases consist of a near uniform distribution of small irregular shaped clusters of colloidal particles. The dynamical and structural characteristics of the ergodic-nonergodic transition between the two phases share much in common with the colloidal hard sphere glass transition.

  10. Modeling the transition region

    NASA Technical Reports Server (NTRS)

    Singer, Bart A.

    1993-01-01

    The current status of transition-region models is reviewed in this report. To understand modeling problems, various flow features that influence the transition process are discussed first. Then an overview of the different approaches to transition-region modeling is given. This is followed by a detailed discussion of turbulence models and the specific modifications that are needed to predict flows undergoing laminar-turbulent transition. Methods for determining the usefulness of the models are presented, and an outlook for the future of transition-region modeling is suggested.

  11. Calorimetric Study of Kinetic Glass Transition in Metallic Glasses

    SciTech Connect

    Hiki, Y.; Takahashi, H.

    2008-02-21

    Differential scanning calorimetry (DSC) experiments were carried out for a bulk metallic glass (BMG), Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10.0}Be{sub 22.5}, below and above the glass transition temperature T{sub g}. The T{sub g} values were determined from the DSC curves. A wide range of heating rate, q = dT/dt = 0.1-100 K/min, was adopted for the experiment, and the q dependence of the apparent T{sub g} was investigated. As q was decreased, the value of T{sub g} decreased rapidly, then more slowly, and seemed to approach a constant value at low q. The experimental result of this kinetic glass transition phenomenon was analyzed on the basis of the relaxation process occurring in the transition temperature range.

  12. 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.

  13. Bulk and interfacial glass transitions of water.

    PubMed

    Bhattacharya, Deepanjan; Payne, Candace N; Sadtchenko, Vlad

    2011-06-16

    Fast scanning calorimetry (FSC) was employed to investigate glass softening dynamics in bulk-like and ultrathin glassy water films. Bulk-like water samples were prepared by vapor-deposition on the surface of a tungsten filament near 140 K where vapor-deposition results in low enthalpy glassy water films. The vapor-deposition approach was also used to grow multiple nanoscale (approximately 50 nm thick) water films alternated with benzene and methanoic films of similar dimensions. When heated from cryogenic temperatures, the ultrathin water films underwent a well manifested glass softening transition at temperatures 20 K below the onset of crystallization. However, no such transition was observed in bulk-like samples prior to their crystallization. These results indicate that thin-film water demonstrates glass softening dynamics that are dramatically distinct from those of the bulk phase. We attribute these differences to water's interfacial glass transition, which occurs at temperatures tens of degrees lower than that in the bulk. Implications of these findings for past studies of glass softening dynamics in various glassy water samples are discussed. PMID:21401034

  14. 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.

  15. Water’s second glass transition

    PubMed Central

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

    2013-01-01

    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. PMID:24101518

  16. 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.

  17. 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.

  18. 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.

  19. LAMPF transition region

    SciTech Connect

    Sander, O.R.

    1982-06-01

    After describing the transition region between the LAMPF drift-tube linac and side-coupled linac, we discuss the function of the region, its present shortcomings, and the need for a redesign. Then we present the new design, its advantages, and its expected performance. Included are detailed results of beam-dynamics studies giving the ranges of input- and output-beam shapes that can be successfully matched in the new transition region. To improve the present operation of the two linacs, we suggest small changes that will allow us to easily match the beam between the two linacs. Finally we describe the methods used in our beam-dynamic studies so that effects of future improvements to the new design can be examined.

  20. 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,

  1. Unreachable glass transition in dilute dipolar magnet.

    PubMed

    Biltmo, A; Henelius, P

    2012-01-01

    In magnetic systems the combined effects of disorder and frustration may cause the moments to freeze into a disordered state at a spin-glass transition. Recent experiments have shown that the rare earth compound LiHo(0.045)Y(0.955)F(4) freezes, but that the transition is unreachable because of dynamics that are 10(7) times slower than in ordinary spin-glass materials. This conclusion refutes earlier investigations reporting a speed-up of the dynamics into an exotic anti-glass phase caused by entanglement of quantum dipoles. Here we present a theory, backed by numerical simulations, which describes the material in terms of classical dipoles governed by Glauber dynamics. The dipoles freeze and we find that the ultra-slow dynamics are caused by rare, strongly ordered clusters, which give rise to a previously predicted, but hitherto unobserved, Griffths phase between the paramagnetic and spin-glass phases. In addition, the hyperfine interaction creates a high energy barrier to flipping the electronic spin, resulting in a clear signature in the dynamic correlation function.

  2. Unreachable glass transition in dilute dipolar magnet

    NASA Astrophysics Data System (ADS)

    Biltmo, A.; Henelius, P.

    2012-05-01

    In magnetic systems the combined effects of disorder and frustration may cause the moments to freeze into a disordered state at a spin-glass transition. Recent experiments have shown that the rare earth compound LiHo0.045Y0.955F4 freezes, but that the transition is unreachable because of dynamics that are 107 times slower than in ordinary spin-glass materials. This conclusion refutes earlier investigations reporting a speed-up of the dynamics into an exotic anti-glass phase caused by entanglement of quantum dipoles. Here we present a theory, backed by numerical simulations, which describes the material in terms of classical dipoles governed by Glauber dynamics. The dipoles freeze and we find that the ultra-slow dynamics are caused by rare, strongly ordered clusters, which give rise to a previously predicted, but hitherto unobserved, Griffths phase between the paramagnetic and spin-glass phases. In addition, the hyperfine interaction creates a high energy barrier to flipping the electronic spin, resulting in a clear signature in the dynamic correlation function.

  3. Dynamic glass transition in two dimensions.

    PubMed

    Bayer, M; Brader, J M; Ebert, F; Fuchs, M; Lange, E; Maret, G; Schilling, R; Sperl, M; Wittmer, J P

    2007-07-01

    The question of the existence of a structural glass transition in two dimensions is studied using mode coupling theory (MCT). We determine the explicit d dependence of the memory functional of mode coupling for one-component systems. Applied to two dimensions we solve the MCT equations numerically for monodisperse hard disks. A dynamic glass transition is found at a critical packing fraction phi(c)d=2 approximately equal 0.697 which is above phi(c)d=3 approximately equal 0.516 by about 35%. Phi(c)d scales approximately with phi(rcp)d, the value for random close packing, at least for d=2, 3. Quantities characterizing the local, cooperative "cage motion" do not differ much for d=2 and d=3, and we, e.g., find the Lindemann criterion for the localization length at the glass transition. The final relaxation obeys the superposition principle, collapsing remarkably well onto a Kohlrausch law. The d=2 MCT results are in qualitative agreement with existing results from Monte Carlo and molecular dynamics simulations. The mean-squared displacements measured experimentally for a quasi-two-dimensional binary system of dipolar hard spheres can be described satisfactorily by MCT for monodisperse hard disks over four decades in time provided the experimental control parameter Gamma (which measures the strength of dipolar interactions) and the packing fraction phi are properly related to each other.

  4. Glass transition and density fluctuations in the fragile glass former orthoterphenyl

    SciTech Connect

    Monaco, G.; Fioretto, D.; Comez, L.; Ruocco, G.

    2001-06-01

    High-resolution Brillouin light scattering is used to measure the dynamic structure factor of the fragile glass former orthoterphenyl (OTP) in a wide temperature range around the glass transition region and up to the boiling point. The whole set of spectra is described in terms of a phenomenological generalized hydrodynamic model. In the supercooled phase, we show the contemporary existence of the structural process, whose main features come out to be consistent with the results obtained with other spectroscopies, and of a secondary, activated process, which occurs on the 10{sup {minus}11} s time scale and has a low activation energy (E{sub a}{sup f}=0.28 kcal/mol). This latter process, which is also present in the glassy phase and seems to be insensitive to the glass transition, is attributed to the coupling between the density modes and intramolecular degrees of freedom. In the normal liquid phase, the two processes merge together, and the resulting characteristic time is no longer consistent with those derived with other spectroscopies. The analysis points to the conclusion that, for what concerns the long-wavelength density fluctuations in fragile glass formers such as OTP, the universal dynamical features related to the glass transition come out clearly only in the supercooled phase and at frequencies lower than {approximately}10{sup 6} Hz.

  5. 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.

  6. 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.

  7. Scaling and universality in glass transition.

    PubMed

    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 〈q(2)(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

  8. Scaling and universality in glass transition

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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 and the dynamical susceptibility  - 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.

  9. 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

  10. 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.

  11. 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.

  12. Instantaneous Normal Modes and the Protein Glass Transition

    PubMed Central

    Schulz, Roland; Krishnan, Marimuthu; Daidone, Isabella; Smith, Jeremy C.

    2009-01-01

    Abstract 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. PMID:19167298

  13. 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.

  14. Ionic conductivity and glass transition of phosphoric acids

    SciTech Connect

    Wang, Yangyang; Lane, Nathan A; Sun, Che-Nan; Fan, Fei; Zawodzinski, Thomas; Sokolov, Alexei P

    2013-01-01

    Here we report the low-temperature dielectric and viscoelastic properties of phosphoric acids in the range of H2O:P2O5 1.5 5. Both dielectric and viscosity measurements allow us to determine the glass-transition temperatures of phosphoric acids. The obtained glass-transition temperatures are in good agreement with previous differential scanning calorimetric measurements. Moreover, our analysis reveals moderate decoupling of ionic conductivity from structural relaxation in the vicinity of the glass transition.

  15. Ionic Ckonductivity and Glass Transition of Phosphoric Acids

    SciTech Connect

    Wang, Yangyang; Lane, Nathan A; Sun, Che-Nan; Fan, Fei; Zawodzinski, Thomas; Sokolov, Alexei P

    2013-01-01

    Here we report the low-temperature dielectric and viscoelastic properties of phosphoric acids in the range of H2O:P2O5 1.5 5. Both dielectric and viscosity measurements allow us to determine the glass-transition temperatures of phosphoric acids. The obtained glass-transition temperatures are in good agreement with previous differential scanning calorimetric measurements. Moreover, our analysis reveals moderate decoupling of ionic conductivity from structural relaxation in the vicinity of the glass transition.

  16. The glass and jamming transitions of soft polyelectrolyte microgel suspensions.

    PubMed

    Pellet, Charlotte; Cloitre, Michel

    2016-04-20

    We explore the influence of particle softness on the state diagram of well characterized polyelectrolyte microgel suspensions using dynamic light scattering and rheology. Upon increasing the polymer concentration, we cross successively the well defined glass and jamming transitions which delimit four different states: dilute colloidal suspension, entropic glass, jammed glass, and dense glass. Each state has a specific dynamical fingerprint dictated by two key ingredients related to particle softness: elastic contact interactions, and osmotic or steric deswelling. Soft interactions control yielding and flow of the jammed glasses. The shrinkage of the microgels makes the glass transition look smoother than in hard sphere suspensions. We quantify the relationship between the polymer concentration and the volume fraction, and show that the glass transition behaviour of soft microgels can be mapped to that of hard sphere glasses once the volume fraction is used as the control parameter. PMID:26984383

  17. 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.

  18. 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.

  19. Reconstruction on Trees and Spin Glass Transition

    NASA Astrophysics Data System (ADS)

    Mézard, Marc; Montanari, Andrea

    2006-09-01

    Consider an information source generating a symbol at the root of a tree network whose links correspond to noisy communication channels, and broadcasting it through the network. We study the problem of reconstructing the transmitted symbol from the information received at the leaves. In the large system limit, reconstruction is possible when the channel noise is smaller than a threshold. We show that this threshold coincides with the dynamical (replica symmetry breaking) glass transition for an associated statistical physics problem. Motivated by this correspondence, we derive a variational principle which implies new rigorous bounds on the reconstruction threshold. Finally, we apply a standard numerical procedure used in statistical physics, to predict the reconstruction thresholds in various channels. In particular, we prove a bound on the reconstruction problem for the antiferromagnetic "Potts" channels, which implies, in the noiseless limit, new results on random proper colorings of infinite regular trees. This relation to the reconstruction problem also offers interesting perspective for putting on a clean mathematical basis the theory of glasses on random graphs.

  20. 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

  1. Calorimetric glass transition explained by hierarchical dynamic facilitation

    PubMed Central

    Keys, Aaron S.; Garrahan, Juan P.; Chandler, David

    2013-01-01

    The glass transition refers to the nonequilibrium process by which an equilibrium liquid is transformed to a nonequilibrium disordered solid, or vice versa. Associated response functions, such as heat capacities, are markedly different on cooling than on heating, and the response to melting a glass depends markedly on the cooling protocol by which the glass was formed. This paper shows how this irreversible behavior can be interpreted quantitatively in terms of an East-model picture of localized excitations (or soft spots) in which molecules can move with a specific direction, and from which excitations with the same directionality of motion can appear or disappear in adjacent regions. As a result of these facilitated dynamics, excitations become correlated in a hierarchical fashion. These correlations are manifested in the dynamic heterogeneity of the supercooled liquid phase. Although equilibrium thermodynamics is virtually featureless, a nonequilibrium glass phase emerges when the model is driven out of equilibrium with a finite cooling rate. The correlation length of this emergent phase is large and increases with decreasing cooling rate. A spatially and temporally resolved fictive temperature encodes memory of its preparation. Parameters characterizing the model can be determined from reversible transport data, and with these parameters, predictions of the model agree well with irreversible differential scanning calorimetry.

  2. 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

  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. 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

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

    PubMed Central

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

    2015-01-01

    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. PMID:26657017

  6. 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)

  7. 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

  8. Spontaneous strain glass to martensite transition in ferromagnetic Ni-Co-Mn-Ga strain glass

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Huang, Chonghui; Wu, Haijun; Gao, Jinghui; Yang, Sen; Wang, Dong; Ding, Xiangdong; Song, Xiaoping; Ren, Xiaobing

    2013-04-01

    We report that a spontaneous strain glass to martensite (STG-M) transition occurs in a Ni45Co10Mn20Ga25 ferromagnetic strain glass. The signatures of the spontaneous STG-M transition of Ni45Co10Mn20Ga25 ferromagnetic strain glass are stronger than those of Ti50Ni44.5Fe5.5 strain glass reported previously. Such a difference is attributed to that the martensitic terminal of the former has larger elastic anisotropy than that of the later. The spontaneous STG-M transition in this ferromagnetic strain glass is due to that the delicate competition between the kinetic limitation and the martensitic thermodynamic driving force changes with temperature.

  9. 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

  10. 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.

  11. 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.

  12. 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.

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

    PubMed

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

    2015-01-01

    The physical modification of glass transition temperature (T(g)) 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 T(g) 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 T(g)s have become available only recently. PMID:25666949

  14. Glass transition and mixing thermodynamics of a binary eutectic system.

    PubMed

    Tu, Wenkang; Chen, Zeming; Gao, Yanqin; Li, Zijing; Zhang, Yaqi; Liu, Riping; Tian, Yongjun; Wang, Li-Min

    2014-02-28

    A quantitative evaluation of the contribution of mixing thermodynamics to glass transition is performed for a binary eutectic benzil and m-nitroaniline system. The microcalorimetric measurements of the enthalpy of mixing give small and positive values, typically ~200 J mol(-1) for the equimolar mixture. The composition dependence of the glass transition temperature, T(g), is found to show a large and negative deviation from the ideal mixing rule. The Gordon-Taylor and Couchman-Karasz models are subsequently applied to interpret the T(g) behavior, however, only a small fraction of the deviation is explained. The analyses of the experimental results manifest quantitatively the importance of the mixing thermodynamics in the glass transition in miscible systems.

  15. A universal reduced glass transition temperature for liquids

    NASA Technical Reports Server (NTRS)

    Fedors, R. F.

    1979-01-01

    Data on the dependence of the glass transition temperature on the molecular structure for low-molecular-weight liquids are analyzed in order to determine whether Boyer's reduced glass transition temperature (1952) is a universal constant as proposed. It is shown that the Boyer ratio varies widely depending on the chemical nature of the molecule. It is pointed out that a characteristic temperature ratio, defined by the ratio of the sum of the melting temperature and the boiling temperature to the sum of the glass transition temperature and the boiling temperature, is a universal constant independent of the molecular structure of the liquid. The average value of the ratio obtained from data for 65 liquids is 1.15.

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

    PubMed

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

    2016-06-01

    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.

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

    PubMed

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

    2016-06-01

    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. PMID:27176640

  18. Liquid-to-glass transition of tetrahydrofuran and 2-methyltetrahydrofuran

    NASA Astrophysics Data System (ADS)

    Tan, Rong-Ri; Shen, Xin; Hu, Lin; Zhang, Feng-Shou

    2012-08-01

    Both tetrahydrofuran (THF) and 2-methyltetrahydrofuran (MTHF) are studied systematically at desired temperatures using molecular dynamics simulations. The results show that the calculated densities are well consistent with experiment. Their glass transition temperatures are obtained: 115 K ~ 130 K for THF and 131 K ~ 142 K for MTHF. The calculated results from the dipolar orientational time correlation functions indicate that the “long time" behavior is often associated with a glass transition. From the radial and spatial distributions, we also find that the methyl has a direct impact on the structural symmetry of molecules, which leads to the differences of physical properties between THF and MTHF.

  19. Glass Transition near Polymeric Surfaces Studied by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Zhang, Junjie; Zhang, Renwu; Li, Ying; Huang, Chia-Ming; Wu, Yichu; Mallon, Peter; Suzuki, R.; Huang, Y. Y.; Sandreczki, T. C.; Peng, Q.; Richardson, J. R.; Ohdaira, T.; Jean, Y. C.

    2001-03-01

    Glass transition as a function of depth in polymers can be studied by using positron annihilation spectroscopy and by controlling positron incident energy. Early positron studies showed that glass transition temperatures could be largely reduced near the surface in films prepared by slovent evaporation method.1 This paper will report more recent results of S parameters and positron lifetimes in polymeric films after different thermal and chemical treatments. 1. Y.C. Jean at al, Phys. Rev. B, 56, R8459 (1997). * Supported by NSF-CMS-9812717; AFOSR:F49629-97-0162,F49629-98-1-0309

  20. 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.

  1. 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.

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

    PubMed

    Matyushov, Dmitry V

    2016-07-21

    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 ρ(γ)/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. PMID:27448893

  3. 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.

  4. 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.

  5. Can the glass transition in bulk polymers be modeled by percolation picture?

    PubMed

    Yilmaz, Yaşar; Kaya, Demet; Pekcan, Onder

    2004-09-01

    Recent observations (Eur. Phys. J. E 9, 135 (2002)) showed that the vitrification process, which sets in during the linear bulk methyl methacrylate (MMA) polymerization carried out below glass transition temperatures, can be modelled by static percolation picture. To generalize this observation for different kind of bulk linear or crosslinked polymers not enough data are present in the literature. To cover partly this deficit we studied the glass transition of MMA and styrene (Sty) crosslinking copolymerization in varying ratios of MMA and Sty. Both the fluorescence intensity I and the lifetime tau of pyrene (Py) used as a nanosecond in situ fluoroprobe were monitored during the gelation time. Both I and tau increase dramatically as a result of the reduced mobility of the probes trapped in the "glassy" regions, appearing near the glass transition point. The average size of the glassy regions just below, and the strength of the infinite network formed upon the connection of the glassy regions above the glass transition point tg obey power law relations. The data around tg were interpreted on the basis of the percolation theory and we observed that the corresponding exponents gamma and beta give static percolation values independent of the polymer composition.

  6. 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.

  7. 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. PMID:12638851

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Discovery of strain glass transition in non-metallic ferroelastic

    NASA Astrophysics Data System (ADS)

    Zhang, Pei; Xue, Dezhen; Ren, Xiaobing

    2012-02-01

    Strain glass, a glassy state of lattice strain, has been identified in alloys with shuffle being the principle order parameter and strain being the secondary order parameter. However, it is well known that many non-metallic ferroelastic systems possess long range order with tilt being the first order parameter. But the existence of the glassy state of such strain caused by tilt remains unclear. In the present study, we report that the strain glass indeed exists in the non-metallic ferroelastic material, a Sr and Nb co-doped LaAlO3 system, with randomly frozen tilt strain local order. With increasing defect concentration x in La1-xSrxAl0.95 Nb0.05O3, the martensitic transition is gradually suppressed and finally strain glass transition occurs. The glassy transition is characterized by a typical frequency dispersion of modulus, a broken of ergodicity for static strain, as well as the formation of nano-domains with R local structure. Due to the strong local barrier caused by the randomly distributed point defects, the ideal freezing temperature T0 of strain glass in this system increases with defect concentration, which can be well understood by a modified Landau free energy landscape.

  14. PREFACE: Statistical Physics of Ageing Phenomena and the Glass Transition

    NASA Astrophysics Data System (ADS)

    Henkel, Malte; Pleimling, Michel; Sanctuary, Roland

    2006-06-01

    A summer school on `Ageing and the glass transition' was held at the University of Luxembourg on 18-24 September 2005. It brought together about 60 scientists actively studying the related fields of physical ageing and of the thermodynamics of glass-forming systems when undergoing a glass transition. The programme of the school can be found on the homepage ( http://www.theorie1.physik.uni-erlangen.de/sommerschule.html). The school contained both invited lectures and contributed talks and posters. This volume presents the works contributed to the summer school, while the invited lectures will be published elsewhere (M Henkel, M Pleimling and R Sanctuary (eds), Ageing and the glass transition, Springer Lecture Notes in Physics, Springer (Heidelberg 2006)). We have tried to encourage the exchange between theorists and experimentalists to which the topics treated in these proceedings bear witness. They range from experimental studies on the mechanical response of glasses, biopolymers, and granular materials to the effects of ageing on the long-time modification of the properties of glass-forming polymers, from simulational and analytical studies of theoretical models describing the non-equilibrium statistical mechanics of systems displaying the dynamical scaling typical of ageing phenomena and which are thought to capture essential aspects of glass-forming materials close to a glass transition to more mathematically oriented investigations on the symmetries of these systems. The `Grande Région' Sar-Lor-Lux is leading European efforts to overcome national and linguistic barriers, with the view of creating a common academic education. Physics has a standing internationalist tradition and the existing trinational integrated course in Physics SLLS (see the homepage http://www.uni-saarland.de/fak7/krueger/integ/sll/d/cursus.htm) is busily developing ways and means towards this goal, in particular through the delivery of multinational and multilingual university degrees in

  15. 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.

  16. 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.

  17. Scaled down glass transition temperature in confined polymer nanofibers.

    PubMed

    Wang, Hongxia; Chang, Tongxin; Li, Xiaohui; Zhang, Weidong; Hu, Zhijun; Jonas, Alain M

    2016-08-11

    Arrays of polymer nanostructures have been widely used in many novel devices and nanofabrication methods. The glass transition temperature, which is a key parameter influencing the long-term stability of polymer nanostructures, has not yet been systematically studied and well understood. Here we study this technological and fundamental issue with polymers of different values of molar mass M confined in nanocylinders of a varying diameter D. The glass transition temperature Tg loses its dependence on the molar mass for D ≲ 100 nm, a range in which the relative depression of Tg varies as D(-0.44). For higher cylinder diameters, Tg progressively recovers its dependence on the molar mass. This is quantitatively reproduced by a model based on an equilibrium interfacial excess of free volume, which needs to be created unless provided by the chain ends. Our findings suggest that the structural perturbations during nanofabrication may strongly affect the long-term stability of arrays of polymer nanostructures. PMID:27476991

  18. Predicting Glass Transition Temperatures of Polyarylethersulphones Using QSPR Methods

    PubMed Central

    Hamerton, Ian; Howlin, Brendan J.; Kamyszek, Grzegorz

    2012-01-01

    The technique of Quantitative Structure Property Relationships has been applied to the glass transition temperatures of polyarylethersulphones. A general equation is reported that calculates the glass transition temperatures with acceptable accuracy (correlation coefficients of between 90–67%, indicating an error of 10–30% with regard to experimentally determined values) for a series of 42 reported polyarylethersulphones. This method is quite simple in assumption and relies on a relatively small number of parameters associated with the structural unit of the polymer: the number of rotatable bonds, the dipole moment, the heat of formation, the HOMO eigenvalue, the molar mass and molar volume. For smaller subsets of the main group (based on families of derivatives containing different substituents) the model can be simplified further to an equation that uses the volume of the substituents as the principal variable. PMID:22719884

  19. 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.

  20. Determination of the glass transition temperature of cyclodextrin polymers.

    PubMed

    Tabary, Nicolas; Garcia-Fernandez, Maria Jose; Danède, Florence; Descamps, Marc; Martel, Bernard; Willart, Jean-François

    2016-09-01

    The aim of this work was to determine the main physical characteristics of β-cyclodextrin polymers, well known for improving complexation capacities and providing enhanced and sustained release of a large panel of drugs. Two polymers were investigated: a polymer of β-cyclodextrin (polyβ-CD) and a polymer of partially methylated (DS=0.57) β-cyclodextrin (polyMe-β-CD). The physical characterizations were performed by powder X-ray diffraction and differential scanning calorimetry. The results indicate that these polymers are amorphous and that their glass transition is located above the thermal degradation point of the materials preventing their direct observation and thus their full characterization. We could however estimate the virtual glass transition temperatures by mixing the polymers with different plasticizers (trehalose and mannitol) which decreases Tg sufficiently to make the glass transition observable. Extrapolation to zero plasticizer concentration then yield the following Tg values: Tg (polyMe-β-CD)=317°C±5°C and Tg (polyβ-CD)=418°C±6°C. PMID:27185128

  1. 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.

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

    PubMed

    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 (T(g)) was measured by observing the softening of polymers with increasing temperature. The measured surface T(g) exhibited a strong size dependence, while the subsurface T(g) increased with decreasing the distance to the substrate. A large increase in the surface T(g) 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 T(g) 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.

  3. 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.

  4. Observation of spin glass transition in spinel LiCoMnO4

    NASA Astrophysics Data System (ADS)

    Chen, Hong; Yang, Xu; Zhang, Pei-Song; Liang, Lei; Hong, Yuan-Ze; Wei, Ying-Jin; Chen, Gang; Du, Fei; Wang, Chun-Zhong

    2015-12-01

    Spinel LiCoMnO4 is prepared by solid-state reaction and its magnetic properties are comprehensively studied by direct current (DC) and alternating current (AC) susceptibilities, isothermal remanent magnetizations, and magnetic hysteresis. Fitting to the Curie-Weiss law by using high-temperature zero-field-cooled susceptibility confirms a low-spin state of Co3+ with S = 0. Both the fitting parameters first increase and then tend to be saturated at high magnetic fields through using isothermal remanent magnetizations, which suggests a spin glass transition at low temperature. AC susceptibility study also supports this conclusion since the frequency dependence of peak position and intensity follows the tendency of a spin glass transition. The origin of the spin-glass transition in LiCoMnO4 might be attributed to a spatial segregation between non-magnetic Co3+ regions and spin glass ordered regions of Mn4+ ions. Project supported by the National Key Basic Research Program of China (Grant No. 2015CB251103), the Development Program of Science and Technology of Jilin Province, China (Grant No. 20140101093JC), and the Program of Science and Technology of Jilin City, China (Grant No. 201434006).

  5. 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.

  6. 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

  7. Are Magnetically Doped Transition-metal Oxides Spin-glasses?

    NASA Astrophysics Data System (ADS)

    Lussier, A.; Dvorak, J.; Idzerda, Y. U.; Ogale, S. B.; Shinde, S. R.; Venkatesan, T.; Lofland, S. E.

    2004-03-01

    Many magnetic impurity doped transition-metal oxides exhibit ferromagnetism at room temperature. Some also exhibit strange magnetic aging behavior. One such material is Co-doped SnO2 which displays a saturation magnetization decrease over time, as well as with successive field applications. From the theoretical perspective, there are two prerequisites for spin-glass behavior which are both satisfied for these samples: disorder and frustration. Disorder is readily satisfied because the dilute magnetic impurities are randomly scattered. Additionally, the suggested RKKY interaction between magnetic impurities, coupled with their random spacing, likely results in frustration. Magnetometry, XAS, and XMCD measurements, with temperature, measurement time, and history dependence help elucidate the magnetic order in these materials, and are consistent with spin-glass character. We would like to acknowledge the support of NSF (MSU), the Office of Naval Research (MSU), DARPA SpinS (UMD) and NSF-MRSEC (UMD).

  8. The glass transition in binary mixtures of hard colloidal spheres

    NASA Astrophysics Data System (ADS)

    Williams, S. R.; van Megen, W.

    2000-06-01

    Particle dynamics have been measured by dynamic light scattering for mixtures of colloidal particles with hard sphere interactions. The diameter ratio (small:large) is 0.6. The optical properties of the suspended particles are such that the relative contrast of the two species is very sensitive to temperature, a feature we exploit to obtain the three partial intermediate scattering functions. The glass transition is identified by the onset of structural arrest, or the arrest of the alpha process, on the time scale of the experiment. This is observed in the one-component suspension at the packing fraction 0.57. Introduction of the smaller particles, at fixed packing fraction, releases the alpha process, ie, the glass melts. Increasing the fraction of smaller particles speeds up the alpha process but interestingly, increases its amplitude. .

  9. Affinity and its derivatives in the glass transition process.

    PubMed

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

    2012-07-14

    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)], by Möller et al. [J. Chem. Phys. 125, 094505 (2006)], and more recently by Tropin et al. [J. Non-Cryst. Solids 357, 1291 (2011); ibid. 357, 1303 (2011)]. 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 C(p),κ(T), and α(p). 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. PMID:22803545

  10. Kinetics of glass transition and thermal stability of Se58Ge42- x Pb x (9≤ x≤20) glasses

    NASA Astrophysics Data System (ADS)

    Deepika; Rathore, K. S.; Saxena, N. S.

    2010-02-01

    Se58Ge42- x Pb x (9≤ x≤20) glasses have been prepared using conventional melt quenching technique. Differential Scanning Calorimetric (DSC) measurements show single glass transition and double crystallization, which indicate the occurrence of phase separation in the samples. The phases present in the samples were identified using XRD. The kinetics of the glass transition has been studied in terms of the variation of glass transition temperature with composition and heating rate. In addition to this, activation energy of the glass transition ( E t ) has also been evaluated and its composition dependence is also investigated. The thermal stability of these glasses has been investigated using various stability criteria: Deiztal first glass criterion, Δ T, Saad and Poulain weighted thermal stability, H' and the S-parameter. The values of these parameters were obtained using various characteristic temperatures such as the glass transition temperature, T g , the onset temperature of crystallization, T c , and the peak crystallization temperature, T p . The values of stability parameters show that the phase corresponding to second crystallization is more stable than the phase corresponding to first one. The stability in terms of the lead (Pb) content has been determined considering the values of stability parameters of the phase corresponding to second peak. It was found that the stability increases with the lead content.

  11. Stable Freestanding Thin Films of Copolymer Melts Far from the Glass Transition

    PubMed Central

    2015-01-01

    Thin polymer films have attracted attention because of both their broad range of applications and of the fundamental questions they raise regarding the dynamic response of confined polymers. These films are unstable if the temperature is above their glass transition temperature Tg. Here, we describe freestanding thin films of centimetric dimensions made of a comb copolymer melt far from its glass transition that are stable for more than a day. These long lifetimes allowed us to characterize the drainage dynamics and the thickness profile of the films. Stratified regions appear as the film drains. We have evidence that the stability, thinning dynamics, and thickness profile of the films result from structural forces in the melt. Understanding the key mechanisms behind our observations may lead to new developments in polymeric thin films, foams, and emulsions without the use of stabilizing agents. PMID:26527410

  12. Viscosity, glass transition and activation energy of solid cis-polyisoprene and trans-polyisoprene blends

    NASA Astrophysics Data System (ADS)

    Baboo, Mahesh; Sharma, Kananbala; Saxena, N. S.

    2011-11-01

    Blends of cis-polyisoprene (CPI) and trans-polyisoprene (TPI) have been prepared by solution casting to study viscosity, glass transition temperature and activation energy for the glass transition. The viscosity of blends having different weight ratios has been obtained through a single experiment measuring storage and loss modulus using the dynamic mechanical analyser technique. The glass transition temperature is determined through the temperature at which the minimum of temperature derivative curve of viscosity falls. The activation energy of glass transition and fragility index have been obtained by employing the Vogel-Fulchar-Tammann (VFT) equation by assuming non-Arrhenius behaviour of viscosity of polymer blends. Results indicate that both glass transition and activation energy for the glass transition are influenced by composition and crosslink density of the blend.

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

    PubMed

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

    2012-07-01

    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. PMID:22686254

  14. 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.

  15. 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.

  16. 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.

  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. Two-Gaussian excitations model for the glass transition

    NASA Astrophysics Data System (ADS)

    Matyushov, Dmitry V.; Angell, C. A.

    2005-07-01

    We develop a modified "two-state" model with Gaussian widths for the site energies of both ground and excited states, consistent with expectations for a disordered system. The thermodynamic properties of the system are analyzed in configuration space and found to bridge the gap between simple two-state models ("logarithmic" model in configuration space) and the random energy model ("Gaussian" model in configuration space). The Kauzmann singularity given by the random energy model remains for very fragile liquids but is suppressed or eliminated for stronger liquids. The sharp form of constant-volume heat capacity found by recent simulations for binary mixed Lennard-Jones and soft-sphere systems is reproduced by the model, as is the excess entropy and heat capacity of a variety of laboratory systems, strong and fragile. The ideal glass in all cases has a narrow Gaussian, almost invariant among molecular and atomic glassformers, while the excited-state Gaussian depends on the system and its width plays a role in the thermodynamic fragility. The model predicts the possibility of first-order phase transitions for fragile liquids. The analysis of laboratory data for toluene and o-terphenyl indicates that fragile liquids resolve the Kauzmann paradox by a first-order transition from supercooled liquid to ideal-glass state at a temperature between Tg and Kauzmann temperature extrapolated from experimental data. We stress the importance of the temperature dependence of the energy landscape, predicted by the fluctuation-dissipation theorem, in analyzing the liquid thermodynamics.

  19. 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

  20. Computational nanofluidics: Nonlocal transport and the glass transition

    NASA Astrophysics Data System (ADS)

    Puscasu, Ruslan M.

    2011-08-01

    -confined geometries. We start with an overview on the nonlocal constitutive relation and the microscopic definitions of the key properties such as momentum density autocorrelation function, stress autocorrelation function and the wavevector dependent viscosity. Then we demonstrate how the nonlocal viscosity kernel can be computed via equilibrium molecular dynamics. Firstly, we showcase the spatially nonlocal viscosity kernel for simple monatomic and diatomic fluids over a wide range of wavevectors, state points and potential energy functions. Further we consider more complex fluids; in particular, we report results for alkanes and polymer melts. Secondly, we study glass-forming liquids and therefore extend the temperature range and report the nonlocal viscosities of polymer melts cooled towards their glassy state. The results reveal the nonlocal nature of the viscous transport and we give evidence that the slow dynamics in supercooled liquids is governed by a dynamic critical point at which time and length scales diverge and link it to the dynamic heterogeneity. It follows that the response of polymer melts to a velocity gradient near the glass transition temperature is highly nonlocal. In systems where the strain rate varies significantly over the width of the real space kernels, the generalized nonlocal viscosity must be used in order to correctly compute the velocity profile of molecular fluids via use of generalized hydrodynamics and thus the nonlocal behaviour of the transport must be integrated into methodologies developed to describe the multi-scale physics of nanoflows.

  1. 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.

  2. Mechanical heating in the transition region

    NASA Technical Reports Server (NTRS)

    Withbroe, G.

    1981-01-01

    Attention is focused on the energy balance in the transition region and the role that mechanical heating plays in determining the temperature density structure of this region in a stellar atmosphere. Because of its role as the interface layer through which mass and energy flow between the chromospheres and corona, direct deposition of mechanical energy is a relatively unimportant factor in the overall energy balance in the transition region, except in the uppermost layers where the temperature approaches coronal values.

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

    PubMed

    Elenius, Måns; Oppelstrup, Tomas; Dzugutov, Mikhail

    2010-11-01

    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.

  4. Effects of microalloying with 3d transition metals on glass formation in AlYFe alloys

    SciTech Connect

    Bondi, K.S.; Gangopadhyay, A.K.; Marine, Z.; Kim, T.H.; Mukhopadhyay, Anindita; Goldman, A.I.; Buhro, William E.; Kelton, K.F.

    2008-05-20

    The effects of microalloying on glass formation and stability were systematically investigated by substituting 0.5 at.% of all 3d transition metals for Al in Al{sub 88}Y{sub 7}Fe{sub 5} alloys. X-ray diffraction and isothermal differential scanning calorimetry studies indicate that samples containing microadditions of Ti, V, Cr, Mn, Fe and Co were amorphous, while those alloyed with Ni and Cu were not. The onset temperatures for crystallization (devitrification) of the amorphous alloys were increased with microalloying and some showed a supercooled liquid region ({Delta}T{sub x} = T{sub x} - T{sub g}) of up to 40 C. In addition, microalloying changes the glass structure and the devitrification sequence, as determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and high energy X-ray diffraction. The results presented here suggest that the order induced in the alloy by the transition metal microaddition decreases the atomic mobility in the glass and raises the barrier for the nucleation of {alpha}-Al, the primary devitrifying phase in most cases. New intermetallic phases also appear with microalloying and vary for different transition metal additions.

  5. 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.

  6. 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

  7. Glass Forming Ability of Hard Magnetic Nd55Al20Fe25 Bulk Glassy Alloy with Distinct Glass Transition

    NASA Astrophysics Data System (ADS)

    Xia, L.; Jo, C. L.; Dong, Y. D.

    Nd55Al20Fe25 bulk sample was prepared in the shape of rods 3 mm in diameter by suction casting. The sample exhibits typical amorphous characters in XRD pattern, distinct glass transition in DSC traces and hard magnetic properties. The distinct glass transition, which is invisible in DSC traces of previously reported Nd—Al—Fe ternary BMGs, allows us to investigate the glass forming ability (GFA) of Nd55Al20Fe25 alloy using the reduced glass transition temperature Trg and the recently defined parameter γ. However, it is found that the obtained diameter of the Nd55Al20Fe25 glassy rod is much larger than the critical section thickness of the BMG predicted by either Trg or γ. The microstructure of Nd55Al20 Fe25 as-cast rod was studied and the apparent GFA of the alloy was supposed to be enhanced by the metastable nano-precipitates dispersed within the glassy matrix.

  8. Cooperative rearranging region size and free volume in As-Se glasses.

    PubMed

    Saiter, A; Saiter, J-M; Golovchak, R; Shpotyuk, M; Shpotyuk, O

    2009-02-18

    Glasses of the As-Se system have been used as model objects of the covalent disordered inorganic polymers to investigate the correlation between the cooperative rearranging region (CRR) size determined at the glass transition temperature and the free volume fraction in the glassy state. The CRR size has been determined using temperature modulated differential scanning calorimetry data according to Donth's approach, while the free volume fraction in the investigated materials has been estimated using positron annihilation lifetime spectroscopy data. The obtained results testify that the appearance of open-volume defects greater than 80 Å(3) leads to a significant decrease in the CRR size.

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

    DOE PAGES

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

    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

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

    PubMed Central

    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.

    2014-01-01

    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 ± 2 K between H2O and D2O, sharply contrasting with other hydrogen-bonded liquids for which H/D exchange increases Tg by typically less than 1 K. 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. PMID:25422420

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

    DOE PAGES

    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; et al

    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

  12. A random first order theory of liquid-glass transition

    NASA Astrophysics Data System (ADS)

    Xia, Xiaoyu

    It is believed that all classical fluids could form glasses if cooled sufficiently fast so as to avoid crystallization. Various phenomena including violation of the usual Arrhenius law, stretched relaxations, deviations from the Stokes-Einstein relation in hydrodynamics, and aging have been observed in the laboratory. In this thesis, a microscopically motivated theory of glassy dynamics based on an underlying random first order transition is developed to explain the magnitude and variation of free energy barriers for glassy relaxation. A variety of empirical correlations embodied in the concept of liquid "fragility" are shown to be quantitatively explained by such a model. Fragility parameters, the size of heterogeneities, the degree of stretching of relaxations, and the enhancement of translational diffusion are derived from theory. The wide variety of kinetic behaviors in liquids of quite disparate chemical nature reflects quantitative rather than qualitative differences in their energy landscapes as it turns out.

  13. Glass Transition of Miscible Binary Polymer-Polymer Thin Films

    NASA Astrophysics Data System (ADS)

    Besancon, Brian M.; Soles, Christopher L.; Green, Peter F.

    2006-08-01

    The average glass transition temperatures, Tg, of thin homopolymer films exhibit a thickness dependence, Tg(h), associated with a confinement effect and with polymer-segment interface interactions. The Tg’s of completely miscible thin film blends of tetramethyl bisphenol-A polycarbonate (TMPC) and deuterated polystyrene (dPS), supported by SiOx/Si, decrease with decreasing h for PS weight fractions ϕ>0.1. This dependence is similar to that of PS and opposite to that of TMPC thin films. Based on an assessment of Tg(h,ϕ), we suggest that the Tg(h,ϕ) of miscible blends should be rationalized, additionally, in terms of the notion of a self-concentration and associated heterogeneous component dynamics.

  14. 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.

  15. 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. PMID:24425957

  16. 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.

  17. 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

  18. Chiral-glass transition in a diluted dipolar-interaction Heisenberg system

    NASA Astrophysics Data System (ADS)

    Zhang, Kai-Cheng; Liu, Gui-Bin; Zhu, Yan

    2011-05-01

    Recently, numerical simulations reveal that a spin-glass transition can occur in the three-dimensional diluted dipolar system. By defining the chirality of triple spins in a diluted dipolar Heisenberg spin glass, we study the chiral ordering in the system using parallel tempering algorithm and heat bath method. The finite-size scaling analysis reveals that the system undergoes a chiral-glass transition at finite temperature.

  19. 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.

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

    DOE PAGES

    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 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

  1. 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.

  2. 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

  3. Glass forming ability and magnetic properties of Nd48Al20Fe27Co5 bulk metallic glass with distinct glass transition

    NASA Astrophysics Data System (ADS)

    Xia, L.; Tang, M. B.; Pan, M. X.; Wang, W. H.; Dong, Y. D.

    2004-06-01

    Nd48Al20Fe27Co5 bulk metallic glass (BMG) was prepared in the shape of rods 3 mm in diameter by suction casting. In contrast to the previously reported hard magnetic Nd-Al-Fe-Co BMGs, the Nd48Al20Fe27Co5 as-cast rod exhibits a distinct glass transition, multi-step crystallizations in DSC traces and much lower coercivity. The glass forming ability as well as the kinetics of the glass transition and crystallizations of the Nd48Al20Fe27Co5 as-cast rod have been studied. The magnetic properties of the alloy were investigated in comparison with Nd60Al10Fe20Co10 glass forming alloys.

  4. 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. PMID:24708977

  5. 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.

  6. Mobility restrictions and glass transition behaviour of an epoxy resin under confinement.

    PubMed

    Djemour, A; Sanctuary, R; Baller, J

    2015-04-01

    Confinement can have a big influence on the dynamics of glass formers in the vicinity of the glass transition. Already 40 to 50 K above the glass transition temperature, thermal equilibration of glass formers can be strongly influenced by the confining substrate. We investigate the linear thermal expansion and the specific heat capacity cp of an epoxy resin (diglycidyl ether of bisphenol A, DGEBA) in a temperature interval of 120 K around the glass transition temperature. The epoxy resin is filled into controlled pore glasses with pore diameters between 4 and 111 nm. Since DGEBA can form H-bonds with silica surfaces, we also investigate the influence of surface silanization of the porous substrates. In untreated substrates a core/shell structure of the epoxy resin can be identified. The glass transition behaviours of the bulk phase and that of the shell phase are different. In silanized substrates, the shell phase disappears. At a temperature well above the glass transition, a second transition is found for the bulk phase - both in the linear expansion data as well as in the specific heat capacity. The cp data do not allow excluding the glass transition of a third phase as being the cause for this transition, whereas the linear expansion data do so. The additional transition temperature is interpreted as a separation between two regimes: above this temperature, macroscopic flow of the bulk phase inside the porous structure is possible to balance the mismatch of thermal expansion coefficients between DGEBA and the substrate. Below the transition temperature, this degree of freedom is hindered by geometrical constraints of the porous substrates. Moreover, this second transition could also be found in the linear expansion data of the shell phase. PMID:25689879

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. The Structural Bases for Polymer Glass-Transition Temperatures

    NASA Astrophysics Data System (ADS)

    Shen, Jialong; Tonelli, Alan

    2015-03-01

    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, though the following three factors are often mentioned as being pivotal: 1. Their inherent conformational flexibilities; 2. The sizes or steric bulk of their side-chains; and 3. Their inter-chain interactions. These three factors are generally interdependent, making it difficult to predict or even rationalize the Tgs of polymers. Structurally analogous aliphatic copolyesters, copolyamides, and copoly(ester/amide)s can be synthesized to produce amorphous samples with Tgs that are unaffected either by crystallinity or polymer chain lengths. Their conformations are virtually identical, and each can be synthesized with or without side-chains, so we can begin to evaluate the relative importance of the above three factors. The Tgs of un-branched analogous samples should differ solely due to factor 3., while analogous samples with singly-branched repeat units should provide a measure of the relative importance of factors 1. and 2.

  13. 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.

  14. 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

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

    PubMed

    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

  16. 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.

  17. Investigation of the creep and glass transition of elastomers by the microindentation method: Epoxy resin and related nanocomposites

    NASA Astrophysics Data System (ADS)

    Natsik, V. D.; Fomenko, L. S.; Lubenets, S. V.

    2013-05-01

    The experimental procedure and theoretical grounds of the applicability of the microindentation method as one of the effective techniques of relaxation spectrometry of solid-state polymers have been developed. It has been shown that the glass transition temperature and rheological parameters of the material (unrelaxed and relaxed elastic moduli, strain viscosity coefficients) can be determined from measurements of the temperature dependence of the microhardness of polymers in a high-elasticity state and in the glass transition region with the recording of the long-term creep under the indenter. These measurements provide sufficient information for the formulation of a rheological model of the material under investigation. The results of these measurements are supplemented by the concepts of thermally activated motion of molecular segments as the microscopic mechanism of structural relaxation in polymers, which makes it possible to obtain empirical estimates for the activation energies and vibrational frequencies of the molecular segments. The method is implemented in experiments on the microindentation of the epoxy resin and its composites with the addition of carbon nanotubes in the temperature range 230-300 K. The glass transition of these polymers has been observed at temperatures near 260 K, the unrelaxed and relaxed Young's moduli have been measured, and two thermally activated relaxation processes determining the glass transition, as well as the shortterm and long-term creeps of these materials (α- and α'-processes), have been revealed.

  18. 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.

  19. 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.

  20. 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.

  1. Using rare gas permeation to probe methanol diffusion near the glass transition temperature.

    PubMed

    Matthiesen, Jesper; Smith, R Scott; Kay, Bruce D

    2009-12-11

    The permeation of rare-gas atoms through deeply supercooled metastable liquid methanol films is used to probe the diffusivity. The technique allows for measurement of supercooled liquid mobility at temperatures near the glass transition. The temperature dependence of the diffusivity is well described by a Vogel-Fulcher-Tamman equation. These new measurements and the temperature dependent kinetic parameters obtained from their analysis provide clear evidence that methanol is a fragile liquid near the glass transition. PMID:20366212

  2. Using Rare Gas Permeation to Probe Methanol Diffusion near the Glass Transition Temperature

    NASA Astrophysics Data System (ADS)

    Matthiesen, Jesper; Smith, R. Scott; Kay, Bruce D.

    2009-12-01

    The permeation of rare-gas atoms through deeply supercooled metastable liquid methanol films is used to probe the diffusivity. The technique allows for measurement of supercooled liquid mobility at temperatures near the glass transition. The temperature dependence of the diffusivity is well described by a Vogel-Fulcher-Tamman equation. These new measurements and the temperature dependent kinetic parameters obtained from their analysis provide clear evidence that methanol is a fragile liquid near the glass transition.

  3. Molecular absorption in transition region spectral lines

    NASA Astrophysics Data System (ADS)

    Schmit, D. J.; Innes, D.; Ayres, T.; Peter, H.; Curdt, W.; Jaeggli, S.

    2014-09-01

    Aims: We present observations from the Interface Region Imaging Spectrograph (IRIS) of absorption features from a multitude of cool atomic and molecular lines within the profiles of Si IV transition region lines. Many of these spectral lines have not previously been detected in solar spectra. Methods: We examined spectra taken from deep exposures of plage on 12 October 2013. We observed unique absorption spectra over a magnetic element which is bright in transition region line emission and the ultraviolet continuum. We compared the absorption spectra with emission spectra that is likely related to fluorescence. Results: The absorption features require a population of sub-5000 K plasma to exist above the transition region. This peculiar stratification is an extreme deviation from the canonical structure of the chromosphere-corona boundary. The cool material is not associated with a filament or discernible coronal rain. This suggests that molecules may form in the upper solar atmosphere on small spatial scales and introduces a new complexity into our understanding of solar thermal structure. It lends credence to previous numerical studies that found evidence for elevated pockets of cool gas in the chromosphere. Movies associated to Figs. 1 and 2 are available in electronic form at http://www.aanda.org

  4. 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.

  5. 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.

  6. A toy MCT model for multiple glass transitions: Double swallow tail singularity

    NASA Astrophysics Data System (ADS)

    Ryzhov, V. N.; Tareyeva, E. E.

    2014-11-01

    We propose a toy model to describe in the frame of Mode Coupling Theory multiple glass transitions. The model is based on the postulated simple form for static structure factor as a sum of two delta-functions. This form makes it possible to solve the MCT equations in almost analytical way. The phase diagram is governed by two swallow tails resulting from two A4 singularities and includes liquid-glass transition and multiple glasses. The diagram has much in common with those of binary and quasibinary systems.

  7. 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%).

  8. Transition region of the earth's upper mantle

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.; Bass, J. D.

    1986-01-01

    The chemistry of the earth's mantle is discussed using data from cosmochemistry, geochemistry, petrology, seismology, and mineral physics. The chondritic earth, the upper mantle and the 400-km discontinuity, the transition region, lower mantle mineralogy, and surface wave tomography are examined. Three main issues are addressed: (1) whether the mantle is homogeneous in composition or chemically stratified, (2) whether the major element chemistry of the mantle is more similar to upper mantle peridotites or to chondrites, and (3) the nature of the composition of the source region of basalts erupted at midocean ridges.

  9. 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.

  10. The decoupling of the glass transitions in the two-component p-spin spherical model

    NASA Astrophysics Data System (ADS)

    Ikeda, Harukuni; Ikeda, Atsushi

    2016-07-01

    Binary mixtures of large and small particles with a disparate size ratio exhibit a rich phenomenology at their glass transition points. In order to gain insights on such systems, we introduce and study a two-component version of the p-spin spherical spin glass model. We employ the replica method to calculate the free energy and the phase diagram. We show that when the strengths of the interactions of each component are not widely separated, the model has only one glass phase characterized by the conventional one-step replica symmetry breaking. However when the strengths of the interactions are well separated, the model has three glass phases depending on the temperature and component ratio. One is the ‘single’ glass phase in which only the spins of one component are frozen while the spins of the other component remain mobile. This phase is characterized by the one-step replica symmetry breaking. The second is the ‘double’ glass phase obtained by cooling the single glass phase further, in which the spins of the remaining mobile component are also frozen. This phase is characterized by the two-step replica symmetry breaking. The third is also the ‘double’ glass phase, which, however, is formed by the simultaneous freezing of the spins of both components at the same temperatures and is characterized by the one-step replica symmetry breaking. We discuss the implications of these results for the glass transitions of binary mixtures.

  11. Direct Experimental Evidence of Growing Dynamical Facilitation on Approaching the Colloidal Glass Transition

    NASA Astrophysics Data System (ADS)

    Gokhale, Shreyas; Nagamanasa, K. Hima; Ganapathy, Rajesh; Sood, A. K.

    2014-03-01

    The dramatic slowing down of dynamics with no apparent change in structure is perhaps the best-known and least understood feature of the glass transition in molecular, polymeric and colloidal liquids. Despite extensive research, the microscopic origin of this slowdown remains mysterious. In particular, it is unclear whether structural relaxation is governed by a growing length scale, as advocated by thermodynamic theories, or by the concerted motion of mobile defects termed excitations, a phenomenon known as dynamical facilitation. Here, by performing video microscopy on a binary colloidal glass-former, we show that dynamical facilitation unambiguously grows on approaching the glass transition. Interestingly, the spatial frequency of occurrence of excitations is anti-correlated with the distribution of local hexatic order, suggesting intriguing connections between structural evolution and relaxation dynamics on approaching the glass transition. SG thanks the Council for Scientifc and Industrial Research (CSIR), India, for a Shyama Prasad Mukherjee Fellowship.

  12. 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

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

    PubMed

    Colmenero, J

    2015-03-18

    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 mixtures with

  14. KT boundary impact glasses from the Gulf of Mexico region

    NASA Technical Reports Server (NTRS)

    Claeys, Philippe; Alvarez, Walter; Smit, Jan; Hildebrand, A. R.; Montanari, Alessandro

    1993-01-01

    Cretaceous-Tertiary boundary (KTB) tektite glasses occur at several sites around the Gulf of Mexico. Contrary to rumor among KTB workers, glass fragments have been found by several researchers in the base of the spherule bed at Arroyo el Mimbral in NE Mexico. The presence of green, red, and transparent glass fragments at Mimbral only, demonstrates that the Mimbral glass is not a laboratory contamination by Beloc glass. The chemistry and ages of the glass are consistent with an origin from the Chixculub impact crater in Yucatan. No evidence supports a volcanic origin for the KTB glasses. A discussion of tektite glass from the KT boundary is presented.

  15. 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.

  16. Vapor phase deposition of transition metal fluoride glasses

    NASA Astrophysics Data System (ADS)

    Boulard, Brigitte; Jacoboni, Charles

    1991-08-01

    Multicomponent fluoride glasses in the PbF2-ZnF2-GaF3 (PZG) vitreous ternary system have been prepared by vapor phase deposition. The thermal stability of the deposited glass was improved by adding stabilizing agents (AlF3, NaF, LiF, InF3). The thin films, deposited on different substrates (fluoride glass, fluoride single crystal, metal, and silica glass) have been characterized by x-ray diffraction. Differential scanning calorimetry (DSC) and secondary ion mass spectroscopy (SIMS). The quality of the film, adherence, and homogeneity was controlled by scanning electronic microscopy (SEM). The optical characteristics of the film and PZG glass are given: the visible-infrared (VIS-IR) window is 0.3-8 micrometers and the refractive index 1.59+/- 0.2 depends on the lead content. Mn2+ doped films (up to 3 mole % MnF2) are optically active: Mn2+ exhibits a broad luminescence band at 560-570 nm (orange). The achieved film thickness varies from 0.5 to 80 micrometers , and the refractive index gradient approaches the required geometry for planar waveguides (doping of the film with lanthanides is in progress).

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

    PubMed

    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.

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

    PubMed

    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 (∞). PMID:26646885

  19. 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 ∞ .

  20. The upper mantle transition region - Eclogite

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1979-01-01

    The upper mantle transition region is usually considered to be peridotite which undergoes a series of phase changes involving spinel and post-spinel assemblages. There are difficulties associated with attempts to explain the 220, 400 and 670 km discontinuities in terms of phase changes in a peridotitic mantle. Moreover, in a differentiated earth there should be large quantities of eclogite in the upper mantle. Eclogite is denser than Al2O3-poor mantle to depths of 670 km, but it stays in the garnet stability field to pressures in excess of those required to transform depleted mantle to denser phases such as ilmenite and perovskite. Eclogite, therefore, remains above 670 km. The seismic properties of the transition region are more consistent with eclogite than peridotite. Most of the mantle's inventory of incompatible trace elements may be in this layer, which is a potential source region for some basalt magmas. The radioactivity in this layer is the main source of mantle heat flow, 0.7 microcalorie/sq cm-sec, and drives upper mantle convection.

  1. 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

  2. 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.

  3. Structure of glasses containing transition metal ions. Progress report, February 1, 1980-January 31, 1981

    SciTech Connect

    White, W.B.; Fox, K.; Herman, J.S.; Houser, C.; Nelson, C.

    1981-01-01

    This research is concerned with the structure and properties of insulator glasses, particularly as these are modified by transition metal ions in solution. This progress report spans a one-year period and describes the status of the work two-thirds into the sixth contract year. Work on the host glasses has been concentrated on the alkali borosilicate, alkali aluminosilicate and alkali-gallia-silicate glasses. The main interest here is the structure setting for aluminum. The optical absorption spectra of nickel and iron in a variety of glasses have been examined. Utilization of luminescence in addition to optical absorption spectra has permitted the identification of several iron arrangements in glass. The investigation of diffusion processes, particularly hydrogen diffusion, by sputter-induced photon spectrometry (SIPS) has moved from qualitative demonstration to quantitative calculation.

  4. Effect of 3d-transition metal doping on the shielding behavior of barium borate glasses: a spectroscopic study.

    PubMed

    ElBatal, H A; Abdelghany, A M; Ghoneim, N A; ElBatal, F H

    2014-12-10

    UV-visible and FT infrared spectra were measured for prepared samples before and after gamma irradiation. Base undoped barium borate glass of the basic composition (BaO 40%-B2O3 60mol.%) reveals strong charge transfer UV absorption bands which are related to unavoidable trace iron impurities (Fe(3+)) within the chemical raw materials. 3d transition metal (TM)-doped glasses exhibit extra characteristic absorption bands due to each TM in its specific valence or coordinate state. The optical spectra show that TM ions favor generally the presence in the high valence or tetrahedral coordination state in barium borate host glass. Infrared absorption bands of all prepared glasses reveal the appearance of both triangular BO3 units and tetrahedral BO4 units within their characteristic vibrational modes and the TM-ions cause minor effects because of the low doping level introduced (0.2%). Gamma irradiation of the undoped barium borate glass increases the intensity of the UV absorption together with the generation of an induced broad visible band at about 580nm. These changes are correlated with suggested photochemical reactions of trace iron impurities together with the generation of positive hole center (BHC or OHC) within the visible region through generated electrons and positive holes during the irradiation process.

  5. 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.

  6. Molecular dynamics simulation of the glass transition in 4,4‧-N,N‧-dicarbazolylbiphenyl

    NASA Astrophysics Data System (ADS)

    Odinokov, Alexey; Freidzon, Alexandra; Bagaturyants, Alexander

    2015-07-01

    Viscoelastic properties of the molecular liquid consisting of 4,4‧-N,N‧-dicarbazolylbiphenyl (CBP) molecules near the glass transition temperature are investigated by molecular dynamics simulations. The relaxation dynamics is analyzed by considering each molecule as a point-like oriented particle. The dependence of the calculated properties on the coarse-grain parameter used in the calculation of orientation correlation is analyzed. The divergence of α-relaxation times is described by the Vogel-Fulcher-Tammann law and the mode coupling theory. The basic concepts of the glass transition theory are applied to a real amorphous organic semiconductor.

  7. Connection between the glass transition temperature Tg and the Arrhenius temperature TA in supercooled liquids

    NASA Astrophysics Data System (ADS)

    Novikov, V. N.

    2016-08-01

    At high temperatures the structural relaxation time in liquids has Arrhenius temperature dependence. At lowering temperature, temperature dependence changes to a super Arrhenius at some temperature TA. This temperature is an important point for the structural relaxation dynamics in supercooled liquids because it reflects the transition to collective relaxation. Here we derive a relation between TA, the glass transition temperature Tg and fragility. We show that the ratio Tg/TA increases with increasing fragility of a liquid. The derived relation is in agreement with the experimental data in a series of molecular, hydrogen bonding and two inorganic glass-formers.

  8. Superfluid/Bose-glass transition in one dimension

    NASA Astrophysics Data System (ADS)

    Ristivojevic, Zoran; Petković, Aleksandra; Le Doussal, Pierre; Giamarchi, Thierry

    2014-09-01

    We consider a one-dimensional system of interacting bosons in a random potential. At zero temperature, it can be either in the superfluid or in the insulating phase. We study the transition at weak disorder and moderate interaction. Using a systematic approach, we derive the renormalization group equations at two-loop order and discuss the phase diagram. We find the universal form of the correlation functions at the transitions and compute the logarithmic corrections to the main universal power-law behavior. In order to mimic large density fluctuations on a single site, we study a simplified model of disordered two-leg bosonic ladders with correlated disorder across the rung. Contrarily to the single-chain case, the latter system exhibits a transition between a superfluid and a localized phase where the exponents of the correlation functions at the transition do not take universal values.

  9. MTRAP: The Magnetic Transition Region Probe

    NASA Technical Reports Server (NTRS)

    Davis, J. M.; West, E. A.; Moore, R. L.; Gary, G. A.; Kobayashi, K.; Oberright, J. F.; Evans, D. C.; Wood, H. J.; Saba, J. L. R.; Alexander, D.

    2005-01-01

    The Magnetic Transition Region Probe is a space telescope designed to measure the magnetic field at several heights and temperatures in the solar atmosphere, providing observations spanning the chromospheric region where the field is expected to become force free. The primary goal is to provide an early warning system (hours to days) for solar energetic particle events that pose a serious hazard to astronauts in deep space and to understand the source regions of these particles. The required magnetic field data consist of simultaneous circular and linear polarization measurements in several spectral lines over the wavelength range from 150 to 855 nm. Because the observations are photon limited an optical telescope with a large (>18sq m) collecting area is required. To keep the heat dissipation problem manageable we have chosen to implement MTRAP with six separate Gregorian telescopes, each with approx. 3 sq m collecting area, that are brought to a common focus. The large field of view (5 x 5 arcmin(sup 2)) and angular resolution (0.025 arcsec pixels) require large detector arrays and, because of the requirements on signal to noise (10(exp 3)), pixels with large full well depths to reduce the readout time and improve the temporal resolution. The optical and engineering considerations that have gone into the development of a concept that meets MTRAP's requirements are described.

  10. Models of transition regions in hybrid stars

    NASA Technical Reports Server (NTRS)

    Brosius, J. W.; Mullan, D. J.

    1986-01-01

    Models for the transition regions of six hybrid stars, four bright giants and two supergiants, are calculated. The models include mass loss and prescribe Alfven waves as the source of mechanical energy. The momentum and energy deposition rates required at each level of the atmosphere are evaluated. The final models for all six stars have mass loss rates lying below the current VLA upper limits by factors of two to ten, and have densities which agree with those derived by density-sensitive line ratios. The density vs. temperature structure in Alpha TrA agree well with that derived by Hartmann et al. (1985). Wave amplitudes and magnetic field strengths are derived as functions of height, and the amplitudes are found to agree well with the observed line widths in Alpha TrA.

  11. Experimental determination of the cooperative length scale of a glass-forming liquid near the glass transition temperature

    NASA Astrophysics Data System (ADS)

    Rizos, A. K.; Ngai, K. L.

    1999-01-01

    Photon correlation spectroscopy and dielectric relaxation are used to examine the molecular reorientation relaxation dynamics of a fragile glass-forming liquid Aroclor (a mixture of polychlorinated biphenyls), modified by the addition of low- and high-molecular-weight polyisoprene and polybutadiene as a function of temperature and polymer solute concentration. Concentration fluctuation contributes a temperature-dependent broadening of the relaxation spectrum of Aroclor. The rate of change of the Aroclor relaxation spectrum with temperature is more pronounced when the polymers added are of low molecular weight and exhibits a steplike decrease in the neighborhood of some characteristic molecular weight. The radius of gyration of the polymer with this characteristic molecular weight is about 15 Å, which determines the cooperative length scale L(T) of Aroclor to be approximately 30 Å near and above the glass transition temperature.

  12. 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.

  13. 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. PMID:19384925

  14. Mode Coupling Theory and the Glass Transition in Molecular Dynamics Simulated NiZr

    NASA Astrophysics Data System (ADS)

    Teichler, H.

    1996-01-01

    Molecular dynamics (MD) simulations for a NiZr model adapted to Hausleitner-Hafner interatomic potentials are analyzed within the mode coupling theory (MCT). Fitting numerical solutions of the (modified) schematic MCT equation with the self-intermediate scattering function of the MD system demonstrates unambiguously the transition scenario from liquidlike to nearly arrested behavior predicted by the MCT as precursor of the glass transition (around 1120 K for the present NiZr model).

  15. Kinetic-freezing and unfreezing of local-region fluctuations in a glass structure observed by heat capacity hysteresis

    SciTech Connect

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

    2015-06-07

    Fluctuations confined to local regions in the structure of a glass are observed as the Johari-Goldstein (JG) relaxation. Properties of these regions and their atomic configuration are currently studied by relaxation techniques, by electron microscopy, and by high-energy X-ray scattering and extended x-ray absorption fine structure methods. One expects that these fluctuations (i) would kinetically freeze on cooling a glass, and the temperature coefficient of its enthalpy, dH/dT, would consequently show a gradual decrease with decrease in T, (ii) would kinetically unfreeze on heating the glass toward the glass-liquid transition temperature, T{sub g}, and dH/dT would gradually increase, and (iii) there would be a thermal hysteresis indicating the time and temperature dependence of the enthalpy. Since no such features have been found, thermodynamic consequences of these fluctuations are debated. After searching for these features in glasses of different types, we found it in one of the most stable metal alloy glasses of composition Pd{sub 40}Ni{sub 10}Cu{sub 30}P{sub 20}. On cooling from its T{sub g}, dH/dT decreased along a broad sigmoid-shape path as local-region fluctuations kinetically froze. On heating thereafter, dH/dT increased along a similar path as these fluctuations unfroze, and there is hysteresis in the cooling and heating paths, similar to that observed in the T{sub g}-endotherm range. After eliminating other interpretations, we conclude that local-region fluctuations seen as the JG relaxation in the non-equilibrium state of a glass contribute to its entropy, and we suggest conditions under which such fluctuations may be observed.

  16. Molecular Weight Dependent and Independent Glass Transition Temperature Reductions Coexisting in High MW Free-Standing Polystyrene Films

    NASA Astrophysics Data System (ADS)

    Pye, Justin; Roth, Connie

    2012-02-01

    Using transmission ellipsometry, we have measured the thermal expansion of ultrathin, high molecular weight (MW), free-standing polystyrene films over an extended temperature range. For two different MWs, we observed two distinct reduced glass transition temperatures (Tgs), separated by up to 60 K, within single films with thicknesses h less than 70 nm. The lower transition follows the previously seen MW dependent, linear Tg(h) behavior, while we also observe the presence of a much stronger upper transition that is MW independent and exhibits the same Tg(h) dependence as supported and low MW free-standing films. This represents the first experimental evidence indicating that two separate mechanisms can act simultaneously on thin free-standing polymer films to propagate enhanced mobility from the free surface into the material. The change in thermal expansion through the transitions indicate that ˜90% of the film (matrix) solidifies at the upper transition with only ˜10% of the material remaining mobile, freezing in at the lower transition. Surprisingly, when we compare our results to the existing literature, and especially the low MW free-standing film data, we conclude that the upper transition encompasses the free surface region and associated gradient in dynamics. This leaves open the question about where the small (˜10%) fraction of material that has ultrafast, MW dependent dynamics resides within the film.

  17. Thermalization calorimetry: A simple method for investigating glass transition and crystallization of supercooled liquids

    NASA Astrophysics Data System (ADS)

    Jakobsen, Bo; Sanz, Alejandro; Niss, Kristine; Hecksher, Tina; Pedersen, Ib H.; Rasmussen, Torben; Christensen, Tage; Olsen, Niels Boye; Dyre, Jeppe C.

    2016-05-01

    We present a simple method for fast and cheap thermal analysis on supercooled glass-forming liquids. This "Thermalization Calorimetry" technique is based on monitoring the temperature and its rate of change during heating or cooling of a sample for which the thermal power input comes from heat conduction through an insulating material, i.e., is proportional to the temperature difference between sample and surroundings. The monitored signal reflects the sample's specific heat and is sensitive to exo- and endothermic processes. The technique is useful for studying supercooled liquids and their crystallization, e.g., for locating the glass transition and melting point(s), as well as for investigating the stability against crystallization and estimating the relative change in specific heat between the solid and liquid phases at the glass transition.

  18. Growing dynamical facilitation on approaching the random pinning colloidal glass transition.

    PubMed

    Gokhale, Shreyas; Hima Nagamanasa, K; Ganapathy, Rajesh; Sood, A K

    2014-01-01

    Despite decades of research, it remains to be established whether the transformation of a liquid into a glass is fundamentally thermodynamic or dynamic in origin. Although observations of growing length scales are consistent with thermodynamic perspectives, the purely dynamic approach of the Dynamical Facilitation (DF) theory lacks experimental support. Further, for vitrification induced by randomly freezing a subset of particles in the liquid phase, simulations support the existence of an underlying thermodynamic phase transition, whereas the DF theory remains unexplored. Here, using video microscopy and holographic optical tweezers, we show that DF in a colloidal glass-forming liquid grows with density as well as the fraction of pinned particles. In addition, we observe that heterogeneous dynamics in the form of string-like cooperative motion emerges naturally within the framework of facilitation. Our findings suggest that a deeper understanding of the glass transition necessitates an amalgamation of existing theoretical approaches. PMID:25119444

  19. Critical exponents of the superfluid-Bose-glass transition in three dimensions.

    PubMed

    Yao, Zhiyuan; da Costa, Karine P C; Kiselev, Mikhail; Prokof'ev, Nikolay

    2014-06-01

    Recent experimental and numerical studies of the critical-temperature exponent ϕ for the superfluid-Bose-glass universality in three-dimensional systems report strong violations of the key quantum critical relation, ϕ=νz, where z and ν are the dynamic and correlation-length exponents, respectively; these studies question the conventional scaling laws for this quantum critical point. Using Monte Carlo simulations of the disordered Bose-Hubbard model, we demonstrate that previous work on the superfluid-to-normal-fluid transition-temperature dependence on the chemical potential (or the magnetic field, in spin systems), T_{c}∝(μ-μ_{c})^{ϕ}, was misinterpreting transient behavior on approach to the fluctuation region with the genuine critical law. When the model parameters are modified to have a broad quantum critical region, simulations of both quantum and classical models reveal that the ϕ=νz law [with ϕ=2.7(2), z=3, and ν=0.88(5)] holds true, resolving the ϕ-exponent "crisis." PMID:24949775

  20. 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. PMID:27064170

  1. The glass transition in cured epoxy thermosets: A comparative molecular dynamics study in coarse-grained and atomistic resolution

    SciTech Connect

    Langeloth, Michael; Böhm, Michael C.; Müller-Plathe, Florian; Sugii, Taisuke

    2015-12-28

    We investigate the volumetric glass transition temperature T{sub g} in epoxy thermosets by means of molecular dynamics simulations. The epoxy thermosets consist of the resin bisphenol A diglycidyl ether and the hardener diethylenetriamine. A structure based coarse-grained (CG) force field has been derived using iterative Boltzmann inversion in order to facilitate simulations of larger length scales. We observe that T{sub g} increases clearly with the degree of cross-linking for all-atomistic (AA) and CG simulations. The transition T{sub g} in CG simulations of uncured mixtures is much lower than in AA-simulations due to the soft nature of the CG potentials, but increases all the more with the formation of rigid cross-links. Additional simulations of the CG mixtures in contact with a surface show the existence of an interphase region of about 3 nm thickness in which the network properties deviate significantly from the bulk. In accordance to experimental studies, we observe that T{sub g} is reduced in this interphase region and gradually increases to its bulk value with distance from the surface. The present study shows that the glass transition is a local phenomenon that depends on the network structure in the immediate environment.

  2. The glass transition in cured epoxy thermosets: A comparative molecular dynamics study in coarse-grained and atomistic resolution

    NASA Astrophysics Data System (ADS)

    Langeloth, Michael; Sugii, Taisuke; Böhm, Michael C.; Müller-Plathe, Florian

    2015-12-01

    We investigate the volumetric glass transition temperature Tg in epoxy thermosets by means of molecular dynamics simulations. The epoxy thermosets consist of the resin bisphenol A diglycidyl ether and the hardener diethylenetriamine. A structure based coarse-grained (CG) force field has been derived using iterative Boltzmann inversion in order to facilitate simulations of larger length scales. We observe that Tg increases clearly with the degree of cross-linking for all-atomistic (AA) and CG simulations. The transition Tg in CG simulations of uncured mixtures is much lower than in AA-simulations due to the soft nature of the CG potentials, but increases all the more with the formation of rigid cross-links. Additional simulations of the CG mixtures in contact with a surface show the existence of an interphase region of about 3 nm thickness in which the network properties deviate significantly from the bulk. In accordance to experimental studies, we observe that Tg is reduced in this interphase region and gradually increases to its bulk value with distance from the surface. The present study shows that the glass transition is a local phenomenon that depends on the network structure in the immediate environment.

  3. Neutron Scattering Analysis of Water's Glass Transition and Micropore Collapse in Amorphous Solid Water.

    PubMed

    Hill, Catherine R; Mitterdorfer, Christian; Youngs, Tristan G A; Bowron, Daniel T; Fraser, Helen J; Loerting, Thomas

    2016-05-27

    The question of the nature of water's glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4  K min^{-1}) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at <121  K to diffusive motion across sample grains and sudden pore collapse at >121  K, in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water's glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K-in contrast to all earlier experiments in the field. PMID:27284664

  4. Determination of the glass-transition temperature of proteins from a viscometric approach.

    PubMed

    Monkos, Karol

    2015-03-01

    All fully hydrated proteins undergo a distinct change in their dynamical properties at glass-transition temperature Tg. To determine indirectly this temperature for dry albumins, the viscosity measurements of aqueous solutions of human, equine, ovine, porcine and rabbit serum albumin have been conducted at a wide range of concentrations and at temperatures ranging from 278 K to 318 K. Viscosity-temperature dependence of the solutions is discussed on the basis of the three parameters equation resulting from Avramov's model. One of the parameter in the Avramov's equation is the glass-transition temperature. For all studied albumins, Tg of a solution monotonically increases with increasing concentration. The glass-transition temperature of a solution depends both on Tg for a dissolved dry protein Tg,p and water Tg,w. To obtain Tg,p for each studied albumin the modified Gordon-Taylor equation was applied. This equation describes the dependence of Tg of a solution on concentration, and Tg,p and a parameter depending on the strength of the protein-solvent interaction are the fitting parameters. Thus determined the glass-transition temperature for the studied dry albumins is in the range (215.4-245.5)K.

  5. 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)

  6. Neutron Scattering Analysis of Water's Glass Transition and Micropore Collapse in Amorphous Solid Water

    NASA Astrophysics Data System (ADS)

    Hill, Catherine R.; Mitterdorfer, Christian; Youngs, Tristan G. A.; Bowron, Daniel T.; Fraser, Helen J.; Loerting, Thomas

    2016-05-01

    The question of the nature of water's glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4 K min-1 ) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at <121 K to diffusive motion across sample grains and sudden pore collapse at >121 K , in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water's glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K—in contrast to all earlier experiments in the field.

  7. 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. PMID:27193003

  8. 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...

  9. Kinetics of a bioactive compound (caffeine) mobility at the vicinity of the mechanical glass transition temperature induced by gelling polysaccharide.

    PubMed

    Jiang, Bin; Kasapis, Stefan

    2011-11-01

    An investigation of the diffusional mobility of a bioactive compound (caffeine) within the high-solid (80.0% w/w) matrices of glucose syrup and κ-carrageenan plus glucose syrup exhibiting distinct mechanical glass transition properties is reported. The experimental temperature range was from 20 to -60 °C, and the techniques of modulated differential scanning calorimetry, small deformation dynamic oscillation in shear, and UV spectrometry were employed. Calorimetric and mechanical measurements were complementary in recording the relaxation dynamics of high-solid matrices upon controlled heating. Predictions of the reaction rate theory and the combined WLF/free volume framework were further utilized to pinpoint the glass transition temperature (T(g)) of the two matrices in the softening dispersion. Independent of composition, calorimetry yielded similar T(g) predictions for both matrices at this level of solids. Mechanical experimentation, however, was able to detect the effect of adding gelling polysaccharide to glucose syrup as an accelerated pattern of vitrification leading to a higher value of T(g). Kinetic rates of caffeine diffusion within the experimental temperature range were taken with UV spectroscopy. These demonstrated the pronounced effect of the gelling κ-carrageenan/glucose syrup mixture to retard diffusion of the bioactive compound near the mechanical T(g). Modeling of the diffusional mobility of caffeine produced activation energy and fractional free-volume estimates, which were distinct from those of the carbohydrate matrix within the glass transition region. This result emphasizes the importance of molecular interactions between macromolecular matrix and small bioactive compound in glass-related relaxation phenomena.

  10. Doppler Shift Correlations in the Solar Transition Region

    NASA Astrophysics Data System (ADS)

    Doschek, G. A.

    2006-09-01

    I investigate dynamical correlations between the lower transition region and the upper transition region using spectra from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The measured quantity is the Doppler shift (mostly solar radial) along the line of sight. The purpose is to shed light on the fraction of the lower transition region that resides in cool structures not physically associated with higher temperature regions and the fraction that can be described by a classical transition region with a physical connection from the chromosphere into the corona. ``Transition region'' in this context means the transition region sufficiently bright in ultraviolet spectral lines to be observed. I find strong Doppler shift correlations between two different lower region lines from C IV and S V, but much weaker correlations between these lines and a line of Ne VIII formed well into the upper transition region. I conclude that most of the lower transition region that is observable because of its brightness arises in cool loop structures. The results also favor a scenario in which the lower transition region is heated and cooled transiently on timescales less than or perhaps comparable to the SUMER exposure times of 21 s for the data analyzed in this work.

  11. 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.

  12. 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

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

    PubMed Central

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

    2015-01-01

    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 12 h 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. PMID:26341321

  14. 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.

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

    PubMed

    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

  16. 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.

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

    PubMed

    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.

  18. 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. PMID:26351671

  19. 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

  20. 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.

  1. Spin-glass transition in geometrically frustrated antiferromagnets with weak disorder

    NASA Astrophysics Data System (ADS)

    Andreanov, A.; Chalker, J. T.; Saunders, T. E.; Sherrington, D.

    2010-01-01

    We study the effect in geometrically frustrated antiferromagnets of weak, random variations in the strength of exchange interactions. Without disorder the simplest classical models for these systems have macroscopically degenerate ground states, and this degeneracy may prevent ordering at any temperature. Weak exchange randomness favors a small subset of these ground states and induces a spin-glass transition at an ordering temperature determined by the amplitude of modulations in interaction strength. We use the replica approach to formulate a theory for this transition, showing that it falls into the same universality class as conventional spin-glass transitions. In addition, we show that a model with a low concentration of defect bonds can be mapped onto a system of randomly located pseudospins that have dipolar effective interactions. We also present detailed results from Monte Carlo simulations of the classical Heisenberg antiferromagnet on the pyrochlore lattice with weak randomness in nearest-neighbor exchange.

  2. 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.

  3. Nanophase separation and hindered glass transition in side-chain polymers.

    PubMed

    Beiner, Mario; Huth, Heiko

    2003-09-01

    Nanophase separation on length scales of 1-5 nanometres has been reported previously for small-molecule liquids, metallic glasses and also for several semicrystalline, liquid-crystalline and amorphous polymers. Here we show that nanophase separation of incompatible main and side-chain parts is a general phenomenon in amorphous side-chain polymers with long alkyl groups. We conclude from X-ray scattering and relaxation spectroscopy data for higher poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) that alkyl groups of different monomeric units aggregate in the melt and form self-assembled alkyl nanodomains with a typical size of 0.5-2 nm. A comparison with data for other polymer series having alkyl groups reveals that important structural and dynamic aspects are main-chain independent. A polyethylene-like glass transition within the alkyl nanodomains is observed and discussed in the context of a hindered glass transition in self-assembled confinements. This is an interesting link between central questions in glass-transition research and structural aspects in nanophase-separated materials.

  4. Optical and infrared absorption spectra of 3d transition metal ions-doped sodium borophosphate glasses and effect of gamma irradiation.

    PubMed

    Abdelghany, A M; ElBatal, F H; Azooz, M A; Ouis, M A; ElBatal, H A

    2012-12-01

    Undoped and transition metals (3d TM) doped sodium borophosphate glasses were prepared. UV-visible absorption spectra were measured in the region 200-900nm before and after gamma irradiation. Experimental optical data indicate that the undoped sodium borophosphate glass reveals before irradiation strong and broad UV absorption and no visible bands could be identified. Such UV absorption is related to the presence of unavoidable trace iron impurities within the raw materials used for preparation of this base borophosphate glass. The TMs-doped glasses show absorption bands within the UV and/or visible regions which are characteristic to each respective TM ion in addition to the UV absorption observed from the host base glass. Infrared absorption spectra of the undoped and TMs-doped glasses reveal complex FTIR consisting of extended characteristic vibrational bands which are specific for phosphate groups as a main constituent but with the sharing of some vibrations due to the borate groups. This criterion was investigated and approved using DAT (deconvolution analysis technique). The effects of different TMs ions on the FTIR spectra are very limited due to the low doping level (0.2%) introduced in the glass composition. Gamma irradiation causes minor effect on the FTIR spectra specifically the decrease of intensities of some bands. Such behavior is related to the change of bond angles and/or bond lengths of some structural building units upon gamma irradiation.

  5. Smectic-glass transition in a liquid-crystal cell with a "dirty" substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Quan; Radzihovsky, Leo

    2012-06-01

    We explore the smectic liquid-crystal order in a cell with a "dirty" substrate imposing random pinnings. Within harmonic elasticity we find a subtle three-dimensional surface disorder-driven transition into a pinned smectic glass, controlled by a three-dimensional Cardy-Ostlund-like fixed line, akin to a super-rough phase of a two-dimensional xy model. We compute the associated random substrate-driven distortions of the smectic-glass state, identify the characteristic length scales on the heterogeneous substrate and in the bulk, and discuss a variety of experimental signatures.

  6. Glass transition of associated solvents studied by fluorescence measurement of doped chromophores

    NASA Astrophysics Data System (ADS)

    Ye, Jing Yong; Hattori, Toshiaki; Inouye, Hideyuki; Ueta, Hiroshi; Nakatsuka, Hiroki; Maruyama, Yoshihiro; Ishikawa, Mitsuru

    1996-04-01

    The fluorescence lifetime of a triphenylmethane dye, malachite green, doped in three glass-forming associated solvents, 1-propanol, propylene glycol, and glycerol, was measured in a wide temperature range. For each sample three temperature regimes were found in the temperature dependence of the nonradiative relaxation time of malachite green. The lower crossover temperature corresponds to the calorimetric glass transition temperature, and the higher one, 30-50 K above the lower one, is attributed to the critical temperature that is predicted by mode-coupling theory.

  7. Microscopic Study of Glass Transition: Time-Resolved Fluorescence Measurements of Doped Dye Molecules

    NASA Astrophysics Data System (ADS)

    Nakatsuka, H.; Ye, J. Y.; Hattori, T.; Maruyama, Y.; Ishikawa, M.

    The microscopic dynamics of several monomeric and polymeric glass formers has been investigated by the time-resolved fluorescence measurement of doped malachite green molecules in a wide temperature range. For monomers and a polymer without side chains, beside a kink around the calorimetric glass transition temperature Tg, another crossover at Tc about 30 - 50 K above Tg has been clearly observed, which is in agreement with the prediction of the mode-coupling theory. On the other hand, for the complex polymers with side chains, although we could not distinguish any singularities above Tg, we observed another kink below Tg, which can be attributed to the side-chain motions.

  8. 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.

  9. Spin glasses - A transition in plain ordinary space

    NASA Astrophysics Data System (ADS)

    Souletie, J.

    We are living a fascinating moment where theorists, faced to ample experimental and (more recent) simulation evidence seem to have little choice other than to accept that the transition which they described, actually occurs in our ordinary space at 3 d. We review here some of the experimental arguments, based on critical measurements performed at equilibrium in the high temperature phase, and we stress the similarities and the differences with superparamagnetism and with an ordinary phase transition. By contrast, the slow relaxations which are observed in the low temperature phase below Tc are interpreted in terms of activation over finite energy barriers and would suggest little more than ordinary superparamagnetism. Some features of the Fulcher law which describes the edge between the equilibrium and the non equilibrium regimes, would allow to conciliate both points of view : it is the critical divergence of the barrier heights, on approaching Tc from above, which is responsible for the fact that the system appears blocked at a temperature Tg(t) slightly larger than Tc for all experiments performed in a finite time t. Nous vivons un moment fascinant ou les théoriciens, confrontés aux résultats de l'expérience et (plus récemment) de la simulation semblent n'avoir guère d'autre choix que d'accepter que la transition qu'ils avaient décrite existe bien dans notre espace à trois dimensions. Nous discutons ici quelques-uns des arguments expérimentaux basés sur l'étude de l'approche critique à Tc dans l'état paramagnétique et nous soulignons les similitudes et les différences avec le superparamagnétisme et avec une transition de phase ordinaire. Quant aux relaxations lentes qui sont observxA9es dans la phase de basse température au-dessous de Tc, leur interprétation en termes d'activation thermique suggérerait des barrières finies et du superparamagnétisme. Quelques aspects de la loi de Fulcher qui décrit bien le comportement de la temp

  10. 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.

  11. Photo-thermo-refractive glass with sensitivity extended to near infrared region

    NASA Astrophysics Data System (ADS)

    Kompan, F.; Venus, G.; Glebova, L.; Mingareev, H.; Glebov, L.

    2016-02-01

    Photo-thermo-refractive (PTR) glass is a multicomponent silicate glass doped with Ce3+ and Ag+ which is extensively used for holographic recording of volume Bragg gratings (VBGs). Possibility of recording of advanced, complex holograms in the PTR glass is of current interest as it offers great opportunities in imaging and laser systems control. However, the glass does not have capabilities for recording of complex holograms with using light from the visible / IR spectral region due to its UV photosensitivity. Extension of the PTR-glass sensitivity range into the visible / IR spectral region was carried out by doping the original glass with trivalent terbium ions. Photosensitivity mechanism was implemented by means of excited state absorption using a UV photon and a visible photon for excitation of the Tb3+ 5d14f7 band. For the first time refractive index modulation on the order of 2x10-4 was obtained in PTR glass after exposure to the visible / IR light. Resulting magnitude of induced refractive index allows for high efficiency complex hologram fabrication in Tb3+ doped PTR glass for use which in the visible / IR region. Holographic capabilities of Tb3+ doped PTR glass were demonstrated by recording a complex hologram in the glass using green and blue light.

  12. Mott glass to superfluid transition for random bosons in two dimensions

    NASA Astrophysics Data System (ADS)

    Iyer, S.; Pekker, D.; Refael, G.

    2012-03-01

    We study the zero-temperature superfluid-insulator transition for a two-dimensional model of interacting, lattice bosons in the presence of quenched disorder and particle-hole symmetry. We follow the approach of a recent series of papers by Altman, Kafri, Polkovnikov, and Refael, in which the strong disorder renormalization group is used to study disordered bosons in one dimension. Adapting this method to two dimensions, we study several different species of disorder and uncover universal features of the superfluid-insulator transition. In particular, we locate an unstable finite disorder fixed point that governs the transition between the superfluid and a gapless, glassy insulator. We present numerical evidence that this glassy phase is the incompressible Mott glass and that the transition from this phase to the superfluid is driven by a percolation-type process. Finally, we provide estimates of the critical exponents governing this transition.

  13. A Mott Glass to Superfluid Transition for Random Bosons in Two Dimensions

    NASA Astrophysics Data System (ADS)

    Pekker, David; Iyer, Shankar; Refael, Gil

    2012-02-01

    We study the zero temperature superfluid-insulator transition for a two-dimensional model of interacting, lattice bosons in the presence of quenched disorder and particle-hole symmetry. We follow the approach of a recent series of papers by Altman, Kafri, Polkovnikov, and Refael, in which the strong disorder renormalization group is used to study disordered bosons in one dimension. Adapting this method to two dimensions, we study several different species of disorder and uncover universal features of the superfluid-insulator transition. In particular, we locate an unstable finite disorder fixed point that governs the transition between the superfluid and a gapless, glassy insulator. We present numerical evidence that this glassy phase is the incompressible Mott glass and that the transition from this phase to the superfluid is driven by percolation-type process. Finally, we provide estimates of the critical exponents governing this transition.

  14. 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.

  15. 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.

  16. Molecular Reorientation Dynamics Govern the Glass Transitions of the Amorphous Ices.

    PubMed

    Shephard, J J; Salzmann, C G

    2016-06-16

    The glass transitions of low-density amorphous ice (LDA) and high-density amorphous ice (HDA) are the topic of controversial discussions. Understanding their exact nature may be the key to explaining the anomalies of liquid water but has also got implications in the general context of polyamorphism, the occurrence of multiple amorphous forms of the same material. We first show that the glass transition of hydrogen-disordered ice VI is associated with the kinetic unfreezing of molecular reorientation dynamics by measuring the calorimetric responses of the corresponding H2O, H2(18)O, and D2O materials in combination with X-ray diffraction. Well-relaxed LDA and HDA show identical isotopic-response patterns in calorimetry as ice VI, and we conclude that the glass transitions of the amorphous ices are also governed by molecular reorientation processes. This "reorientation scenario" seems to resolve the previously conflicting viewpoints and is consistent with the fragile-to-strong transition from water to the amorphous ices.

  17. Influence of molecular-weight polydispersity on the glass transition of polymers.

    PubMed

    Li, Shu-Jia; Xie, Shi-Jie; Li, Yan-Chun; Qian, Hu-Jun; Lu, Zhong-Yuan

    2016-01-01

    It is well known that the polymer glass transition temperature T_{g} is dependent on molecular weight, but the role of molecular-weight polydispersity on T_{g} is unclear. Using molecular-dynamics simulations, we clarify that for polymers with the same number-average molecular weight, the molecular-weight distribution profile (either in Schulz-Zimm form or in bimodal form) has very little influence on the glass transition temperature T_{g}, the average segment dynamics (monomer motion, bond orientation relaxation, and torsion transition), and the relaxation-time spectrum, which are related to the local nature of the glass transition. By analyzing monomer motions in different chains, we find that the motion distribution of monomers is altered by molecular-weight polydispersity. Molecular-weight polydispersity dramatically enhances the dynamic heterogeneity of monomer diffusive motions after breaking out of the "cage," but it has a weak influence on the dynamic heterogeneity of the short time scales and the transient spatial correlation between temporarily localized monomers. The stringlike cooperative motion is also not influenced by molecular-weight polydispersity, supporting the idea that stringlike collective motion is not strongly correlated with chain connectivity.

  18. Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature.

    PubMed

    Bordignon, Enrica; Nalepa, Anna I; Savitsky, Anton; Braun, Lukas; Jeschke, Gunnar

    2015-10-29

    For structural characterization by pulsed EPR methods, spin-labeled macromolecules are routinely studied at cryogenic temperatures. The equilibration of the conformational ensemble during shock-freezing occurs to a good approximation at the glass transition temperature (Tg). In this work, we used X-band power saturation continuous wave (cw) EPR to obtain information on the glass transition temperatures in the microenvironment of nitroxide radicals in solvents or bound to different sites in proteins. The temperature dependence of the saturation curve of nitroxide probes in pure glycerol or ortho-terphenyl showed detectable transitions at the respective Tg values, with the latter solvent characterized by a sharper change of the saturation properties, according to its higher fragility. In contrast, nitroxide probes in a glycerol/water mixture showed a discontinuity in the saturation properties close to the expected glass transition temperature, which made the determination of Tg complicated. Low-temperature W-band cw EPR and W-band ELDOR-detected NMR experiments demonstrated that the discontinuity is due to local rearrangements of H-bonds between water molecules and the nitroxide reporter group. The change in the network of H-bonds formed between the nitroxide and water molecules that occurs around Tg was found to be site-dependent in spin-labeled proteins. This effect can therefore be modulated by neighboring residues with different steric hindrances and/or charge distributions and possibly by the glycerol enrichment on protein surfaces. In conclusion, if the thermal history of the sample is carefully reproduced, the nitroxide probe is extremely sensitive in reporting site-specific changes in the H-bonding to water molecules close to Tg and local glass transition temperatures in spin-labeled macromolecules. PMID:26266707

  19. Changes in the Microenvironment of Nitroxide Radicals around the Glass Transition Temperature.

    PubMed

    Bordignon, Enrica; Nalepa, Anna I; Savitsky, Anton; Braun, Lukas; Jeschke, Gunnar

    2015-10-29

    For structural characterization by pulsed EPR methods, spin-labeled macromolecules are routinely studied at cryogenic temperatures. The equilibration of the conformational ensemble during shock-freezing occurs to a good approximation at the glass transition temperature (Tg). In this work, we used X-band power saturation continuous wave (cw) EPR to obtain information on the glass transition temperatures in the microenvironment of nitroxide radicals in solvents or bound to different sites in proteins. The temperature dependence of the saturation curve of nitroxide probes in pure glycerol or ortho-terphenyl showed detectable transitions at the respective Tg values, with the latter solvent characterized by a sharper change of the saturation properties, according to its higher fragility. In contrast, nitroxide probes in a glycerol/water mixture showed a discontinuity in the saturation properties close to the expected glass transition temperature, which made the determination of Tg complicated. Low-temperature W-band cw EPR and W-band ELDOR-detected NMR experiments demonstrated that the discontinuity is due to local rearrangements of H-bonds between water molecules and the nitroxide reporter group. The change in the network of H-bonds formed between the nitroxide and water molecules that occurs around Tg was found to be site-dependent in spin-labeled proteins. This effect can therefore be modulated by neighboring residues with different steric hindrances and/or charge distributions and possibly by the glycerol enrichment on protein surfaces. In conclusion, if the thermal history of the sample is carefully reproduced, the nitroxide probe is extremely sensitive in reporting site-specific changes in the H-bonding to water molecules close to Tg and local glass transition temperatures in spin-labeled macromolecules.

  20. Disentangling alpha from beta mechanical relaxations in the rubber-to-glass transition of high-sugar-chitosan mixtures.

    PubMed

    Kasapis, Stefan; Desbrières, Jacques; Al-Marhoobi, Insaaf M; Rinaudo, Marguerite

    2002-04-01

    The occurrence of molecular motions in addition to those of the glass-transition region (alpha mechanism) were investigated in chitosan and a branched derivative substituted with alkyl chains having eight carbon atoms. Once hydrophobic interactions of the alkyl groups in aqueous solution were demonstrated, polymers were mixed with glucose syrup at high levels of solids. The real (G') and imaginary (G") components of the complex dynamic modulus in high-solid mixtures were measured between 0.1 and 100 rad s(-1) in the temperature range from -55 to 50 degrees C. The method of reduced variables gave superposed curves of G' and G", which unveiled an anomaly in the dispersion of the alkylated derivative both in terms of higher modulus values and dominant elastic component of the polymeric network, as compared with the glass-transition region of chitosan. It was proposed that the new mechanical feature was due to beta mechanism, and master curves of viscoelastic functions and relaxation processes were constructed to rationalize it.

  1. Anomalous crystallization as a signature of the fragile-to-strong transition in metallic glass-forming liquids.

    PubMed

    Yang, Xiunan; Zhou, Chao; Sun, Qijing; Hu, Lina; Mauro, John C; Wang, Chunzhen; Yue, Yuanzheng

    2014-08-28

    We study the fragile-to-strong (F-S) transition of metallic glass-forming liquids (MGFLs) by measuring the thermal response during annealing and dynamic heating of La55Al25Ni5Cu15 glass ribbons fabricated at different cooling rates. We find that the glasses fabricated in the intermediate regime of cooling rates (15-25 m/s) exhibit an anomalous crystallization behavior upon reheating as compared to the glasses formed at other cooling rates. This anomalous crystallization behavior implies the existence of a thermodynamic F-S transition, could be used as an alternative method for detecting the F-S transition in MGFLs, and sheds light on the structure origin of the F-S transition. This work also contributes to obtaining a general thermodynamic picture of the F-S transition in supercooled liquids.

  2. 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+.

  3. Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics

    NASA Astrophysics Data System (ADS)

    Turner, Robert M.; Jack, Robert L.; Garrahan, Juan P.

    2015-08-01

    We consider thermodynamic and dynamic phase transitions in plaquette spin models of glasses. The thermodynamic transitions involve coupled (annealed) replicas of the model. We map these coupled-replica systems to a single replica in a magnetic field, which allows us to analyze the resulting phase transitions in detail. For the triangular plaquette model (TPM), we find for the coupled-replica system a phase transition between high- and low-overlap phases, occurring at a coupling ɛ*(T ) , which vanishes in the low-temperature limit. Using computational path sampling techniques, we show that a single TPM also displays "space-time" transitions between active and inactive dynamical phases. These first-order dynamical transitions occur at a critical counting field sc(T ) ≳0 that appears to vanish at zero temperature in a manner reminiscent of the thermodynamic overlap transition. In order to extend the ideas to three dimensions, we introduce the square pyramid model, which also displays both overlap and activity transitions. We discuss a possible common origin of these various phase transitions, based on long-lived (metastable) glassy states.

  4. Inverse transitions in a spin-glass model on a scale-free network.

    PubMed

    Kim, Do-Hyun

    2014-02-01

    In this paper, we will investigate critical phenomena by considering a model spin glass on scale-free networks. For this purpose, we consider the Ghatak-Sherrington (GS) model, a spin-1 spin-glass model with a crystal field, instead of the usual Ising-type model. Scale-free networks on which the GS model is placed are constructed from the static model, in which the number of vertices is fixed from the beginning. On the basis of the replica-symmetric solution, we obtain the analytical solutions, i.e., free energy and order parameters, and we derive the various phase diagrams consisting of the paramagnetic, ferromagnetic, and spin-glass phases as functions of temperature T, the degree exponent λ, the mean degree K, and the fraction of the ferromagnetic interactions ρ. Since the present model is based on the GS model, which considers the three states (S = 0, ± 1), the S = 0 state plays a crucial role in the λ-dependent critical behavior: glass transition temperature T(g) has a finite value, even when 2 < λ < 3. In addition, when the crystal field becomes nonzero, the present model clearly exhibits three types of inverse transitions, which occur when an ordered phase is more entropic than a disordered one. PMID:25353530

  5. Inverse transitions in a spin-glass model on a scale-free network

    NASA Astrophysics Data System (ADS)

    Kim, Do-Hyun

    2014-02-01

    In this paper, we will investigate critical phenomena by considering a model spin glass on scale-free networks. For this purpose, we consider the Ghatak-Sherrington (GS) model, a spin-1 spin-glass model with a crystal field, instead of the usual Ising-type model. Scale-free networks on which the GS model is placed are constructed from the static model, in which the number of vertices is fixed from the beginning. On the basis of the replica-symmetric solution, we obtain the analytical solutions, i.e., free energy and order parameters, and we derive the various phase diagrams consisting of the paramagnetic, ferromagnetic, and spin-glass phases as functions of temperature T, the degree exponent λ, the mean degree K, and the fraction of the ferromagnetic interactions ρ. Since the present model is based on the GS model, which considers the three states (S =0,±1), the S =0 state plays a crucial role in the λ-dependent critical behavior: glass transition temperature Tg has a finite value, even when 2<λ<3. In addition, when the crystal field becomes nonzero, the present model clearly exhibits three types of inverse transitions, which occur when an ordered phase is more entropic than a disordered one.

  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. 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.

  8. 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.

  9. Ultrasonic study on some borosilicate glasses doped with different transition metal oxides

    NASA Astrophysics Data System (ADS)

    Marzouk, S. Y.; Gaafar, M. S.

    2007-12-01

    Longitudinal and shear ultrasonic wave velocities were measured in borosilicate glasses doped with different transition metal oxides (TMOs) (where TMO=NiO, V 2O 5, Fe 2O 3, MnO 2, TiO 2, Cr 2O 3, CoO, CuO) using the pulse echo technique. Measurements were carried out at 4 MHz frequency and at room temperature. Elastic moduli and some other physical parameters such as acoustic impedance, softening temperature, Debye temperature, thermal expansion coefficient, and latent heat of melting have been calculated. Results indicated that these parameters depend upon the TMO modifier, i.e., the ionic radius of the transition metal cation. A quantitative analysis has been carried out, in order to obtain more information about the structure of these glasses, based on bond compression model, and the Makishima and Mackenzie model, i.e., the cation-anion bond of each TMO.

  10. Modified shape memory cyanate polymers with a wide range of high glass transition temperatures

    NASA Astrophysics Data System (ADS)

    Xie, Fang; Huang, Longnan; Liu, Yanju; Leng, Jinsong

    2012-04-01

    Shape memory cyanate polymers (SMCPs) are a new kind of smart materials, which have huge development potential and a promising future. A series of shape memory cyanate polymers were prepared by cyanate ester and varying content of a linear modifier. The thermal properties of the SMCPs were investigated by Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA). The SMCPs we prepared have high glass transition temperature and show good heat resistance. The glass transition temperature Tg can be adjusted from 156.9°C to 259.6°C with the modifier. The initial temperature of thermal decomposition comes up to 300°C, which is enough high for the application in aerospace fields. The shape memory polymer we prepared shows a good shape memory effect, as the shape recovery time is less than 65s and the shape recovery rate reaches 95%.

  11. 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. PMID:25872427

  12. 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

    2014-05-01

    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. PMID:24856728

  13. The effect of glass transition in fullerite C60 on Ar impurity diffusion

    NASA Astrophysics Data System (ADS)

    Dolbin, A. V.; Esel'son, V. B.; Gavrilko, V. G.; Manzhelii, V. G.; Vinnikov, N. A.; Basnukaeva, R. M.

    2013-04-01

    The kinetics of sorption and subsequent desorption of argon gas by powdered fullerite C60 has been investigated in the temperature interval 58-290 K. The temperature dependence of the Ar diffusion coefficients in fullerite has been obtained using measured characteristic times of sorption. The diffusion coefficients for Ar decrease monotonically with decreasing temperature in the entire temperature range, which corresponds to the thermally activated diffusion of Ar atoms in fullerite. The glass transition in fullerite induces an order-of magnitude decrease in the activation energy of Ar diffusion in fullerite. This appears to be due to new paths that appeared as a result of the glass transition, in which the barriers separating the interstitial voids in the C60 lattice are significantly lower.

  14. The nature of the glass transition in a silica-rich oxide melt.

    PubMed

    Farnan, I; Stebbins, J F

    1994-08-26

    The atomic-scale dynamics of the glass-to-liquid transition are, in general, poorly understood in inorganic materials. Here, two-dimensional magic angle spinning nuclear magnetic resonance spectra collected just above the glass transition of K(2)Si(4)O(9) at temperatures as high as 583 degrees C are presented. Rates of exchange for silicon among silicate species, which involves Si-O bond breaking, have been measured and are shown to be closely related in time scale to those defined by viscosity. Thus, even at viscosities as high as 10(10) pascal seconds, local bond breaking (in contrast to the cooperative motion of large clusters) is of major importance in the control of macroscopic flow and diffusion. PMID:17787585

  15. The Nature of the Glass Transition in a Silica-Rich Oxide Melt

    NASA Astrophysics Data System (ADS)

    Farnan, Ian; Stebbins, Jonathan F.

    1994-08-01

    The atomic-scale dynamics of the glass-to-liquid transition are, in general, poorly understood in inorganic materials. Here, two-dimensional magic angle spinning nuclear magnetic resonance spectra collected just above the glass transition of K_2Si_4O_9 at temperatures as high as 583^circC are presented. Rates of exchange for silicon among silicate species, which involves Si-O bond breaking, have been measured and are shown to be closely related in time scale to those defined by viscosity. Thus, even at viscosities as high as 1010 pascal seconds, local bond breaking (in contrast to the cooperative motion of large clusters) is of major importance in the control of macroscopic flow and diffusion.

  16. Mechanics at the glass-to-gel transition of thermoresponsive microgel suspensions.

    PubMed

    Appel, Jeroen; Fölker, Bart; Sprakel, Joris

    2016-03-01

    We study the rheology of systems of thermoresponsive microgels which can transition between a repulsive glass and an attractive gel state. We find marked differences between these two colloidal solids, within the same experimental system, due to the different origins for their dynamic arrest. While the rigidity of the repulsive systems depends solely on particle volume fraction, we find that the change in linear elasticity upon introducing attractive bonds in the system scales linearly with the adhesive bond strength which can be tuned with the temperature in our experiments. And while the glasses yield reversibly and with a rate-dependent energy dissipation, bond-reorganisation in the gels is suppressed so that their rupture is irreversible and accompanied by a high, but rate-independent, dissipation. These results highlight how colloids with responsive interactions can be employed to shed new light onto solid-solid transitions. PMID:26843322

  17. The Evolution of Transition Region Loops Using IRIS and AIA

    NASA Technical Reports Server (NTRS)

    Winebarger, Amy R.; DePontieu, Bart

    2014-01-01

    Over the past 50 years, the model for the structure of the solar transition region has evolved from a simple transition layer between the cooler chromosphere to the hotter corona to a complex and diverse region that is dominated by complete loops that never reach coronal temperatures. The IRIS slitjaw images show many complete transition region loops. Several of the "coronal" channels in the SDO AIA instrument include contributions from weak transition region lines. In this work, we combine slitjaw images from IRIS with these channels to determine the evolution of the loops. We develop a simple model for the temperature and density evolution of the loops that can explain the simultaneous observations. Finally, we estimate the percentage of AIA emission that originates in the transition region.

  18. Optical absorption of gamma-irradiated lithium-borate glasses doped with different transition metal oxides

    NASA Astrophysics Data System (ADS)

    Marzouk, S. Y.; Elalaily, N. A.; Ezz-Eldin, F. M.; Abd-Allah, W. M.

    2006-06-01

    We have investigated the effect of gamma irradiation on the optical properties of Li 2O-B 2O 3 containing two concentrations (0.2 or 0.5 g) of each one of the following transition metals, V, Mn, Fe or Ni oxide glass samples. We studied the impacts of gamma irradiation in terms of the mechanism by which radiation-induced defects are generated. A resolution of the observed absorption spectra showed several bands which were induced by photo-reduction or photo-oxidation assumed to take place by photo-chemical reaction according to the type of transition metal oxide (TMO). Small deviations of these induced bands characteristic of the glass constituents were observed and explained in terms of the physical properties, in relation to different oxidation states of TMO in the glass matrix. The series Mn 2+, Fe 2+ and Ni 2+ ions shows a trend of increased photo-oxidation with increasing electronegativity or decreasing mass of the ions. The prepared samples were studied in terms of their dosimetric characteristics: calibration curves from 1.0524 to 42.096 kGy and fading at (25 and 50 °C). Thermal bleaching of irradiated glass was found to permit the reduction of the larger part of TMO ions in Li 2O-B 2O 3. Also, the results showed that the degeneration of the induced bands was faster at 50 than at 25 °C. The optical energy gap Eg was found to decrease with the increase of the radiation dose, and it is suggested that the mechanism of optical transition is forbidden by indirect transition.

  19. Cubic to tetragonal phase transition of Tm3+ doped nanocrystals in oxyfluoride glass ceramics

    NASA Astrophysics Data System (ADS)

    Li, Yiming; Zhao, Lijuan; Fu, Yuting; Shi, Yahui; Zhang, Xiaoyu; Yu, Hua

    2016-02-01

    Tm3+ ions doped β-PbF2 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 Tm3+ 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 Oh to D4h site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm3+ doped nanocrystals at 800 nm was modulated by the phase transition of the surrounding crystal field.

  20. 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.

  1. Experiments reveal different dynamics in two and three dimensions near the colloidal glass transition

    NASA Astrophysics Data System (ADS)

    Vivek, Skanda; Kelleher, Colm; Chaikin, Paul; Weeks, Eric

    We use microscopy to study both 3D and quasi-2D colloidal systems as they approach their glass transitions. We use two different bidisperse 2D systems, one of which has hard particles and the other which has particles interacting with long range dipolar interactions. The 3D system also has hard interactions (3D data obtained from Narumi, et al. Soft Matter 2011). In the 3D data, we observe significant plateaus in the mean square displacement curves, in contrast to 2D. This indicates stronger transient localization in 3D. In both 2D systems, as we approach the glass transition, we observe decoupling between translational time scales and time scales for structural reorientation. In 3D, these time scales always remain coupled. Finally, in 2D we observe large clusters of particles moving in parallel directions, but similar clusters are markedly smaller in 3D. In both 2D systems, these clusters become larger on approaching the glass transition. We attribute the observed decoupling of translational and bond-orientational times in 2D to the presence of these large directional clusters. Overall, our results are in good qualitative agreement with recent simulation results [Flenner and Szamel, Nature Communications 2015].

  2. 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. PMID:27106107

  3. 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.

  4. Unveiling the dependence of glass transitions on mixing thermodynamics in miscible systems.

    PubMed

    Tu, Wenkang; Wang, Yunxi; Li, Xin; Zhang, Peng; Tian, Yongjun; Jin, Shaohua; Wang, Li-Min

    2015-01-01

    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. PMID:25686751

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

    NASA Astrophysics Data System (ADS)

    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 A0378-437110.1016/j.physa.2011.11.020 391, 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.

  6. 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. PMID:23367953

  7. Dynamic Heterogeneity in Highly Cross-linked Epoxy in the Vicinity of Glass Transition

    NASA Astrophysics Data System (ADS)

    Lin, Po-Han; Khare, Rajesh

    2010-03-01

    Cross-linked epoxy has been widely used in aerospace and electronics industries. The highly cross-linked nature of these systems leads to different chain dynamics as compared to the linear polymeric systems. In this work, we have used molecular dynamics (MD) simulations to study the dynamic heterogeneity in cross-linked epoxy near the glass transition temperature. Well-relaxed atomistic models of cross-linked epoxy were first created by employing the simulated annealing polymerization approach. The specific epoxy system studied consisted of diglycidyl ether of bisphenol-A (DGEBA) as the epoxy monomer and trimethylene glycol di-p-aminobenzoate (TMAB) as the cross-linker. The glass transition temperature of these model structures was determined from MD simulation by monitoring their volume-temperature behaviour in a stepwise cooling run. The chain dynamics of these systems were characterized by their local translational and orientational mobility. Furthermore, dynamic heterogeneity was studied by analyzing the spatial distribution of the mobile and immobile atoms in the system near the glass transition temperature.

  8. Vacuum ellipsometry as a method for probing glass transition in thin polymer films

    NASA Astrophysics Data System (ADS)

    Efremov, Mikhail Yu.; Soofi, Shauheen S.; Kiyanova, Anna V.; Munoz, Claudio J.; Burgardt, Peter; Cerrina, Franco; Nealey, Paul F.

    2008-04-01

    A vacuum ellipsometer has been designed for probing the glass transition in thin supported polymer films. The device is based on the optics of a commercial spectroscopic phase-modulated ellipsometer. A custom-made vacuum chamber evacuated by oil-free pumps, variable temperature optical table, and computer-based data acquisition system was described. The performance of the tool has been demonstrated using 20-200nm thick poly(methyl methacrylate) and polystyrene films coated on silicon substrates at 10-6-10-8torr residual gas pressure. Both polymers show pronounced glass transitions. The difficulties in assigning in the glass transition temperature are discussed with respect to the experimental challenges of the measurements in thin polymer films. It is found that the experimental curves can be significantly affected by a residual gas. This effect manifests itself at lower temperatures as a decreased or even negative apparent thermal coefficient of expansion, and is related to the uptake and desorption of water by the samples during temperature scans. It is also found that an ionization gauge—the standard accessory of any high vacuum system—can cause a number of spurious phenomena including drift in the experimental data, roughening of the polymer surface, and film dewetting.

  9. 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.

  10. Glass transition in polymers: Comparison of results from DSC, TMA, and TOA measurements

    SciTech Connect

    Wiedemann, H.G.; Widmann, G.; Bayer, G.

    1994-09-01

    The determination of the glass transition temperature, T{sub g}, of polymers by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) is sometimes problematic and rather subjective. This was shown previously in the ICTA certificate (distributed by NBS as GM-754) for the certified reference material polystyrene (PS). The not very good reproducibility of the measured value of the onset is due to a variety of instrumental and experimental parameters. This is true also for the determination of the glass transition by TMA measurements. The main reasons are temperature gradients caused by the relatively high sample mass required for DSC and by the limited heat transfer in TMA, respectively. Their own experiments which were carried out with polystyrene and with [poly(ethyleneterephthalate)] (PET) proved that a combination of DSC with TOA (thermo-optical analysis or hot stage microscopy under polarized light) can solve some of these problems. TOA is a nonsubjective method since the changes in birefringence and light transmittance during the glass transition which are visible under the microscope are measured with a photocell. TOA allows T{sub g} measurements of small samples (fraction of milligrams).

  11. Interplay of anisotropy and disorder in the doping-dependent melting and glass transitions of vortices in Bi2Sr2CaCu2O 8+delta.

    PubMed

    Beidenkopf, H; Verdene, T; Myasoedov, Y; Shtrikman, H; Zeldov, E; Rosenstein, B; Li, D; Tamegai, T

    2007-04-20

    We study the oxygen doping dependence of the equilibrium first-order melting and second-order glass transitions of vortices in Bi2Sr2CaCu2O 8+delta. Doping affects both anisotropy and disorder. Anisotropy scaling is shown to collapse the melting lines only where thermal fluctuations are dominant. Yet, in the region where disorder breaks that scaling, the glass lines are still collapsed. A quantitative fit to melting and replica symmetry-breaking lines of a 2D Ginzburg-Landau model further reveals that disorder amplitude weakens with doping, but to a lesser degree than thermal fluctuations, enhancing the relative role of disorder.

  12. Apollo 14 Impact Glasses and Clementine Data: Implications for Regional Geology

    NASA Technical Reports Server (NTRS)

    Zellner, N. E. B.; Spudis, P. D.; Delano, J. W.; Whittet, D. C. B.

    2002-01-01

    Clementine color image data and analyses of 778 lunar impact glasses have been used together to suggest that the highlands of the Fra Mauro region consist of a KREEP-rich regolith overlying a feldspathic terrain. Low-KREEP impact glasses may possess a memory of impacts prior to 3.9 Ga ago. Additional information is contained in the original extended abstract.

  13. 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.

  14. A molecular dynamics simulation of the melting points and glass transition temperatures of myo- and neo-inositol.

    PubMed

    Watt, Stephen W; Chisholm, James A; Jones, William; Motherwell, Sam

    2004-11-15

    The heat of sublimation, density, melting point, and glass transition temperature are calculated for myo- and neo-inositol, using the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field and molecular dynamics techniques. Our results show that the calculated heats of sublimation and density are very close to the experimental values for both compounds. Furthermore, our simulated melting temperatures for myo- and neo-inositol also compare very well to the experimentally obtained data. The glass transition temperatures for myo- and neo-inositol have been calculated to be ca. 494 K and ca. 518 K, respectively, and the shape of the volume versus temperature plots produced are typical for a glass transition. As a result, it is our view that the COMPASS force field suitably describes these two compounds in molecular simulations and that molecular dynamics techniques, combined with this force field, can be used to simulate the melt and glass transitions for such molecules.

  15. Glass transition temperature of honey as a function of water content as determined by differential scanning calorimetry.

    PubMed

    Kántor, Z; Pitsi, G; Thoen, J

    1999-06-01

    The glass transition of pure and diluted honey and the glass transition of the maximally freeze-concentrated solution of honey were investigated by differential scanning calorimetry (DSC). The glass transition temperature, of the pure honey samples accepted as unadulterated varied between -42 and -51 degrees C. Dilution of honey to 90 wt % honey content resulted in a shift of the glass transition temperature by -13 to -20 degrees C. The concentration of the maximally freeze-concentrated honey solutions, as expressed in terms of honey content is approximately 102-103%, i.e., slightly more concentrated in sugars than honey itself. The application of DSC measurements of and in characterization of honey may be considered, but requires systematic study on a number of honeys. PMID:10794630

  16. 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.

  17. Thermodynamic evidence for the Bose glass transition in twinnedYBa2Cu3O7-δcrystals

    DOE PAGES

    Pérez-Morelo, D. J.; Osquiguil, E.; Kolton, A. B.; Nieva, G.; Jung, I. W.; López, D.; Pastoriza, H.

    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.

  18. Pressure-Induced Glass Transition Probed via the Mobility of Coumarin 1 Fluorescent Molecule.

    PubMed

    Bonetti, Marco

    2016-05-12

    The route to form a glass is generally achieved upon cooling where the slowing down might be interpreted as the trapping of molecules in potential wells. On the other hand, isothermal compression induces a glassy state by modifying the molecular packing ending in jamming. Here, we focus on how isothermal compression perturbs the mobility of a probe molecule in three different host liquids up to the pressure-induced glass transition. By use of the fluorescence recovery technique, the diffusion of the fluorescent molecule Coumarin 1 (C1) is measured in poly(propylene glycol) (PPG-1000M and -2700M), in the fragile van der Waals propylene carbonate (PC), and in hydrogen-bonded methanol and ethanol. High pressures up to 6 GPa are obtained with a diamond anvil cell. In PC at a pressure ∼1.3 GPa close to the glass-transition pressure, the diffusion coefficient of C1 follows an Arrhenius behavior with an ∼5 orders of magnitude increase of the diffusive time. No decoupling from the Stokes-Einstein equation is noticed. A similar exponential behavior is measured in ethanol and methanol but extended to different pressure ranges up to 2.5 and 6.2 GPa, respectively. In PPG-1000M a decoupling from the Stokes-Einstein relation is observed between 0.3 and 0.8 GPa that could be related to a modification of the interaction between polymer segments and the probe molecule. These results might indicate that interaction between probe and dynamic heterogeneities become less important under applied pressure, unlike in the temperature-induced glass transition. PMID:27110923

  19. Strain glass transition in a multifunctional β-type Ti alloy

    PubMed Central

    Wang, Yu; Gao, Jinghui; Wu, Haijun; Yang, Sen; Ding, Xiangdong; Wang, Dong; Ren, Xiaobing; Wang, Yunzhi; Song, Xiaoping; Gao, Jianrong

    2014-01-01

    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. PMID:24500779

  20. Fine structure of the solar transition region - Observations and interpretation

    NASA Technical Reports Server (NTRS)

    Cook, J. W.; Brueckner, G. E.

    1991-01-01

    An evaluation is conducted of recent high spatial resolution observations of the solar transition region and temperature minimum, in the form of UV spectra and spectroheliographs from both sounding rockets and the Spacelab 2 flights of the High Resolution Telescope and Spectrograph (HRTS). Attention is given to the solar atmosphere structure implications of the HRST's observational results. The inclusion of fine structure in conjectures concerning the transition region affects the plausibility of 1D average models of the solar atmosphere, as well as the determination of temperature gradients, possible nonradiative-heating mechanisms, and the comparison of transition region structures with corresponding observations of the photosphere and corona.

  1. The influence of gamma radiation on the molecular weight and glass transition of PLLA and HAp/PLLA nanocomposite

    NASA Astrophysics Data System (ADS)

    Milicevic, D.; Trifunovic, S.; Dojcilovic, J.; Ignjatovic, N.; Suljovrujic, E.

    2010-09-01

    The influence of gamma radiation on the molecular weight and glass transition behaviour of poly- L-lactide (PLLA) and hydroxyapatite/poly- L-lactide (HAp/PLLA) nanocomposite has been studied. Since PLLA exposed to high-energy radiation in the presence of air is prone to chain scission reactions and large degradation, changes in molecular weight were obtained by gel permeation chromatography (GPC). Alterations in the glass transition behaviour were investigated by differential scanning calorimetry (DSC). The apparent activation energy (Δ H∗) for glass transition was determined on the basis of the heating rate dependence of the glass transition temperature ( T g). Our findings support the fact that chain scission is the main reason for the decrease of T g and Δ H∗ with the absorbed dose. Furthermore, more intensive chain scission degradation of PLLA was observed in HAp/PLLA and can only be ascribed to the presence of HAp nanoparticles. Consequently, initial differences in the glass transition temperature and/or apparent activation energy of PLLA and HAp/PLLA became more pronounced with absorbed dose. This study reveals that radiation-induced changes in molecular weight and glass transition temperature occur in a predictable and fairly accurate manner. Therefore, gamma radiation can be used not only for sterilization but also for tailoring desirable end-use properties of these biomaterials.

  2. Glass electrolytes

    SciTech Connect

    Not Available

    1984-06-25

    The objective of this research is a glass electrolyte for use in sodium/sulfur batteries that has a low resistivity (100 ohm-cm at 300/sup 0/C) and is stable in the cell environment. Experiments in this program are focussed on glasses in the quaternary system: soda, alumina, zirconia and silica. The FY 1983 research on glass analogs of NASICON, parallel thermodynamic calculations, and a review of the literature in the areas of glass conductivity and corrosion resistance led to selection of this system for more detailed investigation. The main program elements are: (1) conductivity measurements at 300 to 500/sup 0/C; (2) differential thermal analysis for determination of glass-transition and crystallization temperatures; (3) static corrosion tests at 400/sup 0/C using Na, Na/sub 2/S/sub 4/, and S; (4) mechanical strength and fracture toughness measurements; and (5) sodium/sulfur cell tests at 350/sup 0/C. Elements (1) and (2) are nearly completed; element (3) is being initiated using the glasses prepared for (1) and (2), and elements (4) and (5) will begin in the first and second quarters of FY 1985, respectively. Fourteen quaternary glasses having a broad range of compositions have been made. The resistivities of these glasses at 300/sup 0/C extended from 130 to 3704 ohm-cm; the activation energies for conduction extended from 0.488 to 0.684 eV, and the glass transition temperatures extended from 397 to 685/sup 0/C. Through a multiple linear regression analysis of these data response surfaces were generated for resistivity, activation energy for conduction, and glass transition temperature over the composition region within the quaternary system that is bounded by SiO/sub 2/, Na/sub 2/O/sub 3/, Na/sub 2/AlO/sub 4/ and Na/sub 2/ZrO/sub 3/. These response surfaces indicated a new region of high conductivity and high glass transition temperature in the neighborhood of 42% soda, 31% silica and 27% alumina plus zirconia.

  3. 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.

  4. 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. PMID:27517325

  5. Response of water to electric fields at temperatures below the glass transition: A molecular dynamics analysis

    NASA Astrophysics Data System (ADS)

    Hu, Xiaohu; Elghobashi-Meinhardt, Nadia; Gembris, Daniel; Smith, Jeremy C.

    2011-10-01

    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.

  6. Phase Transition for Quenched Coupled Replicas in a Plaquette Spin Model of Glasses.

    PubMed

    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. PMID:26894718

  7. 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.

  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. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses.

    PubMed

    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. PMID:27143686

  10. Unusual magnetic transitions and nature of magnetic resonance spectra in oxide glasses containing gadolinium

    NASA Astrophysics Data System (ADS)

    Kliava, Janis; Malakhovskii, Alexander; Edelman, Irina; Potseluyko, Anatoly; Petrakovskaja, Eleonora; Melnikova, Svetlana; Zarubina, Tat'Jana; Petrovskii, Gurii; Bruckental, Yishay; Yeshurun, Yosef

    2005-03-01

    Magnetic susceptibility, electron paramagnetic resonance (EPR), and optical properties have been studied in a glass system {20La2O3-22Al2O3-23B2O3-35(SiO2+GeO2)} with a part of La2O3 substituted by Gd2O3 in different concentrations. Positive Weiss constants have been found in the more heavily doped glasses and ascribed to clustering of Gd3+ ions. Two magnetic phase transitions at 55 and 12 K were detected and ascribed, respectively, to ferromagnetic and antiferromagnetic clusters containing Gd ions. The overall shape of the EPR spectra shows the presence of clustering at the higher Gd contents. At low temperatures the cluster-related resonance signal is altered in shape, indicating an onset of magnetic anisotropy field. This signal is convincingly fitted to superparamagnetic resonance arising from ferromagnetic nanoparticles. The clustering, depending on the Gd concentration, correlates with a significant shift to lower energies of the strong optical absorption band edge, ascribed to a charge transfer transition between Gd ions. A nonmonotonous change of refractive index with the increase of the Gd content indicates changes in the glass matrix and in Gd cluster structure.

  11. 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.

  12. Thermal stability and optical transitions of Er 3+/Yb 3+-codoped barium gallogermanate glass

    NASA Astrophysics Data System (ADS)

    Xiao, Kai; Yang, Zhongmin

    2007-07-01

    Er3+/Yb3+-codoped barium gallogermanate glass that is suitable for use in fiber lasers and optical waveguide devices has been fabricated and characterized. The differential scanning calorimetry, absorption spectra, infrared fluorescence and upconversion luminescence spectra of the glass have been measured. The spontaneous radiative transition probability, branching ratio, and radiative lifetime of the optical transitions have been calculated by using the Judd-ofelt theory. Differential scanning calorimetry result suggests that it is suitable to be a potential candidate for fiber drawing. Intense infrared fluorescence at 1531 nm and bright visible upconversion luminescence have been observed under 980 nm laser diode excitation at room temperature. The quadratic dependence of the upconversion emission on the excitation power indicates that two-photon steps are involved for the three visible emission bands. The possible upconversion mechanisms have also been discussed. All the results reveal that the Er3+/Yb3+-codoped barium gallogermanate glass fabricated in our work could be a suitable candidate for upconversion and infrared applications.

  13. Are rare, long waiting times between rearrangement events responsible for the slowdown of the dynamics at the glass transition?

    NASA Astrophysics Data System (ADS)

    Ahn, Ji Won; Falahee, Bryn; Del Piccolo, Chiara; Vogel, Michael; Bingemann, Dieter

    2013-03-01

    The dramatic slowdown of the structural relaxation at the glass transition is one of the most puzzling features of glass dynamics. Single molecule orientational correlation times show this strong Vogel-Fulcher-Tammann temperature dependence typical for glasses. Through statistical analysis of single molecule trajectories, we can identify individual glass rearrangement events in the vicinity of a probe molecule in the glass former poly(vinyl acetate) from 8 K below to 6 K above the glass transition temperature. We find that changes in the distribution of waiting times between individual glass rearrangement events are much less dramatic with temperature, the main difference being a small, but decisive number of increasingly long waiting times at lower temperatures. We notice similar individual, local relaxation events in molecular dynamics trajectories for a variety of glassy systems further from the glass transition, leading to waiting time distributions with similar features as those observed in the single molecule experiments. We show that these rare long waiting times are responsible for the dramatic increase in correlation time upon cooling.

  14. Observation of the transition state for pressure-induced BO₃→ BO₄ conversion in glass.

    PubMed

    Edwards, Trenton; Endo, Takatsugu; Walton, Jeffrey H; Sen, Sabyasachi

    2014-08-29

    A fundamental mechanistic understanding of the pressure- and/or temperature-induced facile transformation of the coordination environment of boron is important for changing the physical properties of glass. We have used in situ high-pressure (up to 2 gigapascals) boron-11 solid-state nuclear magnetic resonance spectroscopy in combination with ab initio calculations to investigate the nature of the transition state for the pressure-induced BO3→ BO4 conversion in a borosilicate glass at ambient temperature. The results indicate an anisotropic elastic deformation of the BO3 planar triangle, under isotropic stress, into a trigonal pyramid that likely serves as a precursor for the subsequent formation of a BO4 tetrahedron. PMID:25170146

  15. Implausibility of Hydrostatic Funnels Constituting the Sun's Upper Transition Region

    NASA Astrophysics Data System (ADS)

    Oluseyi, Hakeem M.; Carpio, Melisa M.; Sheung, Janet

    2007-09-01

    Over the past thirty years, two bodies of literature have developed in parallel presenting mutually exclusive views of the Sun’s upper transition region. One model holds that the Sun’s upper-transition-region plasmas are confined primarily in hydrostatic funnels with a substantial backheating component. The other model holds that discrete structures, which are effectively isolated from the corona, predominate in the Sun’s upper transition region. Purveyors of the latter position have recently begun to present near-resolved observations of discrete structures. The funnel scenario, in contrast, has only been addressed by modeling unresolved upper transition region emission. To address this paradox we have constructed hydrostatic funnel models and tested them against a wider set of solar observations than previously performed. We reproduce the results of the previous analyses, yet find that the hydrostatic funnels are unable to self-consistently match the wider set of observations against which we test the models. We show that it is not possible for a class of funnels having peak temperatures in the transition region or in the corona to match the observations. We conclude that it is implausible that a class of hydrostatic funnels constitutes the dominant emitting component of the Sun’s upper-transition-region plasmas as has been suggested.

  16. Threshold transitions in a regional urban system

    EPA Science Inventory

    In this paper we analyze the evolution of city size distributions over time in a regional urban system. This urban complex system is in constant flux with changing groups and city migration across existing and newly created groups. Using group formation as an emergent property, t...

  17. 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).

  18. Spin-glass phase transitions and minimum energy of the random feedback vertex set problem

    NASA Astrophysics Data System (ADS)

    Qin, Shao-Meng; Zeng, Ying; Zhou, Hai-Jun

    2016-08-01

    A feedback vertex set (FVS) of an undirected graph contains vertices from every cycle of this graph. Constructing a FVS of sufficiently small cardinality is very difficult in the worst cases, but for random graphs this problem can be efficiently solved by converting it into an appropriate spin-glass model [H.-J. Zhou, Eur. Phys. J. B 86, 455 (2013), 10.1140/epjb/e2013-40690-1]. In the present work we study the spin-glass phase transitions and the minimum energy density of the random FVS problem by the first-step replica-symmetry-breaking (1RSB) mean-field theory. For both regular random graphs and Erdös-Rényi graphs, we determine the inverse temperature βl at which the replica-symmetric mean-field theory loses its local stability, the inverse temperature βd of the dynamical (clustering) phase transition, and the inverse temperature βs of the static (condensation) phase transition. These critical inverse temperatures all change with the mean vertex degree in a nonmonotonic way, and βd is distinct from βs for regular random graphs of vertex degrees K >60 , while βd are identical to βs for Erdös-Rényi graphs at least up to mean vertex degree c =512 . We then derive the zero-temperature limit of the 1RSB theory and use it to compute the minimum FVS cardinality.

  19. Phase field crystal modelling of the order-to-disordered atomistic structure transition of metallic glasses

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Mi, J.

    2016-03-01

    Bulk metallic glass composites are a new class of metallic alloy systems that have very high tensile strength, ductility and fracture toughness. This unique combination of mechanical properties is largely determined by the presence of crystalline phases uniformly distributed within the glassy matrix. However, there have been very limited reports on how the crystalline phases are nucleated in the super-cooled liquid and their growth dynamics, especially lack of information on the order-to-disordered atomistic structure transition across the crystalline-amorphous interface. In this paper, we use phase field crystal (PFC) method to study the nucleation and growth of the crystalline phases and the glass formation of the super cooled liquid of a binary alloy. The study is focused on understanding the order-to-disordered transition of atomistic configuration across the interface between the crystalline phases and amorphous matrix of different chemical compositions at different thermal conditions. The capability of using PFC to simulate the order-to-disorder atomistic transition in the bulk material or across the interface is discussed in details.

  20. Spin-glass phase transitions and minimum energy of the random feedback vertex set problem.

    PubMed

    Qin, Shao-Meng; Zeng, Ying; Zhou, Hai-Jun

    2016-08-01

    A feedback vertex set (FVS) of an undirected graph contains vertices from every cycle of this graph. Constructing a FVS of sufficiently small cardinality is very difficult in the worst cases, but for random graphs this problem can be efficiently solved by converting it into an appropriate spin-glass model [H.-J. Zhou, Eur. Phys. J. B 86, 455 (2013)EPJBFY1434-602810.1140/epjb/e2013-40690-1]. In the present work we study the spin-glass phase transitions and the minimum energy density of the random FVS problem by the first-step replica-symmetry-breaking (1RSB) mean-field theory. For both regular random graphs and Erdös-Rényi graphs, we determine the inverse temperature β_{l} at which the replica-symmetric mean-field theory loses its local stability, the inverse temperature β_{d} of the dynamical (clustering) phase transition, and the inverse temperature β_{s} of the static (condensation) phase transition. These critical inverse temperatures all change with the mean vertex degree in a nonmonotonic way, and β_{d} is distinct from β_{s} for regular random graphs of vertex degrees K>60, while β_{d} are identical to β_{s} for Erdös-Rényi graphs at least up to mean vertex degree c=512. We then derive the zero-temperature limit of the 1RSB theory and use it to compute the minimum FVS cardinality. PMID:27627285

  1. Spontaneous bond orientational ordering in liquids: An intimate link between glass transition and crystallization

    NASA Astrophysics Data System (ADS)

    Tanaka, Hajime; Russo, John; Leocmach, Mathieu; Kawasaki, Takeshi

    2013-02-01

    The origin of slow dynamics near glass transition and the mechanism of crystal nucleation are two unsolved fundamental problems associated with the metastable supercooled state of a liquid. So far these phenomena have been considered rather independently, however, we have revealed an intimate link between them. Recently we found that crystallike bond orientational order develops in the supercooled state of (nearly) single-component systems such as spin liquids and weakly polydisperse colloidal liquids. In these liquids, low free-energy configurations in a supercooled liquid have a link to the rotational symmetry which is going to be broken upon crystallization. We argue that this is a direct consequence of that the same free energy governs both glass transition and crystallization at least in this type of liquids. We found that it is such structural ordering at least in this type of liquids that causes glassy slow dynamics and dynamic heterogeneity. Furthermore, we revealed that such structural order also plays a crucial role in crystal nucleation: Crystallization is a process of the enhancement of spatial coherence of crystal-like bond orientational order and `not' driven by translational order at least in the nucleation stage. These results clearly indicate that the theoretical description at the two-body level is not enough to describe these phenomena and it is crucial to take into account many body correlations, particularly, bond orientational correlations. We argue that there is an intrinsic link between glass transition and crystallization if crystallization does not accompany other processes such as phase separation. If crystallization involves phase separation, on the other hand, such a direct link may be lost. We speculate that even in such a case glassy structural order may still be associated with low free-energy local configurations.

  2. 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.

  3. 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

  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. Glass transition temperature of water confined in lipid membranes as determined by anelastic spectroscopy

    NASA Astrophysics Data System (ADS)

    Castellano, C.; Generosi, J.; Congiu, A.; Cantelli, R.

    2006-12-01

    The research of gene delivery vehicles used in gene therapy is focused on nonviral vectors like lipid membranes. Such vectors, nonimmunogenic and biodegradable, are formed by complexation of DNA with a mixture of cationic lipids and a neutral colipid which improve the transfection efficiency. A main topic related to lipid membrane dynamics is their capability to spontaneously confine water. At present the value of the glass transition temperature (Tg) is largely debated and determined only by some indirect methods. Here the authors show that anelastic spectroscopy allows the confined water Tg value to be directly identified in several lipid mixtures.

  6. 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.

  7. 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

  8. Condensation of Si-rich region inside soda-lime glass by parallel femtosecond laser irradiation.

    PubMed

    Sakakura, Masaaki; Yoshimura, Kouhei; Kurita, Torataro; Shimizu, Masahiro; Shimotsuma, Yasuhiko; Fukuda, Naoaki; Hirao, Kazuyuki; Miura, Kiyotaka

    2014-06-30

    Local melting and modulation of elemental distributions can be induced inside a glass by focusing femtosecond (fs) laser pulses at high repetition rate (>100 kHz). Using only a single beam of fs laser pulses, the shape of the molten region is ellipsoidal, so the induced elemental distributions are often circular and elongate in the laser propagation direction. In this study, we show that the elongation of the fs laser-induced elemental distributions inside a soda-lime glass could be suppressed by parallel fsing of 250 kHz and 1 kHz fs laser pulses. The thickness of a Si-rich region became about twice thinner than that of a single 250 kHz laser irradiation. Interestingly, the position of the Si-rich region depended on the relative positions between 1 kHz and 250 kHz photoexcited regions. The observation of glass melt during laser exposure showed that the vortex flow of glass melt occurred and it induced the formation of a Si-rich region. Based on the simulation of the transient temperature and viscosity distributions during laser exposure, we temporally interpreted the origin of the vortex flow of glass melt and the mechanism of the formation of the Si-rich region.

  9. Testing of transition-region models: Test cases and data

    NASA Technical Reports Server (NTRS)

    Singer, Bart A.; Dinavahi, Surya; Iyer, Venkit

    1991-01-01

    Mean flow quantities in the laminar turbulent transition region and in the fully turbulent region are predicted with different models incorporated into a 3-D boundary layer code. The predicted quantities are compared with experimental data for a large number of different flows and the suitability of the models for each flow is evaluated.

  10. Structural transition and orbital glass physics in near-itinerant CoV2O4

    NASA Astrophysics Data System (ADS)

    Reig-i-Plessis, D.; Casavant, D.; Garlea, V. O.; Aczel, A. A.; Feygenson, M.; Neuefeind, J.; Zhou, H. D.; Nagler, S. E.; MacDougall, G. J.

    2016-01-01

    The ferrimagnetic spinel CoV2O4 has been a topic of intense recent interest, both as a frustrated insulator with unquenched orbital degeneracy and as a near-itinerant magnet which can be driven metallic with moderate applied pressure. Here, we report on our recent neutron diffraction and inelastic scattering measurements on powders with minimal cation site disorder. Our main new result is the identification of a weak (Δ/a a ˜10-4 ), first order structural phase transition at T*=90 K, the same temperature where spin canting was seen in recent single crystal measurements. This transition is characterized by a short-range distortion of oxygen octahedral positions, and inelastic data further establish a weak Δ ˜1.25 meV spin gap at low temperature. Together, these findings provide strong support for the local orbital picture and the existence of an orbital glass state at temperatures below T*.

  11. Combustion characteristics in the transition region of liquid fuel sprays

    NASA Technical Reports Server (NTRS)

    Cernansky, N. P.; Namer, I.; Tidona, R. J.

    1984-01-01

    A number of important effects were observed in the droplet size transition region in spray combustion systems. In this region, where the mechanism of flame propagation is transformed from diffusive to premixed dominated combustion, the following effects have been observed: (1) maxima in burning velocity; (2) extension of flammability limits; (3) minima in ignition energy; and (4) minima in NO(x) formation. Unfortunately, because of differences in experimental facilities and limitations in the ranges of experimental data, a unified description of these transition region effects is not available at this time. Consequently, a fundamental experimental investigation was initiated to study the effect of droplet size, size distribution, and operating parameters on these transition region phenomena in a single well controlled spray combustion facility.

  12. The Impact of Opioid Treatment on Regional Gastrointestinal Transit

    PubMed Central

    Poulsen, Jakob L; Nilsson, Matias; Brock, Christina; Sandberg, Thomas H; Krogh, Klaus; Drewes, Asbjørn M

    2016-01-01

    Background/Aims To employ an experimental model of opioid-induced bowel dysfunction in healthy human volunteers, and evaluate the impact of opioid treatment compared to placebo on gastrointestinal (GI) symptoms and motility assessed by questionnaires and regional GI transit times using the 3-dimensional (3D)-Transit system. Methods Twenty-five healthy males were randomly assigned to oxycodone or placebo for 5 days in a double blind, crossover design. Adverse GI effects were measured with the bowel function index, gastrointestinal symptom rating scale, patient assessment of constipation symptom questionnaire, and Bristol stool form scale. Regional GI transit times were determined using the 3D-Transit system, and segmental transit times in the colon were determined using a custom Matlab® graphical user interface. Results GI symptom scores increased significantly across all applied GI questionnaires during opioid treatment. Oxycodone increased median total GI transit time from 22.2 to 43.9 hours (P < 0.001), segmental transit times in the cecum and ascending colon from 5.7 to 9.9 hours (P = 0.012), rectosigmoid colon transit from 2.7 to 9.0 hours (P = 0.044), and colorectal transit time from 18.6 to 38.6 hours (P = 0.001). No associations between questionnaire scores and segmental transit times were detected. Conclusions Self-assessed GI adverse effects and increased GI transit times in different segments were induced during oxycodone treatment. This detailed information about segmental changes in motility has great potential for future interventional head-to-head trials of different laxative regimes for prevention and treatment of constipation. PMID:26811503

  13. 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

  14. 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.

  15. 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.

  16. 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. PMID:24735317

  17. 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.

  18. Relaxation transition in glass-forming polybutadiene as revealed by nuclear resonance X-ray scattering

    SciTech Connect

    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{sup −9} to 10{sup −5} s) and a scattering vector Q range (9.6–40 nm{sup −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{sub c} in the mode coupling theory. The results suggest the important roles of hopping motions below T{sub 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.

  19. Effect of Glass Transition on Electrical Conduction Characteristics of Poly-L-lactic Acid

    NASA Astrophysics Data System (ADS)

    Maeno, Yasumasa; Yamaguchi, Yuya; Hirai, Naoshi; Tanaka, Toshikatsu; Ohki, Yoshimichi; Tajitsu, Yoshiro; Kohtoh, Masanori; Okabe, Shigemitsu

    The temperature dependence of electrical conduction current in additive-free poly-L-lactic acid was measured from 20 °C to 90 °C under application of dc 2.5 kV. Although the current obeys the Arrhenius formula, a hump appears in some conditions, depending on whether the temperature is being ascended or descended, and also on whether the sample was poled or short-circuited prior to the measurements. Even under short-circuit condition, a similar hump alone appears if the sample was poled by a dc voltage beforehand. From these results, it is assumed that orientational polarization or depolarization occurs around 74 °C by the glass transition, and that its resultant current and the conduction current overlap with each other. The fact that polar groups, mainly carbonyl groups, in the sample really changed their directions was confirmed by Fourier-transform infrared spectroscopy. The permittivity also increases around 74 °C. These facts indicate that the number of dipoles, which become possible to rotate toward the direction of electric field, is increased by the glass transition.

  20. Glass transition, freezing and melting of liquids confined in the mesoporous silicate MCM-41

    NASA Astrophysics Data System (ADS)

    Morineau, Denis; Dosseh, Gilberte; Alba-Simionesco, Christiane; Llewellyn, Philip

    1999-11-01

    MCM-41 is a recently discovered mesoporous silicate that consists of a hexagonal arrangement of cylindrical pores. Because the pores are very well defined in size and shape, MCM-41 can be considered as a model material in comparison with previous types of porous glass and has therefore been used in the present study. In particular, we have focused on the properties of confined liquids and related phase transitions using an MCM-41 with a pore diameter of 4nm. We discuss here the first stage of a study where the thermodynamics of a series of molecular liquids (water, cyclohexane, benzene, toluene, o-terphenyl and m toluidine) are analysed by differential scanning calorimetry. Only a moderate decrease in the melting point of organic liquids has been observed. Moreover, analysing the freezing process, we have established thermal treatments that provide temperature ranges where confined liquids can be studied below the melting temperatures of both the bulk and the confined phases. Surprisingly, no significant change in the glass transition temperature has been observed compared with the bulk.

  1. 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. PMID:26776036

  2. Anomalous glass transition behavior of SBR-Al₂O₃ nanocomposites at small filler concentrations.

    PubMed

    Sushko, Rymma; Filimon, Marlena; Dannert, Rick; Elens, Patrick; Sanctuary, Roland; Baller, Jörg

    2014-10-24

    Elastomers filled with hard nanoparticles are of great technical importance for the rubber industry. In general, fillers improve mechanical properties of polymer materials, e.g. elastic moduli, tensile strength etc. The smaller the size of the particles, the larger is the interface where interactions between polymer molecules and fillers can generate new properties. Using temperature-modulated differential scanning calorimetry and dynamic mechanical analysis, we investigated the properties of pure styrene-butadiene rubber (SBR) and SBR/alumina nanoparticles. Beside a reinforcement effect seen in the complex elastic moduli, small amounts of nanoparticles of about 2 wt% interestingly lead to an acceleration of the relaxation modes responsible for the thermal glass transition. This leads to a minimum in the glass transition temperature as a function of nanoparticle content in the vicinity of this critical concentration. The frequency dependent elastic moduli are used to discuss the possible reduction of the entanglement of rubber molecules as one cause for this unexpected behavior. PMID:25277754

  3. Dielectric relaxation of 2-ethyl-1-hexanol around the glass transition by thermally stimulated depolarization currents.

    PubMed

    Arrese-Igor, S; Alegría, A; Colmenero, J

    2015-06-01

    We explore new routes for characterizing the Debye-like and α relaxation in 2-ethyl-1-hexanol (2E1H) monoalcohol by using low frequency dielectric techniques including thermally stimulated depolarization current (TSDC) techniques and isothermal depolarization current methods. In this way, we have improved the resolution of the overlapped processes making it possible the analysis of the data in terms of a mode composition as expected for a chain-like response. Furthermore the explored ultralow frequencies enabled to study dynamics at relatively low temperatures close to the glass transition (Tg). Results show, on the one hand, that Debye-like and α relaxation timescales dramatically approach to each other upon decreasing temperature to Tg. On the other hand, the analysis of partial polarization TSDC data confirms the single exponential character of the Debye-like relaxation in 2E1H and rules out the presence of Rouse type modes in the scenario of a chain-like response. Finally, on crossing the glass transition, the Debye-like relaxation shows non-equilibrium effects which are further emphasized by aging treatment and would presumably emerge as a result of the arrest of the structural relaxation below Tg. PMID:26049505

  4. 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.

  5. 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. PMID:25638003

  6. Glass transitions in native silk fibres studied by dynamic mechanical thermal analysis.

    PubMed

    Guan, Juan; Wang, Yu; Mortimer, Beth; Holland, Chris; Shao, Zhengzhong; Porter, David; Vollrath, Fritz

    2016-07-01

    Silks are a family of semi-crystalline structural materials, spun naturally by insects, spiders and even crustaceans. Compared to the characteristic β-sheet crystalline structure in silks, the non-crystalline structure and its composition deserves more attention as it is equally critical to the filaments' high toughness and strength. Here we further unravel the structure-property relationship in silks using Dynamic Mechanical Thermal Analysis (DMTA). This technique allows us to examine the most important structural relaxation event of the disordered structure the disordered structure, the glass transition (GT), in native silk fibres of the lepidopteran Bombyx mori and Antheraea pernyi and the spider Nephila edulis. The measured glass transition temperature Tg, loss tangent tan δ and dynamic storage modulus are quantitatively modelled based on Group Interaction Modelling (GIM). The "variability" issue in native silks can be conveniently explained by the different degrees of structural disorder as revealed by DMTA. The new insights will facilitate a more comprehensive understanding of the structure-property relations for a wide range of biopolymers. PMID:27320178

  7. 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.

  8. 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.

  9. 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.

  10. Glass Transition and Molecular Mobility in Styrene-Butadiene Rubber Modified Asphalt.

    PubMed

    Khabaz, Fardin; Khare, Rajesh

    2015-11-01

    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. PMID:26451630

  11. 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)

  12. 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

    2015-01-01

    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, 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)

  13. Glass transition of aqueous solutions involving annealing-induced ice recrystallization resolves liquid-liquid transition puzzle of water

    NASA Astrophysics Data System (ADS)

    Zhao, Li-Shan; Cao, Ze-Xian; Wang, Qiang

    2015-10-01

    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.

  14. SELF-ABSORPTION IN THE SOLAR TRANSITION REGION

    SciTech Connect

    Yan, Limei; He, Jiansen; Wang, Linghua; Tu, Chuanyi; Zhang, Lei; Peter, Hardi; Chen, Feng; Barczynski, Krzysztof; Tian, Hui; Xia, Lidong

    2015-09-20

    Transient brightenings in the transition region of the Sun have been studied for decades and are usually related to magnetic reconnection. Recently, absorption features due to chromospheric lines have been identified in transition region emission lines raising the question of the thermal stratification during such reconnection events. We analyze data from the Interface Region Imaging Spectrograph in an emerging active region. Here the spectral profiles show clear self-absorption features in the transition region lines of Si iv. While some indications existed that opacity effects might play some role in strong transition region lines, self-absorption has not been observed before. We show why previous instruments could not observe such self-absorption features, and discuss some implications of this observation for the corresponding structure of reconnection events in the atmosphere. Based on this we speculate that a range of phenomena, such as explosive events, blinkers or Ellerman bombs, are just different aspects of the same reconnection event occurring at different heights in the atmosphere.

  15. A dynamic model for the solar transition region

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.

    1984-01-01

    A model is developed for the lower transition region that can account for the persistent and ubiquitous redshifts that are observed in the UV emission lines formed at these temperatures. It is shown that these shifts are not likely to be due either to falling spicular material or to steady-state siphon flows. The model consists of two key ingredients. The redshifted radiation originates from a minority of flux tubes which have higher gas pressures than their surroundings, and consequently have their transition regions situated below the transition regions of their surroundings. The coronal heating in these loops is impulsive in nature, and this is responsible for the transient mass flows. The studies, therefore, favor theories for coronal heating which involve flare-like magnetic-energy release. Previously announced in STAR as N83-29163

  16. Spectroscopic and glass transition investigations on Nd{sup 3+}-doped NaF-Na{sub 2}O-B{sub 2}O{sub 3} glasses

    SciTech Connect

    Karthikeyan, B.; Mohan, S

    2004-08-03

    New developments in photonic technology need new materials for various applications. In the present report, Nd{sup 3+}-doped NaF-Na{sub 2}O-B{sub 2}O{sub 3} glasses were prepared and the spectroscopic and glass transition properties were analysed. The Fourier transform infrared spectral studies reveal that the glass contains BO{sub 3} and BO{sub 4} units as the local structures and the Na{sup +} ions as the network modifiers. The absorption studies were carried out by using Judd-Ofelt theory, the experimental and theoretical oscillator strengths were also calculated. The emission spectral study was done for the 1 mol% Nd-doped glass and the spontaneous emission probability and stimulated emission cross-sections for the {sup 4}F{sub 3/2}{yields}{sup 4}I{sub 9/2}, {sup 4}I{sub 11/2} transitions were calculated using the J-O parameters.

  17. 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.

  18. Behavior of the low-frequency conductivity of silver iodide nanocomposites in the superionic phase transition region

    NASA Astrophysics Data System (ADS)

    Vergent'ev, T. Yu.; Koroleva, E. Yu.; Kurdyukov, D. A.; Naberezhnov, A. A.; Filimonov, A. V.

    2013-01-01

    The behavior of the specific conductivity of composites based on silver iodide embedded in porous glasses with an average pore diameter of 7 ± 1 nm and in artificial opals with a pore diameter of 40-100 nm has been investigated in the temperature range from 300 to 500 K. It has been shown that a decrease in the characteristic pore size does not lead to a change in the order of the phase transition and that the temperature of the transition to the superionic state of silver iodide in a porous glass and in an opal upon heating is close to the phase transition temperature T c in the bulk material (˜420 K). Upon cooling, the phase transition temperature T c significantly decreases, and the phase transition becomes diffuse. With a decrease in the pore size, the region of the temperature hysteresis of the phase transition increases. The dc conductivities of the composites have been estimated from the impedance diagrams. The temperature dependence of the dc conductivity of both composites has a thermally activated nature, and the slope of the curve σ(1/ T) changes near the phase transition, which indicates a change in the activation energy. The activation energies in the low-temperature and high-temperature phases have been estimated at ˜450-470 and ˜100 meV, respectively. The equivalent electrical circuit describing the charge transfer processes in the studied samples has been proposed.

  19. Glass transition of two-dimensional 80-20 Kob-Andersen model at constant pressure

    NASA Astrophysics Data System (ADS)

    Li, D.; Xu, H.; Wittmer, J. P.

    2016-02-01

    We reconsider numerically the two-dimensional version of the Kob-Andersen model (KA2d) with a fraction of 80% of large spheres. A constant moderate pressure is imposed while the temperature T is systematically quenched from the liquid limit through the glass transition at {{T}\\text{g}}≈ 0.3 down to very low temperatures. Monodisperse Lennard-Jones (mdLJ) bead systems, forming a crystal phase at low temperatures, are used to highlight several features of the KA2d model. As can be seen, e.g. from the elastic shear modulus G(T), determined using the stress-fluctuation formalism, our KA2d model is a good glass-former. A continuous cusp-singularity, G(T)\\propto {{≤ft(1-T/{{T}\\text{g}}\\right)}α} with α ≈ 0.6 , is observed in qualitative agreement with other recent numerical and theoretical work, however in striking conflict with the additive jump discontinuity predicted by mode-coupling theory.

  20. 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.

  1. 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

  2. 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.

  3. Spin-glass transition in Ni carbide single crystal nanoparticles with Ni3C - type structure

    NASA Astrophysics Data System (ADS)

    Fujieda, S.; Kuboniwa, T.; Shinoda, K.; Suzuki, S.; Echigoya, J.

    2016-05-01

    Hexagonal shaped nanoparticles about 60 nm in size were successfully synthesized in tetraethylene glycol solution containing polyvinylpyrrolidone. By the analysis of the electron diffraction pattern, these were identified as a single crystal of Ni carbide with Ni3C - type structure. Their magnetization curve at 5 K was not completely saturated under a magnetic field of 5 T. The thermomagnetization curves after zero-field cooling and after field cooling exhibited the magnetic cooling effect at low temperatures. Furthermore, the 2nd order nonlinear term of AC magnetic susceptibility exhibited a negative divergence at about 17 K. It is concluded that Ni carbide single crystal nanoparticles with the Ni3C - type structure exhibit spin-glass transition at low temperatures.

  4. Transport properties of a Tl-2201 film close to the critical temperature: The vortex glass transition

    SciTech Connect

    Chen, H.Q.; Johansson, L.G.; Ivanov, Z.G.

    1999-12-01

    The authors have studied the I-V characteristics of a Tl-2201 film at zero field. In the regime in which flux creep is the dominant dissipation mechanism, the J{sub c}-T curve is divided into two parts at a temperature T{sub g} (about 82 K), close to the critical temperature (84 K). The I-V characteristics around T{sub g} are well described using a flux creep model. Differential resistance (dV/dI) as a function of the measuring current shows a change in curvature close to T{sub g}. The I-V curves collapsed nicely into two branches by plotting (V/I)/{vert{underscore}bar}T-T{sub g}{vert{underscore}bar}{sup V(z{minus}1)} vs. (I/T)/{vert{underscore}bar}T{sub g}-T{vert{underscore}bar}{sup 2v}, indicating a current-reduced vortex glass transition.

  5. 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.

  6. Relation Between Glass Transition Temperatures in Polymer Nanocomposites and Polymer Thin Films

    NASA Astrophysics Data System (ADS)

    Kropka, Jamie; Pryamitsyn, Victor; Ganesan, Venkat

    2009-03-01

    Motivated by recent experiments, we examine within a percolation model whether there is a quantitative equivalence in the glass transition temperatures of polymer thin films and polymer nanocomposites (PNCs). Our results indicate that while the qualitative behaviors of these systems are similar, a quantitative equivalence cannot be established in general. However, we propose a phenomenological scaling collapse of our results which suggests a simple framework by which the results of the thin films may be used to quantitatively predict the properties of PNCs. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  7. The Glass Transition of Miscible Binary Polymer-Polymer Thin Films

    NASA Astrophysics Data System (ADS)

    Green, Peter; Besancon, Brian; Soles, Christopher

    2007-03-01

    Studies of the glass transition temperatures, Tg, of completely miscible thin film blends of tetramethyl bisphenol-A polycarbonate (TMPC) and deuterated polystyrene (dPS), supported by SiOx/Si, were examined using spectroscopic ellipsometry (SE) and incoherent elastic neutron scattering (INS). While both sets of measurements independently reveal that Tg exhibits qualitatively similar trends with film thickness, h, there were important quantitative differences, which depended on composition. The Tgs measured by INS were consistently larger than those determined by SE for PS weight fractions φ>0.1. These observations are rationalized in terms of theory based on the notion of a self- concentration and reveal evidence of heterogeneous component behavior in these miscible polymer-polymer systems.

  8. Study of the relaxation dynamics associated with the Glass Transition in two polyols

    NASA Astrophysics Data System (ADS)

    Faivre, Annelise; David, Laurent; Vigier, Gerard; Jal, Jean-Francois

    1998-03-01

    In order to improve the understanding of the glass transition, the molecular mobility of two complementary molecular systems (Sorbitol and Maltitol) was investigated over temperatures ranging from well above Tg, to below Tg. Using various spectroscopic techniques including mechanical and dielectric spectroscopies, viscosity measurements, neutron spin echo (ILL Grenoble), the relaxation maps of these polyols were determined for a very large frequency range. The results reveal two relaxation processes: -the main alpha-relaxation, which exhibits a complex dynamic pattern comprising non-Arrhenius behaviour above Tg and Arrhenius behaviour below Tg, -the secondary beta process, which exhibits an Arrhenius behaviour over the entire time-temperature range, which happens to be the same for both polyols. We attempt to describe these data in the framework of a model relating the dynamic behaviour of the system to the state of disorder, as characterized by the density of nano-fluctuations.

  9. 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.

  10. Kr II transition probability measurements for the UV spectral region

    NASA Astrophysics Data System (ADS)

    Belmonte, M. T.; Gavanski, L.; Peláez, R. J.; Aparicio, J. A.; Djurović, S.; Mar, S.

    2016-02-01

    The determination of radiative transition probabilities or oscillator strengths is of common interest in astrophysics. The analysis of the high-resolution stellar spectra is now available in order to estimate the stellar abundances. In this paper, 93 experimentally obtained transition probability values (Aki) for singly ionized krypton spectral lines belonging to the ultraviolet (UV) wavelength region (208-360) nm are presented. These data, expressed in absolute units, were derived from the measurements of relative spectral line intensities and the values of transition probability data taken from the literature. The results obtained extend considerably the transition probability data base. As a light source, a plasma from a low-pressure pulsed arc was used. Its electron density was in the range of (1.5-3.4) × 1022 m-3, while the temperature was between 28 000 and 35 000 K. A detailed analysis of the results is also given. Only a few relative and a few absolute transition probabilities from other authors, for the mentioned spectral region, are available in the literature.

  11. THE COMPLEX NORTH TRANSITION REGION OF CENTAURUS A: RADIO STRUCTURE

    SciTech Connect

    Neff, Susan G.; Eilek, Jean A.; Owen, Frazer N.

    2015-04-01

    We present deep radio images of the inner ∼50 kpc of Centaurus A, taken with the Karl G. Jansky Very Large Array at 90 cm. We focus on the Transition Regions between the inner galaxy—including the active nucleus, inner radio lobes, and star-forming disk—and the outer radio lobes. We detect previously unknown extended emission around the Inner Lobes, including radio emission from the star-forming disk. We find that the radio-loud part of the North Transition Region (NTR), known as the North Middle Lobe, is significantly overpressured relative to the surrounding interstellar medium. We see no evidence for a collimated flow from the active galactic nucleus through this region. Our images show that the structure identified by Morganti et al. as a possible large-scale jet appears to be part of a narrow ridge of emission within the broader, diffuse, radio-loud region. This knotty radio ridge is coincident with other striking phenomena: compact X-ray knots, ionized gas filaments, and streams of young stars. Several short-lived phenomena in the NTR, as well as the frequent re-energization required by the Outer Lobes, suggest that energy must be flowing through both Transition Regions at the present epoch. We suggest that the energy flow is in the form of a galactic wind.

  12. Influence of crosslinker and ionic comonomer concentration on glass transition and demixing/mixing transition of copolymers poly(N-isopropylacrylamide) and poly(sodium acrylate) hydrogels.

    PubMed

    Zarzyka, Iwona; Pyda, Marek; Di Lorenzo, Maria Laura

    2014-01-01

    Hydrogels based on N-isopropylacrylamide and sodium acrylate as ionic comonomer were synthesized by free radical polymerization in water using N,N'-methylenebisacrylamide as crosslinker and ammonium persulfate as initiator. The glass transition of dried copolymers poly(N-isopropylacrylamide) (PNIPA) and poly(sodium acrylate) (SA) gels and demixing/mixing transition of PNIPA-SA hydrogels swollen with increasing amounts of water were studied using conventional differential scanning calorimetry. In the crosslinked polymers, the glass transition linearly increases, and the transition range becomes broader, with increasing crosslinker content. Increasing content of ionic comonomer also produces an increase of glass transition temperature, which moves to higher temperatures with higher sodium acrylate fraction. The influence of chemical structure of PNIPA-SA hydrogels on the lower critical solution temperature (LCST) of PNIPA-SA/water mixtures during heating and cooling was quantified as function of the content of the crosslinker and the ionic comonomer, as well as water content of the hydrogel in the range from 95 to 70 wt%. At parity of water content, the LCST occurs at higher temperatures for gels containing higher amounts of sodium acrylate. Similarly, the introduction of N,N'-methylenebisacrylamide causes an increase of the LCST, which grows with increasing of crosslinking degree of the hydrogel. PMID:24511175

  13. Time dependent physical properties of semicrystalline poly(arylene ether ether ketone) (PEEK) above its glass transition temperature: Physical aging vs. secondary crystallization

    SciTech Connect

    Velikov, V.; Verma, R.; marand, H.

    1995-12-01

    We monitored the change in small strain short term isothermal creep compliance of semicrystalline. PEEK (T{sub g} {approx} 150{degrees}C - 165{degrees}C) at various temperatures from 120{degrees}C to 260{degrees}C. With increase of aging times creep curves are shifted to longer times, implying slowing down of the mechanical relaxation of the polymer. The isothermal horizontal shift rate is close to unity below and above T{sub g} and exhibits significant drop in the glass transition region.

  14. Structural transition and orbital glass physics in near-itinerant CoV2O4

    DOE PAGES

    Reig-i-Plessis, D.; Casavant, D.; Garlea, Vasile O.; Aczel, Adam A.; Feygenson, Mikhail; Neuefeind, Joerg C.; Zhou, H. D.; Nagler, Stephen E.; MacDougall, Gregory J.

    2016-01-25

    In this study, the ferrimagnetic spinel CoV2O4 has been a topic of intense recent interest, both as a frustrated insulator with unquenched orbital degeneracy and as a near-itinerant magnet which can be driven metallic with moderate applied pressure. Here, we report on our recent neutron di raction and inelastic scattering measurements on powders with minimal cation site disorder. Our main new result is the identification of a weak (Δa/a ~ 10–4), first order structural phase transition at T* = 90 K, the same temperature where spin canting was seen in recent single crystal measurements. This transition is characterized by amore » short-range distortion of oxygen octahedral positions, and inelastic data further establish a weak 1.25meV spin gap at low temperature. Together, these findings provide strong support for the local orbital picture and the existence of an orbital glass state at temperatures below T*.« less

  15. Waveguides and nonlinear index of refraction of borate glass doped with transition metals

    NASA Astrophysics Data System (ADS)

    Almeida, Juliana M. P.; Fonseca, Ruben D.; De Boni, Leonardo; Diniz, Andre Rosa S.; Hernandes, Antonio C.; Ferreira, Paulo H. D.; Mendonca, Cleber R.

    2015-04-01

    The ability to write 3D waveguides by femtosecond laser micromachining and the nonlinear refractive index (n2) spectrum of a new borate glass matrix, containing zinc and lead oxides - (BZP) have been investigated. The transparent matrix was doped with transition metals (CdCl2, Fe2O3, MnO2 and CoO) in order to introduce electronic transitions in visible spectrum, aiming to evaluate their influence on the waveguides and n2 spectrum. We observed that n2 is approximately constant from 600 to 1500 nm, exhibiting an average value of 4.5 × 10-20 m2/W, which is about twice larger than the one for fused silica. The waveguide profile is influenced by the self-focusing effect of the matrix owing to its positive nonlinear index of refraction in the wavelength used for micromachining. A decrease in the waveguide loss of approximately four times was observed for the sample doped with Fe in comparison to the other ones, which may be associated with the change in the optical gap energy.

  16. Multichannel transition emissions of Dy{sup 3+} in fiber-adaptive germanium tellurite glasses

    SciTech Connect

    Li, Y. H.; Chen, B. J.; Lin, H.; Pun, E. Y. B.

    2013-03-28

    Multichannel transition visible and near-infrared (NIR) fluorescences have been captured in Dy{sup 3+}-doped fiber-adaptive Na{sub 2}O-ZnO-PbO-GeO{sub 2}-TeO{sub 2} glasses. The maximum stimulated emission cross-sections {sigma}{sub em-max} were derived to be 0.33 Multiplication-Sign 10{sup -21}, 3.66 Multiplication-Sign 10{sup -21}, and 0.67 Multiplication-Sign 10{sup -21} cm{sup 2} for conventional visible emissions assigned to {sup 4}F{sub 9/2}{yields}{sup 6}H{sub J} (J = 15/2, 13/2, and 11/2) transitions, respectively. Infrequent multi-peak NIR emissions were recorded in the spectral range of 900-1500 nm, among which the values of {sigma}{sub em-max} were solved to be 1.05 Multiplication-Sign 10{sup -22} and 1.56 Multiplication-Sign 10{sup -22} cm{sup 2} for {approx}1.02 and {approx}1.18 {mu}m emission bands. Internal quantum efficiency for the {sup 4}F{sub 9/2} level and external quantum yield for visible emissions of Dy{sup 3+} were determined to be 88.44% and 12.38%, severally. Effective multichannel radiative emissions reveal a potential in developing fiber-lighting sources, tunable lasers, and NIR optical amplifiers.

  17. Current-voltage characteristics near the glass-liquid transition in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Yamafuji, K.; Kiss, T.

    1997-02-01

    Theoretical expressions for the induced DC electric field, E, are derived as a function of the applied current density, J, near the glass-liquid transition temperature of T= TGL as E(J) = Ẽ(J)[1 + ( {δE(J)}/{Ẽ(J) })] , where Ẽ(J) is the scalable part and {δE(j)}/{Ẽ(j) } is the unscalable part given by a power series of | TGL - T| nv( z + 2 - D) wi Then the condition of {δE}/{Ẽ}≪1 gives a measure of the width of the critical regime, in which E = E( J) is well scalable. The general scaling characteristics of E= Ẽ(J) are the same as those predicted by Fisher and coworkers based on the conventional theories of phase transitions with the scaling hypothesis, while the present theory provides a concrete expression for Ẽ(J) . Furthermore, the expressions for the scaled master curves of the AC impedance are derived. The reason, why the observed E vs. J characteristics are scalable over wider ranges of the temperature and flux density than the critical regime, is also discussed.

  18. Origins of the two simultaneous mechanisms causing glass transition temperature reductions in high molecular weight freestanding polymer films

    SciTech Connect

    Prevosto, Daniele E-mail: Prevosto@df.unipi.it; Capaccioli, Simone; Ngai, K. L. E-mail: Prevosto@df.unipi.it

    2014-02-21

    From ellipsometry measurements, Pye and Roth [Phys. Rev. Lett. 107, 235701 (2011)] presented evidence of the presence of two glass transitions originating from two distinctly different and simultaneous mechanisms to reduce the glass transition temperature within freestanding polystyrene films with thickness less than 70 nm. The upper transition temperature T{sub g}{sup u}(h) is higher than the lower transition temperature T{sub g}{sup l}(h) in the ultrathin films. After comparing their data with the findings of others, using the same or different techniques, they concluded that new theoretical interpretation is needed to explain the two transitions and the different dependences of T{sub g}{sup u}(h) and T{sub g}{sup l}(h) on film thickness and molecular weight. We address the problem based on advance in delineating the different viscoelastic mechanisms in the glass-rubber transition zone of polymers. Theoretical considerations as well as experiments have shown in time-scales immediately following the segmental α-relaxation are the sub-Rouse modes with longer length scale but shorter than that of the Rouse modes. The existence of the sub-Rouse modes in various polymers including polystyrene has been repeatedly confirmed by experiments. We show that the sub-Rouse modes can account for the upper transition and the properties observed. The segmental α-relaxation is responsible for the lower transition. This is supported by the fact that the segmental α-relaxation in ultrathin freestanding PS films had been observed by dielectric relaxation measurements and photon correlation spectroscopy. Utilizing the temperature dependence of the segmental relaxation times from these experiments, the glass transition temperature T{sub g}{sup α} associated with the segmental relaxation in the ultrathin film is determined. It turns out that T{sub g}{sup α} is nearly the same as T{sub g}{sup l}(h) of the lower transition, and hence definitely segmental α-relaxation is the

  19. NEAR THE BOUNDARY OF THE HELIOSPHERE: A FLOW TRANSITION REGION

    SciTech Connect

    Opher, M.; Drake, J. F.; Velli, M.; Decker, R. B.; Toth, G.

    2012-06-01

    Since April of 2010, Voyager 1 has been immersed in a region of near zero radial flows, where the solar wind seems to have stopped. The existence of this region contradicts current models that predict that the radial flows will go to zero only at the heliopause. These models, however, do not include the sector region (or include it in a kinematic fashion), where the solar magnetic field periodically reverses polarity. Here we show that the presence of the sector region in the heliosheath, where reconnection occurs, fundamentally alters the flows, giving rise to a Flow Transition Region (FTR), where the flow abruptly turns and the radial velocity becomes near zero or negative. We estimate, based on a simulation, that at the Voyager 1 location, the thickness of the FTR is around 7-11 AU.

  20. Characteristic ion distributions in the dynamic auroral transition region

    NASA Astrophysics Data System (ADS)

    Zeng, W.; Horwitz, J. L.; Tu, J.-N.

    2006-04-01

    A Dynamic Fluid Kinetic (DyFK) simulation is conducted to study the H+/O+ flows and distribution functions in the high-latitude dynamic transition region, specifically from 1000 km to about 4000 km altitude. Here, the collisional-to-collisionless transition region is that region where Coulomb collisions have significant but not dominant effects on the ion distributions. In this study, a simulation flux tube, which extends from 120 km to 3 RE altitude, is assumed to experience a pulse of auroral effects for approximately 20 minutes, including both soft electron precipitation and transverse wave heating, and then according to different geophysical circumstances, either to relax following the cessation of such auroral effects or to be heated further continuously by waves with power at higher frequencies. Our principal purpose in this investigation is to elicit the characteristic ion distribution functions in the auroral transition region, where both collisions and kinetic processes play significant roles. The characteristics of the simulated O+ and H+ velocity distributions, such as kidney bean shaped H+ distributions, and O+ distributions having cold cores with upward folded conic wings, resemble those observed by satellites at similar altitudes and geographic conditions. From the simulated distribution function results under different geophysical conditions, we find that O+-O+ and O+-H+ collisions, in conjunction with the kinetic and auroral processes, are key factors in the velocity distributions up to 4000 km altitude, especially for the low speed portions, for both O+ and H+ ions.

  1. Evidence of liquid–liquid transition in glass-forming La50Al35Ni15 melt above liquidus temperature

    PubMed Central

    Xu, Wei; Sandor, Magdalena T.; Yu, Yao; Ke, Hai-Bo; Zhang, Hua-Ping; Li, Mao-Zhi; Wang, Wei-Hua; Liu, Lin; Wu, Yue

    2015-01-01

    Liquid–liquid transition, a phase transition of one liquid phase to another with the same composition, provides a key opportunity for investigating the relationship between liquid structures and dynamics. Here we report experimental evidences of a liquid–liquid transition in glass-forming La50Al35Ni15 melt above its liquidus temperature by 27Al nuclear magnetic resonance including the temperature dependence of cage volume fluctuations and atomic diffusion. The observed dependence of the incubation time on the degree of undercooling is consistent with a first-order phase transition. Simulation results indicate that such transition is accompanied by the change of bond-orientational order without noticeable change in density. The temperature dependence of atomic diffusion revealed by simulations is also in agreement with experiments. These observations indicate the need of two-order parameters in describing phase transitions of liquids. PMID:26165855

  2. Effect of sugar addition on glass transition temperatures of cassava starch with low to intermediate moisture contents.

    PubMed

    Figueroa, Yetzury; Guevara, Marvilan; Pérez, Adriana; Cova, Aura; Sandoval, Aleida J; Müller, Alejandro J

    2016-08-01

    This work studies how sucrose (S) addition modifies the thermal properties of cassava starch (CS). Neat CS and CS-S blends with 4, 6 and 8% sugar contents (CS-S-4%, CS-S-6% and CS-S-8%) were prepared and analyzed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA), in a wide range of moisture levels (2-20%). In equilibrated samples with moisture contents lower than 10%, twoendothermic steps were observed during first DSC heating scans and two corresponding relaxation maxima in tan δ were detected by DMTA. The first transition, detected at around 45-55°C by both DSC and DMTA, is frequently found in starchy foods, while the second observed at higher temperatures is associated to the glass transition temperature of the blends. At higher moisture contents, only one thermal transition was observed. Samples analyzed immediately after cooling from the melt (i.e., after erasing their thermal history), exhibited a single glass transition temperature, regardless of their moisture content. Addition of sugar promotes water plasticization of CS only at high moisture contents. In the low moisture content range, anti-plasticization was observed for both neat and sugar-added CS samples. Addition of sugar decreases the moisture content needed to achieve the maximum value of the glass transition temperature before plasticization starts. The results of this work may be valuable for the study of texture establishment in low moisture content extruded food products. PMID:27112870

  3. Effect of sugar addition on glass transition temperatures of cassava starch with low to intermediate moisture contents.

    PubMed

    Figueroa, Yetzury; Guevara, Marvilan; Pérez, Adriana; Cova, Aura; Sandoval, Aleida J; Müller, Alejandro J

    2016-08-01

    This work studies how sucrose (S) addition modifies the thermal properties of cassava starch (CS). Neat CS and CS-S blends with 4, 6 and 8% sugar contents (CS-S-4%, CS-S-6% and CS-S-8%) were prepared and analyzed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA), in a wide range of moisture levels (2-20%). In equilibrated samples with moisture contents lower than 10%, twoendothermic steps were observed during first DSC heating scans and two corresponding relaxation maxima in tan δ were detected by DMTA. The first transition, detected at around 45-55°C by both DSC and DMTA, is frequently found in starchy foods, while the second observed at higher temperatures is associated to the glass transition temperature of the blends. At higher moisture contents, only one thermal transition was observed. Samples analyzed immediately after cooling from the melt (i.e., after erasing their thermal history), exhibited a single glass transition temperature, regardless of their moisture content. Addition of sugar promotes water plasticization of CS only at high moisture contents. In the low moisture content range, anti-plasticization was observed for both neat and sugar-added CS samples. Addition of sugar decreases the moisture content needed to achieve the maximum value of the glass transition temperature before plasticization starts. The results of this work may be valuable for the study of texture establishment in low moisture content extruded food products.

  4. Combustion characteristics in the transition region of liquid fuel sprays

    NASA Technical Reports Server (NTRS)

    Cernansky, N. P.; Namer, I.; Tidona, R. J.; Sarv, H.

    1984-01-01

    A monodisperse aerosol generator was modified to study ignition requirements, flammability limits, and flame speeds in the transition region. An ignition system was developed and tested. The fabrication of an optical drop sizing system is nearly complete. Preliminary measurements of droplet size effects on the minimum ignition energy for n-heptane sprays performed. Parameteric studies of droplet size effects on minimum ignition energies of various fuels including alcohols are in progress.

  5. Wave propagation in the chromosphere and transition region

    NASA Technical Reports Server (NTRS)

    Steffens, S.; Deubner, F.-L.; Fleck, B.; Wilhelm, K.; Harrison, R.; Gurman, J.

    1997-01-01

    The results from a joint observing program involving the solar ultraviolet measurement of emitted radiation (SUMER), the coronal diagnostic spectrometer (CDS) and the extreme-ultraviolet imaging telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO) are presented. These operations were coordinated with ground-based observations at the vacuum tower telescope at Izana (Tenerife). The purpose was to characterize the wave propagation properties in the solar atmosphere, from the photosphere through the chromosphere into the transition region.

  6. Scaling behavior of domain walls at the T = 0 ferromagnet to spin-glass transition

    NASA Astrophysics Data System (ADS)

    Melchert, O.; Hartmann, A. K.

    2009-01-01

    Using mappings to combinatorial optimization problems, one can often study physical systems better by means of sophisticated algorithms from computer science. Here, we study the geometric properties of domain-wall excitations in a two-dimensional random-bond Ising spin system, where each realization of the disorder consists of a random fraction ρ of ferromagnetic bonds and a fraction (1-ρ) of bonds drawn from a Gaussian distribution with zero mean and unit width. We formulate an auxiliary graph theoretical problem in which domain walls are given by undirected shortest paths with possibly negative distances [O. Melchert and A.K. Hartmann Phys. Rev. B 76, 174411 (2007)]. Due to the details of the mapping, standard shortest path algorithms (e.g. the Dijkstra algorithm) cannot be applied. To solve such shortest path problems it requires minimum weight perfect matching algorithms. We first locate the critical point ρc, where the ferromagnet (large ρ) to spin-glass transition occurs. For certain values of ρ close to the critical point we investigate the stiffness exponent θ and the fractal dimension df that describe the scaling of the average domain-wall energy and length, respectively. Performing a finite-size scaling analysis we find that both exponents remain constant in the spin-glass phase, i.e. θ~-0.28 and df~1.275. This is consistent with conformal field theory, where it seems to be possible [C. Amoruso et al. Phys. Rev. Lett. 97, 267202 (2006)] to relate the exponents via df-1 = 3/[4(3+θ)].

  7. Multidiffusion mechanisms for noble gases (He, Ne, Ar) in silicate glasses and melts in the transition temperature domain: Implications for glass polymerization

    NASA Astrophysics Data System (ADS)

    Amalberti, Julien; Burnard, Pete; Laporte, Didier; Tissandier, Laurent; Neuville, Daniel R.

    2016-01-01

    Noble gases are ideal probes to study the structure of silicate glasses and melts as the modifications of the silicate network induced by the incorporation of noble gases are negligible. In addition, there are systematic variations in noble gas atomic radii and several noble gas isotopes with which the influence of the network itself on diffusion may be investigated. Noble gases are therefore ideally suited to constrain the time scales of magma degassing and cooling. In order to document noble gas diffusion behavior in silicate glass, we measured the diffusivities of three noble gases (4He, 20Ne and 40Ar) and the isotopic diffusivities of two Ar isotopes (36Ar and 40Ar) in two synthetic basaltic glasses (G1 and G2; 20Ne and 36Ar were only measured in sample G1). These new diffusion results are used to re-interpret time scales of the acquisition of fractionated atmospheric noble gas signatures in pumices. The noble gas bearing glasses were synthesized by exposing the liquids to high noble gas partial pressures at high temperature and pressure (1750-1770 K and 1.2 GPa) in a piston-cylinder apparatus. Diffusivities were measured by step heating the glasses between 423 and 1198 K and measuring the fraction of gas released at each temperature step by noble gas mass spectrometry. In addition we measured the viscosity of G1 between 996 and 1072 K in order to determine the precise glass transition temperature and to estimate network relaxation time scales. The results indicate that, to a first order, that the smaller the size of the diffusing atom, the greater its diffusivity at a given temperature: D(He) > D(Ne) > D(Ar) at constant T. Significantly, the diffusivities of the noble gases in the glasses investigated do not display simple Arrhenian behavior: there are well-defined departures from Arrhenian behavior which occur at lower temperatures for He than for Ne or Ar. We propose that the non-Arrhenian behavior of noble gases can be explained by structural modifications

  8. Thermodynamic calculation and interatomic potential to predict the favored composition region for the Cu-Zr-Al metallic glass formation.

    PubMed

    Cui, Y Y; Wang, T L; Li, J H; Dai, Y; Liu, B X

    2011-03-01

    For the Cu-Zr-Al system, the glass forming compositions were firstly calculated based on the extended Miedema's model, suggesting that the amorphous phase could be thermodynamically favored over a large composition region. An n-body potential was then constructed under the smoothed and long-range second-moment-approximation of tight-binding formulism. Applying the constructed Cu-Zr-Al potential, molecular dynamics simulations were conducted using solid solution models to compare relative stability of crystalline solid solution versus its disordered counterpart. Simulations reveal that the physical origin of metallic glass formation is crystalline lattice collapsing while solute concentration exceeding the critical value, thus predicting a hexagonal composition region, within which the Cu-Zr-Al ternary metallic glass formation is energetically favored. The molecular dynamics simulations predicted composition region is defined as the quantitative glass-forming-ability or glass-forming-region of the Cu-Zr-Al system. PMID:21229150

  9. Transition threshold in Ge{sub x}Sb{sub 10}Se{sub 90−x} glasses

    SciTech Connect

    Wei, Wen-Hou; Fang, Liang; Shen, Xiang; Wang, Rong-Ping

    2014-03-21

    Ge{sub x}Sb{sub 10}Se{sub 90−x} glasses with Ge content from 7.5 to 32.5 at. % have been prepared by melt-quench technique, and the physical parameters including glass transition temperature (T{sub g}), density (ρ), compactness (C), shear elastic moduli (C{sub s}), compression elastic moduli (C{sub c}), refractive index (n), and optical bandgap (E{sub g}) have been investigated. While all these physical parameters show threshold behavior in the glass with a chemically stoichiometric composition. Raman spectra analysis also indicates that, with increasing Ge content, Se-chains or rings gradually disappear until all Se-atoms are consumed in the glass with a chemically stoichiometric composition. With further increasing Ge content, homopolar Ge-Ge and Sb-Sb bonds are formed and the chemical order in the glasses is violated. The threshold behavior of the physical properties in the Ge{sub x}Sb{sub 10}Se{sub 90−x} glasses can be traced to demixing of networks above the chemically stoichiometric composition.

  10. Experimentally determined dissolution kinetics of Na-rich borosilicate glass at far from equilibrium conditions: Implications for Transition State Theory

    SciTech Connect

    Icenhower, Jonathan P.; McGrail, B. Peter; Shaw, Wendy J.; Pierce, Eric M.; Nachimuthu, Ponnusamy; Shuh, David K.; Rodriguez, Elsa A.; Steele, Jackie L.

    2008-04-14

    correlates with the forward rate of reaction. Thus, dissolution appears to be rate-limited by rupture of the Si—O bond, which is consistent with the tenants of Transition State Theory (TST). Therefore, dissolution at far from equilibrium conditions is dependent upon the speed of the rate-controlling elementary reaction and not on the sum of the free energies of hydration of the constituents of boroaluminosilicate glass.

  11. Experimentally determined dissolution kinetics of Na-rich borosilicate glass at far from equilibrium conditions: Implications for Transition State Theory

    NASA Astrophysics Data System (ADS)

    Icenhower, Jonathan P.; McGrail, B. Peter; Shaw, Wendy J.; Pierce, Eric M.; Nachimuthu, P.; Shuh, David K.; Rodriguez, Elsa A.; Steele, Jackie L.

    2008-06-01

    rate-limited by rupture of the Si-O bond, which is consistent with the tenants of Transition State Theory (TST). Therefore, dissolution at far from equilibrium conditions is dependent upon the speed of the rate-controlling elementary reaction and not on the sum of the free energies of hydration of the constituents of boroaluminosilicate glass.

  12. Manifestation of random first-order transition theory in Wigner glasses

    NASA Astrophysics Data System (ADS)

    Kang, Hongsuk; Kirkpatrick, T. R.; Thirumalai, D.

    2013-10-01

    We use Brownian dynamics simulations of a binary mixture of highly charged spherical colloidal particles to test some of the predictions of the random first-order transition (RFOT) theory [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.58.2091 58, 2091 (1987); Phys. Rev. A1050-294710.1103/PhysRevA.40.1045 40, 1045 (1989)]. In accord with mode-coupling theory and RFOT, we find that as the volume fraction of the colloidal particles ϕ approaches the dynamical transition value ϕA, three measures of dynamics show an effective ergodic to nonergodic transition. First, there is a dramatic slowing down of diffusion, with the translational diffusion constant decaying as a power law as ϕ→ϕA-. Second, the energy metric, a measure of ergodicity breaking in classical many-body systems, shows that the system becomes effectively nonergodic as ϕA is approached. Finally, the time t*, at which the four-point dynamical susceptibility achieves a maximum, also increases as a power law near ϕA. Remarkably, the translational diffusion coefficients, ergodic diffusion coefficient, and (t*)-1 all vanish as (ϕ-1-ϕA-1)γ with both ϕA(≈0.1) and γ being the roughly the same for all three quantities. Above ϕA, transport involves crossing free energy barriers. In this regime, the density-density correlation function decays as a stretched exponential [exp-((t)/(τα))β] with β≈0.45. The ϕ dependence of the relaxation time τα could be fit using the Vogel-Tamman-Fulcher law with the ideal glass transition at ϕK≈0.47. By using a local entropy measure, we show that the law of large numbers is not obeyed above ϕA, and gives rise to subsample to subsample fluctuations in all physical observables. We propose that dynamical heterogeneity is a consequence of violation of law of large numbers.

  13. Titan Ion Composition at Magnetosphere-Ionosphere Transition Region

    NASA Technical Reports Server (NTRS)

    Sittler, Edward C.; Hartle, R. E.; Shappirio, M.; Simpson, D. J.; COoper, J. F.; Burger, M. H.; Johnson, R. E.; Bertucci, C.; Luhman, J. G.; Ledvina, S. A.; Szego, K.; Coates, A. J.; Young, D. T.

    2006-01-01

    Using Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) ion composition data, we will investigate the compositional changes at the transition region between Saturn's magnetospheric flow and Titan's upper ionosphere. It is this region where scavenging of Titan's upper ionosphere can occur, where it is then dragged away by the magnetospheric flow as cold plasma for Saturn's magnetosphere. This cold plasma may form plumes as originally proposed by (1) during the Voyager 1 epoch. This source of cold plasma may have a unique compositional signature such as methane group ions. Water group ions that are observed in Saturn's outer magnetosphere (2,3) are relatively hot and probably come from the inner magnetosphere where they are born from fast neutrals escaping Enceladus (4) and picked up in the outer magnetosphere as hot plasma (5). This scenario will be complicated by pickup methane ions within Titan's mass loading region, as originally predicted by (6) based on Voyager 1 data and observationally confirmed by (3,7) using CAPS IMS data. But, CH4(+) ions or their fragments can only be produced as pickup ions from Titan's exosphere which can extend beyond the transition region of concern here, while CH5(+) ions can be scavenged from Titan's ionosphere. We will investigate these possibilities.

  14. A spinning thermometer to monitor microwave heating and glass transitions in dynamic nuclear polarization.

    PubMed

    Miéville, Pascal; Vitzthum, Veronika; Caporini, Marc A; Jannin, Sami; Gerber-Lemaire, Sandrine; Bodenhausen, Geoffrey

    2011-11-01

    As previously demonstrated by Thurber and Tycko, the peak position of (79)Br in potassium bromide (KBr) allows one to determine the temperature of a spinning sample. We propose to adapt the original design by using a compact KBr tablet placed at the bottom of the magic angle spinning rotor, separated from the sample under investigation by a thin disk made of polytetrafluoroethylene (or 'Teflon'®). This design allows spinning the sample up to at least 16 kHz. The KBr tablet can remain in the rotor when changing the sample under investigation. Calibration in the range of 98 < T < 320 K has been carried out in a static rotor by inserting a platinum thermometer. The accuracy is better than ± 0.9 K, even in the presence of microwave irradiation. Irradiation with 5 W microwaves at 263 GHz leads to a small temperature increase of 3.6 ± 1.4 K in either static or spinning samples. The dynamic nuclear polarization enhancement decreases with increasing temperature, in particular when a frozen glassy sample undergoes a glass transition.

  15. Structure-to-glass transition temperature relationships in high temperature stable condensation polyimides

    NASA Technical Reports Server (NTRS)

    Alston, W. B.; Gratz, R. F.

    1985-01-01

    The presence of a hexafluoroisopropylidene (6F) connecting group in aryl dianhydrides used to prepare aromatic condensation polyimides provides high glass transition temperature (T sub g) polyimides with excellent thermo-oxidative stability. The purpose of this study was to determine if a trifluorophenyl-ethylidene (3F) connecting group would have a similar effect on the T sub g of aromatic condensation polyimides. A new dianhydride containing the 3F connecting group was synthesized. This dianhydride and an aromatic diamine also containing the 3F connecting group were used together and in various combinations with known diamines or known dianhydrides, respectively, to prepare new 3F containing condensation polyimides. Known polyimides, including some with the 6F connecting linkage, were also prepared for comparison purposes. The new 3F containing polymers and the comparison polymers were prepared by condensation polymerization via the traditional amic-acid polymerization method in N,N-dimethylacetamide solvent. The solutions were characterized by determining their inherent viscosities and then were thermally converted into polyimide films under nitrogen atmosphere at 300 to 500 C, usually 350 C. The T sub g's of the films and resin discs were then determined by thermomechanical analysis and were correlated as a function of the final processing temperatures of the films and resin discs. The results showed that similarities existed in the T sub g's depending on the nature of the connecting linkage in the monomers used to prepare the condensation polyimides.

  16. Ionic liquids and their bases: Striking differences in the dynamic heterogeneity near the glass transition

    NASA Astrophysics Data System (ADS)

    Grzybowska, K.; Grzybowski, A.; Wojnarowska, Z.; Knapik, J.; Paluch, M.

    2015-11-01

    Ionic liquids (ILs) constitute an active field of research due to their important applications. A challenge for these investigations is to explore properties of ILs near the glass transition temperature Tg, which still require our better understanding. To shed a new light on the issues, we measured ILs and their base counterparts using the temperature modulated calorimetry. We performed a comparative analysis of the dynamic heterogeneity at Tg for bases and their salts with a simple monoatomic anion (Cl-). Each pair of ionic and non-ionic liquids is characterized by nearly the same chemical structure but their intermolecular interactions are completely different. We found that the size of the dynamic heterogeneity of ILs near Tg is considerably smaller than that established for their dipolar counterparts. Further results obtained for several other ILs near Tg additionally strengthen the conclusion about the relatively small size of the dynamic heterogeneity of molecular systems dominated by electrostatic interactions. Our finding opens up new perspectives on designing different material properties depending on intermolecular interaction types.

  17. Ionic liquids and their bases: Striking differences in the dynamic heterogeneity near the glass transition.

    PubMed

    Grzybowska, K; Grzybowski, A; Wojnarowska, Z; Knapik, J; Paluch, M

    2015-01-01

    Ionic liquids (ILs) constitute an active field of research due to their important applications. A challenge for these investigations is to explore properties of ILs near the glass transition temperature Tg, which still require our better understanding. To shed a new light on the issues, we measured ILs and their base counterparts using the temperature modulated calorimetry. We performed a comparative analysis of the dynamic heterogeneity at Tg for bases and their salts with a simple monoatomic anion (Cl(-)). Each pair of ionic and non-ionic liquids is characterized by nearly the same chemical structure but their intermolecular interactions are completely different. We found that the size of the dynamic heterogeneity of ILs near Tg is considerably smaller than that established for their dipolar counterparts. Further results obtained for several other ILs near Tg additionally strengthen the conclusion about the relatively small size of the dynamic heterogeneity of molecular systems dominated by electrostatic interactions. Our finding opens up new perspectives on designing different material properties depending on intermolecular interaction types.

  18. Using Combined Computational Techniques to Predict the Glass Transition Temperatures of Aromatic Polybenzoxazines

    PubMed Central

    Mhlanga, Phumzile; Wan Hassan, Wan Aminah; Hamerton, Ian; Howlin, Brendan J.

    2013-01-01

    The Molecular Operating Environment software (MOE) is used to construct a series of benzoxazine monomers for which a variety of parameters relating to the structures (e.g. water accessible surface area, negative van der Waals surface area, hydrophobic volume and the sum of atomic polarizabilities, etc.) are obtained and quantitative structure property relationships (QSPR) models are formulated. Three QSPR models (formulated using up to 5 descriptors) are first used to make predictions for the initiator data set (n = 9) and compared to published thermal data; in all of the QSPR models there is a high level of agreement between the actual data and the predicted data (within 0.63–1.86 K of the entire dataset). The water accessible surface area is found to be the most important descriptor in the prediction of Tg. Molecular modelling simulations of the benzoxazine polymer (minus initiator) carried out at the same time using the Materials Studio software suite provide an independent prediction of Tg. Predicted Tg values from molecular modelling fall in the middle of the range of the experimentally determined Tg values, indicating that the structure of the network is influenced by the nature of the initiator used. Hence both techniques can provide predictions of glass transition temperatures and provide complementary data for polymer design. PMID:23326419

  19. Molecular relaxation behavior and isothermal crystallization above glass transition temperature of amorphous hesperetin.

    PubMed

    Shete, Ganesh; Khomane, Kailas S; Bansal, Arvind Kumar

    2014-01-01

    The purpose of this paper was to investigate the relaxation behavior of amorphous hesperetin (HRN), using dielectric spectroscopy, and assessment of its crystallization kinetics above glass transition temperature (Tg ). Amorphous HRN exhibited both local (β-) and global (α-) relaxations. β-Relaxation was observed below Tg , whereas α-relaxation prominently emerged above Tg . β-Relaxation was found to be of Johari-Goldstein type and was correlated with α-process by coupling model. Secondly, isothermal crystallization experiments were performed at 363 K (Tg + 16.5 K), 373 K (Tg + 26.5 K), and 383 K (Tg + 36.5 K). The kinetics of crystallization, obtained from the normalized dielectric strength, was modeled using the Avrami model. Havriliak-Negami (HN) shape parameters, αHN and αHN .βHN , were analyzed during the course of crystallization to understand the dynamics of amorphous phase during the emergence of crystallites. HN shape parameters indicated that long range (α-like) were motions affected to a greater extent than short range (β-like) motions during isothermal crystallization studies at all temperature conditions. The variable behavior of α-like motions at different isothermal crystallization temperatures was attributed to evolving crystallites with time and increase in electrical conductivity with temperature.

  20. Influence of the torsional potential on the glass transition temperature and the structure of amorphous polyethylene.

    PubMed

    Canales, Manel

    2009-05-01

    The effect of the torsional potential on several thermodynamic and structural properties of a system of polyethylene chains has been analyzed. To this end, molecular dynamics simulations of a coarse-grained model, whose sites interact through a force field with bending, torsional, and nonbonded terms, have been considered. The torsional potential has three stable configurations: gauche-, trans, and gauche+ . It has been modeled using a simple functional form with only two parameters: the trans-gauche and the gauche-gauche energy barriers. In order to analyze the influence of these parameters on the properties considered in this work, five models with different values of the torsional barriers have been considered. We have observed that the glass transition temperature, the intrachain radial distribution function, the radius of gyration, and the end to end distribution functions are very sensitive to the changes in the trans-gauche torsional barrier. Moreover, at low temperatures, the interchain radial distribution function, the orientational correlation function, and the volume distribution functions of the Voronoi polyhedra, that surround every site of the polymeric chains, also depend on the trans-gauche torsional barrier. On the contrary, the gauche-gauche energy barrier has a minor influence in the properties considered in this work.

  1. A novel powder sample holder for the determination of glass transition temperatures by DMA.

    PubMed

    Mahlin, Denny; Wood, John; Hawkins, Nicholas; Mahey, Jas; Royall, Paul G

    2009-04-17

    The use of a new sample holder for dynamic mechanical analysis (DMA) as a means to characterise the Tg of powdered hydroxypropyl methyl cellulose (HPMC) has been investigated. A sample holder was constructed consisting of a rectangular stainless steel container and a lid engineered to fit exactly within the walls of the container when clamped within a TA instruments Q800 DMA in dual cantilever configuration. Physical mixtures of HPMC (E4M) and aluminium oxide powders were placed in the holder and subjected to oscillating strains (1 Hz, 10 Hz and 100 Hz) whilst heated at 3 degrees C/min. The storage and loss modulus signals showed a large reduction in the mechanical strength above 150 degrees C which was attributed to a glass transition. Optimal experimental parameters were determined using a design of experiment procedure and by analysing the frequency dependence of Tg in Arrhenius plots. The parameters were a clamping pressure of 62 kPa, a mass ratio of 0.2 HPMC in aluminium oxide, and a loading mass of either 120 mg or 180 mg. At 1 Hz, a Tg of 177+/-1.2 degrees C (n=6) for powdered HPMC was obtained. In conclusion, the new powder holder was capable of measuring the Tg of pharmaceutical powders and a simple optimization protocol was established, useful in further applications of the DMA powder holder. PMID:19167475

  2. Linking high-pressure structure and density of albite liquid near the glass transition

    NASA Astrophysics Data System (ADS)

    Gaudio, Sarah J.; Lesher, Charles E.; Maekawa, Hideki; Sen, Sabyasachi

    2015-05-01

    The pressure-induced densification of NaAlSi3O8 liquid is determined following annealing immediately above the glass transition and upon quenching from superliquidus temperatures. High-field 27Al magic-angle-spinning NMR spectroscopy is used to investigate the corresponding changes in Al coordination environment that accompany the densification. We show that samples synthesized by quenching from superliquidus temperatures record lower fictive pressures (Pf) than annealed samples at the same nominal load and have lower recovered densities and average Al coordination number. Accounting for differences in Pf brings melt-quench and annealed samples into excellent agreement. The proportion of [5]Al increases from ∼3% to 29% and [6]Al from 0% to 8% between 1.8 and 7.2 GPa. The production of high-coordinated Al ([5]Al + [6]Al) with pressure is most dramatic above 3 GPa. Changes in network topology and structural disorder as revealed by the high-field 27Al NMR spectra provide new insights into the structural mechanisms of densification of the albite liquid. We posit that it is an overall weakening of the network structure on compression that is largely responsible for the anomalous pressure dependence of the transport properties observed for this liquid below ∼5 GPa.

  3. Length Scales of Local Glass Transition Temperature Gradients Near Soft and Hard Polymer-Polymer Interfaces

    NASA Astrophysics Data System (ADS)

    Baglay, Roman; Roth, Connie

    Polymer-polymer interfaces are ubiquitous in polymer blends and block copolymers, while opening up another avenue for the study of interfacial perturbations to the local glass transition temperature Tg(z). We have previously reported the full local Tg(z) profile across a glassy-rubbery polymer interface between polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA), an 80 K difference in bulk Tg [Baglay & Roth, J Chem Phys 2015, 143, 111101]. By using local fluorescence measurements, we revealed how the Tg(z) profile extends hundreds of nanometers away from the interface showing an asymmetric behavior penetrating deeper into the glassy PS side relative to the composition profile. Here, we extend these measurements to investigate how the local Tg profile in PS varies when in contact with a variety of immiscible polymers whose Tgs vary between +90 K and -80 K relative to the bulk Tg of PS, so-called hard vs. soft confinement. The data reveal that the onset of local Tg deviation from bulk in PS occurs at two distinct length scales, which depend on whether PS is the low Tg component (hard confinement) or the high Tg component (soft confinement). In addition, we explore the influence of finite system size on the range of dynamics by the introduction of periodic boundary conditions, as is commonly encountered in computer simulations or block copolymer systems.

  4. GLASS TRANSITION AND DEGREE OF CONVERSION OF A LIGHT-CURED ORTHODONTIC COMPOSITE

    PubMed Central

    Sostena, Michela M. D. S.; Nogueira, Renata A.; Grandini, Carlos R.; Moraes, João Carlos Silos

    2009-01-01

    Objective: 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. Material and Methods: 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). Results: Fill Magic presented lower Tg than Concise (35-84°C versus 135°C), but reached a higher DC. Conclusions: 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/cm2 is necessary to reach adequate conversion level and obtain satisfactory adhesion. PMID:20027428

  5. Autohesion of semi-crystalline PEEK near and under the glass transition temperature

    NASA Astrophysics Data System (ADS)

    Awaja, Firas; Zhang, Shengnan; McKenzie, David R.

    2013-10-01

    Autohesion of semi-crystalline polymers under the glass transition temperature (Tg) is fundamentally difficult due to severe restriction in molecular chain mobility. We demonstrate that enhanced autohesion of semi-crystalline polyetheretherketone (PEEK) at temperatures close or under Tg can be achieved through plasma immersion ion implantation (PIII) treatment. Autohesive bonding strength of PEEK increased linearly with PIII bias voltage up to tenfold compared to untreated controls at 160 °C (Tg +10 °C). At 130 °C (Tg -20 °C), PIII treatment increased bonding strength of PEEK by more than fivefold compared to the untreated control. PIII treated surface exhibited higher surface energy, polar component and oxygen content. A model based on the formation of covalent bonds on the plasma treated PEEK by radicals present at the interface was found to predict the bonding strength above and below Tg. The major mechanism responsible for improved autohesion of PEEK near and under Tg is believed to be free radicals based covalent bonding assisted by an increase of surface wettability and reduction in surface crystal structure as was evidenced by SEM images.

  6. Interplay between glass transition and thermal expansivity in absorbed and spincoated polymer films

    NASA Astrophysics Data System (ADS)

    Napolitano, Simone; Wubbenhorst, Michael

    2010-03-01

    We investigated the kinetics of formation, the glass transition dynamics and the thermal expansivity of absorbed layers of polystyrene and other amorphous polymers on aluminum oxide. Extremely thin films (2 - 10 nm) were prepared following the experiment of Guiselin: polymers were either spincoated or casted on metallic surfaces and annealed at constant temperature immediately after film formation; non-absorded chains were washed away by a good solvent. Different molecular weights and solvent conditions were explored. We analyzed the shape of the observed kinetics in terms of density of active absorption sites and compared with recent experimental results. The combination of a tremendous reduction of the thermal expansion coefficients, TEC, together with non-universal changes in Tg is discussed. Finally, we add more evidence on the unusual confinement effects of poly(tert-butylstyrene). Below 50 nm, both Tg and TEC decreased. Such a mixed behavior implies an enhancement of the molecular mobility, without the presence of any free surface, but dead layers. The effect of density-conformation coupling in proximity of a non-attractive interface allows coexistence of an immobilized fraction in contact with the metal and an excess of thermal expansivity, arising from the long range effects of packing frustration penetrating inside the bulk-like core of the film.

  7. Ionic liquids and their bases: Striking differences in the dynamic heterogeneity near the glass transition

    PubMed Central

    Grzybowska, K.; Grzybowski, A.; Wojnarowska, Z.; Knapik, J.; Paluch, M.

    2015-01-01

    Ionic liquids (ILs) constitute an active field of research due to their important applications. A challenge for these investigations is to explore properties of ILs near the glass transition temperature Tg, which still require our better understanding. To shed a new light on the issues, we measured ILs and their base counterparts using the temperature modulated calorimetry. We performed a comparative analysis of the dynamic heterogeneity at Tg for bases and their salts with a simple monoatomic anion (Cl–). Each pair of ionic and non-ionic liquids is characterized by nearly the same chemical structure but their intermolecular interactions are completely different. We found that the size of the dynamic heterogeneity of ILs near Tg is considerably smaller than that established for their dipolar counterparts. Further results obtained for several other ILs near Tg additionally strengthen the conclusion about the relatively small size of the dynamic heterogeneity of molecular systems dominated by electrostatic interactions. Our finding opens up new perspectives on designing different material properties depending on intermolecular interaction types. PMID:26582136

  8. Transitions between refrigeration regions in extremely short quantum cycles.

    PubMed

    Feldmann, Tova; Kosloff, Ronnie

    2016-05-01

    The relation between the geometry of refrigeration cycles and their performance is explored. The model studied is based on a coupled spin system. Small cycle times, termed sudden refrigerators, develop coherence and inner friction. We explore the interplay between coherence and energy of the working medium employing a family of sudden cycles with decreasing cycle times. At the point of maximum coherence the cycle changes geometry. This region of cycle times is characterized by a dissipative resonance where heat is dissipated both to the hot and cold baths. We rationalize the change of geometry of the cycle as a result of a half-integer quantization which maximizes coherence. From this point on, increasing or decreasing the cycle time, eventually leads to refrigeration cycles. The transition point between refrigerators and short circuit cycles is characterized by a transition from finite to singular dynamical temperature. Extremely short cycle times reach a universal limit where all cycles types are equivalent. PMID:27300872

  9. Transitions between refrigeration regions in extremely short quantum cycles

    NASA Astrophysics Data System (ADS)

    Feldmann, Tova; Kosloff, Ronnie

    2016-05-01

    The relation between the geometry of refrigeration cycles and their performance is explored. The model studied is based on a coupled spin system. Small cycle times, termed sudden refrigerators, develop coherence and inner friction. We explore the interplay between coherence and energy of the working medium employing a family of sudden cycles with decreasing cycle times. At the point of maximum coherence the cycle changes geometry. This region of cycle times is characterized by a dissipative resonance where heat is dissipated both to the hot and cold baths. We rationalize the change of geometry of the cycle as a result of a half-integer quantization which maximizes coherence. From this point on, increasing or decreasing the cycle time, eventually leads to refrigeration cycles. The transition point between refrigerators and short circuit cycles is characterized by a transition from finite to singular dynamical temperature. Extremely short cycle times reach a universal limit where all cycles types are equivalent.

  10. Fluid dynamics at transition regions of enhanced heat transfer channels

    NASA Astrophysics Data System (ADS)

    Case, Jennifer C.; Pohlman, Nicholas A.

    2012-11-01

    Helical wire coil inserts are used to enhance heat transfer in high heat flux cooling channels. Past research using temperature probes has sufficiently proven that wire coils increase heat transfer by factors of three to five through the disruption of the boundary layer in the channels. The coils are passive devices that are inexpensive to manufacture and easily integrate into existing heat exchangers given the limited pressure drop they produce. Most of the fluid mechanics research in flow over helical coils has focused on the dynamics and vortex structure in fully developed regions rather than the short transition region where the enhanced heat transfer is often expected. Understanding how the development of the flow occurs over the axial length of the cooling channel will determine minimum dimensions necessary for enhanced heat transfer. Results of particle-shadow velocimetry (PSV) measurements report on the flow velocities and turbulence that occurs in the transition regions at the beginning of wire coil inserts. The ability to relate parameters such as flow rate, wire diameter, coil pitch, and the total tube length will increase fundamental knowledge and will allow for more efficient heat exchanger designs. Funding provided by NIU's Undergraduate Special Opportunities in Artistry & Research grant program.

  11. Transition Region and Chromospheric Signatures of Impulsive Heating Events

    NASA Astrophysics Data System (ADS)

    Warren, Harry; Reep, Jeffrey; Crump, Nicholas

    2016-05-01

    We exploit the high spatial resolution and high cadence of the Interface Region Imaging Spectrograph (IRIS) to investigate the response of the transition region and chromosphere to energy deposition during several small flares. We find that during the impulsive phase of these events the intensities of the C II 1334.535 and Si IV 1402.770 A emission lines are characterized by numerous, small-scale impulsive bursts typically lasting 60 s or less followed by a slower decay over several minutes. These variations in intensity are usually accompanied by impulsive redshifts of 20-40 km/s, although some blueshifted profiles are also observed. For one particularly well observed event we combine the IRIS observations with co-temporal measurements of hard X-ray emission from RHESSSI, transition region density from EIS, and high-temperature coronal loops with XRT and AIA to constrain 1D hydrodynamic models of loop evolution. Many aspects of the observations can be explained with simple heating scenarios, but some cannot. The simulated Doppler shifts, for example, show very short-duration redshifts during the initial phase of the heating while the observed redshifts persist over several minutes.

  12. Self-similar magnetic structures during the vortex-glass to vortex-liquid transition of type II superconductors

    NASA Astrophysics Data System (ADS)

    Krasnyuk, I. B.; Taranets, R. M.; Yurchenko, V. M.

    2011-04-01

    We examine the response to an external magnetic field by a multi-layer superconductor with an electrical resistance ρff(b)αbσ, where b is the dimensionless magnetic induction and σ is a parameter characterizing the ratio of the pinning activation energy to the energy of thermal fluctuations. When σ > 1 the sample is in the vortex glass phase, when 0 < σ < 1, it is in the vortex liquid phase, and a vortex glass to vortex liquid phase transition takes place at σ = 1. In the vortex glass phase, the magnetic field penetrates into the superconductor in the form of a self-similar wave. At all times it penetrates to a finite depth and its front moves at a finite velocity which depends on the parameters of the problem, such as the rate of pumping by the external magnetic field. In the vortex liquid phase the magnetic field penetrates to an infinite depth. Thus, the magnetic field penetrates to an infinite depth in the superconductor during a transition from the vortex glass phase into the vortex liquid phase.

  13. Glass transition dynamics of anti-inflammatory ketoprofen studied by Raman scattering and terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Shibata, Tomohiko; Igawa, Hikaru; Kim, Tae Hyun; Mori, Tatsuya; Kojima, Seiji

    2014-03-01

    A liquid-glass transition and a crystalline state of pharmaceutical racemic ketoprofen were studied by Raman scattering and the broadband terahertz time-domain spectroscopy (THz-TDS) in the frequency range from 9 to 260 cm-1. The low-frequency Raman scattering spectra clearly shows the remarkable change related to a liquid-glass transition at about Tg = 267 K. After melt-quenching at liquid nitrogen temperature, a boson peak appears at about 16.5 cm-1 near and below Tg and the intensity of quasi-elastic scattering related to structural relaxation increases markedly on heating. The crystalline racemic ketoprofen of "conformer A" shows the noncoincidence effect of mode frequencies below 200 cm-1 between Raman scattering spectra and dielectric spectra observed by THz-TDS.

  14. Glass electrolyte composition

    DOEpatents

    Kucera, Gene H.; Roche, Michael F.

    1985-01-01

    An ionically conductive glass is disclosed for use as electrolyte in a high temperature electrochemical cell, particularly a cell with sodium anode and sulfur cathode. The glass includes the constituents Na.sub.2 O, ZrO.sub.2, Al.sub.2 O.sub.3 and SiO.sub.2 in selected proportions to be a single phase solid solution substantially free of crystalline regions and undissolved constituents. Other advantageous properties are an ionic conductivity in excess of 2.times.10.sup.-3 (ohm-cm).sup.-1 at 300.degree. C. and a glass transition temperature in excess of 500.degree. C.

  15. Glass electrolyte composition

    DOEpatents

    Kucera, G.H.; Roche, M.F.

    1985-01-08

    An ionically conductive glass is disclosed for use as electrolyte in a high temperature electrochemical cell, particularly a cell with sodium anode and sulfur cathode. The glass includes the constituents Na/sub 2/O, ZrO/sub 2/, Al/sub 2/O/sub 3/ and SiO/sub 2/ in selected proportions to be a single phase solid solution substantially free of crystalline regions and undissolved constituents. Other advantageous properties are an ionic conductivity in excess of 2 x 10/sup -3/ (ohm-cm)/sup -1/ at 300/sup 0/C and a glass transition temperature in excess of 500/sup 0/C.

  16. Results from the transition region camera. [for solar ultraviolet photography

    NASA Technical Reports Server (NTRS)

    Foing, B. H.; Bonnet, R. M.

    1984-01-01

    Three series of high resolution ultra-violet pictures of the sun have been obtained during the three flights of rocket experiment T.R.C. Transition Region Camera) which took place on 3 July 1979, 23 September 1980 and 13 July 1982. These pictures reveal many structures in Ly alpha and ultraviolet continua at 160 nm and 220 nm. The scientific objectives, instrumentation, flight conditions and campaigns of simultaneous observations are described. The contribution of T.R.C. to solar physics is discussed in the framework of chromospheric multicomponent models, magnetic flux tubes, local heating and periodic structures in the chromosphere.

  17. Signatures of many-body localisation in a system without disorder and the relation to a glass transition

    NASA Astrophysics Data System (ADS)

    Hickey, James M.; Genway, Sam; Garrahan, Juan P.

    2016-05-01

    We study a quantum spin system—adapted from a facilitated spin model for classical glasses—with local bilinear interactions and without quenched disorder which seems to display characteristic signatures of a many-body localisation (MBL) transition. From direct diagonalisation of small systems, we find a change in certain dynamical and spectral properties at a critical value of a coupling, from those characteristic of a thermalising phase to those characteristic of a MBL phase. The system we consider is known to have a quantum phase transition in its ground-state in the limit of large size, related to a first-order active-to-inactive phase transition in the stochastic trajectories of an associated classical model of glasses. Our results here suggest that this first-order transition in the low-lying spectrum may influence the rest of the spectrum of the system in the large size limit. These findings may help understand the connection between MBL and structural glass transitions.

  18. 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. PMID:20629875

  19. 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.

  20. Effect of polymer-nanoparticle interactions on the glass transition dynamics and the conductivity mechanism in polyurethane titanium dioxide nanocomposites

    SciTech Connect

    Polyzos, Georgios; Tuncer, Enis; Agapov, Alexander L; Stevens, Derrick; Sokolov, Alexei P; Kidder, Michelle; Jacobs,; Koerner, Hilmar; Vaia, Richard; More, Karren Leslie; Sauers, Isidor

    2012-01-01

    We report on the glass transition dynamics and the conductivity properties of a nanodielectric system composed of pre-synthesized TiO{sub 2} nanoparticles embedded in thermoplastic polyurethane. Increase of TiO{sub 2} loading results in enhanced segmental mobility of the composites and less steep temperature dependence, i.e., lower fragility index. The decrease in the fragility index and glass transition temperature is discussed based on the FTIR results. We observe different behavior of conductivity for temperatures above and below the glass transition temperature. At high temperatures the composites exhibit conductivity values more than 2 orders of magnitude higher than those in the pristine matrix. At the same time, at sub-Tg temperatures composites are characterized by superior electrical insulation properties compared to pristine matrix material. Such drastic temperature dependence of the conductivity/insulating ability of the flexible and light-weight, low-Tg composite material can be utilized in various applications including sensing and temperature switching materials.

  1. CIV VUV FPI Interferometer for Transition Region Magnetography

    NASA Technical Reports Server (NTRS)

    Gary, G. A.

    2005-01-01

    Much in the same way photonics harnesses light for engineering and technology applications, solar physics harnesses light for the remote sensing of the sun. In photonics the vacuum ultraviolet region offers shorter wavelength and higher energies per photon, while in solar physics the VUV allows the remote sensing of the upper levels of the solar atmosphere where magnetic fields dominate the physics. Understanding solar magnetism is a major aim for astrophysics and for understanding solar-terrestrial interaction. The poster is on our instrument development program for a high-spectral-resolution, high-finesse, Vacuum Ultraviolet Fabry-Perot Interferometer (VUV FPI) for obtaining narrow-passband images, magnetograms, and Dopplergrams of the transition region emission line of CIV (155nm). The poster will cover how the V W interferometer will allow us to understand solar magnetism, what is special about the MSFC VUV FPI, and why the University of Toronto F2 eximer has been of particular value to this program.

  2. TRANSITION REGION EMISSION FROM SOLAR FLARES DURING THE IMPULSIVE PHASE

    SciTech Connect

    Johnson, H.; Raymond, J. C.; Murphy, N. A.; Suleiman, R.; Giordano, S.; Ko, Y.-K.; Ciaravella, A.

    2011-07-10

    There are relatively few observations of UV emission during the impulsive phases of solar flares, so the nature of that emission is poorly known. Photons produced by solar flares can resonantly scatter off atoms and ions in the corona. Based on off-limb measurements by the Solar and Heliospheric Observatory/Ultraviolet Coronagraph Spectrometer, we derive the O VI {lambda}1032 luminosities for 29 flares during the impulsive phase and the Ly{alpha} luminosities of 5 flares, and we compare them with X-ray luminosities from GOES measurements. The upper transition region and lower transition region luminosities of the events observed are comparable. They are also comparable to the luminosity of the X-ray emitting gas at the beginning of the flare, but after 10-15 minutes the X-ray luminosity usually dominates. In some cases, we can use Doppler dimming to estimate flow speeds of the O VI emitting gas, and five events show speeds in the 40-80 km s{sup -1} range. The O VI emission could originate in gas evaporating to fill the X-ray flare loops, in heated chromospheric gas at the footpoints, or in heated prominence material in the coronal mass ejection. All three sources may contribute in different events or even in a single event, and the relative timing of UV and X-ray brightness peaks, the flow speeds, and the total O VI luminosity favor each source in one or more events.

  3. Localization and elasticity in entangled polymer liquids as a mesoscopic glass transition

    NASA Astrophysics Data System (ADS)

    Schweizer, Kenneth

    2010-03-01

    The reptation-tube model is widely viewed as the correct zeroth order model for entangled linear polymer dynamics under quiescent conditions. Its key ansatz is the existence of a mesoscopic dynamical length scale that prohibits transverse chain motion beyond a tube diameter of order 3-10 nm. However, the theory is phenomenological and lacks a microscopic foundation, and many fundamental questions remain unanswered. These include: (i) where does the confining tube field come from and can it be derived from statistical mechanics? (ii) what is the microscopic origin of the magnitude, and power law scaling with concentration and packing length, of the plateau shear modulus? (iii) is the tube diameter time-dependent? (iv) does the confinement field contribute to elasticity ? (v) do entanglement constraints have a finite strength? Building on our new force-level theories for the dynamical crossover and activated barrier hopping in glassy colloidal suspensions and polymer melts, a first principles self-consistent theory has been developed for entangled polymers. Its basic physical elements, and initial results that address the questions posed above, will be presented. The key idea is that beyond a critical degree of polymerization, the chain connectivity and excluded volume induced intermolecular correlation hole drives temporary localization on an intermediate length scale resulting in a mesoscopic ``ideal kinetic glass transition.'' Large scale isotropic motion is effectively quenched due to the emergence of chain length dependent entropic barriers. However, the barrier height is not infinite, resulting in softening of harmonic localization at large displacements, temporal increase of the confining length scale, and a finite strength of entanglement constraints which can be destroyed by applied stress.

  4. Shikimic acid ozonolysis kinetics of the transition from liquid aqueous solution to highly viscous glass.

    PubMed

    Steimer, Sarah S; Berkemeier, Thomas; Gilgen, Anina; Krieger, Ulrich K; Peter, Thomas; Shiraiwa, Manabu; Ammann, Markus

    2015-12-14

    Ageing of particulate organic matter affects the composition and properties of atmospheric aerosol particles. Driven by temperature and humidity, the organic fraction can vary its physical state between liquid and amorphous solid, or rarely even crystalline. These transitions can influence the reaction kinetics due to limitations of mass transport in such (semi-) solid states, which in turn may influence the chemical ageing of particles containing such compounds. We have used coated wall flow tube experiments to investigate the reaction kinetics of the ozonolysis of shikimic acid, which serves as a proxy for oxygenated, water-soluble organic matter and can form a glass at room temperature. Particular attention was paid to how the presence of water influences the reaction, since it acts a plasticiser and thereby induces changes in the physical state. We analysed the results by means of a traditional resistor model, which assumes steady-state conditions. The ozonolysis rate of shikimic acid is strongly increased in the presence of water, a fact we attribute to the increased transport of O3 and shikimic acid through the condensed phase at lower viscosities. The analysis using the resistor model suggests that the system undergoes both surface and bulk reaction. The second-order rate coefficient of the bulk reaction is 3.7 (+1.5/-3.2) × 10(3) L mol(-1) s(-1). At low humidity and long timescales, the resistor model fails to describe the measurements appropriately. The persistent O3 uptake at very low humidity suggests contribution of a self-reaction of O3 on the surface. PMID:26536455

  5. Computational modelling of large deformations in layered-silicate/PET nanocomposites near the glass transition

    NASA Astrophysics Data System (ADS)

    Figiel, Łukasz; Dunne, Fionn P. E.; Buckley, C. Paul

    2010-01-01

    Layered-silicate nanoparticles offer a cost-effective reinforcement for thermoplastics. Computational modelling has been employed to study large deformations in layered-silicate/poly(ethylene terephthalate) (PET) nanocomposites near the glass transition, as would be experienced during industrial forming processes such as thermoforming or injection stretch blow moulding. Non-linear numerical modelling was applied, to predict the macroscopic large deformation behaviour, with morphology evolution and deformation occurring at the microscopic level, using the representative volume element (RVE) approach. A physically based elasto-viscoplastic constitutive model, describing the behaviour of the PET matrix within the RVE, was numerically implemented into a finite element solver (ABAQUS) using an UMAT subroutine. The implementation was designed to be robust, for accommodating large rotations and stretches of the matrix local to, and between, the nanoparticles. The nanocomposite morphology was reconstructed at the RVE level using a Monte-Carlo-based algorithm that placed straight, high-aspect ratio particles according to the specified orientation and volume fraction, with the assumption of periodicity. Computational experiments using this methodology enabled prediction of the strain-stiffening behaviour of the nanocomposite, observed experimentally, as functions of strain, strain rate, temperature and particle volume fraction. These results revealed the probable origins of the enhanced strain stiffening observed: (a) evolution of the morphology (through particle re-orientation) and (b) early onset of stress-induced pre-crystallization (and hence lock-up of viscous flow), triggered by the presence of particles. The computational model enabled prediction of the effects of process parameters (strain rate, temperature) on evolution of the morphology, and hence on the end-use properties.

  6. An Ultrasonic Study on the Polyamorphic Transition in La/Ce-based Bulk Metallic Glass to 12 GPa

    NASA Astrophysics Data System (ADS)

    Qi, X.; Wang, X.; Chen, T.; Welch, D. O.; Jiang, J.; Li, B.

    2015-12-01

    Bulk metallic glasses (BMGs), also known as amorphous alloys, are one of the most promising materials in the 21st century. With their unique structures, BMGs are at the cutting edge of materials study for both commercial applications and fundamental studies. In the light of engineering applications, some metal-metal alloy BMGs are stronger than steels but able to be shaped and molded like plastics. As a new member of glass family, metallic glasses are also good models for studies of fundamental problems in condensed matter physics. Pressure-induced polyamorphism in Ce-based bulk metallic glasses have attracted interest in recent years. Ultrasonic measurements of the compressional and shear wave velocities not only provide critical information about their interatomic forces, but also offer a unique approach for precise determination of mass densities under pressure that are quite difficult to access by other methods. In this study, the acoustic velocities of La32Ce32Al16Ni5Cu15 bulk metallic glass were measured up to 12.3 GPa using ultrasonic interferometry in a multi-anvil apparatus at room temperature. Both compressional and shear waves exhibited softening behaviors at 0-4 GPa, followed by a continuous increase (stiffening) with pressures. Measurements under decompression exhibit a hysteretic behavior compared to that on compression. The mass density as a function of pressure revealed three different amorphous states and the transition pressures were accompanied by distinct changes in the pressure derivatives of elastic moduli. The interpretation of the residual densification and the softening/stiffening across the polyamorphic transition can be sought via the topological rearrangement of the solute-centered clusters in medium-range order and the possibility of 4f electron localization/delocalization in Ce.

  7. Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields

    NASA Astrophysics Data System (ADS)

    Morais, C. V.; Zimmer, F. M.; Lazo, M. J.; Magalhães, S. G.; Nobre, F. D.

    2016-06-01

    The behavior of the nonlinear susceptibility χ3 and its relation to the spin-glass transition temperature Tf in the presence of random fields are investigated. To accomplish this task, the Sherrington-Kirkpatrick model is studied through the replica formalism, within a one-step replica-symmetry-breaking procedure. In addition, the dependence of the Almeida-Thouless eigenvalue λAT (replicon) on the random fields is analyzed. Particularly, in the absence of random fields, the temperature Tf can be traced by a divergence in the spin-glass susceptibility χSG, which presents a term inversely proportional to the replicon λAT. As a result of a relation between χSG and χ3, the latter also presents a divergence at Tf, which comes as a direct consequence of λAT=0 at Tf. However, our results show that, in the presence of random fields, χ3 presents a rounded maximum at a temperature T* which does not coincide with the spin-glass transition temperature Tf (i.e., T*>Tf for a given applied random field). Thus, the maximum value of χ3 at T* reflects the effects of the random fields in the paramagnetic phase instead of the nontrivial ergodicity breaking associated with the spin-glass phase transition. It is also shown that χ3 still maintains a dependence on the replicon λAT, although in a more complicated way as compared with the case without random fields. These results are discussed in view of recent observations in the LiHoxY1 -xF4 compound.

  8. Isothermal internal friction behaviour of a Zr based bulk metallic glass with large supercooled liquid region

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Lu, J.; Gu, F. J.; Xu, H.; Dong, Y. D.

    2006-07-01

    In this paper, the internal friction behaviour of Zr-Ti-Cu-Ni-Be bulk metallic glass (BMG) containing 2 at% Fe at elevated temperatures has been studied in isothermal dynamic mechanical analysis experiments. The experiments lead to the determination of metastable equilibrium internal friction Q_{\\rme}^{-1} , as a function of temperature, which can be well described by the Maxwell model with viscosity, η(T), following a Vogel-Fulcher-Tammann (VFT) relation or Arrehnius law. Comparison with the Zr-Ti-Cu-Ni-Be glass-forming liquid shows that a small addition of Fe results in a stronger liquid behaviour of the alloy, exhibiting a higher strength parameter as well as lower VFT temperature and therefore correlates better glass forming ability and thermal stability. From the isothermal internal friction data, the activation energies for viscous flow and primary crystallization of the Zr based supercooled metallic liquid are also derived. It is found that the former is comparable to the activation energy controlling the diffusion process of atoms, e.g. the Ni element of medium size and higher mobility among the components of this alloy, while the latter to that of atoms, e.g. the Ti element of larger size and lower mobility. Thus, it is proposed that both isothermal viscous flow and primary crystallization of the alloy in the supercooleld liquid region are atom diffusion-controlled processes. However, the dominating atomic species are different from each other in the multicomponent Zr based BMG.

  9. Enthalpy relaxation kinetics of Ge20Te(80-y)Sey far-infrared glasses in the glass transition range

    NASA Astrophysics Data System (ADS)

    Svoboda, Roman; Málek, Jiří

    2016-06-01

    Differential scanning calorimetry was used to study enthalpy relaxation kinetics of the Ge20Te(80-y)Sey infrared chalcogenide glasses for the compositional range y = 0-8. The relaxation behaviour was described in terms of the phenomenological Tool-Narayanaswamy-Moynihan (TNM) model. The direct curve-fitting procedure was used to determine the values of TNM parameters. Compositional evolution of the TNM parameters was interpreted with respect to the involved structural entities and their motions. Based on the joint Raman scattering study, the addition of Se leads to increased amount of edge-shared GeTe4-xSex tetrahedra. While the primary structural basis for the relaxation movements appears not to be affected by addition of Se (constant value of non-linearity), changes of the non-exponentiality parameter indicate increased structural variability occurring within the groups of directly interlinked tetrahedra, which were found to carry the main portion of relaxation movements. Increased activation energy was explained by the presence of significantly stronger Ge-Se bonds and increased amount of edge-shared tetrahedra.

  10. Glass transition and composite formation in InF3-containing oxyfluoroniobate system

    NASA Astrophysics Data System (ADS)

    Savchenko, N. N.; Ignatieva, L. N.; Marchenko, Yu. V.; Bouznik, V. M.

    2016-05-01

    The glasses in the system MnNbOF5-BaF2-InF3 have been firstly synthesized and studied. The thermal parameters of these glasses are analyzed. It was stated that glass of the composition 40MnNbOF5-40BaF2-20InF3 is the most thermal stable in the system under study. By X-ray analysis the compositions of the crystalline phases obtained at the glass thermal treatment were determined: the main phases are Ba3In2F12 and BaNbOF5. By Raman and IR spectra analysis it was stated that the networks of glasses in the system are built by the structural type of the glasses in NbO2F-BaF2 system: (NbOnFm) polyhedra joined oxygen bridges. Indium trifluoride forms InF6 polyhedra, which are embeded between oxyfluoroniobate ions, forming a common networks or forms its own layers from InF6 polyhedra. IR-spectroscopy method showed that at devitrification of the sample 30MnNbOF5-50BaF2-20InF3 the band position and shape change in going from glass state to crystalline. The bands in the range 900-700 cm-1 shift into the low-frequency range and transformed into narrow peaks characteristic for the crystalline state. It was determined that for this sample the IR-spectroscopy method fixes the presence of the crystalline phases at 340°C without time of exposure, despite the fact that X-ray analysis shows an amorphous state for this sample at the same temperature. It was suggested, that controlling the composition and conditions of annealing of the glasses it can be obtain the transparent glass-ceramics of definite composition.

  11. Glass transition behavior of octyl β-D-glucoside and octyl β-D-thioglucoside/water binary mixtures.

    PubMed

    Ogawa, Shigesaburo; Asakura, Kouichi; Osanai, Shuichi

    2010-11-22

    The lyotropic behavior and glass-forming properties of octyl β-D-glucoside (C8Glu) and octyl β-D-thioglucoside (C8SGlu)/water binary mixtures were evaluated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The results clearly indicate that the mixture forms a glass in the supercooling state of liquid crystalline phases such as cubic, lamellar, and smectic. The glass transition temperature (T(g)) of the mixture was strongly dependent on solute concentration, with a higher concentration correlating with a higher T(g). The experimental T(g) was consistent with the predicted value calculated using the Couchman-Karasz equation in both the C8Glu and C8SGlu/water mixtures. The change of heat capacity at T(g) showed the two bending points under variation of concentrations. And the highest temperature of phase transition from lamellar to isotropic solution was observed at around 50% molar concentration. It was expected that non-percolated state of water existed in extremely higher concentration ranges.

  12. The use of transition region characteristics to improve the numerical simulation of heat transfer in bypass transitional flows

    NASA Technical Reports Server (NTRS)

    Simon, Frederick F.

    1993-01-01

    A method is presented for improving the numerical prediction of bypass transition heat transfer on a flat plate in a high-disturbance environment with zero or favorable pressure gradient. The method utilizes low Reynolds number k-epsilon turbulence models in combination with the characteristic parameters of the transition region. The parameters representing the characteristics of the transition region used are the intermittency, transition length and turbulent spot properties. An analysis is made of the transition length in terms of turbulent spot variables. The nondimensional spot formation rate, required for the prediction of the transition length, is shown by the analysis to be a function of the spot spreading angle, the dimensionless spot velocity ratio and the dimensionless spot area ratio. The intermittency form of the k-epsilon equations were derived from conditionally averaged equations which have been shown to be an improvement over global-time-averaged equations for the numerical calculation of the transition region. The numerical predictions are in general good agreement with the experimental data and indicate the potential use of the method in accelerating flows. Turbulence models of the k-epsilon type are known to underpredict the transition length. The present work demonstrates how incorporating transition region characteristics improves the ability of two-equation turbulence models to simulate bypass transition for flat plates with potential application to turbine vanes and blades.

  13. Mean-field theory of the glass transition in the one-component classical plasma

    NASA Astrophysics Data System (ADS)

    Cardenas, M.; Tosi, M. P.

    2004-08-01

    We study the supercooled-fluid region and the transition to an amorphous glassy state in the one-component classical plasma, within the replica-symmetry-breaking scenario developed by Franz and Parisi. This approach implements the slowing down of jumps of the disordered system between the minima in a rugged free-energy landscape by examining its correlations with a quenched replica as a function of their coupling expressed through a suitable short-range attractive potential. We carry out these calculations within a mean-field theory for the structure of a quenched-annealed mixture, using both the hypernetted chain approximation and a refinement to include an account of the bridge function. In both formulations our theoretical results demonstrate the existence of a glassy state for the plasma and yield an estimate of the phase-transition line, which has the form T∝ Z2n1/3 where n is the particle number density, T the temperature and Z the valence, with a numerical coefficient which is about one eighth of that for equilibrium freezing. The consequences for various types of ionic fluids (simple molten salts, colloidal dispersions, and astrophysical plasmas) are illustrated.

  14. Fragilities of liquids predicted from the random first order transition theory of glasses

    NASA Astrophysics Data System (ADS)

    Xia, Xiaoyu; Wolynes, Peter G.

    2000-03-01

    A microscopically motivated theory of glassy dynamics based on an underlying random first order transition is developed to explain the magnitude of free energy barriers for glassy relaxation. A variety of empirical correlations embodied in the concept of liquid "fragility" are shown to be quantitatively explained by such a model. The near universality of a Lindemann ratio characterizing the maximal amplitude of thermal vibrations within an amorphous minimum explains the variation of fragility with a liquid's configurational heat capacity density. Furthermore, the numerical prefactor of this correlation is well approximated by the microscopic calculation. The size of heterogeneous reconfiguring regions in a viscous liquid is inferred and the correlation of nonexponentiality of relaxation with fragility is qualitatively explained. Thus the wide variety of kinetic behavior in liquids of quite disparate chemical nature reflects quantitative rather than qualitative differences in their energy landscapes.

  15. Dynamic processes in a silicate liquid from above melting to below the glass transition

    NASA Astrophysics Data System (ADS)

    Nascimento, Marcio Luis Ferreira; Fokin, Vladimir Mihailovich; Zanotto, Edgar Dutra; Abyzov, Alexander S.

    2011-11-01

    We collect and critically analyze extensive literature data, including our own, on three important kinetic processes—viscous flow, crystal nucleation, and growth—in lithium disilicate (Li2O.2SiO2) over a wide temperature range, from above Tm to 0.98Tg where Tg ≈ 727 K is the calorimetric glass transition temperature and Tm = 1307 K, which is the melting point. We found that crystal growth mediated by screw dislocations is the most likely growth mechanism in this system. We then calculated the diffusion coefficients controlling crystal growth, D_{eff}^U, and completed the analyses by looking at the ionic diffusion coefficients of Li+1, O2-, and Si4+ estimated from experiments and molecular dynamic simulations. These values were then employed to estimate the effective volume diffusion coefficients, D_{eff}^V, resulting from their combination within a hypothetical Li2Si2O5 "molecule". The similarity of the temperature dependencies of 1/η, where η is shear viscosity, and D_{eff}^V corroborates the validity of the Stokes-Einstein/Eyring equation (SEE) at high temperatures around Tm. Using the equality of D_{eff}^V and D_{eff}^η, we estimated the jump distance λ ˜ 2.70 Å from the SEE equation and showed that the values of D_{eff}^U have the same temperature dependence but exceed D_{eff}^η by about eightfold. The difference between D_{eff}^η and D_{eff}^U indicates that the former determines the process of mass transport in the bulk whereas the latter relates to the mobility of the structural units on the crystal/liquid interface. We then employed the values of η(T) reduced by eightfold to calculate the growth rates U(T). The resultant U(T) curve is consistent with experimental data until the temperature decreases to a decoupling temperature T_d^U ≈ 1.1 - 1.2T_g, when D_{eff}^η begins decrease with decreasing temperature faster than D_{eff}^U. A similar decoupling occurs between D_{eff}^η and D_{eff}^τ (estimated from nucleation time-lags) but at a

  16. Humidity-dependent compression-induced glass transition of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA).

    PubMed

    Kim, Hyun Chang; Lee, Hoyoung; Jung, Hyunjung; Choi, Yun Hwa; Meron, Mati; Lin, Binhua; Bang, Joona; Won, You-Yeon

    2015-07-28

    Constant rate compression isotherms of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA) show a distinct feature of an exponential increase in surface pressure in the high surface polymer concentration regime. We have previously demonstrated that this abrupt increase in surface pressure is linked to the glass transition of the polymer film, but the detailed mechanism of this process is not fully understood. In order to obtain a molecular-level understanding of this behavior, we performed extensive characterizations of the surface mechanical, structural and rheological properties of Langmuir PLGA films at the air-water interface, using combined experimental techniques including the Langmuir film balance, X-ray reflectivity and double-wall-ring interfacial rheometry methods. We observed that the mechanical and structural responses of the Langmuir PLGA films are significantly dependent on the rate of film compression; the glass transition was induced in the PLGA film only at fast compression rates. Surprisingly, we found that this deformation rate dependence is also dependent on the humidity of the environment. With water acting as a plasticizer for the PLGA material, the diffusion of water molecules through the PLGA film seems to be the key factor in the determination of the glass transformation properties and thus the mechanical response of the PLGA film against lateral compression. Based on our combined results, we hypothesize the following mechanism for the compression-induced glass transformation of the Langmuir PLGA film; (1) initially, a humidified/non-glassy PLGA film is formed in the full surface-coverage region (where the surface pressure shows a plateau) during compression; (2) further compression leads to the collapse of the PLGA chains and the formation of new surfaces on the air side of the film, and this newly formed top layer of the PLGA film is transiently glassy in character because the water evaporation rate

  17. Humidity-dependent compression-induced glass transition of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA).

    PubMed

    Kim, Hyun Chang; Lee, Hoyoung; Jung, Hyunjung; Choi, Yun Hwa; Meron, Mati; Lin, Binhua; Bang, Joona; Won, You-Yeon

    2015-07-28

    Constant rate compression isotherms of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA) show a distinct feature of an exponential increase in surface pressure in the high surface polymer concentration regime. We have previously demonstrated that this abrupt increase in surface pressure is linked to the glass transition of the polymer film, but the detailed mechanism of this process is not fully understood. In order to obtain a molecular-level understanding of this behavior, we performed extensive characterizations of the surface mechanical, structural and rheological properties of Langmuir PLGA films at the air-water interface, using combined experimental techniques including the Langmuir film balance, X-ray reflectivity and double-wall-ring interfacial rheometry methods. We observed that the mechanical and structural responses of the Langmuir PLGA films are significantly dependent on the rate of film compression; the glass transition was induced in the PLGA film only at fast compression rates. Surprisingly, we found that this deformation rate dependence is also dependent on the humidity of the environment. With water acting as a plasticizer for the PLGA material, the diffusion of water molecules through the PLGA film seems to be the key factor in the determination of the glass transformation properties and thus the mechanical response of the PLGA film against lateral compression. Based on our combined results, we hypothesize the following mechanism for the compression-induced glass transformation of the Langmuir PLGA film; (1) initially, a humidified/non-glassy PLGA film is formed in the full surface-coverage region (where the surface pressure shows a plateau) during compression; (2) further compression leads to the collapse of the PLGA chains and the formation of new surfaces on the air side of the film, and this newly formed top layer of the PLGA film is transiently glassy in character because the water evaporation rate

  18. Combustion characteristics in the transition region of liquid fuel sprays

    NASA Technical Reports Server (NTRS)

    Cernansky, N. P.; Namer, I.; Tidona, R. J.

    1986-01-01

    A number of important effects have been observed in the droplet size transition region in spray combustion systems. In this region, where the mechanism of flame propagation is transformed from diffusive to premixed dominated combustion, the following effects have been observed: (1) maxima in burning velocity; (2) extension of flammability limits; (3) minima in ignition energy; and (4) minima in NOx formation. A monodisperse aerosol generator has been used to form and deliver a well controlled liquid fuel spray to the combustion test section where measurements of ignition energy have been made. The ignition studies were performed on monodisperse n-heptane sprays at atmospheric pressure over a range of equivalence ratios and droplet diameters. A capacitive discharge spark ignition system was used as the ignition source, providing independent control of spark energy and duration. Preliminary measurements were made to optimize spark duration and spark gap, optimum conditions being those at which the maximum frequency or probability of ignition was observed. Using the optimum electrode spacing and spark duration, the frequency of ignition was determined as a function of spark energy for three overall equivalence ratios (0.6, 0.8, and 1.0) and for initial droplet diameters of 25, 40, 50, 60, and 70 micro m.

  19. Microscopic view of glass transition dynamics: A quasielastic neutron scattering study on trans-1,4-polychloroprene

    NASA Astrophysics Data System (ADS)

    Kanaya, T.; Kawaguchi, T.; Kaji, K.

    1996-09-01

    We have studied the glass transition dynamics of trans-1,4-chloroprene from microscopic view points using a quasielastic neutron scattering technique in a time range of ˜4×10-13 to ˜4×10-10 s. It was found that the so-called fast process of picosecond order appears at around the Vogel-Fulcher temperature T0, similarly to cis-1,4-polybutadiene having no large side groups [J. Chem. Phys. 98, 8262 (1993)]. It is considered that the onset temperature at around T0 must be characteristic to polymers having no large side groups or no large internal degrees of freedom. In addition to the fast process, the slow process of subnanosecond order sets in at around the glass transition temperature Tg and the activation energy of the relaxation time was found to be ˜2.5 kcal/mol. The nature of the slow process is discussed in terms of conformational transition near Tg.

  20. Stability of anthocyanins in frozen and freeze-dried raspberries during long-term storage: in relation to glass transition.

    PubMed

    Syamaladevi, Roopesh M; Sablani, Shyam S; Tang, Juming; Powers, Joseph; Swanson, Barry G

    2011-08-01

    Anthocyanins, natural plant pigments in the flavonoid group, are responsible for the red color and some of the nutraceutical benefits of raspberries. This study explores anthocyanin degradation in frozen and freeze-dried raspberries during storage in relation to glass transition temperatures. Frozen raspberries were stored at -80, -35, and -20 °C, while freeze-dried raspberries were stored at selected water activity (a(w)) values ranging from 0.05 to 0.75 at room temperature (23 °C) for more than a year. The characteristic glass transition temperatures (T'(g)) of raspberries with high water content and glass transition temperature (T(g)) of raspberries with small water content were determined using a differential scanning calorimeter. The pH differential method was used to determine the quantity of anthocyanins in frozen and freeze-dried raspberries at selected time intervals. The total anthocyanins in raspberries fluctuated during 378 d of storage at -20 and -35, and -80 °C. Anthocyanin degradation in freeze-dried raspberries ranged from 27% to 32% and 78% to 89% at a(w) values of 0.05 to 0.07 and 0.11 to 0.43, respectively, after 1 y. Anthocyanins were not detectable in freeze-dried raspberries stored at a(w) values of 0.53 to 0.75 after 270 d. First order and Weibull equations were used to fit the anthocyanin degradation in freeze-dried raspberries. The 1(st)-order rate constant (k) of anthocyanin degradation ranged from 0.003 to 0.023 days⁻¹ at the selected water activities. Significant anthocyanin degradation occurred in both the glassy and rubbery states of freeze-dried raspberries during long-term storage. However, the rate of anthocyanin degradation in freeze-dried raspberries stored in the glassy state was significantly smaller than the rate of anthocyanin degradation in the rubbery state. PMID:22417493

  1. Phase transition and glass transition concerning configurational order/disorder of ions in crystalline (TMA) 2[Sr{Ni(pro) 2} 6](ClO 4) 4 and (TMA)[Sm{Ni(pro) 2} 6](ClO 4) 4

    NASA Astrophysics Data System (ADS)

    Yukawa, Y.; Igarashi, S.; Masuda, Y.; Oguni, M.

    2002-03-01

    Crystalline (TMA) 2[Sr{Ni(pro) 2} 6](ClO 4) 4 was synthesized newly and its structure was determined, where TMA and pro denote tetramethylammonium and L-prolinato, respectively. Heat capacities of crystalline (TMA) 2[Sr{Ni(pro) 2} 6](ClO 4) 4 and (TMA)[Sm{Ni(pro) 2} 6](ClO 4) 4 were measured at low temperatures by using an adiabatic calorimeter. In the former compound, a phase transition of the first order was found to occur at (160±1) K with a sharp heat-capacity peak. The enthalpy and entropy of the transition were estimated to be (11.0±0.2) and (69.4±1.5) JK -1 mol -1, respectively. In the latter compound, a phase transition of the first order and a glass transition were found at (190±1) and (162±2) K, respectively. The entropy of the phase transition was estimated to be in the range 20-45 JK -1 mol -1. The phase transitions were attributed to the orientational order/disorder process of perchlorate ions ClO 4-, and it was suggested that each ClO 4- ion has six and three distinguishable, reasonably stable orientations in the high-temperature disordered phase for the Sr II and Sm III complex compounds, respectively. The glass transition was interpreted as a freezing-in phenomenon of the reorientational motion of ClO 4- ions, and the activation energy for the motion was estimated to be (53±1) kJ mol -1 and less than 39 kJ mol -1 for the Sm III and Sr II complex compounds, respectively; the removal of one of the two TMA ions neighboring to the ClO 4- ion leads to an increase in the activation energy. It is discussed that the cooperative interaction between the orientations of the ClO 4- ions operates through the orientational and positional shifts of TMA ions, and thus the lattice deformation in the relevant region, associated with the orientational change of the ClO 4- ions. Then it is noted that the position of the ClO 4- ion itself would shift to form preferable ionic interaction, for example through a kind of hydrogen bond of C-H δ+ ⋯ δ- O-Cl, for

  2. Thermal stress modification in regenerated fiber Bragg grating via manipulation of glass transition temperature based on CO₂-laser annealing.

    PubMed

    Lai, Man-Hong; Lim, Kok-Sing; Gunawardena, Dinusha S; Yang, Hang-Zhou; Chong, Wu-Yi; Ahmad, Harith

    2015-03-01

    In this work, we have demonstrated thermal stress relaxation in regenerated fiber Bragg gratings (RFBGs) by using direct CO₂-laser annealing technique. After the isothermal annealing and slow cooling process, the Bragg wavelength of the RFBG has been red-shifted. This modification is reversible by re-annealing and rapid cooling. It is repeatable with different cooling process in the subsequent annealing treatments. This phenomenon can be attributed to the thermal stress modification in the fiber core by means of manipulation of glass transition temperature with different cooling rates. This finding in this investigation is important for accurate temperature measurement of RFBG in dynamic environment. PMID:25723423

  3. Nonlinear Propagation of Mag Waves Through the Transition Region

    NASA Astrophysics Data System (ADS)

    Jatenco-Pereira, V.; Steinolfson, R. S.; Mahajan, S.; Tajima, T.

    1990-11-01

    RESUMEN. Una onda de gravitaci5n magneto acustica (GMA), se inicia en el regimen de alta beta cerca de la basa de fot5sfera solar y es segui- da, usando simulaciones numericas, mientras viaja radialmente a traves de la cromosfera, la regi5n de transici6n y dentro de la corona. Se ha' seleccionado parametros iniciales de manera que la beta resulte menor que uno cerca de la parte alta de la regi6n de transici6n. Nuestro interes maximo se concentra en la cantidad y forma del flujo de energia que puede ser llevada por la onda hasta la corona dados una atm6sfera inicial y amplitud de onda especificas. Segun los estudios a la fecha, el flujo de energ1a termico domina, aumentando linealmente con la ampli tud deonda y resulta de aproximadamente i05 ergs/cm2-s en una amplitud de 0.5. El flujo de energia cinetica siempre permanece despreciable, mientras que el flujo de energia magnetica depende de la orientaci5n inicial del campo. Un modo GMA rapido y casi paralelo, el cual es esen- cialmente un modo MHD en la corona se convierte a un modo rapido modificado y a uno lento, cuando la beta atmosferica disminuye a uno. ABSTRACT: A magneto-acoustic-gravity (MAG) wave is initiated in the high-beta regime near the base of the solar photosphere and followed, using numerical siriiulations, as it travels radially through the chromosphere, the transition region, and into the corona. Initial parameters are selected such that beta becomes less than one near the top of the transition region. Our primary interest is in the amount and form of energy flux that can be carried by the wave train into the corona for a specified initial atmosphere and wave amplitude. For the studies conducted to date, the thermal energy flux dominates, it about linearly with wave amplitude and becomes approximately 10 ergs/cm2-s at an amplitude of 0.5. The kinetic energy flux always remains negligible, while the magnetic energy flux depends on the inLtial field orientation. A nearly parallel fast MAG mode, which

  4. Different routes to the glass transition: A comparison between chemical and physical vitrification

    NASA Astrophysics Data System (ADS)

    Caponi, Silvia; Corezzi, Silvia

    2012-07-01

    Despite the differences in the molecular processes involved in chemical and physical vitrification, surprising similarities are observed in the dynamics and in the thermodynamical properties of the resulting glasses. We report on a systematic study of reactive glass-formers undergoing a process of progressive polymerization of the constituent molecules via the formation of irreversible chemical bonds. The formation of most of the materials used in engineering plastics and the hardening of natural and synthetic resins, including epoxy resins, are based on chemical vitrification. The clear analogies characterizing the dynamic evolution of physical and chemical glass-formers, on the time scale of the structural and the low-frequency vibrational dynamics, are briefly reviewed.

  5. Photospheric electric current and transition region brightness within an active region

    NASA Technical Reports Server (NTRS)

    Deloach, A. C.; Hagyard, M. J.; Rabin, D.; Moore, R. L.; Smith, B. J., Jr.; West, E. A.; Tandberg-Hanssen, E.

    1984-01-01

    Distributions of vertical electrical current density J(z) calculated from vector measurements of the photospheric magnetic field are compared with ultraviolet spectroheliograms to investigate whether resistive heating is an important source of enhanced emission in the transition region. The photospheric magnetic fields in Active Region 2372 were measured on April 6 and 7, 1980 with the Marshall Space Flight Center vector magnetograph; ultraviolet wavelength spectroheliograms (L-alpha and N V 1239 A) were obtained with the UV Spectrometer and Polarimeter experiment aboard the Solar Maximum Mission satellite. Spatial registration of the J(z) (5 arcsec resolution) and UV (3 arcsec resolution) maps indicates that the maximum current density is cospatial with a minor but persistent UV enhancement, but there is little detected current associated with other nearby bright areas. It is concluded that, although resistive heating may be important in the transition region, the currents responsible for the heating are largely unresolved in the present measurements and have no simple correlation with the residual current measured on 5-arcsec scales.

  6. A new method for separating first row transition metals and actinides from synthetic melt glass

    DOE PAGES

    Roman, Audrey Rae; Bond, Evelyn M.

    2016-01-14

    A new method was developed for separating Co, Fe, and Sc from complex debris matrices using the extraction chromatography resin DGA. The activation products Co-58, Mn-54, and Sc-46 were used to characterize the separation of the synthetic melt glass solutions. In the separation scheme that was developed, Au, Co, Cu, Fe, Sc, and Ti were separated from the rest of the sample constituents. In this paper, the synthetic melt glass separation method, efficiency, recoveries, and the length of procedure will be discussed. In conclusion, batch contact adsorption studies for Na and Sc for DGA resin are discussed as well.

  7. Highly sensitive pseudo-differential ac-nanocalorimeter for the study of the glass transition

    SciTech Connect

    Laarraj, Mohcine; Adhiri, Rahma; Moussetad, Mohamed; Ouaskit, Said; Guttin, Christophe; Richard, Jacques; Garden, Jean-Luc

    2015-11-15

    We present a nanocalorimeter designed for the measurement of the dynamic heat capacity of thin films. The microfabricated sensor, the thermal conditioning of the sensor, as well as the highly stable and low noise electronic chain allow measurements of the real and imaginary parts of the complex specific heat with a resolution Δ C/C of about 10{sup −5}. The performances of this quasi-differential nanocalorimeter were tested on a model of polymeric glass-former, the polyvinyl acetate (PVAc). The high stability and low noise of the device are essential for accurate studies on non-equilibrium slow relaxing systems such as glasses.

  8. Transition Region Abundance Measurements During Impulsive Heating Events

    NASA Astrophysics Data System (ADS)

    Warren, Harry P.; Brooks, David H.; Doschek, George A.; Feldman, Uri

    2016-06-01

    It is well established that elemental abundances vary in the solar atmosphere and that this variation is organized by first ionization potential (FIP). Previous studies have shown that in the solar corona, low-FIP elements such as Fe, Si, Mg, and Ca, are generally enriched relative to high-FIP elements such as C, N, O, Ar, and Ne. In this paper we report on measurements of plasma composition made during impulsive heating events observed at transition region temperatures with the Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these events the intensities of O iv, v, and vi emission lines are enhanced relative to emission lines from Mg v, vi, and vii and Si vi and vii, and indicate a composition close to that of the photosphere. Long-lived coronal fan structures, in contrast, show an enrichment of low-FIP elements. We conjecture that the plasma composition is an important signature of the coronal heating process, with impulsive heating leading to the evaporation of unfractionated material from the lower layers of the solar atmosphere and higher-frequency heating leading to long-lived structures and the accumulation of low-FIP elements in the corona.

  9. Cool transition region loops observed by the Interface Region Imaging Spectrograph

    NASA Astrophysics Data System (ADS)

    Huang, Z.; Xia, L.; Li, B.; Madjarska, M. S.

    2015-12-01

    An important class of loops in the solar atmosphere, cool transition region loops, have received little attention mainly due to instrumental limitations. We analyze a cluster of these loops in the on-disk active region NOAA 11934 recorded in a Si IV 1402.8 Å spectral raster and 1400Å slit-jaw (SJ) images taken by the Interface Region Imaging Spectrograph. We divide these loops into three groups and study their dynamics, evolution and interaction.The first group comprises geometrically relatively stable loops, which are finely scaled with 382~626 km cross-sections. Siphon flows in these loops are suggested by the Doppler velocities gradually changing from -10 km/s (blue-shifts) in one end to 20 km/s (red-shifts) in the other. Nonthermal velocities from 15 to 25 km/s were determined. The obtained physical properties suggest that these loops are impulsively heated by magnetic reconnection occurring at the blue-shifted footpoints where magnetic cancellation with a rate of 1015 Mx/s is found. The released magnetic energy is redistributed by the siphon flows. The second group corresponds to two active footpoints rooted in mixed-magnetic-polarity regions. Magnetic reconnection in both footpoints is suggested by explosive-event line profiles with enhanced wings up to 200 km/s and magnetic cancellation with a rate of ~1015 Mx/s. In the third group, an interaction between two cool loop systems is observed. Mixed-magnetic polarities are seen in their conjunction area where explosive-event line profiles and magnetic cancellation with a rate of 3×1015 Mx/s are found. This is a clear indication that magnetic reconnection occurs between these two loop systems. Our observations suggest that the cool transition region loops are heated impulsively most likely by sequences of magnetic reconnection events.

  10. Cool Transition Region Loops Observed by the Interface Region Imaging Spectrograph

    NASA Astrophysics Data System (ADS)

    Huang, Zhenghua; Xia, Lidong; Li, Bo; Madjarska, Maria S.

    2015-09-01

    We report on the first Interface Region Imaging Spectrograph (IRIS) study of cool transition region loops, a class of loops that has received little attention in the literature. A cluster of such loops was observed on the solar disk in active region NOAA11934, in the Si iv 1402.8 Å spectral raster and 1400 Å slit-jaw images. We divide the loops into three groups and study their dynamics. The first group comprises relatively stable loops, with 382-626 km cross-sections. Observed Doppler velocities are suggestive of siphon flows, gradually changing from -10 km s-1 at one end to 20 km s-1 at the other end of the loops. Nonthermal velocities of 15 ˜ 25 km s-1 were determined. Magnetic cancellation with a rate of 1015 Mx s-1 is found at the blueshifted footpoints. These physical properties suggest that these loops are impulsively heated by magnetic reconnection, and the siphon flows play an important role in the energy redistribution. The second group corresponds to two footpoints rooted in mixed-magnetic-polarity regions, where magnetic cancellation with a rate of 1015 Mx s-1 and explosive-event line profiles with enhanced wings of up to 200 km s-1 were observed. In the third group, interaction between two cool loop systems is observed. Evidence for magnetic reconnection between the two loop systems is reflected in the explosive-event line profiles and magnetic cancellation with a rate of 3× {10}15 Mx s-1 observed in the corresponding area. The IRIS has provided opportunity for in-depth investigations of cool transition region loops. Further numerical experiments are crucial for understanding their physics and their roles in the coronal heating processes.

  11. Orange glass - Evidence for regional deposits of pyroclastic origin on the moon

    NASA Technical Reports Server (NTRS)

    Adams, J. B.; Pieters, C.; Mccord, T. B.

    1974-01-01

    Crystallized spheres of orange glass from Shorty Crater at the Apollo 17 site are shown by spectral reflectance data to be the characteristic ingredient of the dark mantling deposit of the Taurus-Littrow region. This deposit, mapped on spectral vidicon images taken using earth-based telescopes, apparently is thickest 50 km northwest of the Apollo 17 landing area, and has a gradational contact with the surrounding materials. The irregular areal distribution of the dark-mantle deposit and the gradational borders support conclusions based on laboratory studies of the orange soils that these are volcanic pyroclastic materials. Similar deposits are identified by spectral reflectance properties near Rima Bode, Schroeter W, Fauth H, and Higinus W. The same material is likely to occur at Sulpucius Gallus based on visual and photographic observations of orange soil. The apparently restricted occurrence of the orange-glass deposits in a belt along the edges of major mare basins implies structural control of volcanic vents and a possible deep-seated origin.

  12. Specific features of the glass transition in C60 fullerite saturated with carbon monoxide molecules: Photoluminescence studies

    NASA Astrophysics Data System (ADS)

    Zinoviev, P. V.; Zoryansky, V. N.; Stetsenko, Yu. E.; Danchuk, V. V.

    2016-02-01

    Low temperature (20-230 K) spectral-luminescence studies were conducted on C60 fullerite saturated with carbon monoxide in a physisorption regime. Substantial changes in the photoluminescence characteristics of C60-CO solutions with different impurity concentrations were found already for short intercalation times. Strong dependence of the CO solubility on the saturation temperature was revealed by analyzing the contribution of "deep X-traps" to the luminescence. Furthermore, it was found that filling of the octahedral voids by CO molecules occurs with a lower gradient of the impurity distribution into the bulk C60 crystals as compared with N2. The temperature dependences of the integral emission intensity for the samples with different concentrations of carbon monoxide were studied. For the first time, using the spectral-luminescence method, it was revealed that CO molecules, in contrast to H2 and N2, exhibit a significant effect on the formation of the orientational glass and the rotational dynamics of C60 molecules. Within the model of the transfer of electronic excitation in C60 crystals, the effect of polar CO molecules on the reorientation of C60 molecules and the change in the nature of their rotation in concentrated C60-CO solutions, leading to the observed strong shift of the temperatures of orientational Tc and glass Tg transitions to lower temperatures accompanied by "blurring" of the transition boundaries, were explained.

  13. Development of DMBZ-15 High-Glass-Transition-Temperature Polyimides as PMR-15 Replacements Given R&D 100 Award

    NASA Technical Reports Server (NTRS)

    Chuang, Kathy

    2004-01-01

    PMR-15, a high-temperature polyimide developed in the mid-1970s at the NASA Lewis Research Center,1 offers the combination of low cost, easy processing, and good high-temperature performance and stability. It has been recognized as the leading polymer matrix resin for carbon-fiber-reinforced composites used in aircraft engine components. The state-of-the-art PMR-15 polyimide composite has a glass-transition temperature (Tg) of 348 C (658 F). Since composite materials must be used at temperatures well below their glass-transition temperature, the long-term use temperatures of PMR-15 composites can be no higher than 288 C (550 F). In addition, PMR-15 is made from methylene dianiline (MDA), a known liver toxin. Concerns about the safety of workers exposed to MDA during the fabrication of PMR-15 components and about the environmental impact of PMR-15 waste disposal have led to the industry-wide implementation of special handling procedures to minimize the health risks associated with this material. These procedures have increased manufacturing and maintenance costs significantly and have limited the use of PMR-15 in commercial aircraft engine components.

  14. Entropy dependence of viscosity and the glass-transition temperature of melts in the system diopside-anorthite

    NASA Astrophysics Data System (ADS)

    Taniguchi, H.

    1992-01-01

    Viscosities of diopside-anorthite melts were measured over the wide range of temperature (near the glass-transition temperature-1580°C/1bar) and pressure (5 20 kb/above the liquidus temperature). The measurements were carried out by the fibre-elongation method for low temperature and the counter-balanced sphere method for high temperature at 1 bar, and the sinking and floating spheres method for high temperature at high pressure. Some of the values obtained deviated slightly from those in the literature. The data on viscosity and the glasstransition temperature have been interpreted on the basis of the configurational entropy theory, by which temperature and compositional effects on viscosity were explained well. The configurational entropies at the glasstransition temperature of magmatic silicate melts are almost constant if we use an average molecular weight (amw) or “bead” as a unit; 8.0±1.2 J/K·amw, 1.1 ±0.2cal/K·bead. The latter value coincides well with the value from the literature for organic polymers. The negative deviation from linearity of the glass-transition temperature of intermediate melts may be interpreted as the effect of the mixing entropy. The calculated glasstransition temperature-composition curve using the mixing entropy agreed well with the experimental values.

  15. Mobility of Supercooled liquid Toluene, Ethylbenzene, and Benzene near their Glass Transition Temperatures Investigated using Inert Gas Permeation

    SciTech Connect

    May, Robert A.; Smith, R. Scott; Kay, Bruce D.

    2013-11-21

    We investigate the mobility of supercooled liquid toluene, ethylbenzene, and benzene near their respective glass transition temperatures (Tg). The permeation rate of Ar, Kr, and Xe through the supercooled liquid created when initially amorphous overlayers heated above their glass transition temperature is used to determine the diffusivity. Amorphous benzene crystallizes at temperatures well below its Tg and as a result the inert gas underlayer remains trapped until the onset of benzene desorption. In contrast, for toluene and ethylbenzene the onset of inert gas permeation is observed at temperatues near Tg. The inert gas desorption peak temperature as a function of the heating rate and overlayer thickness is used to quantify the diffusivity of supercooled liquid toluene and ethylbenzene from 115 K to 135 K. In this temperature range, diffusivities are found to vary across five orders of magnitude (~10-14 to 10-9 cm2/s). These data are compared to viscosity measurements and used to determine the low temperature fractional Stokes-Einstein exponent. Efforts to determine the diffusivity of a mixture of benzene and ethylbenzene are detailed, and the effect of mixing these materials on benzene crystallization is explored using infrared spectroscopy.

  16. Preparation of a series of model poly(n-alkyl styrene)s and their viscoelasticity and glass transition temperatures

    NASA Astrophysics Data System (ADS)

    Matsushima, Satoru; Takano, Atsushi; Takahashi, Yoshiaki; Matsushita, Yushu

    Viscoelasticity and glass transition temperatures for linear polymers of many species have been investigated so far, and it is well-known that the melt viscosity for the linear polymers varies with molecular weight in essentially the same manner such as packing length theory. It is important to understand the relationship between the viscosity and the molecular structure of various kinds of linear polymers. To investigate the relationship deeply, viscoelastic measurements using linear polymer analogues which the molecular structure is systematically varied should be useful. For example, poly(n-alkyl-substituted polymers) such as poly(n-alkyl methacrylate)s are one of the good candidate. In this study, a series of poly(n-alkyl styrene)s with the different number of carbon atoms(n) in the side alkyl groups (n =1, 2, 3, 4, 6, 8, 10 and 12) were carefully synthesized by an anionic polymerization technique, and the viscoelasticity and the glass transition temperatures of the poly(n-alkyl styrene)s with high molecular weight (Mw >=4Me) and narrow molecular weight distribution (Mw/Mn <=1.1) were discussed.

  17. Understanding the dynamics of glass-forming liquids with random pinning within the random first order transition theory

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Saurish; Das, Rajsekhar; Karmakar, Smarajit; Dasgupta, Chandan

    2016-07-01

    Extensive computer simulations are performed for a few model glass-forming liquids in both two and three dimensions to study their dynamics when a randomly chosen fraction of particles are frozen in their equilibrium positions. For all the studied systems, we find that the temperature-dependence of the α relaxation time extracted from an overlap function related to the self-part of the density autocorrelation function can be explained within the framework of the Random First Order Transition (RFOT) theory of the glass transition. We propose a scaling description to rationalize the simulation results and show that our data for the α relaxation time for all temperatures and pin concentrations are consistent with this description. We find that the fragility parameter obtained from fits of the temperature dependence of the α relaxation time to the Vogel-Fulcher-Tammann form decreases by almost an order of magnitude as the pin concentration is increased from zero. Our scaling description relates the fragility parameter to the static length scale of RFOT and thus provides a physical understanding of fragility within the framework of the RFOT theory. Implications of these findings for the values of the exponents appearing in the RFOT theory are discussed.

  18. EFFECTS OF TRITIUM GAS EXPOSURE ON THE GLASS TRANSITION TEMPERATURE OF EPDM ELASTOMER AND ON THE CONDUCTIVITY OF POLYANILINE

    SciTech Connect

    Clark, E; Marie Kane, M

    2008-12-12

    Four formulations of EPDM (ethylene-propylene diene monomer) elastomer were exposed to tritium gas initially at one atmosphere and ambient temperature for between three and four months in closed containers. Material properties that were characterized include density, volume, mass, appearance, flexibility, and dynamic mechanical properties. The glass transition temperature was determined by analysis of the dynamic mechanical property data per ASTM standards. EPDM samples released significant amounts of gas when exposed to tritium, and the glass transition temperature increased by about 3 C. during the exposure. Effects of ultraviolet and gamma irradiation on the surface electrical conductivity of two types of polyaniline films are also documented as complementary results to planned tritium exposures. Future work will determine the effects of tritium gas exposure on the electrical conductivity of polyaniline films, to demonstrate whether such films can be used as a sensor to detect tritium. Surface conductivity was significantly reduced by irradiation with both gamma rays and ultraviolet light. The results of the gamma and UV experiments will be correlated with the tritium exposure results.

  19. Disentangling molecular motions involved in the glass transition of a twist-bend nematic liquid crystal through dielectric studies.

    PubMed

    López, D O; Sebastian, N; de la Fuente, M R; Martínez-García, J C; Salud, J; Pérez-Jubindo, M A; Diez-Berart, S; Dunmur, D A; Luckhurst, G R

    2012-07-21

    Broadband dielectric spectroscopy spanning frequencies from 10(-2) to 1.9 × 10(9) Hz has been used to study the molecular orientational dynamics of the glass-forming liquid crystal 1",7"-bis (4-cyanobiphenyl-4'-yl)heptane (CB7CB) over a wide temperature range of the twist-bend nematic phase. In such a mesophase two different relaxation processes have been observed, as expected theoretically, to contribute to the imaginary part of the complex dielectric permittivity. For measurements on aligned samples, the processes contribute to the dielectric response to different extents depending on the orientation of the alignment axis (parallel or perpendicular) with respect to the probing electric field direction. The low-frequency relaxation mode (denoted by μ(1)) is attributed to a flip-flop motion of the dipolar groups parallel to the director. The high-frequency relaxation mode (denoted by μ(2)) is associated with precessional motions of the dipolar groups about the director. The μ(1)-and μ(2)-modes are predominant in the parallel and perpendicular alignments, respectively. Relaxation times for both modes in the different alignments have been obtained over a wide temperature range down to near the glass transition temperature. Different analytic functions used to characterize the temperature dependence of the relaxation times of the two modes are considered. Among them, the critical-like description via the dynamic scaling model seems to give not only quite good numerical fittings, but also provides a consistent physical picture of the orientational dynamics on approaching the glass transition.

  20. The coronal and transition region temperature structure of a solar active region

    NASA Technical Reports Server (NTRS)

    Levine, R. H.; Pye, J. P.

    1980-01-01

    Using measurements of EUV and X-ray spectral lines, the differential emission measure vs electron temperature from the transition region to the corona of an active region (electron temperature between 100,000 and 5,000,000 K) is derived. The total emission measure and radiative losses are of the order 3 x 10 to the 48th/cu cm and 4 x 10 to the 26th ergs/sec, respectively. The emission measure at electron temperatures greater than approximately 1,000,000 K (i.e. that mainly responsible for the X-ray emission) is about 75% of the total. The use of the Mg x line at 625 A as an indicator of coronal electron density is also examined. A set of theoretical energy balance models of coronal loops in which the loop divergence is a variable parameter is presented and compared with the observations.

  1. Hypernetted-chain investigation of the random first-order transition of a Lennard-Jones liquid to an ideal glass

    NASA Astrophysics Data System (ADS)

    Bomont, Jean-Marc; Hansen, Jean-Pierre; Pastore, Giorgio

    2015-10-01

    The structural and thermodynamic behavior of a deeply supercooled Lennard-Jones liquid, and its random first-order transition (RFOT) to an ideal glass is investigated, using a system of two weakly coupled replicas and the hypernetted chain integral equation for the pair structure of this symmetric binary system. A systematic search in the density-temperature plane points to the existence of two glass branches below a density-dependent threshold temperature. The branch of lower free energy exhibits a rapid growth of the structural overlap order parameter upon cooling and may be identified with the ideal glass phase conjectured by several authors for both spin and structural glasses. The RFOT, signaled by a sharp discontinuity of the order parameter, is predicted to be weakly first order from a thermodynamic viewpoint. The transition temperature Tcr increases rapidly with density and approximately obeys a scaling relation valid for a reference system of particles interacting via a purely repulsive 1 /r18 potential.

  2. Partial glass isosymmetry transition in multiferroic hexagonal ErMn O3

    NASA Astrophysics Data System (ADS)

    Barbour, A.; Alatas, A.; Liu, Y.; Zhu, C.; Leu, B. M.; Zhang, X.; Sandy, A.; Pierce, M. S.; Wang, X.; Cheong, S.-W.; You, H.

    2016-02-01

    Ferroelectric transitions of a hexagonal multiferroic, ErMn O3 , are studied by x-ray scattering techniques. An isosymmetry transition, similar to that previously observed for YMn O3 , approximately 300 K below the well-known ferroic transition temperature, is investigated. The partially glassy behavior of the isosymmetry transition is identified by the appearance of quasielastic scattering lines in high-energy-resolution scans. The glassy behavior is further supported by the increased interlayer decorrelation of (√{3 }×√{3 }) R 30∘ ordering below the isosymmetry transition. The transition behavior is considered for possible hidden sluggish modes and two-step phase transitions theoretically predicted for the stacked triangular antiferromagnets. The in-plane azimuthal (orientational) ordering behaviors were also compared to the theoretical predictions. Coherent x-ray speckle measurements show unambiguously that the domain sizes decrease anomalously near both the isosymmetry and ferroic transitions. However, domain boundary fluctuations increase monotonically with an Arrhenius form with an activation energy of 0.54(5) eV through both transitions.

  3. The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation.

    PubMed

    Starr, Francis W; Douglas, Jack F; Sastry, Srikanth

    2013-03-28

    We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the "mosaic" length of the RFOT model relaxes the conventional assumption that the "entropic droplets" are compact. We also confirm the

  4. The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation

    PubMed Central

    Starr, Francis W.; Douglas, Jack F.; Sastry, Srikanth

    2013-01-01

    We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the “mosaic” length of the RFOT model relaxes the conventional assumption that the “entropic droplets” are compact. We also confirm

  5. The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation

    NASA Astrophysics Data System (ADS)

    Starr, Francis W.; Douglas, Jack F.; Sastry, Srikanth

    2013-03-01

    We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the "mosaic" length of the RFOT model relaxes the conventional assumption that the "entropic droplets" are compact. We also confirm the

  6. The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation.

    PubMed

    Starr, Francis W; Douglas, Jack F; Sastry, Srikanth

    2013-03-28

    We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the "mosaic" length of the RFOT model relaxes the conventional assumption that the "entropic droplets" are compact. We also confirm the

  7. Beyond Solar-B: MTRAP, the Magnetic Transition Region Probe

    NASA Technical Reports Server (NTRS)

    Davis, John M.; Moore, Ronald L.; Hathaway, David H.

    2003-01-01

    The next generation of solar missions will reveal and measure fine-scale solar magnetic fields and their effects in the solar atmosphere at heights, small scales, sensitivities, and fields of view well beyond the reach of Solar-B. The necessity for, and potential of, such observations for understanding solar magnetic fields, their generation in and below the photosphere, and their control of the solar atmosphere and heliosphere, were the focus of a science definition workshop, 'High-Resolution Solar Magnetography from Space: Beyond Solar-B,' held in Huntsville Alabama in April 2001. Forty internationally prominent scientists active in solar research involving fine-scale solar magnetism participated in this Workshop and reached consensus that the key science objective to be pursued beyond Solar-B is a physical understanding of the fine-scale magnetic structure and activity in the magnetic transition region, defined as the region between the photosphere and corona where neither the plasma nor the magnetic field strongly dominates the other. The observational objective requires high cadence (less than 10s) vector magnetic field maps, and spatially resolved spectra from the IR, visible, vacuum UV, to the EUV at high resolution (less than 50km) over a large FOV (approximately 140,000 km). A polarimetric resolution of one part in ten thousand is required to measure transverse magnetic fields of less than 30G. The latest SEC Roadmap includes a mission identified as MTRAP to meet these requirements. Enabling technology development requirements include large, lightweight, reflecting optics, large format sensors (16K x 16K pixels) with high QE at 150 nm, and extendable spacecraft structures. The Science Organizing Committee of the Beyond Solar-B Workshop recommends that: (1) Science and Technology Definition Teams should be established in FY04 to finalize the science requirements and to define technology development efforts needed to ensure the practicality of MTRAP

  8. Equilibrium first-order melting and second-order glass transitions of the vortex matter in Bi2Sr2CaCu2O8.

    PubMed

    Beidenkopf, H; Avraham, N; Myasoedov, Y; Shtrikman, H; Zeldov, E; Rosenstein, B; Brandt, E H; Tamegai, T

    2005-12-16

    The thermodynamic phase diagram of Bi2Sr2CaCu2O8 was mapped by measuring local equilibrium magnetization M(H,T) in the presence of vortex shaking. Two equally sharp first-order magnetization steps are revealed in a single temperature sweep, manifesting a liquid-solid-liquid sequence. In addition, a second-order glass transition line is revealed by a sharp break in the equilibrium M(T) slope. The first- and second-order lines intersect at intermediate temperatures, suggesting the existence of four phases: Bragg glass and vortex crystal at low fields, glass and liquid at higher fields.

  9. Degradation of Terfenol-D particle epoxy composites under low-frequency cyclic magneto-mechanical loading at the matrix glass transition start and finish temperatures

    NASA Astrophysics Data System (ADS)

    Armstrong, William D.; Shanmugham, Manikantan; Bailey, Harold

    2004-07-01

    The present paper presents cyclic strain amplitude and longitudinal strain measurements of longitudinally compressed Terfenol-D particle samples subjected to magneto-strain cycling. A comparison is made of the responses of material strain cycle tested at temperatures near the matrix glass transition start temperature, and material strain cycle tested at a temperature near the matrix glass transition finish temperature. The cyclic strain amplitude of the material was significantly larger when tested at a temperature near the matrix glass transition finish temperature. A useful range of longitudinal applied stress exists where the composite suffers little apparent degradation. Beyond this range the composite exhibits steadily decreasing cyclic strain amplitude with increases in longitudinal compressive stress magnitude.

  10. Validation of Force Fields of Rubber through Glass-Transition Temperature Calculation by Microsecond Atomic-Scale Molecular Dynamics Simulation.

    PubMed

    Sharma, Pragati; Roy, Sudip; Karimi-Varzaneh, Hossein Ali

    2016-02-25

    Microsecond atomic-scale molecular dynamics simulation has been employed to calculate the glass-transition temperature (Tg) of cis- and trans-1,4-polybutadiene (PB) and 1,4-polyisoprene (PI). Both all-atomistic and united-atom models have been simulated using force fields, already available in literature. The accuracy of these decade old force fields has been tested by comparing calculated glass-transition temperatures to the corresponding experimental values. Tg depicts the phase transition in elastomers and substantially affects various physical properties of polymers, and hence the reproducibility of Tg becomes very crucial from a thermodynamic point of view. Such validation using Tg also evaluates the ability of these force fields to be used for advanced materials like rubber nanocomposites, where Tg is greatly affected by the presence of fillers. We have calculated Tg for a total of eight systems, featuring all-atom and united-atom models of cis- and trans-PI and -PB, which are the major constituents of natural and synthetic rubber. Tuning and refinement of the force fields has also been done using quantum-chemical calculations to obtain desirable density and Tg. Thus, a set of properly validated force fields, capable of reproducing various macroscopic properties of rubber, has been provided. A novel polymer equilibration protocol, involving potential energy convergence as the equilibration criterion, has been proposed. We demonstrate that not only macroscopic polymer properties like density, thermal expansion coefficient, and Tg but also local structural characteristics like end-to-end distance (R) and radius of gyration (Rg) and mechanical properties like bulk modulus have also been equilibrated using our strategy. Complete decay of end-to-end vector autocorrelation function with time also supports proper equilibration using our strategy. PMID:26836395

  11. Validation of Force Fields of Rubber through Glass-Transition Temperature Calculation by Microsecond Atomic-Scale Molecular Dynamics Simulation.

    PubMed

    Sharma, Pragati; Roy, Sudip; Karimi-Varzaneh, Hossein Ali

    2016-02-25

    Microsecond atomic-scale molecular dynamics simulation has been employed to calculate the glass-transition temperature (Tg) of cis- and trans-1,4-polybutadiene (PB) and 1,4-polyisoprene (PI). Both all-atomistic and united-atom models have been simulated using force fields, already available in literature. The accuracy of these decade old force fields has been tested by comparing calculated glass-transition temperatures to the corresponding experimental values. Tg depicts the phase transition in elastomers and substantially affects various physical properties of polymers, and hence the reproducibility of Tg becomes very crucial from a thermodynamic point of view. Such validation using Tg also evaluates the ability of these force fields to be used for advanced materials like rubber nanocomposites, where Tg is greatly affected by the presence of fillers. We have calculated Tg for a total of eight systems, featuring all-atom and united-atom models of cis- and trans-PI and -PB, which are the major constituents of natural and synthetic rubber. Tuning and refinement of the force fields has also been done using quantum-chemical calculations to obtain desirable density and Tg. Thus, a set of properly validated force fields, capable of reproducing various macroscopic properties of rubber, has been provided. A novel polymer equilibration protocol, involving potential energy convergence as the equilibration criterion, has been proposed. We demonstrate that not only macroscopic polymer properties like density, thermal expansion coefficient, and Tg but also local structural characteristics like end-to-end distance (R) and radius of gyration (Rg) and mechanical properties like bulk modulus have also been equilibrated using our strategy. Complete decay of end-to-end vector autocorrelation function with time also supports proper equilibration using our strategy.

  12. Beating the bulk: Bypassing the bulk glass transition by fast heating

    NASA Astrophysics Data System (ADS)

    Gonzalez-Silveira, Marta; Rodriguez-Tinoco, Cristian; Rafols-Ribe, Joan; Lopeandia, Aitor F.; Clavaguera-Mora, Maria Teresa; Rodriguez-Viejo, Javier

    2015-03-01

    Transformation into the supercooled liquid via propagating fronts has been thoroughly studied in several ultrastable thin film glasses. In this work we show that the transformation mechanism in vapor deposited films of IMC has profound implications in the analysis of the specific heat curves. We propose an ad-hoc surface normalization of the heat capacity data that yields curves which collapse into a single one irrespective of their thickness. The surface-normalized specific heat curves are fitted with a heterogeneous transformation model to evaluate the velocity of the growth front over a much wider temperature interval than previously reported. In addition, we evaluate the transformation rate in films with lower stability. Interestingly, the transformation via parallel fronts is not an exclusive characteristic of ultrastable glasses. We observe how fast heating rates can induce this type of transformation in glassy films whose stabilities are close to the conventional glass. Although the absolute velocity of the growth front depends on stability, no change is observed in the relation between velocity and relaxation time as a function of stability.

  13. Characterization of structural relaxation in inorganic glasses using length dilatometry

    NASA Astrophysics Data System (ADS)

    Koontz, Erick

    The processes that govern how a glass relaxes towards its thermodynamic quasi-equilibrium state are major factors in understanding glass behavior near the glass transition region, as characterized by the glass transition temperature (Tg). Intrinsic glass properties such as specific volume, enthalpy, entropy, density, etc. are used to map the behavior of the glass network below in and near the transition region. The question of whether a true thermodynamic second order phase transition takes place in the glass transition region is another pending question. Linking viscosity behavior to entropy, or viewing the glass configuration as an energy landscape are just a couple of the most prevalent methods used for attempting to understand the glass transition. The structural relaxation behavior of inorganic glasses is important for more than scientific reasons, many commercial glass processing operations including glass melting and certain forms of optical fabrication include significant time spent in the glass transition region. For this reason knowledge of structural relaxation processes can, at a minimum, provide information for annealing duration of melt-quenched glasses. The development of a predictive model for annealing time prescription has the potential to save glass manufacturers significant time and money as well as increasing volume throughput. In optical hot forming processes such as precision glass molding, molded optical components can significantly change in shape upon cooling through the glass transition. This change in shape is not scientifically predictable as of yet though manufacturers typically use empirical rules developed in house. The classification of glass behavior in the glass transition region would allow molds to be accurately designed and save money for the producers. The work discussed in this dissertation is comprised of the development of a dilatometric measurement and characterization method of structural relaxation. The measurement and

  14. Glass electrolytes for sodium/sulfur cells

    NASA Astrophysics Data System (ADS)

    Roche, M. F.; Kucera, G. H.

    A glass electrolyte for use in sodium/sulfur batteries that has a low resistivity (100 ohm-cm at 300 (0)C) ans is stable in the cell environment was investigated. Glasses in the quaternary system: soda, alumina, zirconia and silica were studied. The main program elements are: (1) conductivity measurements at 300 to 500(0)C; (2) differential thermal analysis for determination of glass transition and crystallization temperatures; (3) static corrosion tests at 400(0)C using Na, Na2S4, and S; (4) mechanical strength and fracture toughness measurements; and (5) sodium/sulfur cell tests at 350(0)C. Fourteen quaternary glasses with a broad range of compositions were made. The resistivities of these glasses at 300(0)C extended from 130 to 3704 ohm-cm; the activation energies for conduction extended from 0.48 to 0.684 eV, and the glass transition temperatures extended from 397 to 685(0)C. Through a multiple linear regression analysis of these data response surfaces were generated for resistivity, activation energy for conduction, and glass transition temperture over the composition region within the quaternary system that is bounded by SiO2, Na2O3, Na2AlO4 and Na2ZrO3. The response surfaces indicate a new region of high conductivity and high glass transition temperature in the neighborhood of 42% soda, 31% silica and 27% alumina plus zirconia.

  15. Global Natural Disaster Risk Hotspots: Transition to a Regional Approach

    NASA Astrophysics Data System (ADS)

    Lerner-Lam, A.; Chen, R.; Dilley, M.

    2005-12-01

    economic losses, are also limited. On one hand the data are adequate for general identification of areas of the globe that are at relatively higher single- or multiple-hazard risk than other areas. On the other hand they are inadequate for understanding the absolute levels of risk posed by any specific hazard or combination of hazards. Nevertheless it is possible to assess in general terms the exposure and potential magnitude of losses to people and their assets in these areas. Such information, although not ideal, can still be very useful for informing a range of disaster prevention and preparedness measures, including prioritization of resources, targeting of more localized and detailed risk assessments, implementation of risk-based disaster management and emergency response strategies, and development of long-term plans for poverty reduction and economic development. In addition to summarizing the results of the Hotspots Project, we discuss data collection issues and suggest methodological approaches for making the transition to more detailed regional and national studies. Preliminary results for several regional case studies will be presented.

  16. The bose glass transition in columnar defected untwinned YBa{sub 2}Cu{sub 3}O{sub 7-delta}.

    SciTech Connect

    Olsson, R. J.; Kwok, W.-K.; Paulius, L. M.; Petrean, A. M.; Hofman, D. J.; Crabtree, G. W.; Materials Science Division

    2002-03-01

    We demonstrate the Bose glass scaling behavior in a single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-delta} (YBCO) free from twin boundary pinning. We determine the scaling exponents from voltage-current measurements near the transition temperature and infer a lock-in transition from measurements of the angular dependence of the resistivity. In addition we demonstrate that the kink in the Bose glass irreversibility line in irradiated untwinned YBCO occurs systematically at the dose matching field.

  17. Yield stress in metallic glasses: The jamming-unjamming transition studied through Monte Carlo simulations based on the activation-relaxation technique

    SciTech Connect

    Rodney, David; Schuh, Christopher A.

    2009-11-01

    A Monte Carlo approach allowing for stress control is employed to study the yield stress of a two-dimensional metallic glass in the limit of low temperatures and long (infinite) time scales. The elementary thermally activated events are determined using the activation-relaxation technique (ART). By tracking the minimum-energy state of the glass for various applied stresses, we find a well-defined jamming-unjamming transition at a yield stress about 30% lower than the steady-state flow stress obtained in conventional strain-controlled quasistatic simulations. ART is then used to determine the evolution of the distribution of thermally activated events in the glass microstructure both below and above the yield stress. We show that aging below the yield stress increases the stability of the glass, both thermodynamically (the internal potential energy decreases) and dynamically (the aged glass is surrounded by higher-energy barriers than the initial quenched configuration). In contrast, deformation above the yield stress brings the glass into a high internal potential energy state that is only marginally stable, being surrounded by a high density of low-energy barriers. The strong influence of deformation on the glass state is also evidenced by the microstructure polarization, revealed here through an asymmetry of the distribution of thermally activated inelastic strains in glasses after simple shear deformation.

  18. Final Report on DE-FG02-04ER46107: Glasses, Noise and Phase Transitions

    SciTech Connect

    Yu, Clare C.

    2011-12-31

    We showed that noise has distinct signatures at phase transitions in spin systems. We also studied charge noise, critical current noise, and flux noise in superconducting qubits and Josephson junctions.

  19. Near-Wall Velocity and Temperature Measurements in the Meniscus Region for Staggered Glass Beads.

    PubMed

    Wang, Zhaochun; Zhou, Leping; Du, Xiaoze; Yang, Yongping

    2015-04-01

    Velocity and temperature fields in the meniscus are crucial for the heat transfer mechanism in porous medium. The meniscus zone, however, is narrow so that it is difficult for observation. The velocimetry and thermometry in the near-wall region of the surface provide possible measurement methods with the development of micro/nanotechnology. Being exponentially decay in the intensity, the evanescent-wave illumination has the advantage of high spatial resolution and non-intrusion for these measurement methods. The multilayer nano-particle image velocimetry (MnPIV) uses the evanescent-wave illumination, decayed exponentially with the wall-normal distance, to obtain near-wall velocity data at different distances from the wall. The thermometry in the meniscus region could also use the evanescent-wave to illuminate the fluorescence dye, the emitted intensity of which changes with temperature. In this paper, these techniques are employed to measure the near-wall velocity and temperature between the porous media and the ITO heater, in order to explore the role of meniscus during convection of water. Near-wall velocity and temperature of the deionized water, seeded with 100 nm fluorescent colloidal tracers and flow in the staggered glass beads with diameters ranging from 2 mm to 6 mm, are obtained and discussed.

  20. Lower solar chromosphere-corona transition region. I - Theoretical models with small temperature gradients

    NASA Technical Reports Server (NTRS)

    Woods, D. Tod; Holzer, Thomas E.; Macgregor, Keith B.

    1990-01-01

    A study of transition region models including the effects of classical thermal conduction, heating, and radiative cooling is carried out with attention directed toward the problem of understanding the observed emission in the lower transition region. It is found that the observationally inferred emission measure curve implies a near-balance between heating and radiative cooling in the lower transition region, and that the presence of strong hydrogen Ly-alpha cooling leads to the existence of singularities in the solutions of the force balance and energy balance equations when such a near-balance between heating and cooling is assumed. These singularities place strong constraints on the nature of viable models of the lower transition region and must be considered when Ly-alpha cooling is important. Previously suggested explanations of the observed emission from the lower transition region are considered in the context of the results of the present study, and conditions for the applicability of these suggested explanations are discussed.

  1. The structure and heating of the chromosphere-corona transition region

    NASA Technical Reports Server (NTRS)

    Moore, R. L.

    1972-01-01

    The structure and heating (or energy balance) of the transition region and the role of the transition region in the structure and heating of the solar atmosphere as a whole are investigated. The features of the structure of the atmosphere and radiative energy losses of the atmosphere are summarized. A static, planar model of the solar temperature which has a temperature profile representative of the actual solar atmosphere is considered. Then a static, planar model of the transition region which is heated by thermal conduction from the corona and cooled by radiative losses is developed. A general conclusion is that the temperature profile of the transition region and lower corona results primarily from the energy balance of the corona, while the number density is determined by the energy balance of the transition region.

  2. From boiling point to glass transition temperature: Transport coefficients in molecular liquids follow three-parameter scaling

    NASA Astrophysics Data System (ADS)

    Schmidtke, B.; Petzold, N.; Kahlau, R.; Hofmann, M.; Rössler, E. A.

    2012-10-01

    The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10-12 s < τ(T) < 102 s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E∞ and a low-temperature regime for which Ecoop(T) ≡ E(T)-E∞ increases exponentially while cooling. A scaling is introduced, specifically Ecoop(T)/E∞ ∝ exp[-λ(T/TA-1)], where λ is a fragility parameter and TA a reference temperature proportional to E∞. In order to describe τ(T) still the attempt time τ∞ has to be specified. Thus, a single interaction parameter E∞ describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics.

  3. From boiling point to glass transition temperature: transport coefficients in molecular liquids follow three-parameter scaling.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Hofmann, M; Rössler, E A

    2012-10-01

    The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10(-12) s < τ(T) < 10(2) s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E(∞) and a low-temperature regime for which E(coop)(T) ≡ E(T)-E(∞) increases exponentially while cooling. A scaling is introduced, specifically E(coop)(T)/E(∞) [proportionality] exp[-λ(T/T(A)-1)], where λ is a fragility parameter and T(A) a reference temperature proportional to E(∞). In order to describe τ(T) still the attempt time τ(∞) has to be specified. Thus, a single interaction parameter E(∞) describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics. PMID:23214591

  4. From boiling point to glass transition temperature: transport coefficients in molecular liquids follow three-parameter scaling.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Hofmann, M; Rössler, E A

    2012-10-01

    The phenomenon of the glass transition is an unresolved problem in condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients, remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined τ(T) collected from dielectric spectroscopy and dynamic light scattering covering a range 10(-12) s < τ(T) < 10(2) s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E(∞) and a low-temperature regime for which E(coop)(T) ≡ E(T)-E(∞) increases exponentially while cooling. A scaling is introduced, specifically E(coop)(T)/E(∞) [proportionality] exp[-λ(T/T(A)-1)], where λ is a fragility parameter and T(A) a reference temperature proportional to E(∞). In order to describe τ(T) still the attempt time τ(∞) has to be specified. Thus, a single interaction parameter E(∞) describing the high-temperature regime together with λ controls the temperature dependence of low-temperature cooperative dynamics.

  5. Effect of Nanoconfinement on the Glass Transition Temperature and Small Molecule Diffusion in Polymers of Varying Backbone Stiffness

    NASA Astrophysics Data System (ADS)

    Deng, Hui; Mundra, Manish; Torkelson, John

    2010-03-01

    Fluorescence spectroscopy was used to determine the glass transition temperature in ultrathin supported bisphenol-A polysulfone (BPAPS) and bisphenol-A polycarbonate (BPAPC) films and compared to previous results for ultrathin supported polystyrene (PS) films. BPAPC and BPAPS are more rigid than PS due to the presence of aromatic rings in their polymer backbones. A dramatic increase in Tg-reduction upon confinement was seen for polymers with increased backbone stiffness. A fluorescence-multilayer film technique was then used to determine the diffusion coefficient of a small molecule probe in ultrathin supported PS films. A decrease in the diffusion coefficient of the probe was observed upon confinement of the PS films. This procedure is also being applied to ultrathin supported BPAPC and BPAPS films to explore the impact of polymer backbone rigidity on small molecule diffusion in nanoconfined polymers.

  6. Mixing it up - Measuring diffusion in supercooled liquid solutions of methanol and ethanol at temperatures near the glass transition

    SciTech Connect

    Matthiesen, Jesper; Smith, R. Scott; Kay, Bruce D.

    2011-03-17

    Do liquid mixtures, cooled to temperatures below their freezing point, behave as normal liquids? We address this question using nanoscale films of methanol and ethanol supercooled liquid solutions of varying composition (7 -93% methanol) at temperatures near their glass transition,Tg. The permeation of Kr through these films is used to determine the diffusivities of the supercooled liquid mixtures. We find that the temperature dependent diffusivities of the mixtures are well-fit by a Vogel-Fulcher-Tamman equation indicating that the mixtures exhibit fragile behavior at temperatures just above their Tg. Further, for a given temperature, the composition dependent diffusivity is well-fit by a Vignes-type equation, i.e. the diffusivity of any mixture can be predicted using an exponential weighting of the diffusion of the pure methanol and ethanol diffusivities. These results show that deeply supercooled liquid mixtures can be used to provide valuable insight into the properties of normal liquid mixtures.

  7. Influence of Irreversible Adsorption on the Glass Transition Temperature of Polymer Thin Films as Measured by Fluorescence

    NASA Astrophysics Data System (ADS)

    Burroughs, Mary; Priestley, Rodney

    2014-03-01

    Polymers confined to the nanometer length scale have been shown to exhibit deviations in the glass transition temperature (Tg) from the bulk. With the increasing use of confined polymers in nanotechnology, understanding and predicting this behavior is extremely relevant to industries ranging from pharmaceuticals to organic electronics. Recent work (Napolitano, Wübbenhorst, Nature Communications, 2, 260 (2011)) has connected deviations in Tg under confinement with irreversible physical adsorption of polymer chains at substrate interfaces. Here we investigate the influence of irreversibly adsorbed layers on the Tg of polystyrene (PS) thin films supported on silica via fluorescence. We examine the Tg of the brushes as a function of annealing time and irreversibly adsorbed layer thickness. By incorporating fluorescently labeled polymer layers into multilayered films of unlabeled polymer, we will examine the influence of brushes on adjacent layers dynamics. Finally, we will compare the results on PS with those of poly(methyl methacrylate).

  8. Hilbert-Glass Transition: New Universality of Temperature-Tuned Many-Body Dynamical Quantum Criticality

    NASA Astrophysics Data System (ADS)

    Pekker, David; Refael, Gil; Altman, Ehud; Demler, Eugene; Oganesyan, Vadim

    2014-01-01

    We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. One example of such a transition is the recently proposed many-body localization-delocalization transition, in which transport coefficients vanish at a critical temperature with no singularities in thermodynamic observables. Describing this purely dynamical quantum criticality is technically challenging as understanding the finite-temperature dynamics necessarily requires averaging over a large number of matrix elements between many-body eigenstates. Here, we develop a real-space renormalization group method for excited states that allows us to overcome this challenge in a large class of models. We characterize a specific example: the 1 D disordered transverse-field Ising model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using the real-space renormalization group method for excited states we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by nonanalyticities in the low-frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.

  9. Heating the sun's lower transition region with fine-scale electric currents

    NASA Technical Reports Server (NTRS)

    Rabin, D.; Moore, R.

    1984-01-01

    Analytical and observational data are presented to show that the lower transition zone, a 100 km thick region at 10,000-200,000 K between the solar chromosphere and corona, is heated by local electric currents. The study was spurred by correlations between the enhanced atmospheric heating and magnetospheric flux in the chromospheric network and active regions. Field aligned current heated flux loops are asserted to mainly reside in and make up most of the transition region. It is shown that thermal conduction from the sides of hot gas columns generated by the current dissipation is the source of the observed temperature distribution in the transition regions.

  10. Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: From boiling point to glass transition temperature

    NASA Astrophysics Data System (ADS)

    Schmidtke, B.; Petzold, N.; Kahlau, R.; Rössler, E. A.

    2013-08-01

    We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10-12 s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature Tg is covered. We focus on low-Tg liquids for which the high-temperature limit τ ≅ 10-12 s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" Ecoop(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)], 10.1103/PhysRevE.86.041507. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a Ecoop(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon.

  11. Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: from boiling point to glass transition temperature.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Rössler, E A

    2013-08-28

    We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10(-12) s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature T(g) is covered. We focus on low-T(g) liquids for which the high-temperature limit τ ≅ 10(-12) s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" E(coop)(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)]. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a E(coop)(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon. PMID:24007015

  12. Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: from boiling point to glass transition temperature.

    PubMed

    Schmidtke, B; Petzold, N; Kahlau, R; Rössler, E A

    2013-08-28

    We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10(-12) s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature T(g) is covered. We focus on low-T(g) liquids for which the high-temperature limit τ ≅ 10(-12) s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" E(coop)(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)]. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a E(coop)(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon.

  13. Composition-driven spin glass to ferromagnetic transition in the quasicrystal approximant Au-Al-Gd

    NASA Astrophysics Data System (ADS)

    Ishikawa, A.; Hiroto, T.; Tokiwa, K.; Fujii, T.; Tamura, R.

    2016-01-01

    We investigated the composition dependence of the magnetic susceptibility of the quasicrystal approximant Au-Al-Gd. A composition-driven ferromagnetic transition is observed in a quasicrystal approximant, which is attributed to the Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation via a variation in the Fermi wave vector. The ferromagnetic transition is most simply understood as a result of the close matching of the nearest and second-nearest spin distances with the maximum positions of the RKKY potential. The present work provides an idea that allows us to tailor the magnetic order via the electron concentration in quasicrystal approximants as well as in quasicrystals.

  14. Application of atomic force microscopy in determining the fractal dimension of the mirror, mist, and hackle region of silica glass

    SciTech Connect

    Smith, R.L. Mecholsky, J.J.

    2011-05-15

    Fractal analysis has been used as a method to study fracture surfaces of brittle materials. However, it has not been determined if the fractal characteristics of brittle materials is consistent throughout the fracture surface. Therefore, the fractal dimensional increment of the mirror, mist, and hackle regions of the fracture surface of silica glass was determined using atomic force microscopy. The fractal dimensional increment of the mirror region (0.17-0.26) was determined to be statistically greater than that for the mist (0.08-0.12) and hackle (0.08-0.13) regions. It is thought that the increase in the fractal dimensional increment is caused by a greater tortuosity in the mirror region due to, most likely, the slower crack velocity of the propagating crack in that region and that there is a point between the mirror and mist region at which the fractal dimension decreases and becomes constant. - Research Highlights: {yields} The fracture surface of silica glass does not have a constant fractal dimension. {yields} Mirror region has greater fractal dimension than mist or hackle region. {yields} Fractal dimension decreases between mirror and mist region. {yields} Greater fractal dimension could be due to slower crack velocity in mirror region.

  15. Strontium environment transition in tin silicate glasses by neutron and x-ray diffraction.

    SciTech Connect

    Johnson, J. A.; Urquidi, D.; Holland, D.; Johnson, C. E.; Appelyard, P. G.; New Mexico State Univ.; LANL; Warwick Univ.; Northern Illinois Univ.; Cranfield Univ.

    2007-11-15

    The effect of Sr modifier atoms on the structure of stannosilicate glasses of composition (Sr0){sub x}(SnO){sub 0.5-x}(SiO{sub 2}){sub 0.5}, with 0 {le} x {le} 0.15, has been studied using Moessbauer spectroscopy and neutron and X-ray diffraction. The tin is mostly in the Sn{sup 2+} state. The Sr-O bond length undergoes a step decrease from (2.640 {+-} 0.005) {angstrom} to (2.585 {+-} 0.005) {angstrom} as x increases from 0.10 to 0.15, indicating a decrease in co-ordination number from 8 to 7. A Sn-Sn distance of 3.507 {+-} 0.005 {angstrom} is revealed by a first-order difference calculation from the x = 0 sample. This is too short to be consistent with significant edge sharing of [SnO{sub 3}] trigonal pyramids.

  16. Electrical Currents and Adhesion of Edge-Delete Regions of EVA-to-Glass Module Packaging: Preprint

    SciTech Connect

    McMahon, T. J.; Jorgensen, G. J.

    2001-10-01

    Presented at the 2001 NCPV Program Review Meeting: Electrical conductivity pathways from the grounded frame to the cell area in a PV module are reviewed here. Electrical conductivity pathways from the grounded frame to the cell area in a PV module are reviewed here. Measurements are made on 4 inch x 8 inch soda lime (SL) glass substrates with contact patterns defined using 3-mil and 10-mil diameter bead-blast removal of the SnO{sub 2} coating to study the dominant path, which is the EVA/glass interface. The remaining SnO{sub 2} contact strips are separated by what would simulate the module edge delete regions. EVA encapsulated bead-blast surface resistances are 8 x 10{sup 15} ohm/sq compared to 8 x 10{sup 12} ohm/sq for native SL glass surfaces. Adhesion strengths to bead-blast surfaces are 25 to 30 lbs/in. Stress test results on these interfaces after removal from damp heat suggest corrosion of the glass at the glass-EVA interface.

  17. A size-dependent constitutive model of bulk metallic glasses in the supercooled liquid region

    NASA Astrophysics Data System (ADS)

    Yao, Di; Deng, Lei; Zhang, Mao; Wang, Xinyun; Tang, Na; Li, Jianjun

    2015-01-01

    Size effect is of great importance in micro forming processes. In this paper, micro cylinder compression was conducted to investigate the deformation behavior of bulk metallic glasses (BMGs) in supercooled liquid region with different deformation variables including sample size, temperature and strain rate. It was found that the elastic and plastic behaviors of BMGs have a strong dependence on the sample size. The free volume and defect concentration were introduced to explain the size effect. In order to demonstrate the influence of deformation variables on steady stress, elastic modulus and overshoot phenomenon, four size-dependent factors were proposed to construct a size-dependent constitutive model based on the Maxwell-pulse type model previously presented by the authors according to viscosity theory and free volume model. The proposed constitutive model was then adopted in finite element method simulations, and validated by comparing the micro cylinder compression and micro double cup extrusion experimental data with the numerical results. Furthermore, the model provides a new approach to understanding the size-dependent plastic deformation behavior of BMGs.

  18. The impact of transition training on adapting to Technically Advanced Aircraft at regional airlines: Perceptions of pilots and instructor pilots

    NASA Astrophysics Data System (ADS)

    di Renzo, John Carl, Jr.

    Scope and method of study. The purpose of this study was to test a hypothesis about pilot and instructor pilot perceptions of how effectively pilots learn and use new technology, found in Technically Advanced Aircraft (TAA), given initial type of instrumentation training. New aviation technologies such as Glass Cockpits in technically advanced aircraft are complex and can be difficult to learn and use. The research questions focused on the type of initial instrumentation training to determine the differences among pilots trained using various types of instrumentation ranging from aircraft equipped with traditional analog instrumentation to aircraft equipped with glass cockpits. A convenience sample of Pilots in Training (PT) and Instructor Pilots (IP) was selected from a regional airline. The research design used a mixed methodology. Pilots in training completed a thirty-two question quantitative questionnaire and instructor pilots completed a five question qualitative questionnaire. Findings and conclusions. This investigation failed to disprove the null hypothesis. The type of instrumentation training has no significant effect on newly trained regional airline pilot perceived ability to adapt to advanced technology cockpits. Therefore, no evidence exists from this investigation to support the early introduction and training of TAA. While the results of this investigation were surprising, they are nonetheless, instructive. Even though it would seem that there would be a relationship between exposure to and use of technically advanced instrumentation, apparently there was no perceived relationship for this group of airline transport pilots. However, a point of interest is that these pilots were almost evenly divided in their opinion of whether or not their previous training had prepared them for transition to TAA. The majority also believed that the type of initial instrumentation training received does make a difference when transitioning to TAA. Pilots believed

  19. Vibrational frequency shifts as a probe of hydrogen bonds: thermal expansion and glass transition of myoglobin in mixed solvents.

    PubMed

    Demmel, F; Doster, W; Petry, W; Schulte, A

    1997-01-01

    The contribution of hydrogen bonds to protein-solvent interactions and their impact on structural flexibility and dynamics of myoglobin are discussed. The shift of vibrational peak frequencies with the temperature of myoglobin in sucrose/water and glycerol/water solutions is used to probe the expansion of the hydrogen bond network. We observe a characteristic change in the temperature slope of the O-H stretching frequency at the glass transition which correlates with the discontinuity of the thermal expansion coefficient. The temperature-difference spectra of the amide bands show the same tendency, indicating that stronger hydrogen bonding in the bulk affects the mainchain solvent interactions in parallel. However, the hydrogen bond strength decreases relative to the bulk solvent with increasing cosolvent concentration near the protein surface, which suggests preferential hydration. Weaker and/or fewer hydrogen bonds are observed at low degrees of hydration. The central O-H stretching frequency of protein hydration water is red-shifted by 40 cm-1 relative to the bulk. The shift increases towards lower temperatures, consistent with contraction and increasing strength of the protein-water bonds. The temperature slope shows a discontinuity near 180 K. The contraction of the network has reached a critical limit which leads to frozen-in structures. This effect may represent the molecular mechanism underlying the dynamic transition observed for the mean square displacements of the protein atoms and the heme iron of myoglobin. PMID:9378100

  20. Quantum critical scaling at a Bose-glass/superfluid transition: Theory and experiment for a model quantum magnet

    NASA Astrophysics Data System (ADS)

    Yu, Rong; Miclea, Corneliu F.; Weickert, Franziska; Movshovich, Roman; Paduan-Filho, Armando; Zapf, Vivien S.; Roscilde, Tommaso

    2012-10-01

    In this paper we investigate the quantum phase transition from magnetic Bose Glass to magnetic Bose-Einstein condensation induced by a magnetic field in NiCl2·4SC(NH2)2 (dichloro-tetrakis-thiourea-nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z=d; moreover the correlation length exponent is found to be ν=0.75(10), and the order parameter exponent to be β=0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.40.546 40, 546 (1989)]. However they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.

  1. Physical Aging of Thin and Ultrathin Free-Standing Polymer Films: Effect of Stress and Reduced Glass Transitions

    NASA Astrophysics Data System (ADS)

    Pye, Justin; Roth, Connie

    2014-03-01

    While great effort has been made in elucidating the effect of confinement on the glass transition (Tg) in polymers, considerably less work has been done on physical aging. Starting with supported films, we have previously shown that the reduced physical aging rates in ultrathin polystyrene (PS) films can be linked to the reduced Tg near the free surface [Macromolecules 2010, 43, 8296]. We then showed that high molecular weight (MW) free-standing PS films have two reduced Tgs suggesting that two separate mechanisms are acting simultaneously to propagate enhanced mobility at the free surface deeper into the film [PRL 2011, 107, 235701]. To help determine the mechanisms of these two reduced Tgs, we performed physical aging measurements on these high MW free-standing PS films. For thick films (220-1800 nm) in which there are no Tg reductions, we find that the physical aging rate depends strongly on stress caused by thermal expansion mismatch between film and support. This stress, applied to the films as they are quenched into the glassy state, can nearly double the physical aging rate when changing the frame material from polycarbonate to silicon [Macromolecules 2013, DOI:10.1021/ma401872u]. Finally, ultrathin high MW PS films held at a temperature between the two Tgs do exhibit physical aging, indicating that at least some of the film is glassy between these two transitions.

  2. Coherent state approach to the interacting boson model: Test of its validity in the transitional region

    SciTech Connect

    Inci, I.; Alonso, C. E.; Arias, J. M.; Fortunato, L.; Vitturi, A.

    2009-09-15

    The predictive power of the coherent state (CS) approach to the interacting boson model (IBM) is tested far from the IBM dynamical symmetry limits. The transitional region along the {gamma}-unstable path from U(5) to O(6) is considered. Excitation energy of the excited {beta} band and intraband and interband transitions obtained within the CS approach are compared with the exact results as a function of the boson number N. We find that the CS formalism provides approximations to the exact results that are correct up to the order 1/N in the transitional region, except in a narrow region close to the critical point.

  3. Systematic study of glass transition in low-molecular phthalonitriles: Insight from computer simulations

    NASA Astrophysics Data System (ADS)

    Guseva, D. V.; Chertovich, A. V.; Rudyak, V. Yu.

    2016-10-01

    Phthalonitrile compounds with Si bridges were recently suggested for producing thermosetting polymer composites with reduced Tg and thus expanded processing range. The detailed experimental investigation of this class of phthalonitriles is still difficult due to development time and costs limitations and the need to take into account the structural changes during the crosslinking. In this paper, we try to overcome these limitations using computer simulations. We performed full-atomistic molecular dynamics simulations of various phthalonitrile compounds to understand the influence of molecular structure on the bulk glass temperature Tg. Two molecular properties affect Tg of the resulting bulk compound: the size of the residue and the length of the Si bridge. The larger residues lead to higher Tgs, while compounds with longer Si bridges have lower Tgs. We have also studied relaxation mechanisms involved in the classification of the samples. Two different factors influence the relaxation mechanisms: energetic, which is provided by the rigidity of molecules, and entropic, connected with the available volume of the conformational space of the monomer.

  4. An application for impedance spectroscopy in the characterisation of the glass transition during the lyophilization cycle: the example of a 10% w/v maltodextrin solution.

    PubMed

    Smith, Geoff; Arshad, Muhammad Sohail; Polygalov, Eugene; Ermolina, Irina

    2013-11-01

    Impedance spectroscopy has been used for the measurement of the glass transition of a 10 % maltodextrin solution contained within a glass vial, with externally attached electrodes. Features of the pseudo-relaxation process, associated with the composite impedance of the glass vial-solution assembly, were characterised by the peak amplitude, C(peak)(″), and peak frequency, f(peak), of the capacitance spectra and the equivalent circuit elements that model the impedance spectra (i.e. the solution resistance and solution capacitance) and monitored every 3 min during re-heating of the solution. The time derivatives of all four parameters studied provided a glass transition in close agreement with DSC measurements (-17 °C) and at a precision of ± 0.5 °C. The temperature dependencies of the solution resistance and peak frequency were then characterised with the Arrhenius and Vogel-Fulcher-Tammann fit functions, at temperatures below and above Tg, respectively. The energy of activation (below Tg) was estimated at ~20 kJ mol(-1), and the fragility index (If) of the glass forming liquid (above Tg) was estimated at 0.9. The significance of the fragility index to the development, optimisation and control of the freeze-drying cycle is highlighted.

  5. A Regional Approach to Rail Transit Training for the New York Metropolitan Area. Final Report.

    ERIC Educational Resources Information Center

    McKnight, Claire E.; Rotter, Naomi

    A study examined the feasibility of a regional approach to rail transit training in the New York metropolitan area. First, case studies were collected to document existing training practices at the five agencies currently responsible for training rail transit workers in the New York metropolitan area and to identify mutual training needs that…

  6. An investigation of the liquid to glass transition using integral equations for the pair structure of coupled replicae.

    PubMed

    Bomont, Jean-Marc; Hansen, Jean-Pierre; Pastore, Giorgio

    2014-11-01

    Extensive numerical solutions of the hypernetted-chain (HNC) and Rogers-Young (RY) integral equations are presented for the pair structure of a system of two coupled replicae (1 and 2) of a "soft-sphere" fluid of atoms interacting via an inverse-12 pair potential. In the limit of vanishing inter-replica coupling ɛ12, both integral equations predict the existence of three branches of solutions: (1) A high temperature liquid branch (L), which extends to a supercooled regime upon cooling when the two replicae are kept at ɛ12 = 0 throughout; upon separating the configurational and vibrational contributions to the free energy and entropy of the L branch, the Kauzmann temperature is located where the configurational entropy vanishes. (2) Starting with an initial finite coupling ɛ12, two "glass" branches G1 and G2 are found below some critical temperature, which are characterized by a strong remnant spatial inter-replica correlation upon taking the limit ɛ12 → 0. Branch G2 is characterized by an increasing overlap order parameter upon cooling, and may hence be identified with the hypothetical "ideal glass" phase. Branch G1 exhibits the opposite trend of increasing order parameter upon heating; its free energy lies consistently below that of the L branch and above that of the G2 branch. The free energies of the L and G2 branches are found to intersect at an alleged "random first-order transition" (RFOT) characterized by weak discontinuities of the volume and entropy. The Kauzmann and RFOT temperatures predicted by RY differ significantly from their HNC counterparts.

  7. Structure, glass transition temperature and spectroscopic properties of 10Li2O-xP2O5-(89-x)TeO2-1CuO (5≤x≤25 mol%) glass system.

    PubMed

    Upender, G; Babu, J Chinna; Mouli, V Chandra

    2012-04-01

    X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC), infrared (IR), Raman, electron paramagnetic resonance (EPR) and optical absorption studies on 10Li2O-xP2O5-(89-x)TeO2-1CuO glasses (where x=5, 10, 15, 20 and 25 mol%) have been carried out. The amorphous nature of the glasses was confirmed using XRD and FESEM measurements. The glass transition temperature (Tg) of glass samples have been estimated from DSC traces and found that the Tg increases with increasing P2O5 content. Both the IR and Raman studies have been showed that the present glass system consists of [TeO3], [TeO4], [PO3] and [PO4] units. The spin-Hamiltonian parameters such as g∥, g⊥, and A∥ have been determined from EPR spectra and it was found that the Cu2+ ion is present in tetragonal distorted octahedral site with [Formula: see text] as the ground state. Bonding parameters and bonding symmetry of Cu2+ ions have been calculated by correlating EPR and optical data and were found to be composition dependent.

  8. Regional Gastrointestinal Transit Times in Patients With Carcinoid Diarrhea: Assessment With the Novel 3D-Transit System

    PubMed Central

    Gregersen, Tine; Haase, Anne-Mette; Schlageter, Vincent; Gronbaek, Henning; Krogh, Klaus

    2015-01-01

    Background/Aims The paucity of knowledge regarding gastrointestinal motility in patients with neuroendocrine tumors and carcinoid diarrhea restricts targeted treatment. 3D-Transit is a novel, minimally invasive, ambulatory method for description of gastrointestinal motility. The system has not yet been evaluated in any group of patients. We aimed to test the performance of 3D-Transit in patients with carcinoid diarrhea and to compare the patients’ regional gastrointestinal transit times (GITT) and colonic motility patterns with those of healthy subjects. Methods Fifteen healthy volunteers and seven patients with neuroendocrine tumor and at least 3 bowel movements per day were investigated with 3D-Transit and standard radiopaque markers. Results Total GITT assessed with 3D-Transit and radiopaque markers were well correlated (Spearman’s rho = 0.64, P = 0.002). Median total GITT was 12.5 (range: 8.5–47.2) hours in patients versus 25.1 (range: 13.1–142.3) hours in healthy (P = 0.007). There was no difference in gastric emptying (P = 0.778). Median small intestinal transit time was 3.8 (range: 1.4–5.5) hours in patients versus 4.4 (range: 1.8–7.2) hours in healthy subjects (P = 0.044). Median colorectal transit time was 5.2 (range: 2.9–40.1) hours in patients versus 18.1 (range: 5.0–134.0) hours in healthy subjects (P = 0.012). Median frequency of pansegmental colonic movements was 0.45 (range: 0.03–1.02) per hour in patients and 0.07 (range: 0–0.61) per hour in healthy subjects (P = 0.045). Conclusions Three-dimensional Transit allows assessment of regional GITT in patients with diarrhea. Patients with carcinoid diarrhea have faster than normal gastrointestinal transit due to faster small intestinal and colorectal transit times. The latter is caused by an increased frequency of pansegmental colonic movements. PMID:26130638

  9. Soft-sphere model for the glass transition in binary alloys. II. Relaxation of the incoherent density-density correlation functions

    NASA Astrophysics Data System (ADS)

    Pastore, G.; Bernu, B.; Hansen, J. P.; Hiwatari, Y.

    1988-07-01

    Using molecular-dynamics (MD) data on a binary-alloy model, we have computed the self (incoherent) -part of the density autocorrelation functions of both species in the supercooled liquid and near the glass transition, over an extensive range of wave numbers. Standard theoretical models of liquid-state theory fail to reproduce the data, while the Chudley-Elliott jump diffusion model yields reasonable results in the glass range. With a suitable scaling of the time axis, the data for different temperatures can be brought onto a single master curve, which is well fitted by a Kohlrausch (``stretched-exponential'') function with a wave-number-dependent exponent.

  10. Gas permeation through nanoporous membranes in the transitional flow region

    NASA Astrophysics Data System (ADS)

    Petukhov, D. I.; Eliseev, A. A.

    2016-02-01

    An experimental study on the permeability of anodic alumina (20-120 nm) and track-etched (30 nm) nanoporous membranes for different gases in the transitional flow regime is reported in the range of Knudsen numbers from 0.1 to 10. A significant variation (up to 30%) of the membrane permeance for different gases at the same Knudsen numbers is reported with certainty. It is established that this discrepancy relates to a molecule’s effective collision area, which is poorly described in the frameworks of conventional gas permeation models. Two models are proposed for the description of the effect: self-diffusion of penetrate gases due to intermolecular collisions and enhancement of the slip flow contribution due to tangential momentum accommodation growth with the decrease of a molecule’s effective collision area. The best fit parameters for the simultaneous fit of the experimental data with different models for 30 membrane-gas pairs are given.

  11. [Observation and diagnostic of ultraviolet spectra in the solar transition region].

    PubMed

    Zhang, Min; Wang, Dong

    2011-12-01

    The solar transition region is the thin atmosphere layer between the chromosphere and corona. Although the thickness of the solar transition region is only several hundred kilometers, the parameters of the plasma change dramatically. The temperature increases from 10(4) to 10(6) K and the density drops from 10(10) to 10(8) cm(-3). The emission of the solar transition region is generally of optical-thin far-ultraviolet (FUV) spectral lines, extreme-ultraviolet (EUV) spectral lines and background continuous spectral lines. However, the traditional ground-based observations can not be made for FUV/EUV lines, owing to their strong absorption by ozone and other molecules in the earth's atmosphere. Thus, FUV/EUV lines only can be obtained with space-based observations. In recent decades, the successful launch of space-borne instruments opened a new era of the research for the solar transition region. The present paper reviews the observation history of ultraviolet spectra in the solar transition region and some kinds of space-borne instruments, especially several important spectrometers in recent ten years. At the same time, the diagnostics of the emissivity, electron density and electronic temperature of ultraviolet spectra in the solar transition region are expounded in detail. The shape of ultraviolet line is discussed and several important parameters with physical significance are showed using SOHO/SUMER spectrometer. PMID:22295780

  12. Simultaneous measurements of sunspot umbral oscillations in the photosphere, chromosphere, and transition region

    NASA Technical Reports Server (NTRS)

    Thomas, John H.; Lites, Bruce W.; Gurman, Joseph B.; Ladd, Edwin F.

    1987-01-01

    Measurements of umbral oscillations in a sunspot were made simultaneously from space (with the SMM/UVSP instrument) in the C IV transition-region line and from the ground (with the tower telescope at NSO/sunspot) in spectral lines formed in the photosphere and chromosphere. The power spectra of velocity and intensity variations show multiple peaks in the 3 min band (4.5-10 mHz). A strong oscillation at 5.5 mHz is coherent between the chromosphere and transition region. Another strong oscillation mode at 7.5 mHz is coherent between the photosphere and transition region and appears to have a node in the chromosphere. The rms velocity in the 3 min band is a little over 12 km/sec in both the chromosphere and transition region, but the kinetic energy density is lower in the transition region (by a factor of 10 or more) due to the lower mass density there. These measurements of amplitude and phase of the waves at different heights provided a new, independent method of testing or fitting models of the vertical temperature distribution in the umbral chromosphere and transition regions.

  13. [Observation and diagnostic of ultraviolet spectra in the solar transition region].

    PubMed

    Zhang, Min; Wang, Dong

    2011-12-01

    The solar transition region is the thin atmosphere layer between the chromosphere and corona. Although the thickness of the solar transition region is only several hundred kilometers, the parameters of the plasma change dramatically. The temperature increases from 10(4) to 10(6) K and the density drops from 10(10) to 10(8) cm(-3). The emission of the solar transition region is generally of optical-thin far-ultraviolet (FUV) spectral lines, extreme-ultraviolet (EUV) spectral lines and background continuous spectral lines. However, the traditional ground-based observations can not be made for FUV/EUV lines, owing to their strong absorption by ozone and other molecules in the earth's atmosphere. Thus, FUV/EUV lines only can be obtained with space-based observations. In recent decades, the successful launch of space-borne instruments opened a new era of the research for the solar transition region. The present paper reviews the observation history of ultraviolet spectra in the solar transition region and some kinds of space-borne instruments, especially several important spectrometers in recent ten years. At the same time, the diagnostics of the emissivity, electron density and electronic temperature of ultraviolet spectra in the solar transition region are expounded in detail. The shape of ultraviolet line is discussed and several important parameters with physical significance are showed using SOHO/SUMER spectrometer.

  14. Reorganization energy of electron transfer in viscous solvents above the glass transition.

    PubMed

    Ghorai, Pradip K; Matyushov, Dmitry V

    2006-02-01

    We present a molecular-dynamics study of the solvent reorganization energy of electron transfer in supercooled water. We observe a sharp decrease of the reorganization energy at a temperature identified as the temperature of structural arrest due to cage effect as discussed by the mode coupling theory. Both the heat capacity and dielectric susceptibility of the pure water show sharp drops at about the same temperature. This temperature also marks the onset of the enhancement of translational diffusion relative to rotational relaxation signaling the breakdown of the Stokes-Einstein relation. The change in the reorganization energy at the transition temperature reflects the dynamical arrest of the slow, collective relaxation of the solvent related to Debye relaxation of the solvent dipolar polarization.

  15. Void-nanograting transition by ultrashort laser pulse irradiation in silica glass.

    PubMed

    Dai, Ye; Patel, Aabid; Song, Juan; Beresna, Martynas; Kazansky, Peter G

    2016-08-22

    The structural evolution from void modification to self-assembled nanogratings in fused silica is observed for moderate (NA > 0.4) focusing conditions. Void formation, appears before the geometrical focus after the initial few pulses and after subsequent irradiation, nanogratings gradually occur at the top of the induced structures. Nonlinear Schrödinger equation based simulations are conducted to simulate the laser fluence, intensity and electron density in the regions of modification. Comparing the experiment with simulations, the voids form due to cavitation in the regions where electron density exceeds 1020 cm-3 but is below critical. In this scenario, the energy absorption is insufficient to reach the critical electron density that was once assumed to occur in the regime of void formation and nanogratings, shedding light on the potential formation mechanism of nanogratings. PMID:27557213

  16. Nanoscale confinement and interfacial effects on the dynamics and glass transition/crystallinity of thin adsorbed films on silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Madathingal, Rajesh Raman

    in the latter case bridging of PMMA between aggregates occurred. The anchoring point densities were comparable to the silanol densities, suggesting that PMMA adsorbed as trains rather than loops. For hydrophilic SiO2, Tg increased with [SiOH], as more carbonyl groups hydrogen bonded to the silanols, and was independent of particle morphology. For methylated silica, (CH3) 3-SiO2, the adsorption isotherms were identical for colloidal and fumed silica, but Tg was depressed for the former, and comparable to the bulk value for the latter. The increased Tg of PMMA adsorbed onto fumed (CH3)3-SiO2 was attributed to the larger loops formed by the bridging PMMA chains between the silica aggregates. For nanocomposites the interphase region becomes more important as the surface/volume ratio of the nanoparticles increases. Polymers have chain dimensions (characterized by the radius of gyration, Rg) similar to the nanoparticles (Rnanoparticle) themselves, so that chain conformation, mobility and crystallinity can be affected by Rg/Rnanoparticle. Here, both the glass transition temperature (Tg) and degree of crystallinity (Xc) of polyethylene oxide (PEO) on individual SiO 2 nanoparticles of nominal 15, 50 and 100 nm diameter (2 RSiO2 ) , in which Rg (PEO) was greater, equal to or less than RSiO2 was investigated. Plateau adsorption of PEO on SiO2 nanoparticles (PEO-SiO2) increased in the order PEO-SiO 2 (100 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (15 nm). At plateau adsorption after melting and solidification, the samples were completely amorphous. The Tg of the adsorbed PEO increased in the order PEO-SiO 2 (100 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (15 nm); since the Tgs were above 25°C in all cases, the PEO behaved more like a brittle solid than an elastomer. For comparable amounts of PEO that were adsorbed from solution but not melted, the melt endotherm increased in the order PEO-SiO2 (15 nm) > PEO-SiO2 (50 nm) > PEO-SiO 2 (100 nm). These trends were interpreted as due to an increase

  17. Selecting polymers for two-phase partitioning bioreactors (TPPBs): Consideration of thermodynamic affinity, crystallinity, and glass transition temperature.

    PubMed

    Bacon, Stuart L; Peterson, Eric C; Daugulis, Andrew J; Parent, J Scott

    2015-01-01

    Two-phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymer's (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc ), and (3) glass transition temperature (Tg ). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n-butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n-butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymer's absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg , and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection. PMID:26259846

  18. Influence of compression on water sorption, glass transition, and enthalpy relaxation behavior of freeze-dried amorphous sugar matrices.

    PubMed

    Imamura, Koreyoshi; Kagotani, Ryo; Nomura, Mayo; Tanaka, Kazuhiro; Kinugawa, Kohshi; Nakanishi, Kazuhiro

    2011-04-15

    An amorphous matrix comprised of sugar molecules are frequently used in the pharmaceutical industry. The compression of the amorphous sugar matrix improves the handling. Herein, the influence of compression on the water sorption of an amorphous sugar matrix was investigated. Amorphous sugar samples were prepared by freeze-drying, using several types of sugars, and compressed at 0-443 MPa. The compressed amorphous sugar samples as well as uncompressed samples were rehumidified at given RHs, and the equilibrium water content and glass transition temperature (T(g)) were then measured. Compression resulted in a decrease in the equilibrium water content of the matrix, the magnitude of which was more significant for smaller sized sugars. Diffusivity of water vapor in the sample was also decreased to one-hundredth by the compression. The T(g) value for a given RH remained unchanged, irrespective of the compression. Accordingly, the decrease in T(g) with increasing water content increased as the result of compression. The structural relaxation of the amorphous sugar matrices were also examined and found to be accelerated to the level of a non-porous amorphous sugar matrix as the result of the compression. The findings indicate that pores contained in freeze-dried sugar samples interfere with the propagation of structural relaxation.

  19. Influence of compression on water sorption, glass transition, and enthalpy relaxation behavior of freeze-dried amorphous sugar matrices.

    PubMed

    Imamura, Koreyoshi; Kagotani, Ryo; Nomura, Mayo; Tanaka, Kazuhiro; Kinugawa, Kohshi; Nakanishi, Kazuhiro

    2011-04-15

    An amorphous matrix comprised of sugar molecules are frequently used in the pharmaceutical industry. The compression of the amorphous sugar matrix improves the handling. Herein, the influence of compression on the water sorption of an amorphous sugar matrix was investigated. Amorphous sugar samples were prepared by freeze-drying, using several types of sugars, and compressed at 0-443 MPa. The compressed amorphous sugar samples as well as uncompressed samples were rehumidified at given RHs, and the equilibrium water content and glass transition temperature (T(g)) were then measured. Compression resulted in a decrease in the equilibrium water content of the matrix, the magnitude of which was more significant for smaller sized sugars. Diffusivity of water vapor in the sample was also decreased to one-hundredth by the compression. The T(g) value for a given RH remained unchanged, irrespective of the compression. Accordingly, the decrease in T(g) with increasing water content increased as the result of compression. The structural relaxation of the amorphous sugar matrices were also examined and found to be accelerated to the level of a non-porous amorphous sugar matrix as the result of the compression. The findings indicate that pores contained in freeze-dried sugar samples interfere with the propagation of structural relaxation. PMID:21291973

  20. Pressure effect on magnetic phase transition and spin-glass-like behavior of GdCo2B2

    NASA Astrophysics Data System (ADS)

    Guang-Hui, Hu; Ling-Wei, Li; Umehara, Izuru

    2016-06-01

    We systematically investigate the effect of pressure on the magnetic properties of GdCo2B2 on the basis of alternating current (AC) susceptibility, AC heat capacity and electrical resistivity measurements under pressures up to 2.2 GPa. A detailed magnetic phase diagram under pressure is determined. GdCo2B2 exhibits three anomalies that apparently reflect magnetic phase transitions, respectively, at temperatures T C = 20.5 K, T 1 = 18.0 K and T N = 11.5 K under ambient pressure. Under pressures up to 2.2 GPa, these anomalies are observed to slightly increase at T C and T 1, and they coincide with each other above 1.6 GPa. Conversely, they decrease at T N and disappear under pressures higher than 1.4 GPa. The results indicate that the low-temperature magnetic phases can be easily suppressed by pressure. Moreover, the spin-glass-like behavior of GdCo2B2 is examined in terms of magnetization, aging effect and frequency dependence of AC susceptibility. A separation between the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves becomes evident at a low magnetic field of 0.001 T. A long-time relaxation behavior is observed at 4 K. The freezing temperature T f increases with frequency increasing. Project supported by JSPS KAKENHI (Grant No. 24540366, Grant-in-Aid for Scientific Research (C)).

  1. Selecting polymers for two-phase partitioning bioreactors (TPPBs): Consideration of thermodynamic affinity, crystallinity, and glass transition temperature.

    PubMed

    Bacon, Stuart L; Peterson, Eric C; Daugulis, Andrew J; Parent, J Scott

    2015-01-01

    Two-phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymer's (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc ), and (3) glass transition temperature (Tg ). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n-butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n-butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymer's absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg , and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection.

  2. Correlation Of Ortho-Positronium Intensity With Doppler Broadening For Rubber Above And Below The Glass Transition Temperature

    SciTech Connect

    Towry, Amanda; Quarles, C. A.

    2011-06-01

    Previous research has demonstrated a correlation between the Doppler broadening S parameter and the intensity of the ortho-positronium lifetime component in polymers that depends on the composition of the polymer. On the other hand, rubber polymers do not show this correlation and behave more like liquids for which the S parameter is essentially independent of the ortho-positronium intensity. The bubble model has been suggested as an explanation of the lack of correlation in analogy with liquids, but the bubble model applied to rubber is controversial. There are two important differences between the rubber and the polymers samples: first, the rubber samples at room temperature were all above the glass transition temperature (T{sub G}). Second, the rubber samples all contained sulfur and were vulcanized. These differences were investigated by first measuring the S parameter for six rubber samples below T{sub G} where the bubble model would not be expected to work. Second, raw rubber samples that did not contain any sulfur and were unvulcanized were studied at room temperature. The results show that the lack of correlation between the S parameter and the ortho-positronium intensity previously observed for vulcanized rubber is due to the inhibition of positronium formation by the sulfur in the vulcanized rubber samples rather than to the rubber being above T{sub G}.

  3. Glass-like dynamics of the strain-induced coil/helix transition on a permanent polymer network

    NASA Astrophysics Data System (ADS)

    Ronsin, O.; Caroli, C.; Baumberger, T.

    2016-02-01

    We study the stress response to a step strain of covalently bonded gelatin gels in the temperature range where triple helix reversible crosslink formation is prohibited. We observe slow stress relaxation towards a T-dependent finite asymptotic level. We show that this is assignable to the strain-induced coil → helix transition, previously evidenced by Courty et al. [Proc. Natl. Acad. Sci. U. S. A. 102, 13457 (2005)], of a fraction of the polymer strands. Relaxation proceeds, in a first stage, according to a stretched exponential dynamics, then crosses over to a terminal simple exponential decay. The respective characteristic times τK and τf exhibit an Arrhenius-like T-dependence with an associated energy E incompatibly larger than the activation barrier height for the isomerisation process which sets the clock for an elementary coil → helix transformation event. We tentatively assign this glass-like slowing down of the dynamics to the long-range couplings due to the mechanical noise generated by the local elementary events in this random elastic medium.

  4. Influence of manufacturing factors on physical stability and solubility of solid dispersions containing a low glass transition temperature drug.

    PubMed

    Sakurai, Atsushi; Sako, Kazuhiro; Maitani, Yoshie

    2012-01-01

    In this study, we investigated the effect of manufacturing factors such as particle size, water content and manufacturing method on the physical stability and solubility of solid dispersion formulations of a low-glass-transition-temperature (T(g)) drug. Solid dispersions were prepared from polyvinylpyrrolidone (PVP) and hydroxypropylmethylcellulose (HPMC) by hot melt extrusion or spray drying. Water content of solid dispersions prepared by hot melt extrusion determined by dynamic moisture sorption measurement was increased drastically with relative humidity below a certain level of particle size. The blends with a lower water content (0.8%) prepared by hot melt extrusion during storage were more stable than those with a higher water content (3.5%) prepared by spray drying, which caused rapid recrystallization. Physical stability in the hot melt blends may be attributed to reduced molecular mobility due to a higher T(g). Dissolution study revealed that solid dispersions prepared by hot melt extrusion with the smallest particle size showed decreased solubility, attributed to reduced wetting properties (surface energy), which is not predictable by the Noyes-Whitney equation. Taken together, these results indicate that the control of particle size concerned in water content or wetting properties is critical to ensuring the physical stability or enhancing solubility of low-T(g) drugs. Further, hot melt extrusion, which can reduce water content, is a suitable manufacturing method for solid dispersions of low-T(g) drugs. PMID:23124559

  5. Synthesis and Characterization of Fluorescently Labeled Diblock Copolymers for Location-Specific Measurements of The Glass Transition Temperature

    NASA Astrophysics Data System (ADS)

    Christie, Dane; Register, Richard; Priestley, Rodney

    Interfaces play a determinant role in the size dependence of the glass transition temperature (Tg) of polymers confined to nanometric length scales. Interfaces are intrinsic in diblock copolymers, which, depending on their molecular weight and composition, are periodically nanostructured in the bulk. As a result diblock copolymers are model systems for characterizing the effect of interfaces on Tg in bulk nanostructured materials. Investigating the effect of intrinsic interfaces on Tg in diblock copolymers has remained unexplored due to their small periodic length scale. By selectively incorporating trace amounts of a fluorescent probe into a diblock copolymer, Tg can be characterized relative to the diblock copolymer's intrinsic interface using fluorescence spectroscopy. Here, pyrene is selectively incorporated into the poly(methyl methacrylate) (PMMA) block of lamellar forming diblock copolymers of poly(butyl- b-methyl methacrylate) (PBMA-PMMA). Preliminary results show a correlation of Tg as measured by fluorescence with the onset of Tg as measured by calorimetry in labeled homopolymers of PMMA. This result is consistent with previous characterizations of Tg using fluorescence spectroscopy. In selectively labeled diblock copolymers Tg is found to vary systematically depending on the distance of the probe from the PBMA-PMMA interface. We acknowledge funding from the Princeton Center for Complex Materials, a MRSEC supported by NSF Grant DMR 1420541.

  6. Effect of Interfaces on Self-diffusion and Glass Transition Temperature of Poly(isobutyl methacrylate) Thin Films

    NASA Astrophysics Data System (ADS)

    Katsumata, Reika; Dulaney, Austin; Ellison, Christopher

    2015-03-01

    In thin films, physical properties such as the glass transition temperature (Tg), modulus, and viscosity, are different compared to that in thick films due to higher interfacial area to volume ratio. However, the effects of film thickness and associated interfaces on self-diffusion are not well understood, partly because only a few techniques are available for such studies. In this study, we employed fluorescence recovery after patterned photobleaching to evaluate the self-diffusion coefficient (D) of fluorescently labeled poly(isobutyl methacrylate) (PiBMA, Mn = 11 kg/mol, PDI = 1.2). Films 16 - 300 nm in thickness were spin coated onto two substrates then D and Tg were examined: one set of films possessing attractive polymer/substrate interactions on silica substrates, and the other set possessing repulsive polymer/substrate interactions using poly(cyclohexylethylene) substrates. D was measured in the melt state (Tg + 48 K) and the D of thick films were identical to the bulk value regardless of the substrate type. The D of a ~ 19 nm thick film on a repulsive substrate was four times larger than its bulk value while Tg was increased by about 10-15 K. In contrast, attractive substrates typically do not affect D or Tg of PiBMA.

  7. Sorption isotherms, thermodynamic properties and glass transition temperature of mucilage extracted from chia seeds (Salvia hispanica L.).

    PubMed

    Velázquez-Gutiérrez, Sandra Karina; Figueira, Ana Cristina; Rodríguez-Huezo, María Eva; Román-Guerrero, Angélica; Carrillo-Navas, Hector; Pérez-Alonso, César

    2015-05-01

    Freeze-dried chia mucilage adsorption isotherms were determined at 25, 35 and 40°C and fitted with the Guggenheim-Anderson-de Boer model. The integral thermodynamic properties (enthalpy and entropy) were estimated with the Clausius-Clapeyron equation. Pore radius of the mucilage, calculated with the Kelvin equation, varied from 0.87 to 6.44 nm in the temperature range studied. The point of maximum stability (minimum integral entropy) ranged between 7.56 and 7.63kg H2O per 100 kg of dry solids (d.s.) (water activity of 0.34-0.53). Enthalpy-entropy compensation for the mucilage showed two isokinetic temperatures: (i) one occurring at low moisture contents (0-7.56 kg H2O per 100 kg d.s.), controlled by changes in water entropy; and (ii) another happening in the moisture interval of 7.56-24 kg H2O per 100 kg d.s. and was enthalpy driven. The glass transition temperature Tg of the mucilage fluctuated between 42.93 and 57.93°C.

  8. Influence of manufacturing factors on physical stability and solubility of solid dispersions containing a low glass transition temperature drug.

    PubMed

    Sakurai, Atsushi; Sako, Kazuhiro; Maitani, Yoshie

    2012-01-01

    In this study, we investigated the effect of manufacturing factors such as particle size, water content and manufacturing method on the physical stability and solubility of solid dispersion formulations of a low-glass-transition-temperature (T(g)) drug. Solid dispersions were prepared from polyvinylpyrrolidone (PVP) and hydroxypropylmethylcellulose (HPMC) by hot melt extrusion or spray drying. Water content of solid dispersions prepared by hot melt extrusion determined by dynamic moisture sorption measurement was increased drastically with relative humidity below a certain level of particle size. The blends with a lower water content (0.8%) prepared by hot melt extrusion during storage were more stable than those with a higher water content (3.5%) prepared by spray drying, which caused rapid recrystallization. Physical stability in the hot melt blends may be attributed to reduced molecular mobility due to a higher T(g). Dissolution study revealed that solid dispersions prepared by hot melt extrusion with the smallest particle size showed decreased solubility, attributed to reduced wetting properties (surface energy), which is not predictable by the Noyes-Whitney equation. Taken together, these results indicate that the control of particle size concerned in water content or wetting properties is critical to ensuring the physical stability or enhancing solubility of low-T(g) drugs. Further, hot melt extrusion, which can reduce water content, is a suitable manufacturing method for solid dispersions of low-T(g) drugs.

  9. Sorption isotherms, thermodynamic properties and glass transition temperature of mucilage extracted from chia seeds (Salvia hispanica L.).

    PubMed

    Velázquez-Gutiérrez, Sandra Karina; Figueira, Ana Cristina; Rodríguez-Huezo, María Eva; Román-Guerrero, Angélica; Carrillo-Navas, Hector; Pérez-Alonso, César

    2015-05-01

    Freeze-dried chia mucilage adsorption isotherms were determined at 25, 35 and 40°C and fitted with the Guggenheim-Anderson-de Boer model. The integral thermodynamic properties (enthalpy and entropy) were estimated with the Clausius-Clapeyron equation. Pore radius of the mucilage, calculated with the Kelvin equation, varied from 0.87 to 6.44 nm in the temperature range studied. The point of maximum stability (minimum integral entropy) ranged between 7.56 and 7.63kg H2O per 100 kg of dry solids (d.s.) (water activity of 0.34-0.53). Enthalpy-entropy compensation for the mucilage showed two isokinetic temperatures: (i) one occurring at low moisture contents (0-7.56 kg H2O per 100 kg d.s.), controlled by changes in water entropy; and (ii) another happening in the moisture interval of 7.56-24 kg H2O per 100 kg d.s. and was enthalpy driven. The glass transition temperature Tg of the mucilage fluctuated between 42.93 and 57.93°C. PMID:25659716

  10. Production and dissolution of nuclear explosive melt glasses at underground test sites in the Pacific Region

    SciTech Connect

    Bourcier, W.L.; Smith, D.K.

    1998-11-06

    From 1975 to 1996 the French detonated 140 underground nuclear explosions beneath the atolls of Mururoa and Fangataufa in the South Pacific; from 1965 to 1971 the United States detonated three high yield nuclear tests beneath Amchitka Island in the Aleutian chain. Approximately 800 metric tons of basalt is melted per kiloton of nuclear yield; almost lo7 metric tons of basalt were melted in these tests. Long-lived and toxic radionuclides are partitioned into the melt glass at the time of explosion and are released by dissolution with seawater under saturated conditions. A glass dissolution model predicts that nuclear melt glasses at these sites will dissolve in lo6 to lo7 yea

  11. Regional variation in energy storage strategies in American glass eels from Eastern Canada.

    PubMed

    Gaillard, Mélanie; Bernatchez, Louis; Tremblay, Réjean; Audet, Céline

    2015-10-01

    Energy status was analyzed in glass eels captured during two early waves of arrival at the mouths of the Mersey River, Nova Scotia, Canada (MR), and Grande-Rivière-Blanche, Québec, Canada (GRB), and according to their salinity preference (freshwater, brackish, or saltwater). Glass eels captured in the GRB estuary were larger, more pigmented, and exhibited higher whole-body glycogen, phospholipid, and sterol and wax ester contents. Those from MR had a higher condition index and a higher whole-body triacylglycerol content, suggesting different patterns of storage and/or use of energy reserves. Within a river, a delay of two weeks in estuarine arrival was characterized by significantly lower energy reserves. No differences in energy storage were observed according to salinity preference. Thus, the results revealed the occurrence of different energy storage strategies according to glass eel migration distance and duration, but not according to salinity preference. PMID:26119597

  12. Regional variation in energy storage strategies in American glass eels from Eastern Canada.

    PubMed

    Gaillard, Mélanie; Bernatchez, Louis; Tremblay, Réjean; Audet, Céline

    2015-10-01

    Energy status was analyzed in glass eels captured during two early waves of arrival at the mouths of the Mersey River, Nova Scotia, Canada (MR), and Grande-Rivière-Blanche, Québec, Canada (GRB), and according to their salinity preference (freshwater, brackish, or saltwater). Glass eels captured in the GRB estuary were larger, more pigmented, and exhibited higher whole-body glycogen, phospholipid, and sterol and wax ester contents. Those from MR had a higher condition index and a higher whole-body triacylglycerol content, suggesting different patterns of storage and/or use of energy reserves. Within a river, a delay of two weeks in estuarine arrival was characterized by significantly lower energy reserves. No differences in energy storage were observed according to salinity preference. Thus, the results revealed the occurrence of different energy storage strategies according to glass eel migration distance and duration, but not according to salinity preference.

  13. Cape York Peninsula, Australia: A Frontier Region Undergoing a Multifunctional Transition with Indigenous Engagement

    ERIC Educational Resources Information Center

    Holmes, John

    2012-01-01

    Within Australia's tropical savanna zone, the northernmost frontier regions have experienced the swiftest transition towards multifunctional occupance, as a formerly flimsy productivist mode is readily displaced by more complex modes, with greater prominence given to consumption, protection and Indigenous values. Of these frontier regions, Cape…

  14. Hypernetted-chain investigation of the random first-order transition of a Lennard-Jones liquid to an ideal glass.

    PubMed

    Bomont, Jean-Marc; Hansen, Jean-Pierre; Pastore, Giorgio

    2015-10-01

    The structural and thermodynamic behavior of a deeply supercooled Lennard-Jones liquid, and its random first-order transition (RFOT) to an ideal glass is investigated, using a system of two weakly coupled replicas and the hypernetted chain integral equation for the pair structure of this symmetric binary system. A systematic search in the density-temperature plane points to the existence of two glass branches below a density-dependent threshold temperature. The branch of lower free energy exhibits a rapid growth of the structural overlap order parameter upon cooling and may be identified with the ideal glass phase conjectured by several authors for both spin and structural glasses. The RFOT, signaled by a sharp discontinuity of the order parameter, is predicted to be weakly first order from a thermodynamic viewpoint. The transition temperature T(cr) increases rapidly with density and approximately obeys a scaling relation valid for a reference system of particles interacting via a purely repulsive 1/r(18) potential.

  15. No meridional plasma flow in the heliosheath transition region.

    PubMed

    Decker, Robert B; Krimigis, Stamatios M; Roelof, Edmond C; Hill, Matthew E

    2012-09-01

    Over a two-year period, Voyager 1 observed a gradual slowing-down of radial plasma flow in the heliosheath to near-zero velocity after April 2010 at a distance of 113.5 astronomical units from the Sun (1 astronomical unit equals 1.5 × 10(8) kilometres). Voyager 1 was then about 20 astronomical units beyond the shock that terminates the free expansion of the solar wind and was immersed in the heated non-thermal plasma region called the heliosheath. The expectation from contemporary simulations was that the heliosheath plasma would be deflected from radial flow to meridional flow (in solar heliospheric coordinates), which at Voyager 1 would lie mainly on the (locally spherical) surface called the heliopause. This surface is supposed to separate the heliosheath plasma, which is of solar origin, from the interstellar plasma, which is of local Galactic origin. In 2011, the Voyager project began occasional temporary re-orientations of the spacecraft (totalling about 10-25 hours every 2 months) to re-align the Low-Energy Charged Particle instrument on board Voyager 1 so that it could measure meridional flow. Here we report that, contrary to expectations, these observations yielded a meridional flow velocity of +3 ± 11 km s(-1), that is, one consistent with zero within statistical uncertainties.

  16. Integrating fuzzy logic and statistics to improve the reliable delimitation of biogeographic regions and transition zones.

    PubMed

    Olivero, Jesús; Márquez, Ana L; Real, Raimundo

    2013-01-01

    This study uses the amphibian species of the Mediterranean basin to develop a consistent procedure based on fuzzy sets with which biogeographic regions and biotic transition zones can be objectively detected and reliably mapped. Biogeographical regionalizations are abstractions of the geographical organization of life on Earth that provide frameworks for cataloguing species and ecosystems, for answering basic questions in biogeography, evolutionary biology, and systematics, and for assessing priorities for conservation. On the other hand, limits between regions may form sharply defined boundaries along some parts of their borders, whereas elsewhere they may consist of broad transition zones. The fuzzy set approach provides a heuristic way to analyse the complexity of the biota within an area; significantly different regions are detected whose mutual limits are sometimes fuzzy, sometimes clearly crisp. Most of the regionalizations described in the literature for the Mediterranean biogeographical area present a certain degree of convergence when they are compared within the context of fuzzy interpretation, as many of the differences found between regionalizations are located in transition zones, according to our case study. Compared with other classification procedures based on fuzzy sets, the novelty of our method is that both fuzzy logic and statistics are used together in a synergy in order to avoid arbitrary decisions in the definition of biogeographic regions and transition zones. PMID:22744774

  17. Integrating fuzzy logic and statistics to improve the reliable delimitation of biogeographic regions and transition zones.

    PubMed

    Olivero, Jesús; Márquez, Ana L; Real, Raimundo

    2013-01-01

    This study uses the amphibian species of the Mediterranean basin to develop a consistent procedure based on fuzzy sets with which biogeographic regions and biotic transition zones can be objectively detected and reliably mapped. Biogeographical regionalizations are abstractions of the geographical organization of life on Earth that provide frameworks for cataloguing species and ecosystems, for answering basic questions in biogeography, evolutionary biology, and systematics, and for assessing priorities for conservation. On the other hand, limits between regions may form sharply defined boundaries along some parts of their borders, whereas elsewhere they may consist of broad transition zones. The fuzzy set approach provides a heuristic way to analyse the complexity of the biota within an area; significantly different regions are detected whose mutual limits are sometimes fuzzy, sometimes clearly crisp. Most of the regionalizations described in the literature for the Mediterranean biogeographical area present a certain degree of convergence when they are compared within the context of fuzzy interpretation, as many of the differences found between regionalizations are located in transition zones, according to our case study. Compared with other classification procedures based on fuzzy sets, the novelty of our method is that both fuzzy logic and statistics are used together in a synergy in order to avoid arbitrary decisions in the definition of biogeographic regions and transition zones.

  18. Luminescence properties of gallium phosphate glass doped with trivalent titanium ions

    SciTech Connect

    Batyaev, I.M.; Golodova, I.V.

    1994-07-01

    Luminescence properties of gallium phosphate glasses doped with trivalent titanium ions are studied. The glasses luminesce in the 680- to 880-nm region (the {sup 2}E{sub g}-{sup 2}T{sub 2g} transition in the distorted octahedral field) and can be used as matrices for the development of luminophors in the near infrared region. 8 refs., 2 figs.

  19. Irreversibility temperatures in superconducting oxides: The flux-line-lattice melting, the glass-liquid transition, or the depinning temperatures

    SciTech Connect

    Xu, Y.; Suenaga, M. )

    1991-03-01

    The magnetic-field dependence of the irreversibility temperatures follows an {ital H}={ital a}(1{minus}{ital T}{sub {ital r}}({ital H})/{ital T}{sub {ital c}}(0)){sup {ital n}} relationship with {ital n}{congruent}1.5, for pure and alloyed YBa{sub 2}(Cu{sub 1{minus}{ital x}}M{sub {ital x}}){sub 3}O{sub 7+{delta}} with {ital x}=0 and 0.02, where {ital M}=Al, Fe, Ni, and Zn, measured for an applied field parallel to the {ital c} axis. However, for {ital M}=Ni and {ital x}=0.04 and 0.06, {ital n}{congruent}2.0. This relationship is not applicable for either Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} or (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} powders. It is also shown that the irreversibility temperature is a strong function of the magnetic hysteresis width {Delta}{ital M} for pure and alloyed YBa{sub 2}Cu{sub 3}O{sub 7}. These results and the measurements of the flux creep {Delta}{ital M}({ital t}) for these specimens suggest that {ital T}{sub {ital r}}({ital H}) is a depinning line rather than a lattice melting or glass-to-liquid phase-transition temperature. However, the conventional flux-creep model cannot account for all of the observed temporal dependences of {Delta}{ital M}({ital t}).

  20. When is a single molecule heterogeneous? A multidimensional answer and its application to dynamics near the glass transition

    NASA Astrophysics Data System (ADS)

    Verma, Sachin Dev; Vanden Bout, David A.; Berg, Mark A.

    2015-07-01

    Even for apparently simple condensed-phase processes, bulk measurements of relaxation often yield nonexponential decays; the rate appears to be dispersed over a range of values. Taking averages over individual molecules is an intuitive way to determine whether heterogeneity is responsible for such rate dispersion. However, this method is in fundamental conflict with ergodic behavior and often yields ambiguous results. This paper proposes a new definition of rate heterogeneity for ergodic systems based on multidimensional time correlation functions. Averages are taken over both time and molecules. Because the data set is not subdivided, the signal-to-noise ratio is improved. Moment-based quantities are introduced to quantify the concept of rate dispersion. As a result, quantitative statements about the fraction of the dispersion due to heterogeneity are possible, and the experimental noise is further averaged. The practicality of this approach is demonstrated on single-molecule, linear-dichroism trajectories for R6G in poly(cyclohexyl acrylate) near its glass transition. Single-molecule averaging of these data does not provide useful conclusions [C. Y. Lu and D. A. Vanden Bout, J. Chem. Phys. 125, 124701 (2006)]. However, full-ensemble, two- and three-dimensional averages of the same data give clear and quantitative results: the rate dispersion is 95% ± 5% due to heterogeneity, and the rate exchange is at least 11 times longer than the mean rotation time and possibly much longer. Based on these results, we suggest that the study of heterogeneous materials should not focus on "ensemble" versus "single-molecule" experiments, but on one-dimensional versus multidimensional measurements.