Showing papers on "Glass transition published in 1972"

Thermal behavior of annealed organic glasses

Abstract: The influence of annealing processes on the thermal behavior of organic glasses in the glass-transition interval has been investigated and analyzed quantitatively. In detailed annealing studies of atactic polystyrene and Aroclor 5460, the absorption of thermal energy superposed on the increase in the specific heat at the glass transition, observed with suitably chosen heating rates, was followed by the differential thermal method. It is concluded that the absorption of thermal energy observed under these conditions parallels the extent of molecular relaxation that has taken place during the annealing period. It is not necessary to postulate a first-order process to account for the energy absorption. Moreover, such a postulate leads to severe conceptual difficulties regarding the development of crystallinity in crystallizable materials. The areas and the shapes of the endotherms are considered in terms of the original physical properties of the quenched glasses and the anticipated equilibrium properties. Relationships between the extent of energy absorption and time-dependent processes such as volume relaxation are discussed.

Anomalous Viscoelastic Behavior of Metallic Glasses of Pd–Si‐Based Alloys

Abstract: The temperature and the stress dependence of viscoelastic properties of metallic glasses of three compositions: Pd0795Au004Si0165, Pd0795Ag004Si0165 and Pd0775Cu006Si0165 have been studied near the glass temperature The total retarded tensile compliance of these alloy glasses, Jd0 is small at low temperature (of the order of glass compliance Jg) but increases rapidly in a narrow temperature range when the temperature approaches Ta, at which the viscosity of the glass attains 1012 P, and attains a value as high as 200 times the glass compliance Jg for the Pd0775Cu006Si0165 glassy alloy, at T > Ta + 15°K Concurrent with an increase in Jd0 near Ta, the alloy liquids become non‐Newtonian in the stress range employed (σ varies from 6×106 to 3×108 dyn/cm2) The apparent shear activation volume for the viscous flow deduced from the non‐Newtonian behavior increases with temperature and attains a value as high as 100 times the atomic volume These results have been compared with viscoelastic beha

Quartz and feldspar glasses produced by natural and experimental shock

Abstract: Refractive index, density, and infrared absorption studies of naturally and experimentally shocked-produced glasses formed from quartz, plagioclase, and alkali-feldspar confirm the existence of two main groups of amorphous forms of the framework silicates: solid-state and liquid-state glasses. These were apparently formed as metastable release products of high-pressure-phases above and below the glass transition temperatures. Solid-state glasses exhibit a series of structural states with increasing disorder caused by increasing shock pressures and temperatures. They gradually merge into the structural state of fused minerals similar to that of synthetic glasses quenched from a melt. Shock-fused alkali feldspars can, however, be distinguished from their laboratory-fused counterparts by infrared absorption and by higher density.

Bound rubber in elastomers: Analysis of elastomer-filler interaction and its effect on viscosity and modulus of composite systems

Abstract: Bound rubber measurement may be very misleading as a measure of elastomer–carbon black interaction because sometimes only part of the apparently bound rubber is truly adsorbed on the carbon black surface. A theory is proposed which utilizes bound rubber measurements, but separates truly adsorbed rubber from other insoluble gel and enables calculation of the adsorbed elastomer layer thickness, a numerical value of interaction. Measurements of interaction were obtained for many different rubbers, including polybutadienes, styrene–butadienes, EPDMs, and butyl, with several different furnace blacks. An equation for viscosity of a rubber–carbon black composite is proposed, based on the degree of interaction obtained from the theory and the possible varying degree of orientation of the composite as the rate of shear is changed. This has been applied experimentally both to soluble elastomers and to an elastomer containing a nonrigid gel. The modulus of a vulcanized composite is shown to be related to the effective volume fraction of filler, which is equivalent to the volume fraction of filler plus adsorbed rubber, at temperatures above the glass transition temperature, regardless of the type of rigid filler. Below the glass transition temperature, the modulus depends only on the filler volume concentration.

Chemical aspects of glass formation in telluride systems

Abstract: The compositional dependence of the electrical activation energy, the optical absorption and the glass transition temperature in typical binary, pseudo-binary and ternary glass forming telluride systems has been measured in an effort to correlate chemical binding with physical properties. A modification of the valency satisfaction model to include chemical ordering effects is required to account for the property singularities observed in the GeTe system at the composition GeTe2. The ordering effects in Te-based alloys containing Ge are further verified by an endothermic disordering reaction in these liquids peaking between 400–475°C depending on composition.

Glass formation and D.S.C. data in the GeTe and AsTe memory glass systems

Abstract: The glass forming regions for 2.0 g liquid nitrogen quenched melts in the GeTe and AsTe systems are reported, together with glass transition temperatures, metastable melt crystallization temperatures and calorimetric data for glass powder heated at 5°C/min in an argon atmosphere under standardised conditions. Various elemental additions such as B, Al, Si, P, S, Ga, As, Se, In, I and Tl have been substituted for Te in the basic Ge 15 Te 85 eutectic and a possible role of these minor additions in prolonging device lifetime is discussed. The element aluminium has been found to have a beneficial effect on glass formation in telluride systems and a new glass forming region, AlAsTe, is separately reported in the appendix.

Thermally induced phase separation of polystyrene‐poly(vinyl methyl ether) mixtures

Abstract: Past differential scanning calorimetry and dielectric relaxation measurements have established that polystyrene (PS)-poly(vinyl methyl ether) (PVME) mixtures exhibit a degree of compatibility when cast from toluene, whereas they are incompatible when cast from chloroform or trichloroethylene. The present study reports that toluene-cast mixtures can be phase-separated by thermal treatment at temperatures exceeding 125°C. This is true for samples containing 20–80 wt-% PS. The temperature of phase separation varies with heating rate; isothermal heating times needed to cause phase separation increase rapidly as the temperature approaches 125°C. Reversibility of the phase separation process depends upon such factors as cooling rate, annealing time, treatment temperature, and thermal history. By annealing and/or slow cooling, all thermally phase-separated mixtures have been brought back to their original state of compatibility. That is, there is no evidence for true irreversiblity of phase separation in thermally treated samples. Quench-cooled samples remain phase-separated indefinitely at room temperature, but this is attributed to rapid cooling below the glass transition of the PS. Chloroform-cast and trichloroethylene-cast mixtures have not been brought to a compatible state by thermal treatment, even after lengthy annealing and slow cooling steps.

The switching behaviour of thin films of chalcogenide glass

Abstract: Studies have been made of the temperature dependence of the switching characteristics of thin and thick chalcogenide switches. The onset of break down in both can be described quantitatively be thermal avalanching, although in the former switching disappears at the glass transition temperature. This observation, together with a large activation energy (1·6 ev) deduced from measurement of the recovery time after a single switching event, have been used to formulate a qualitative model of the switching action, after breakdown. It has been suggested that at the glass transition temperature a hightly-conducting phase is precipitated out of the glass matrix to stabilize the temperature, so preventing dielectric breakdown and enabling repeated switching from a resistive to a conducting state.

Perfluoroalkylene‐linked aromatic polyimides. II. Further property studies

Abstract: The synthesis and general physical characteristics of the perfluoroalkylene-linked aromatic polyimides have been discussed in Part I. In this paper the hydrolytic, oxidative, and thermal stabilities of these polymers are compared with those of certain wholly aromatic polyimides. Comparative studies are also made on the effect of the fluoroalkylene chain on the glass transition temperatures. The polymer from di-(4-aminophenyl) ether and 1,3-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride has been studied in most detail and various mechanical and electrical properties of this polymer in film and solid molded form are discussed.

Dielectric composition capable of electrical activation

Abstract: A dielectric composition, and layered structure thereof, comprising a dielectric polymeric binder, for example, a polyimide having a glass transition temperature of at least 100*C., and normally dielectric filler particles having smooth rounded edges, for example, spheroidal or nodular non-conductive aluminum particles, dispersed therein, which composition is capable of becoming conductive on exposure to an activating potential.

Compositional dependence of the thermal, structural, and electrical properties of AsTeI glasses

Abstract: Thermal, structural, and electrical properties of semiconducting AsTeI (and AsTe) glasses have been examined as a function of concentration. Analytical techniques have been developed for quantitative chemical analysis of all three components. Differential scanning calorimetry data indicate a broad endothermic reaction, Tmin ∼ 145 °C, above the glass transition (Tg = 120 ± 8 °C) for iodine compositions of 0 to ∼ 20 at%. Above this reaction temperature the thermal data are composition dependent. For glasses with I ⪆ 35 at %, Tg is much lower (65–70 °C) and the endothermic reaction is much sharper with a minimum at ∼ 133 °C. The wide variation in thermal properties with composition suggests that electrical effects associated with high temperatures (e.g. switching and memory phenomena) may also be composition dependent, as well as being dependent upon kinetics. Structural studies show that phase segregation above Tg is dependent upon kinetics as well as upon temperature. Thermal, structural, and electrical data give evidence that As2Te3 exists as a unit in the non-crystalline state. This structural unit, stable at high temperatures, is present in the molten material and is thought to be present as the supercooled liquid is quenched. The short-range order extends to long-range order upon devitrification and the first crystalline phase detected is monoclinic As2Te3. Apparently metastable under the conditions of formation, this phase converts to a previously unreported fcc phase upon further heat treatment. Similar crystalline structures are known to be associated with thermally- and electrically-induced memory phenomena in AsTeGe and AsTeI glasses. Density measurements at room temperature show that (1) there are no phase miscibility gaps in the glass substructure or different crystalline phases segregating as the I content is varied, and (2) there is a large change in molar volume with increasing I concentration, whereas the molar weight does not change significantly. Electrical conductivity, σ, data in the region around room temperature, show that the σ0 values, determined from σ = σ0e−E/kt, range from 102 to 103 (Ω-cm)−1. A possible dependence of σ0 on I content may be due to changes in molar volume. The more homogeneous glasses appear to show breakpoints in the σ versus 1/T data; the corresponding changes in E are only 0.02–0.06 eV, with E = 0.04 eV being most frequently observed. For As50Te50−xIx glasses, σ at a given temperature increases as the iodine concentration is increased to about 5 at % and then decreases with further increase in I content. Correspondingly there is a minimum in the E versus I concentration data at I ∼ 5 at %. Results suggest that dependence of the σ breakpoints on glass homogeneity and the variation of E with I concentration may be due to trapping effects.

Hypersonic absorption in amorphous polymers by light scattering

Abstract: Brillouin lines have been observed in the spectrum of light scattered by poly(methylmethacrylate) and, for the first time, for poly(vinylchloride). The line widths have been measured, by a special technique, as a function of temperature. The attenuation per wavelength of thermal phonons below the glass transition temperature is almost constant over a wide frequency range (5 MHz to 10 GHz). The attentuation is ascribed to the mechanical strain field round static imperfections. Above the glass transition temperature the attenuation is associated with the well-known mechanical ∝ process. The Rayleigh light scattered by these polymers and their transparency is also discussed.

Influence of diluent mobility on the plasticization of polymers

Abstract: In an attempt to formulate a general picture of the influence of diluents on the physical properties of polymers without invoking specific molecular characteristics of the diluents, a systematic study has been undertaken of the mobility of both the polymer and the diluent in polymer‐diluent systems, and of the resulting effects on the physical properties of these systems. In dynamic mechanical and dielectric loss studies of polymer‐diluent systems, the influence of the mobility of the diluent on the background loss as well as on the loss associated with subsidiary relaxation transitions has been followed as a function of temperature and correlated with the temperature dependence of the modulus, over temperature ranges which include the low‐temperature γ and β transitions. The temperature ranges of plasticization and antiplasticization have been established for bisphenol A polycarbonate and atactic polystyrene plasticized with various phthalates and chlorinated biphenyls and terphenyls, which were selected to have a wide range of glass transition temperatures and plasticizing efficiencies.

The decay of free radicals in polymer media

Abstract: Kinetic laws and particularities of migration mechanisms of free valence in the processes of decay of free radicals in polymers are dealt with. The basic examples correspond to the results for polyethylene and polymethyl methacrylate. The kinetics of the decay reactions are discussed from the viewpoint of Waite's cage diffusion theory and Levedev's model. From the kinetic data of various authors the cage radius and diffusion coefficient are calculated. With increasing temperature the cage radius in polyethylene increases from 5.3a (120°K) to 40–60 a (360°K) and it has to be looked upon as an effective kinetic parameter. The diffusion coefficient corresponding to free valence displacement at long distances is in the range 10−16 to 10−18 cm2 s−1. In amorphous polymers at temperatures exceeding the glass temperature diffusion proves to be of major importance for long-distance migration. In a series of other examples, chemical reactions play a more important role, such as hydrogen atom transfer and radical decomposition. Results of measurement of the corresponding elementary reaction compared with the rate constants of decay are mentioned. Under real conditions, migration is affected simultaneously by both diffusion and chemical mechanisms.

Ductile and brittle behavior of amorphous polymers. Relationship with activation energy for glass transition and mechanical fracture

Abstract: An equation correlating the activation energy for the glass transition with TR, a characteristic reference temperature, the fractional free volume, and the rate of change of the fractional free volume was developed. The resultant activation energies for about 30 polymers are given and favorably compare with the literature. The relationship between the activation energy and the bond-rupture energy indicates whether a polymer will fail in a ductile or brittle fashion. More accurate results are shown to be dependent on the stress, the stress concentration, molecular orientation, frequency of load application, and temperature. Equations correlating all these with the activation energies are given. These results are in agreement with the molecular domain model. Experimental observations from the literature seem to corroborate the suggestion that the molecular domain model holds in the amorphous solid, too.

Calorimetric and Magnetic Studies of Crystalline and Glassy Bis[N-(3-methoxysalicylidene)isopropylamine]nickel(II)

Abstract: Thermal and magnetic properties of Ni(3-CH3O-SAL·iso-C3H7)2 were investigated by measuring thermograms, infrared and electronic spectra, heats of solution, magneitc susceptibilities, and heat capacities around glass transition temperature. In addition to the known paramagnetic crystalline phase III and the diamagnetic crystalline phase IV, two new crystalline phases (I and II) were discovered. Phase I was found to be paramagnetic, its molecular geometry being of a tetrahedral four-coordinated form like that of phase III, while phase II, similar to phase IV, is diamagnetic and has a square-planar four-coordinated form. Although the order of thermodynamic stability of these four crystalline phases was not determined, they were isolated stably at room temperature. The supercooled liquid and glassy states of this compound were realized for the first time by quenching the sample in the molten state. Unusual magnetic behaviors of these two states were satisfactorily accounted for by assuming an equilibrium betw...

The Relationship of Glass Transition Temperature to Adhesive Strength

Abstract: The effects of glass transition temperature (Tg ) on mechanical properties have been further demonstrated by the observation of adirect relationship between the Tg of an epoxy adhesive and its lap shear bond strength to metal at elevated test temperatures. An additive (coupling agent) which lowers the Tg from a point near or above the test temperature to below it causes a subsequent decrease in the strength of the system and generally increased cohesive failure. Therefore effects on the Tg of the adhesive are more important than on interfacial properties. The end result is that differential thermal analysis (DTA) can be utilized as a effective screening method for adhesives and additives, and can be a good indicator of maximum use temperature. From these data Tg can also be used to estimate adhesive strength at a given use temperature.

Glass-forming region and DTA survey of some glasses in the Si-Ge-As-Te threshold switching glass system

Abstract: The glass forming region for 2.0 g melts in the Si-As-Te system and pseudo ternary Si 5%-Ge-As-Te and Si 10%-Ge-As-Te systems are reported together with glass transition temperatures and metastable glass melt crystallisation temperatures for bulk glass pieces of different compositions heated at 20°C/min under standardised conditions in a nitrogen atmosphere.

Flexible thermosetting acrylic coating compositions

Abstract: The thermosetting acrylic enamel has as film-forming constituents A POLYBLEND OF A RELATIVELY HARD ACRYLIC POLYMER THAT HAS A GLASS TRANSITION TEMPERATURE OF GREATER THAN -20*C, and a soft acrylic polymer that has a glass transition temperature of less than -20*C, wherein the difference in glass transition temperature between the hard and soft acrylic polymer is at least 30*C; and A HEAT REACTIVE CONDENSATE SUCH AS HEXA-(METHOXYMETHYL)MELAMINE, A BUTYLATED OR METHYLATED MELAMINE FORMALDEHYDE RESIN, OR A POLYISOCYANATE THAT IS COMPATIBLE WITH THE POLYBLEND; THE ACRYLIC ENAMEL FORMS A FLEXIBLE, DURABLE FINISH USEFUL FOR EXAMPLE FOR RUBBER-COATED AUTOMOBILE AND TRUCK BUMPERS, AS A FINISH FOR PLASTICS FOR FOAMED STRUCTURES, FOR FLEXIBLE METAL SUBSTRATES, FOR EXAMPLE, FOR COIL COATINGS

Free volume and the annealing and antiplasticizing of bisphenol A polycarbonate

Abstract: Annealing below the glass transition temperature and the addition of an antiplasticizer are each known to increase the yield stress and the density of glassy bisphenol A polycarbonate. We have studied the combined effects of annealing and antiplasticizing to see if the individual effects would interfere with one another, as might be expected if the same free volume were involved in each. We find that the effects, even when they individually approach saturation, remain additive. This suggests that the free volume in the glass has at least two parts, one of which is affected by annealing and the other by antiplasticization. The available data indicate that the rate at which the yield stress changes with measured volume is different for the two parts.

Domain structure and bulk properties of solvent‐cast films of A–B–A block copolymers of styrene‐isoprene‐styrene

Abstract: Domain structures of solvent-cast films of A–B–A block copolymers of styrene-isoprene-styrene were studied by electron microscopy by use of the OsO4 fixation technique. The effects of varying proportions of the two components and the casting solvent upon the domain structures were examined. It is concluded that the domain formation mechanism can be discussed like that of A–B block copolymers irrespective of sequence arrangements, as Matsuo et al. suggested, by treating A–B–A or B–A–B block copolymers as A–(1/2)B or B–(1/2)A block copolymers. The five types of fundamental domain structures—spherical domains of component A in a matrix of component B, rodlike domains of A in a matrix of B, alternating lamellae of the two components, rodlike domains of B in a matrix of A, and spherical domains of B in a matrix of A—are achieved mainly by the change of the fractional composition of the two components for a given solvent. One of the most significant features of the A–B–A block copolymers in contrast to the A–B block copolymers, i.e., that A–B–A chains can interconnect two A domains, was explored by investigating (1) the swelling behavior in a solvent that is a good one for isoprene but a nonsolvent for styrene and (2) mechanical behavior above the glass transition temperature of the styrene segments.