Glass-forming liquids,anomalous liquids,and polyamorphism in liquids and biopolymers

Summary Glass formation in nature and materials science is reviewed and the recent recognition of polymorphism within the glassy state, polyamorphism, is discussed. The process by which the glassy state originates during the continuous cooling or viscous slowdown process, is examined and the three canonical characteristics of relaxing liquids are correlated through the fragility. The conversion of strong liquids to fragile liquids by pressure-induced coordination number increases is discussed, and then it is shown that for the same type of system it is possible to have the same conversion accomplished via a first-order transition within the liquid state. The systems in which this can happen are of the same type which exhibit polyamorphism, and the whole phenomenology can be accounted for by a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The concept of complex amorphous systems which can lose a significant number of degrees of freedom through weak first-order transitions is then used to discuss the relation between native and denatured hydrated proteins, since the latter have much in common with plasticized chain polymer systems. Finally, we close the circle by taking a short-time-scale phenomenon given much attention by protein physicists,viz., the onset of an anomaly in the Debye-Waller factor with increasing temperature, and showing that for a wide variety of liquids, including computer-simulated strong and fragile ionic liquids, this phenomenon is closely correlated with the experimental glass transition temperature. This implies that the latter owes its origin to the onset of strong anharmonicity in certain components of the vibrational density of states (evidently related to the boson peak) which then permits the system to gain access to its configurational degrees of freedom. The more anharmonic these vibrational components, the closer to the Kauzmann temperature will commence the exploration of configuration space and, for a given configurational microstate degeneracy, the more fragile the liquid will be. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

含氰基的酚醛树脂及其碳纤维复合材料

含氰基的酚醛树脂，具有优异的耐高温性能和高温下的机械强度，在３１５℃下性能变化甚小；不着火，发烟量低，有良好的加工成型性能。热固化过程中氰基成三嗪环而交联，没有小分子脱出，是一类具有广泛发展前景的新型热固性树脂。     

Improvement of the properties of polyarylate reinforced with liquid crystalline polymers

Blends of polyarylate of bisphenol A, PAr, with two commercial main chain liquid crystalline polymers, Vectra A950 and Vectra B950, are studied. From dynamic viscoelastic measurements it is deduced that both systems (PAr/Vectra A950 and PAr/Vectra B950) are immiscible and scanning electron microscopy (SEM) micrographs show the presence of spherical domains of the liquid crystalline polymer when PAr constitutes the matrix. Extrusion capillary measurements reveal that, under conditions of temperature and shear rate similar to those of processing, the viscosity is reduced to approximately 10% of its value when the content of liquid crystalline polymer is only 20%. This great improvement of the rheological properties is observed in both PAr/Vectra A950 and PAr/Vectra B950 blends. The effect of draw ratio on Young's modulus for different compositions is also analyzed, pointing out the reinforcing action of both liquid crystalline polymers on polyarylate: for instance, 20% of Vectra B950 in the blend gives rise to a 700% increase of the modulus of fibres prepared at a draw ratio of 50. SEM of the extrudates reveals that the spherical domains are elongated at the entrance of the capillary giving rise to a microfibrillar morphology which is related to the excellent rheological and mechanical properties of the blends.     

Thermoanalytical procedures to identify the morphology of polycrystalline materials

Polypropylenes of differing morphologies were examined by differential thermal analysis. The problems of reordering during the programmed heating are discussed. Four potential procedures by which the reordering could be inhibited are considered, and three of these are experimentally assessed. Their advantages and deficiencies are identified. Two pretreatments, an etching and a crosslinking, are recognised as able to qualitatively characterise the initial morphology, with a preference for the former. A test to identify the occurrence of reordering is identified. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

An efficient lasing action from pyrromethene 556 dye-doped organically modified silicates

Organically modified solid-state silicates (ORMOSILS) doped with a new laser dye 1,3,5,7,8-pentamethylpyrromethene-2,6-disulfonate-BF₂ complex (pyrromethene 556) have been synthesized by a sol-gel method and the compositional effects on pore characteristics, fluorescence and lasing properties have been investigated. It is found that the use of dimethylsulfoxide and γ-glycidoxypropyltrimethoxysilane could greatly change the structure properties of sol-gel derived ORMOSILS cage, and thus the fluorescence and lasing properties of the materials could improve significantly. A successful laser oscillation from this dye-doped ORMOSILS sample has been achieved upon pumping with a Q-switched frequency-doubled Nd:YAG laser at 532 nm. A slope efficiency of 54% with a useful lifetime greater than 10,000 shots has been demonstrated at a pump repetition rate of 1 Hz and a pump intensity of 1 J/cm² by using the new ORMOSILS cage on our newly designed laser system. Our results have shown that it is possible to obtain a high-efficiency with a long-lifetime for a compact new laser device by low cost dye-doped solid-state ORMOSILS.     

Use of a long-spacer-side-chain liquid crystalline polysiloxane containing a crown ether as a stationary phase for capillary gas chromatography

A new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC-11) has been prepared and coated on a fused silica capillary column. The main chroma-tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC-3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side chain.     

Physical properties and phase separation structure of Antheraea pernyi/Bombyx mori silk fibroin blend films

The physical structure and compatibility of solution-cast Antheraea pernyi/Bombyx mori silk fibroin blend films were stuided by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, dynamic viscoelastic measurement, infrared spectroscopy, and x-ray diffractometry. The DSC curves of the blend films showed independent endotherms at 280 and 358°C, corresponding to the thermal decomposition of B. mori and A. pernyi silk fibroins with random coil conformation. The intensity was roughly proportionate to the amount of each component in the blend. The thermal behavior corresponding to the conformational transitions induced by heating on A. pernyi and B. mori silk fibroins overlapped in the temperature range 190–230°C. Thermal expansion and contraction properties, as well as weight retention behavior of the blend films were intermediate between the pure components, as shown by the TMA and TGA curves. The onset temperature of the storage modulus curve decreased markedly, approaching that of B. mori silk fibroin film when the amount of this component in the blend increased. The loss modulus curve of the blend films showed two peaks at ca. 190 and 210°C, the former corresponding to B. mori, and the latter to A. pernyi silk fibroin. Infrared spectra of the blends exhibited absorption bands characteristic of the pure components overlapping in the spectral region 2000–400 cm^?1. The x-ray diffraction peaks at 23 and 21.5°, attributed to the crystalline spacings of A. pernyi and B. mori fibroins, respectively, overlapped in the diffraction curves of the blends, while the peak at 11.4°, of A. pernyi, increased as the content of this fibroin in the blend increased. The degree of crystallinity, calculated from the x-ray diffraction curves, diminished as the amount of B. mori silk fibroin decreased. A low degree of compatibility exists between the two fibroins when they are cast from aqueous solution in the experimental conditions adopted in this work. © 1994 John Wiley & Sons, Inc.     

High-T c superconducting magnetic bearings for rotation-based devices

Summary A Modified-Melt-Powder-Melt-Growth (MMPMG) technique has been developed for the preparation of melt-textured Y-Ba−Cu−O pellets. To test their performances, the samples were characterized with respect to their microstructure, pinning strength and interaction force with permanent magnets. A superconducting magnetic bearing was built and integrated in a levitating flywheel system for energy storage. Paper presented at the “VII Congresso SATT?, Torino, 4–7 October 1994. Under a Fondazione Confalonieri grant.     

Towards understanding the increase in strength of thermotropic polyesters with heat treatment

Thermotropic copolyester fibers of oxynaphthoate and oxybenzoate have been subjected to conditions that promote solid-state polymerization as well as annealing. The annealing process causes the crystals to perfect with a simultaneous increase in heat of fusion and melting temperature. Solid-state polymerization, a reaction rate-controlled process, causes the polymer viscosity average molecular weight to increase by chain extension from about 14,000 g/mole to more than 87,000 g/mole with a simultaneous impressive increase in tenacity from about 10 g/d (1.2 GPa) to almost 30 g/d (3.7 GPa). To understand the changes in mechanical properties, we have modeled the fiber structure as short rod-like molecules poorly bonded to a continuous matrix of parallel molecules. Lengthening of the reinforcing molecules facilitates better transfer of load from matrix to molecules, resulting in higher tenacity fibers. © 1994 John Wiley & Sons, Inc.     

Progress in the quality assurance of environmental trace organic analysis

An overview is given on the stepwise learning programmes undertaken to identify the main sources of error associated with the determination of the mandatory organic contaminants in the marine monitoring programmes. Details are given on the preparation and use of LRMs and CRMs to maintain analytical control and quantify the laboratory errors in relation to the measurement of changes in the environment.