Showing papers on "Glass transition published in 1984"

Physics of amorphous materials

Abstract: Part 1 Preparation: definitions preparation of amorphous materials. Part 2 the glass transition theories for the glass transition factors that determine the glass-transition temperature glass-forming systems and ease of glass formation. Part 3 Structure: microscopic structure - experimental techniques, short-range order, medium-range order, structural modelling macroscopic structure - experimental techniques, examples of macroscopic structure. Part 4 Atomic dynamics: vibrational excitations computational methods experimental probes low-frequency modes and low temperature properties two-level systems ionic conduction. Part 5 Electrons: electronic density of states localization transport properties small polarons optical properties. Part 6 Defects: types of defect defect-controlled properties.

Crystallization and morphology of a bacterial thermoplastic: poly-3-hydroxybutyrate

Abstract: This paper presents a number of interesting results on the physical properties of poly-3-hydroxybutyrate (PHB). Data are presented on crystallization kinetics, morphology of melt- and solution-crystallized PHB, the variation of lamellar thickness with crystallization temperature, and the assessment of some thermodynamic quantities. These properties include surface free energies, heat of fusion and melting, and glass transition temperatures. It is shown that the special properties of PHB such as the large spherulite size, which is probably due to its exceptional purity, make it an ideal material for model studies of polymer crystallization and morphology. For example, we show that the variation of growth rate with crystallization temperature is consistent with the very latest theories; and that the single crystal morphology has important implications for the understanding of crystal growth in other polymer systems.

Dynamics of supercooled liquids and the glass transition

Abstract: Closed nonlinear equations are derived for a self-consistent treatment of density propagation, self-diffusion and current relaxation in a classical monatomic fluid. The solution for a hard-sphere model system brings out a phase transition to a glass at the packing fraction 0.516. Approaching the transition from the glass side the particle mean-square displacement increases to a finite value. A simplified model is analysed in detail. Approaching the transition from the liquid side the diffusivity is predicted to decrease to zero with a power law with exponent 1.76 which the authors find to agree well with some experimental data. The low-frequency density spectrum is found to consist of two contributions; one is an elastic line of the frozen structure on the glass side, which then decays to a narrow diffusion broadened quasielastic peak on the fluid side; the other part is described by a dynamical scaling law and it yields in particular a spectrum diverging at the glass point with certain exponents.

Kinetic Ising Model of the Glass Transition

Abstract: A graph theory of single-spin-flip kinetic Ising models is developed and applied to a class of spin models with strongly cooperative dynamics. Self-consistent approximations for the spin time correlation function are presented. One of the dynamical models exhibits a glass transition with no underlying thermodynamic singularity. The approximation for the time correlation function predicts a critical temperature, below which small fluctuations from equilibrium in the thermodynamic limit cannot relax in a finite amount of time.

The effect of hydrogen bonding on the glass transition temperatures of polymer mixtures

Abstract: Decouvertes preliminaires sur la Tg de melanges de i-PMMA ou s-PMMA avec des resines Novolaque

Viscoelastic properties ofin situ lignin under water-saturated conditions

Abstract: The viscoelastic properties of wood under water-saturated conditions have been studied in the temperature range 20 to 140° C at frequencies ranging between 0.05 and 20 Hz. It is demonstrated that the major transition in this temperature range is related to aglass transition, i.e. the glass transition of thein situ lignin. The difference in softening behaviour along and across the fibre direction is shown to be related to the stiffening effect of the cellulose microfibrils preferentially aligned along the fibre direction. The softening behaviour is also estimated for frequencies applicable to wood defibration processes, ∼104Hz. The implications of the wood properties under these conditions are discussed.

Thermal contraction and volume relaxation of amorphous polymers

Abstract: Two experimental techniques are described for the determination of the change of specific volume of polymers with temperature and aging time, which allow measurements between − 160 °C and + 200 °C. Four technical amorphous polymers, PS, PVC, PMMA and PC have been investigated. Volume-temperature curves under constant rate of cooling are presented and interpreted with respect to relaxation processes known from other physical investigations. The rate dependence of dilatometric glass transition temperatures is compared with the time dependence of rheometric glass transition temperatures from shear creep data. Volume relaxation data at constant aging temperature are presented. Aging is found to proceed until very low temperatures in the glassy state for e.g. PMMA.

Electro-optical effects of azo dye containing liquid crystalline copolymers

Abstract: The synthesis and phase behaviour of azo dye containing liquid crystalline side group copolymers are described. These Copolymers show the same electro-optical effects as low molar mass guest-host systems. Their macroscopic oriented nematic structure can be frozen in below the glass transition temperature resulting in a polymer film with dichroic properties. The behaviour of the copolymers (phase behaviour, surface and electric field orientation) can be improved via mixtures with low molar mass liquid crystals.

High ionic conductivity in poly(dimethyl siloxane‐co‐ethylene oxide) dissolving lithium perchlorate

Abstract: Preparation du copolymere par polycondensation de dimethyldichlorosilane avec le mono-, di-, tetra-, ou nonaethyleneglycol

The thermodynamic properties of polytetrafluoroethylene

Abstract: Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ3 of 54 K, and θ1 of 250 K, and a full set of group vibrations. Cv to Cp conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10−3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔCp of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.

Model hydrocarbon polymers: rheological properties of linear polyisoprenes and hydrogenated polyisoprenes

Abstract: Hydrogenation de polyisoprene lineaires anioniques en presence de palladium-carbonate de calcium

A liquid crystal information storage device

Abstract: A liquid crystal information storage device comprising a layer of material containing a side chain polymeric liquid crystal. At least a part of the material is heated from a viscous state above its glass transition temperature, to a fluid region in which the liquid crystalline material can readily undergo field-induced alignment. The material is addressed in this fluid region so as to achieve the selective variation in texture and orientation of molecules within the material and so record information, and the material is subsequently cooled and returned to its viscous state whereupon the information is retained.

Polymer Compatibilization Through Hydrogen Bonding

Abstract: Partially modified polystyrene containing vinyl phenyl hexafluorodimethyl carbinol was mixed with a number of counterpolymers containing poly(vinyl-acetate), poly(methyl methacry1 ate), poly(ethy] methacrylate, poly (n-butyl methacry late), poly(viny] methyl ether), poly(2,6 dimethyl-1,4 phenylene oxide), bisphenol A polycarbonate poly(styrene-co-acryloni-trile), poly (dimethyl siloxane), a crystallizable polyester, an amorphous polyamide and two amorphous polyamides. Hydrogen bonding interactions to effect miscibility were related to the number of proton donating groups in the modified polystyrene, and these were studied in regard to lower critical solution temperatures and the glass transition temperatures of the hydrogen bonded blends.

Vibrational Spectra of Me2SiCl2, Me3SiCl, Me3SiOSiMe3, (Me2SiO)3, (Me2SiO)4, (Me2SiO)x, and Their Deuterated Analogs:

Abstract: This work had three objectives: to improve the reported assignments of the vibrational frequencies in several organosilicon monomers and oligomers; to assign the vibrational frequencies of polydimethylsiloxane (PDMS); and to relate the vibrational spectra of PDMS to its other physical properties, especially at sub-ambient temperatures, Infrared and Raman spectra were obtained on the title compounds, and five sets of low-temperature IR spectra were obtained on PDMS. Some low-temperature spectra were also taken on the cyclosiloxanes. Assignment of all frequencies was accomplished, although in some cases, e.g., the methyl rocking frequencies at 650-870 cm−1 and the skeletal deformations below 400 cm−1, our confidence in their correctness is less than complete. The low-temperature study showed striking changes in the IR spectrum of PDMS below its glass transition temperature Tg, Bands became sharper and in some cases showed splitting. This behavior is consistent with the concept of polymer motion being frozen below Tg, Except for the appearance of a strong, sharp band at 662 cm−1, not much change was seen in the spectrum at the "cold crystallization" point. Possibly the expected spectral changes were swamped by absorption from the more plentiful amorphous portion of the polymer matrix.

Preparation and characterisation of V2O5B2O3 glasses

Abstract: The binary V2O5B2O3 glasses were prepared. With low V2O5 content the samples were amorphous but very unstable due to their hygroscopic character; these developed crystallinity due to B2O3 content. There was some crystallinity in compositions ranging from 30 mol.% to 50 mol.% V2O5. In higher compositions good amorphous structure was noticed. The structure was also highly dependent on the quenching rate. The physical parameters such as density, glass transition temperature and the X-ray diffraction, infrared absorption spectra are discussed with respect to all compositions. The dc electrical conductivity was measured for only those samples (70 to 90 mol.% of V2O5) which were found to be amorphous in nature. It is observed that in this glass system too, the high temperature conduction phenomenon is due to adiabatic hopping like that in V2O5TeO2 glasses. The electrical properties are highly sensitive to the thermal history of preparation of the samples.

Thermal and mechanical behavior of polycarbonate–poly(ethylene terephthalate) blends

Abstract: : Melt blends of polycarbonate and poly(ethylene terephthalate) were formed by continuous extrusion and injection-molded into bars for mechanical testing. Thermal analysis was used to ascertain transitional behavior and the level of PET crystallinity at various points in the fabrication and testing process. The mechanical properties showed little departure from additivity except for the percent elongation at break which was substantially larger for certain blends than expected. Glass transition behavior suggest two amorphous phases for PC rich mixtures and only one mixed phase in the PET rich region. Crystallizability of the PET after the blend was held or prolonged times in the melt stage suggests that interchange reactions do not occur to any great extent. Originator supplied key words include: Poly(ethylene terephthalate)(PET), PC(Polycarbonate), Polyester, Blends, Thermal Analysis, Miscibility, Interchange Reactions, Reprints.

Thermal analysis and NMR study of a poly(ethylene oxide) complex electrolyte: PEO(LiCF3SO3)x

Abstract: We have determined the equilibrium diagram between the different phases which coexist in the complexes between the poly(ethylene oxide) PEO and the salt LiCF3SO3, by using DSC and NMR techniques. We have also measured the variation of the glass transition temperature as a function of the salt concentration dTg/dx = 280 K/(mole of salt per mole of monomer unit). We show that in the temperature range 340-420 K the ionic conduction 03C3 only takes place in the amorphous phase. The thermal dependence of 03C3, previously interpreted in term of Arrhenius law, indeed results from that of three terms : the salt concentration in the amorphous phase (number of carriers), the local dynamics of the polymer chains (diffusion coefficient) and the respective amounts of crystalline and amorphous phases. The temperature dependence of each of these parameters has been estimated from experiments in the sample x-1 = 8 and they combine to give a fair description of 03C3(T). A striking result is the small temperature dependence of the diffusion coefficient (D03C3 ~ 6 x 10-8 cm2 s-1 at 375 K).

Miscibility enhancement via ion-dipole interactions. 1. Polystyrene ionomer/poly(alkylene oxide) systems

Abstract: : It is shown that ion-dipole interactions can lead t miscibility enhancement in polymer blends. While polystyrene is not miscible with poly(ethylene oxide) or poly(propylene oxide), styrene ionomers show very high miscibility with these materials at low alkylene oxide contents (10 wt %) and high, though not complete, miscibility at higher loading levels. For these systems it is seen that the glass transition temperature (from G' peak positions) of the styrene ionomer is depressed dramatically with increasing alkylene oxide contents and that the glass transition of the alkylene oxide rises appreciably (in most cases) with increasing styrene ionomer content. Increases in ion content at constant styrene levels increase the miscibility. The degree of miscibility enhancement is comparable to that achieved in hydrogen-bonded system. Finally, molecular weight effects observed here are quite similar to those seen in other blend systems.

Glass Transition Temperature of Wool as a Function of Regain

Abstract: The relation between the glass transition temperature and the water content of wool can be described by the Fox equation. Data on transitions from a wide range of sources, including mechanical, dielectric, and calorimetric measurements, are well described by the equation. The utility of the relation for understanding and interpreting experiments on the wrinkle recovery of wool fabrics is shown.

Dielectric behavior and ferroelectric transition of copolymers of vinylidene fluoride and trifluoroethylene

Abstract: Dielectric behavior of copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with VDF contents of 52 to 78 mol % has been investigated over wide frequency and temperature ranges with particular reference to the ferroelectric transition. Some related physical properties such as the dynamic tensile modulus, the thermal expansion, and the enthalpy of transition were also studied. The copolymers exhibited three dielectric relaxations γ, β, and Tt in the increasing order of temperature. The γ process is the local mode relaxation of part of frozen molecular chains below the glass transition. The β relaxation is related with micro-Brownian motions of molecular chain backbone in amorphous regions. The Tt relaxation which is featured with a rather narrow distribution of relaxation times is associated with cooperative motions of molecular chain in crystalline regions in the vicinity of the ferroelectric transition. Dielectric measurements under hydrostatic pressure revealed that the anomalou...

Viscosity and crystallization kinetics of As2Se3

Abstract: The crystallization kinetics, viscosity, and temperature coefficient of expansion of amorphous As2Se3 were investigated. The crystallization kinetics of As2Se3 are characterized under isothermal conditions for undercoolings ranging from 37°C to 122°C using thermal analysis techniques. The crystallization kinetics can be accurately described by the Johnson-Mehl-Avrami transformation equation. At least at the lower observed temperatures As2Se3 exhibits an increasing nucleation rate with respect to time. Microscopic examination of partially crystallized specimens reveals constant isothermal growth rates with respect to time and a spherulitic growth habitat for the crystalline phase. All spherulites nucleated at free surfaces. The individual As2Se3 crystallites in the spherulites have a plate-like growth morphology at temperatures well below the crystalline melting point. At temperatures approaching the crystalline melting point the crystallites assume a rod-like growth morphology. The activation energy for the crystal growth rate was determined to be 1.6 eV by direct observation. A model for the crystallization kinetics consistent with the data is suggested which yields an activation energy of 2.7 eV for secondary nucleation within the spherulites for 240°C The viscosity of As2Se3 in the pure and doped states (1 at.% Ag) was measured in the glass transition region. Utilizing these data for pure As2Se3 and the high temperature data of previous investigators the interpolated activation energy for viscous flow in the temperature region of rapid crystallization was determined to be 2.7 eV. The linear temperature coefficient of expansion was determined to be 1.55 × 10−5/°C for T

Optical fibers comprising cores clad with amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole

Abstract: Amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole with tetrafluoroethylene and, optionally, with another ethylenically unsaturated monomer, have high glass transition temperatures, e.g., 85° C. or higher, low indices of refraction, and good physical properties which make them suitable for cladding optical fibers.

The nature of the glass transition

Abstract: The free-volume model was first proposed to study movement in dense liquids near the liquid → glass transition Tg. The model has been extended in the last few years to apply to the thermodynamics near Tg, to relaxation and the glass transition and to tunneling centers at very low temperatures. In this paper, we first review the essential elements of our new free-volume model and then discuss several recent experimental results on relaxation phenomena which support this picture of the glass transition.

Compatibility of poly(ε-caprolactone) (PCL) and poly(styrene-Co-acrylonitrile) (SAN) blends. II: The influence of the AN content in SAN copolymer upon blend compatibility

Abstract: The compatibility of polymer blends of poly(ϵ-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing various acrylonitrile (AN) contents was studied to evaluate the influences of copolymer composition and PCL concentration upon blend compatibility. Blend compatibility was characterized by the occurence of a single glass transition intermediate between the transitions of the respective pure components. The glass transitions were determined by differential scanning calorimetry (DSC) and dynamic mechanical measurement (Rheovibron). It was found that SAN and PCL form compatible blends when the AN content of SAN ranges from 8% to 28% by weight. These blends are compatible in all proportions except for SAN 28 (AN wt % = 28) and PCL blends containing 70 or 85 wt % PCL. Blends of PCL and SAN were found to be incompatible when the AN content in SAN is greater than 30 wt % or less than 6 wt %. Lower critical solution temperature (LCST) behavior, which can be attributed to phase separation, was found to occur when these blends were heated to elevated temperatures. The cloud point, or phase separation, was found to vary with AN content in SAN and the concentration of SAN in the blend.

Structural developments during the gel to glass transition

Abstract: In the sol-gel process of preparing glasses, metal-organic compounds are mixed in the liquid state, reacted and slowly solidified to form gels. The gels are then heated, lose water and organics, and shrink to some final specific volumes which frequently are identical to those of melt-formed glasses of similar chemical compositions. This paper is concerned with the development of structures during the gel to glass transition.