Showing papers on "Glass transition published in 1986"
TL;DR: A general survey of glass transition phenomena and concepts is presented in an introductory section as discussed by the authors, and the physical significance of computer simulations of glass transitions in simple liquids and the question of a hidden phase transition underlying an observed glass transition are examined critically.
Abstract: The different physical aspects of glass transitions are reviewed and models aiming at their explanation are described. The following three main aspects are distinguished: the degree of stability of supercooled liquids with respect to crystallisation; the variation of physical properties of supercooled liquids in metastable equilibrium above the glass transition; the arrest of structural relaxation at the glass transition. The physical significance of computer simulations of glass transitions in simple liquids and the question of a hidden phase transition underlying an observed glass transition are examined critically. In relation to the stability problem, the geometrical constraints operative in typical disordered structures, such as random sphere packings and random covalent networks, are also discussed. A general survey of glass transition phenomena and concepts is presented in an introductory section.
777 citations
Book•
24 Apr 1986
TL;DR: In this article, the authors present a model of structural relaxation in OXIDE GLASSES, including the Sandwich Seal and the Composite Cylinder, as well as the split ring composite.
Abstract: VISCOELASTICITY IN OXIDE GLASSES. The Glass Transition. Elasticity and Viscoelasticity. Linear Viscoelastic Behavior in Oxides. Experimental Studies of Relaxation and Creep. Thermorheological Simplicity. Unstabilized Glass. The Visoelastic Analogy. The Sandwich Seal. STRUCTURAL RELAXATION Fictive Temperature. Phenomenological Model of Structural Relaxation Time. Universality of Glass Transition Phenomena. RELAXATION IN COMPOSITES. Relaxation in the Sandwich Seal. Composite Cylinder. Composite Sphere. Split Ring Composite. Interrelating Setting Temperatures. Elastic-Clad Composites. Glass-to-Glass Composites. Approximate Methods of Viscoelastic Analysis. Appendixes. Index.
649 citations
TL;DR: In this article, results of thermal analysis performed at different heating rates on eight glasses of the As-Sb-Se system, with compositions represented by (As, Sb) 40 Se 60 and As x Sb 15 Se 85 − x are reported and discussed.
Abstract: Results of thermal analysis performed at different heating rates on eight glasses of the As-Sb-Se system, with compositions represented by (As, Sb) 40 Se 60 and As x Sb 15 Se 85 − x are reported and discussed. The values of the glass transition temperature ( T g ), the crystallisation temperature ( T c ) and the peak temperature of crystallisation ( T p ) are found to be independent of particle size. From the heating rate dependence of T g and T p values of the activation energy for glass transition ( E t ) and the activation energy for crystallisation ( E c ) are evaluated and their composition dependence discussed. The crystallisation data are examined in terms of recent analyses developed for non-isothermal crystallisation studies to arrive at E c and details of the crystallisation mechanism. The results indicate bulk nucleation and crystallisation with two and three dimensional growth respectively for the As x Sb 15 Se 85 − x and (As, Sb) 40 Se 60 glasses.
438 citations
TL;DR: In this article, a low-temperature differential scanning calorimetry technique was used to measure the characteristic sub-zero glass transition temperature, T′ g, of a maximally freeze-concentrated aqueous solution.
427 citations
363 citations
TL;DR: In this paper, the frequency-dependent specific heat of glycerol and propylene glycol near the glass transition was measured, covering a frequency range of five decades, probing the linear response of these supercooled liquids to small perturbations from equilibrium.
Abstract: We have measured the frequency-dependent specific heat of glycerol and propylene glycol near the glass transition. The measurements, covering a frequency range of five decades, probe the linear response of these supercooled liquids to small perturbations from equilibrium. The specific heat of these two liquids contains a contribution which relaxes increasingly slowly as the temperature is lowered. The relaxation time measured by specific-heat spectroscopy has the same temperature dependence as that measured by other techniques. This suggests that a single mechanism is responsible for all of the observed phenomena associated with the glass transition in these materials.
332 citations
TL;DR: In this article, the preparation of small alloy particles by reduction of metal ions by KBH4 in aqueous solutions is described, which may have applications in ferrofluids, magnetic memory systems and catalysis.
Abstract: Amorphous alloys are normally prepared as thin ribbons or films by the liquid quench technique or by vapour deposition. Recently we have shown1 that ultra-fine amorphous Fe–C alloy particles can be prepared by thermal decomposition of Fe(CO)5 in an organic liquid; that is, by a chemical reaction. Here we report the preparation of small alloy particles by reduction of metal ions by KBH4 in aqueous solutions. Mossbauer and X-ray diffraction studies show that the particles are amorphous. The amorphous phase is formed because the chemical reaction takes place below the glass transition temperature and because boron atoms are present in the particles. The method may be used for the large-scale production of ultra-fine amorphous alloy particles, which may have applications in ferrofluids, magnetic memory systems and catalysis.
291 citations
TL;DR: Copolymeres segmentes a base de polyoxypropylene contenant 30,4% en poids d'oxyde d'ethylene were used in this article.
Abstract: Copolymeres segmentes a base de polyoxypropylene contenant 30,4% en poids d'oxyde d'ethylene
270 citations
TL;DR: The water of hydration in myoglobin crystals and solutions was studied at subzero temperatures by calorimetry and infrared spectroscopy and a hydrogen bond network model is proposed to explain these features.
213 citations
TL;DR: In this article, Li conductive glasses with the composition xLi 2 S(1-x)SiS 2 [x ⩽ 0.6] have been prepared by twin roller quenching.
159 citations
TL;DR: In this paper, the effect of variations in the amine-to-epoxy ratio r on the glass transition temperature Tg is examined and a method is developed to determine the activation energy.
Abstract: Differential Scanning Calorimetry (DSC) is used to study the curing behavior of epoxy systems. For non-catalyzed diamine-epoxy systems, the reaction enthalpy ΔH and the glass transition temperature Tg are evaluated and related to the structure of the hardener. A method is developed to determine the activation energy. The effect of variations in the amine-to-epoxy ratio r on Tg is also examined. A maximum value is observed for r = 1. Then, the influence of benzyldimethylamine as catalyst in an anhydride/DGEBA system and in three diamine/DGEBA systems is reported. In the cases of DDS and DDA curing agent the maximum value of Tg is shifted, to r = 0, 6. The results are explained by different reaction mechanisms.
TL;DR: In this article, the lead-iron phosphate nuclear waste glasses were prepared by dissolving simulated US defense wastes or simulated commercial power reactor wastes in molten lead-irony phosphate melts at temperatures between 900 and 1050°C and the measured physical and chemical properties of the nuclear waste glass formed by cooling these melts and annealing included the following: (1) aqueous corrosion resistance as a function of the solution pH, solution temperature, and glass composition, (2) glass density, (3) thermal expansion coefficient, (4) glass transition temperature and softening point,
Abstract: Experimental determinations of the properties of lead-iron phosphate glasses pertinent to their application to the problem of the permanent disposal of high-level nuclear wastes have been carried out. These investigations included studies of the composition and physical properties of nuclear waste glasses (NWG), as well as the effect of preparation conditions. Lead-iron phosphate nuclear waste glasses were prepared by dissolving simulated US defense wastes or simulated commercial power reactor wastes in molten lead-iron phosphate melts at temperatures between 900 and 1050°C. The measured physical and chemical properties of the nuclear waste glasses formed by cooling these melts and annealing included the following: (1) aqueous corrosion resistance as a function of the solution pH, solution temperature, and glass composition, (2) glass density, (3) thermal expansion coefficient, (4) glass transition temperature and softening point, (5) heat capacity, (6) critical rate (7) temperature for the maximum crystallization rate, (8) relative solubility of waste oxides in the glass melt, (9) reactions between the molten glass and the melting crucible (Pt, ZrO2, Al2O3), and (10) studies of possible metal cannister materials. Experimental results for the lead-iron phosphate NWG are compared to available data for borosilicate NWG. Relative to borosilicate NWG, the lead-iron phosphate glasses have several distinct advantages which include a much lower aqueous corrosion rate, a lower preparation temperature, and the ability to immobilize many types of commercial and defense-related high-level radioactive wastes.
TL;DR: Although indomethacin remained as a glass for 2 years at room temperature, pulverized glassy indometHacin was found to crystallize, and the rate of crystallization was determined by the X-ray diffraction method and followed first-order kinetics.
Abstract: Glassy indomethacin was prepared by cooling the melt, and the glassy state was confirmed by the jump of heat capacity and the anomalous endothermic park (heat capacity maximum) in the differential scanning calorimetry (DSC) curve. The influences of the cooling rate of the melt and the heating rate of the glass formed on the glass transition temperature (Tg) were examined, and the apparent activation energy of glass transition was calculated to be 212.5kJ/mol. The relaxation process below Tg was traced in terms of the area under the anomalous endothermic park of the DSC curve and the rate of relaxation during annealing was found to reach the maximum at about 303 K. The rate of dissolution of glassy indomethacin was far greater than that of crystalline indomethacin. Although indomethacin remained as a glass for 2 years at room temperature, pulverized glassy indomethacin was found to crystallize, and the rate of crystallization was determined by the X-ray diffraction method. The degree of crystallization was determined by Hermans' method, and was found to reach a maximum of 60% after 2 months. The process of crystallization followed first-order kinetics.
TL;DR: In this paper, electrical conductivity and relaxation studies have been carried out on Parel 58 elastomer with a variety of lithium salts in vacuum over the temperature range 5-380 K and at pressures up to 0.65 GPa.
Abstract: Audio frequency electrical conductivity and relaxation studies have been carried out on Parel 58 elastomer and Parel 58 elastomer complexed with a variety of lithium salts. The measurements have been carried out in vacuum over the temperature range 5–380 K and at pressures up to 0.65 GPa over the temperature range 230–380 K. Both the electrical conductivity for the complexed material and the electrical relaxation time associated with the α relaxation in the uncomplexed material exhibit VTF or WLF behavior. From a VTF analysis for both the vacuum electrical relaxation time and electrical conductivity, Ea is found to be about 0.09 eV and T0 is found to be about 40 °C below the ‘‘central’’ glass transition temperature. In addition, it is found that the activation volumes for the electrical relaxation time and the electrical conductivity are the same when compared relative to T0. These results imply that the mechanism controlling ionic conductivity is the same as that for the α relaxation, namely large‐scale segmental motions of the polymer chain.
Patent•
18 Dec 1986TL;DR: A solid photopolymerizable composition as mentioned in this paper contains polymerizable ethylenically unsaturated monomer, initiating system, polymer binder and a microgel, where the polymer and microgel form substantially a single phase and have a similar glass transition temperature above 25°C.
Abstract: A solid photopolymerizable composition, contains addition polymerizable ethylenically unsaturated monomer, initiating system, polymer binder and a microgel wherein preferably the binder and microgel form substantially a single phase and have a similar glass transition temperature above 25° C. Although less preferred the solid composition can function without the binder. A preferred use is as a photoresist.
TL;DR: In this article, the authors determined the free-volume hole sizes in amine-cured epoxy polymers by comparing the observed ortho-positronium lifetimes with the known lifetime-free volume correlation for low-molecular-weight systems.
Abstract: Positronium annihilation spectroscopy (PAS) has been used to study the microstructural properties of amine-cured epoxy polymers. We have determined the free-volume “hole” sizes in these polymers by comparing the observed ortho-positronium lifetimes with the known lifetime–free volume correlation for low-molecular-weight systems. The free volumes for four epoxies with different crosslink densities are found to vary significantly over the temperature range between −78° and 250°C. The free-volume holes for these polymers are found to range from 0.025 to 0.220 nm3. Two important transition temperatures were found: one corresponds to the glass transition temperature Tg determined by differential scanning calorimetry (DSC), and the other occurs about 80–130°C below Tg. The sub-Tg transition temperature is interpreted tentatively as being where hole size reaches dimensions adequate for positronium trapping or else the onset temperature for local mode or side-chain motions. These two transition temperatures plus two additional onset temperatures are found to be correlated with crosslink densities calculated from stoichiometry.
TL;DR: In this article, the annealing time dependence of enthalpy relaxation of a sample of polycarbonate pre-annealed at various temperatures close to the glass transition temperature, Tg, is investigated over an extended range to check the consequences implied by a previous treatment.
TL;DR: In this article, a spin glass model on the Bethe lattice is formulated and studied, and it is shown that there is a transition temperature above which the single-site magnetizations vanish, and below which the Edwards-Anderson order parameter is strictly positive.
Abstract: We formulate and study a spin glass model on the Bethe lattice. Appropriate boundary fields replace the traditional self-consistent methods; they give our model well-defined thermodynamic properties. We establish that there is a spin glass transition temperature above which the single-site magnetizations vanish, and below which the Edwards-Anderson order parameter is strictly positive. In a neighborhood below the transition temperature, we use bifurcation theory to establish the existence of a nontrivial distribution of single-site magnetizations. Two properties of this distribution are studied: the leading perturbative correction to the Gaussian scaling form at the transition, and the (nonperturbative) behavior of the tails.
TL;DR: In this article, a brittle-ductile transition was observed in the Kc−T curve of poly(ether ether ketone) (PEEK) and its short glass-fibre reinforced composite.
TL;DR: In this paper, the solvent evaporation process has been used to form progesterone-loaded microspheres from poly( d,l -lactide). Methylene chloride was the casting solvent.
TL;DR: In this article, the solid-liquid phase diagram, experimental glass transition points, densities, viscosities, and electrical conductivities of the aluminum bromide ionic liquid are reported.
Abstract: The solid‐liquid phase diagram, experimental glass transition points, densities, viscosities, and electrical conductivities of the aluminum bromide‐1‐methyl‐3‐ethylimidazolium bromide ionic liquid are reported. Certain compositions of this two‐component molten salt are liquid at room temperature. Density, viscosity, and conductivity data were collected over the range of aluminum bromide mole fractions from ca. 0.35 to 0.75 and over the range of temperatures from ca. 25° to 100°C. Equations are presented that describe both the composition and temperature dependence of the densities and transport properties. Both the viscosities and the conductivities display the non‐Arrhenius temperature dependence typically associated with glass forming ionic liquids. Temperature‐dependent activation energies are derived for these transport processes by using the Vogel‐Tammann‐Fulcher equation.
TL;DR: Vitrification is the process by which a liquid solidifies at temperatures usually far below the normal freezing point, but without the formation of any crystalline phase as mentioned in this paper, the product is then a partially crystallized glass.
TL;DR: In this article, the preparation of oxynitride glass by melting sodium metaphosphate in anhydrous ammonia is described, and models for nitrogen dissolution are used to calculate the glass composition from the measured weight loss and analyzed nitrogen content.
Abstract: The preparation of oxynitride glass by melting sodium metaphosphate in anhydrous ammonia is described. Glasses containing up to ≈ 12 wt% nitrogen were prepared with the nitrogen content depending upon the melting temperature, time, and ammonia flow rate through the furnace. Nitriding the NaPO 3 starting glass decreased the dissolution rate in water and thermal expansion coefficient while increasing the dilatometric softening temperature, glass transition temperature, refractive index, and microhardness. Oxynitride glasses were considerably more difficult to crystallize than the starting NaPO 3 glass. Models for nitrogen dissolution are used to calculate the glass composition from the measured weight loss and analyzed nitrogen content.
TL;DR: In this paper, the dielectric permittivity and loss of poly(propylene oxide) of molecular weight 4000, PPO(4000), have been measured in the temperature range 77K-305K and frequency range 10−2 −2 × 105 Hz.
TL;DR: In this article, the dynamics in a Lennard-Jones system close to the glass transition were analyzed using a kinetic model presented in an earlier paper, based on the Zwanzig-Mori procedure for deriving formally exact transport equations combined with mode-coupling approximations.
Abstract: Numerical results on the dynamics in a Lennard-Jones system close to the glass transition are presented, using a kinetic model presented in an earlier paper. The theory is based on the Zwanzig-Mori procedure for deriving formally exact transport equations combined with mode-coupling approximations. Results for a number of different dynamical quantities of experimental interest are presented and the model is shown to reproduce many of the characteristic features of a liquid-glass transition. Comparisons are made with available computer simulation data and analytical results for the same mode-coupling model.
TL;DR: The plasticizing efficiency of polyethylene glycols when added to both ethyl cellulose and hydroxypropyl methylcellulose films has been evaluated by measuring the glass transition temperatures of formulations using the torsional braid pendulum as discussed by the authors.
TL;DR: In this paper, the Gordon-Taylor-Wood, Johnston and Barton equations have been applied to predict the glass transition temperatures, Tg of vinylidene fluoride-hexafluoropropene copolymers and VDF-HFP-tetrafluoroethene (TFE) terpolymers.
TL;DR: In this paper, differential scanning calorimetric (DSC) studies were carried out on xerographic photoreceptor materials of amorphous selenium (a-Se), a-Se 1∃-xTex and a- Se: 0.5 wt% As alloys with various amounts of chlorine doping.
Abstract: Differential scanning calorimetric (DSC) studies were carried out on xerographic photoreceptor materials of amorphous selenium (a-Se), a-Se1∃-xTex and a-Se:0.5 wt% As alloys with various amounts of chlorine doping. Glass transformation kinetics of bulk and vapour-deposited film samples were essentially identical indicating a similar amorphous structure for both forms. The glass transition temperature,Tg, in the a-Se1∃-xTexsystem was found to increase monotonically with the tellurium content up to ∼13 wt% which was accompanied by a fall in the activation energy,Egl, for the structural relaxation. 0.5wt% As increasedTg, whereas chlorine doping in the amounts used (∼100 ppm) had no effect onTg. Crystallization exotherms were analysed using the Kissinger method which was shown to remain a valid analysis by integrating the fundamental Kolmogoroff equation describing crystallization transformations by nucleation and growth. The signifiance of the activation energy,EA, and the frequency factor,C0, in the Kissinger analysis is discussed and used in interpreting the different crystallization behaviour exhibited by the various alloys. The apparent activation energy,EA, of the crystallization kinetics was found to fall with the temperature range accessed in the DSC experiment. When other authors' previous crystallization studies by other methods were also considered, then 1/EA was found to fall nearly linearly with the mean reciprocal temperature, 〈1/T〉, used in the experiment. It is argued that this behaviour arises if the crystal growth rate scales with the inverse viscosity of the melt and the latter is described by a Vogel-Tammann-Fulcher type of behaviour. The additives tellurium and arsenic retard the crystallization essentially by increasing the viscosity. Chlorine doping was also found to have an inhibitory effect but due probably to a change in the nucleation kinetics, rather than a viscosity rise.
TL;DR: In this paper, the atomic arrangement of a zinc-tellurite glass with composition 80% TeO2 + 20 mol% ZnO has been studied by means of the neutron diffraction method.