Comblike polymer electrolyte with main chain glass transition near room temperature

A new amorphous comblike polymer (CBP) based on methylvinyl ether/maleic anhydride altering copolymer backbone and on oligooxyethylene side chain was synthesized. The dynamic mechanical properties of CBP and its Li salt complexes were investigated by means of DDV-11-EA type viscoelastic spectrometry. Results showed that there were two glass transitions (alpha-transition and beta-transition) in the temperature range from -100 to 100 degrees C. The beta-transition was assigned to oligo-PEO side chains and the temperature of beta-transition increases with increasing Li salt content. The alpha-transition was assigned to the main chain of CBP. The temperature of the alpha-transition (T-alpha) is also dependent upon the Li-salt content, but not monotonic. The value of T-alpha lies between 30-45 degrees C in the Li salt concentration range studied, near room temperature. It was found that the CBP-Li salt complexes showed an unusual dependence of ionic conductivity on Li salt content. There are two peaks in the plot of the ionic conductivity vs. Li salt concentration, which has been ascribed to the movability of the CBP main chain at ambient temperature. The temperature dependence bf the ionic conductivity indicated that the Arrhenius relationship was not obeyed, and the plot of log sigma against 1/(T - T-0) showed the unusual dual VTF behavior when using side chain glass transition temperature (T-beta) as T-0.

Relationship between viscoelastic transition and yield behavior of phenolphthalein poly(ether ketone)

The viscoelastic behavior of phenolphthalein poly(ether ketone) (PEK-C) and its relationship to yielding was studied. The following phenomena were observed: (1) The relaxation behavior at strain near yield closely approximated that at low strain but near the T-g; (2) the temperature and strain rate dependence of yield stress could be modeled by the one-process Eyring theory and the value of the activation volume was the same as that of the glass transition; and (3) according to the Zhurkov-Bueche equation, the cu transition was related to the yield behavior. All these results indicated that the glass transition was the main factor that controlled the yield behavior. (C) 1996 John Wiley & Sons, Inc.

Crystallization behavior of poly(ether ether ketone ketone)

The melting behavior of semicrystalline poly(ether ether ketone ketone) (PEEKK) has been studied by differential scanning calorimetry (DSC). When PEEKK is annealed from the amorphous state, it usually shows two melting peaks. The upper melting peaks arise first, and the lower melting peaks are developed later. The upper melting peaks shown in the DSC thermogram are the combination (addition) of three parts: initial crystal formed before scanning; reorganization; and melting-recrystallization of lower melting peaks in the DSC scanning period. In the study of isothermal crystallization kinetics, the Avrami equation was used to analyze the primary process of the isothermal crystallization; the Avrami constant, n, is about 2 for PEEKK from the melt and 1.5 for PEEKK from the glass state. According to the Lauritzen-Hoffman equation, the kinetic parameter of PEEKK from the melt is 851.5 K; the crystallization kinetic parameter of PEEKK is higher than that of PEEK, and suggests the crystallizability of PEEKK is less than that of PEEK. The study of crystallization on PEEKK under nonisothermal conditions is also reported for cooling rates from 2.5 degrees C/min to 40 degrees C/min, and the nonisothermal condition was studied by Mandelkern analysis. The results show the nonisothermal crystallization is different from the isothermal crystallization. (C) 1996 John Wiley & Sons, Inc.

Sulfonation of polyetheretherketone and its effects on permeation behavior to nitrogen and water vapor

The novel polyetheretherketone (PEK-C) prepared from phenolphthalein in our institute is an amorphous, rigid, tough material with good mechanical properties over a wide temperature range. To improve its water vapor permeability for the application of gas drying, PEK-C was sulfonated with concentrated sulfuric acid and transferred in sodium, cupric, and ferric salt forms. Sulfonation degree can be regulated by controlling the temperature and reaction time. Characterization of sulfonated PEK-C in sodium form was made by infrared spectroscopy. Some properties of the sulfonated PEK-C, such as solubility, glass transition temperature, thermal stability, mechanical properties, and transport properties to nitrogen and water vapor, are also discussed. (C) 1996 John Wiley & Sons, Inc.

THE EFFECT OF LOADING PARAMETERS ON FATIGUE BEHAVIOR OF INJECTION-MOLDED COMPOSITE

Flexural fatigue tests were performed on an injection-moulded glass-fiber reinforced blend of polyphenylene ether ketone and polyphenylene sulfide composite using four-point bending at a series of fixed mean stress levels with varying stress amplitude. Attention was given to identifying the effects of mean stress and stress amplitude on the fatigue life and failure mechanisms. It was found that the fatigue life of the studied material decreased sharply with increasing stress amplitude at a constant mean stress level and also decreased at a fixed stress amplitude with increasing mean stress. However, analyses of the fatigue data and failure behaviour reveal that, for the studied material, fatigue failure mechanisms depend on the relative importance of mean stress and stress amplitude. At a mean stress level of 80% ultimate flexural strength, the failure results from accumulation of creep strain, while at mean stress levels of 40%, 50% and 60% ultimate flexural strength, the magnitude of stress amplitude influences the type of failure mechanism. As stress amplitude is reduced, the fatigue failure mechanism changes from matrix yielding dominated to crack growth dominated fracture.

PHASE-BEHAVIOR IN MIXTURES OF A HOMOPOLYMER AND A BLOCK-COPOLYMER .1. FTIR AND DSC STUDIES

Miscibility in blends of three styrene-butadiene-styrene and one styrene-isoprene-styrene triblock copolymers containing 28%, 30%, 48%, and 14% by weight of polystyrene, respectively, with poly(vinyl methyl ether) (PVME) were investigated by FTIR spectroscopy and differential scanning calorimetry (DSC). It was found from the optical clarity and the glass transition temperature behavior that the blends show miscibility for each kind of triblock copolymers below a certain concentration of PVME. The concentration range to show miscibility becomes wider as the polystyrene content and molecular weight of PS segment in the triblock copolymers increase. From the FTIR results, the relative peak intensity of the 1100 cm-1 region due to COCH3 band of PVME and peak position of 698 cm-1 region due to phenyl ring are sensitive to the miscibility of SBS(SIS)/PVME blends. The results show that the miscibility in SBS(SIS)/PVME blends is greatly affected by the composition of the copolymers and the polystyrene content in the triblock copolymers. Molecular weights of polystyrene segments have also affected the miscibility of the blends. (C) 1995 John Wiley & Sons, Inc.

A HIGH-RESOLUTION SOLID-STATE NMR AND DSC STUDY OF MISCIBILITY AND CRYSTALLIZATION BEHAVIOR OF POLY(VINYL ALCOHOL)/POLY(N-VINYL-2-PYRROLIDONE) BLENDS

Blends of crystallizable poly(vinyl alcohol) (PVA) with poly(N-vinyl-2-pyrrolidone) (PVPy) were studied by C-13 cross-polarization/magic angle spinning (CP/MAS) n.m.r. and d.s.c. The C-13 CP/MAS spectra show that the blends were miscible on a molecular level over the whole composition range studied, and that the intramolecular hydrogen bonds of PVA were broken and intermolecular hydrogen bonds between PVA and PVPy formed when the two polymers were mixed. The results of a spin-lattice relaxation study indicate that blending of the two polymers reduced the average intermolecular distance and molecular motion of each component, even in the miscible amorphous phase, and that addition of PVPy into PVA has a definite effect on the crystallinity of PVA in the blends over the whole composition range, yet there is still detectable crystallinity even when the PVPy content is as high as 80 wt%. These results are consistent with those obtained from d.s.c. studies.

PHASE-BEHAVIOR IN EPOXY-RESIN CONTAINING PHENOLPHTHALEIN POLY(ETHER ETHER SULFONE)

Phenolphthalein poly(ether ether sulphone) (PES-C) was found to be miscible with uncured bisphenol-A-type epoxy resin, i.e. diglycidyl ether of bisphenol A (DGEBA), as shown by the existence of a single glass transition temperature within the whole composition range. Miscibility between PES-C and DGEBA is considered to be due mainly to the entropy contribution. However, dynamic mechanical analysis (d.m.a.) and scanning electron microscopy (SEM) studies revealed that PES-C exhibits different miscibility with four cured epoxy resins (ER). The overall compatibility and the resulting morphology of the cured blends are dependent on the choice of cure agent. For the blends cured with amines (4,4'-diaminodiphenylmethane (DDM) and 4,4'-diaminodiphenylsulphone (DDS)), no phase separation occurs as indicated by either d.m.a. or SEM. However, for the blends cured with anhydrides (maleic anhydride (MA) and phthalic anhydride (PA)), both d.m.a. and SEM clearly show evidence of phase separation. SEM study shows that the two phases interact well in the MA-cured blend while the interface between the phases in the PA-cured blend is poorly bonded. The differences in the overall compatibility and the resulting morphology between the amine-cured and anhydride-cured systems have been discussed from the points of view of both thermodynamics and kinetics.

INVESTIGATION OF PHASE SEPARATION BEHAVIOR IN POLY (METHYL METHACRYLATE)/POLY (STYRENE-CO-ACRYLONITRILE) MIXTURES WITH PULSED NUCLEAR MAGNETIC RESONANCE

Thermally induced phase separation in the mixture of poly (methyl methacrylate) (PMMA) with poly(styrene-co-acrylonitite (SAN) has intern studied with pulsed nuclear magnetic resonance(NMR) in single spin-lattice retaxation time T-1 of the eornpatibl. mixture two T-1 corresponding to those of PM MA-rich and SAN-rich comairis. Meanwhile, both T-1 gradually changing with annealing time provides the direct evidence that the phase separation takes place with a decomposition mechanism. Diffusion coeffieient was to lac negative, indicating an uphal diffusion characteristics, The basic parameters governing its kinetics were estimated using NMR date which were in good agreement with those evaluated from time-resolved light scattering experiments for a 60/40(PMMA/SAN) mixture annealed at 180.0 degrees C.

Zoospores of Undaria pinnatifida: their efficiency to attach under different water velocities and conjugation behavior during attachment

In the invading course of Undaria pinnatifida, zoospore attachment in a dynamically changed subtidal water environment is crucial for the establishment of a potential population in alien waters. Among many abiotic factors that may interfere with the attachment process, water velocity is the most important one. In this investigation, the effect of water velocity on zoospore attachment of U. pinnatifida was investigated in an artificially designed system. It was found that freshly released zoospores that were transported by water flowing at 0 similar to 16 cm/s showed no difficulty in attaching the smooth surface. Zoospore attachment decreased at elevated water flowing rates. At 70 cm/s no spore attachment occurred. Spores that have settled on glass slide for up to I h could not be stripped away by flowing water at a rate of 129 cm/s, the same was true of the 20 d old filamentous gametophytes. It was found that more than 70% of free-swimming zoospores tended to settle down adjacent to the settled spores and formed conjugated clusters from two up to a few hundred cells in still culture.

Water transport in resin-modified glass-ionomer dental cement

Water uptake and water loss have been studied in a commercial resin-modified glass-ionomer cement, Fuji II LC, under a variety of conditions. Uptake was generally non-Fickian, but affected by temperature. At room temperature, the equilibrium water uptake values varied from 2.47 to 2.78% whereas at low temperature (12 degrees C), it varied from 0.85 to 1.18%. Cure time affected uptake values significantly. Water uptake was much lower than in conventional glass-ionomer restorative cements exposed to water vapor. Loss of water under desiccating conditions was found to be Fickian for the first 5 h loss at both 22 and 12 degrees C. Diffusion coefficients were between 0.45 and 0.76 x 10( -7) cm(2)/s, with low temperature diffusion coefficients slightly greater than those at room temperature. Plotting water loss as percentage versus s(-(1/2)) allowed activation energies to be determined from the Arrhenius equation and these were found to be 65.6, 79.8, and 7.7 kJ/mol respectively for 30, 20, and 10 s cure times. The overall conclusion is that the main advantage of incorporating HEMA into resin-modified-glass-ionomers is to alter water loss behavior. Rate of water loss and total amount lost are both reduced. Hence, resin-modified glass-ionomers are less sensitive to water loss than conventional glass-ionomers.

An investigation into the subambient behavior of aqueous mannitol solutions using differential scanning calorimetry, cold stage microscopy, and X-ray diffractometry

The subambient behavior of aqueous mannitol solutions is of considerable relevance to the preparation of freeze dried formulations. In this investigation the properties of 3% w/v mannitol solutions were investigated using differential scanning calorimetry (DSC), cold stage microscopy (CSM), and X-ray diffraction (XRD) to identify the thermal transitions and structural transformations undergone by this system. It was found that on cooling from ambient the system formed ice at circa -20°C while a further exotherm was seen at approximately -30°C. Upon reheating an endotherm was seen at circa -30°C followed immediately by an exotherm at circa -25°C. Temperature cycling indicated that the thermal transitions observed upon reheating were not reversible. Modulated temperature DSC (MTDSC) indicated that the transitions observed upon reheating corresponded to a glass transition immediately followed by recrystallization, XRD data showed that recrystallization was into the ß form. Annealing at -35°C for 40 min prior to cooling and reheating resulted in a maximum enthalpy being observed for the reheating exotherm. It is concluded that on cooling 3% w/v aqueous mannitol solutions an amorphous phase is formed that subsequently recrystallises into the ß form. The study has also shown that DSC, CSM, and XRD are useful complementary techniques for the study of frozen systems

Spontaneous spin polarization and electron localization in constrained geometries: The Wigner transition in nanowires

The Wigner transition in a jellium model of cylindrical nanowires has been investigated by density-functional computations using the local spin-density approximation. A wide range of background densities rho(b) has been explored from the nearly ideal metallic regime (r(s)=[3/4 pi rho(b)](1/3)=1) to the high correlation limit (r(s)=100). Computations have been performed using an unconstrained plane wave expansion for the Kohn-Sham orbitals and a large simulation cell with up to 480 electrons. The electron and spin distributions retain the cylindrical symmetry of the Hamiltonian at high density, while electron localization and spin polarization arise nearly simultaneously in low-density wires (r(s)similar to 30). At sufficiently low density (r(s)>= 40), the ground-state electron distribution is the superposition of well defined and nearly disjoint droplets, whose charge and spin densities integrate almost exactly to one electron and 1/2 mu(B), respectively. Droplets are arranged on radial shells and define a distorted lattice whose structure is intermediate between bcc and fcc. Dislocations and grain boundaries are apparent in the droplets' configuration found by our simulations. Our computations aim at modeling the behavior of experimental low-carried density systems made of lightly doped semiconductor nanostructures or conducting polymers.

Testing the reliability of the JEOL FEGSEM 6500F electron microprobe for quantitative major element analysis of glass shards from rhyolitic tephra.

Electronprobe microanalysis is now widely adopted in tephra studies as a technique for determining the major element geochemistry of individual glass shards. Accurate geochemical characterization is crucial for enabling robust tephra-based correlations; such information may also be used to link the tephra to a specific source and often to a particular eruption. In this article, we present major element analyses for rhyolitic natural glass standards analysed on three different microprobes and the new JEOL FEGSEM 6500F microprobe at Queen’s University Belfast. Despite the scatter in some elements, good comparability is demonstrated among data yielded from this new system, the previous Belfast JEOL-733 Superprobe, the JEOL-8200 Superprobe (Copenhagen) and the existing long-established microprobe facility in Edinburgh. Importantly, our results show that major elements analysed using different microprobes and variable operating conditions allow two high-silica glasses to be discriminated accurately.

Manipulating and protecting entanglement by means of spin environments

We study the dynamical behavior of two initially entangled qubits, each locally coupled to an environment embodied by an interacting spin chain. We consider energy-exchange qubit-environment couplings resulting in rich and highly non-trivial entanglement dynamics. We obtain exact results for the time evolution of the concurrence between the two qubits and find that, by tuning the interaction parameters, one can freeze the dynamics of entanglement, therefore inhibiting their relaxation into the spin environments, as well as activate a sudden-death phenomenon. We also discuss the effects of an environmental quantum phase transition on the features of the two-qubit entanglement dynamics.