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  • 11
    Electronic Resource
    Electronic Resource
    A differential scanning calorimetry study on poly(ethylene terephthalate) isothermally crystallized at stepwise temperatures: multiple melting behavior re-investigated (1996)
    Springer
    Colloid & polymer science 274 (1996), S. 309-315 
    Details
    ISSN: 1435-1536
    Keywords: Multiple melting ; DSC-crystallization ; poly(ethylene terephthalate) ; lamellar thickness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The multiple melting behavior of poly(ethylene terephthalate) (PET) was investigated with differential scanning calorimetry (DSC) by examining PET samples having been subjected to special schemes of crystallization and annealing treatment at multiple descending temperatures. Upon such step-wise annealing in decreasing temperatures, the existence of doublet melting peaks in addition to a series of multiple minor peaks in the PET has been demonstrated using carefully designed thermal schemes. Using the Hoffman theory, multiple lamellae populations, might be suggested to be simultaneously present in the PET subjected to such thermal treatments. However, direct experimental evidence has yet to be provided. The low-temperature minor crystals simply melt during normal scanning without having time enough to reorganize into higher-melt crystals. Nevertheless, the effect of scanning on non-isothermal crystallization does exist but is primarily confined to the temperature range much below the main melting region where the crystallization of polymer chains can progress at a reasonable rate. At higher temperatures near the main melting region, annealing for extended times is required in order to result in relative changes of the melting endotherms of the upper and lower peaks in the main melting doublet. In all we have shown that interpretations of the multiple melting phenomenon in semicrystalline polymers can be better refined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00654051
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  • 12
    Electronic Resource
    Electronic Resource
    Blends of a novel high-temperature poly(oxy-1,4′-diphenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) with poly(ether imide): structure, interaction, and miscibility (2000)
    Springer
    Colloid & polymer science 278 (2000), S. 392-398 
    Details
    ISSN: 1435-1536
    Keywords: Key words Miscibility ; Poly (ether imide) ; Poly(ether diphenyl ether ketone) ; Interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Polymer miscibility has been discovered in a blend system comprising poly(ether imide) (PEI) and a new poly(ether diphenyl ether ketone) (PEDEK). The miscibility of the PEDEK/PEI polymer system (quenched from the molten state) was investigated in this study using differential scanning calorimetry and Fourier transform (FT-IR) spectroscopy. A composition-dependent single glass-transition temperature (T g) in the PEDEK/PEI blends over a full composition range was observed; the sharp transition width and the T g–composition relationship both suggest that the scale of mixing is fine and uniform. Evidence based on observation of the cold-crystallization peak and suppression of the blend crystallinity and melting peak also indicated intimate intermolecular mixing. The FT-IR result yielded further evidence that the physical interactions leading to miscibility were weak, with no apparent specific interactions between the constituent polymers. Relationships between structures and interactions responsible for the miscibility in PEI and several ether-ketone-type polymers are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050531
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  • 13
    Electronic Resource
    Electronic Resource
    Characterization of heterogeneous matrix composites using scanning acoustic microscopy (1993)
    Springer
    Journal of materials science 28 (1993), S. 329-336 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Acoustic microscopy was used to examine the morphology of multi-phase matrices and composites. The acoustic microscopy imaging could easily resolve the rubber domains dispersed within a thermosetting or thermoplastic continuous phase. However, because the thermoplastic and thermosetting phase domains had comparable elastic moduli, the resolution between them was not always clear. Rayleigh wave distortion of imaging remained as one of the serious limitations that needed to be overcome in order for this technique to be widely utilized in heterogeneous/anisotropic media. In its present form, the acoustic imaging technique can be used to augment other existing analytical tools in order to generate more detailed morphological information that is useful in understanding structure-property relationships for multi-phase toughened matrices used in advanced composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357803
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  • 14
    Electronic Resource
    Electronic Resource
    Processing-structure relationships for multiphase epoxy matrix systems (1991)
    Springer
    Journal of materials science 26 (1991), S. 1691-1698 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A styrene-modified diglycidyl ether of bisphenol-A (DGEBA) epoxy system cured with trimellitic anhydride (TMA) has been investigated to explore processing and structure relationships. During cure, the reactive styrene precipitated with polymerization into phase domains separate from the epoxy phase. Dynamic mechanical analysis and microscopy studies were performed to gain insight to matrix structure. The DMA studies showed that the styrenemodified epoxy system after cure exhibited two partially overlapped but distinct relaxation peaks, which are associated with the T gs of the polystyrene and epoxy phases. The glass transition of the polystyrene phase was shown to be broadened and the T g to depend strongly on processing temperature profiles. While the T g of the epoxy phase increases with curing agent concentrations, the T g of the polystyrene phase does not. Microscopic studies showed that the styrene-modified system exhibited a rougher fracture surface but did not reveal well defined phase domains in which the precipitated polystyrene component was aggregated. Overall, the study has demonstrated correlations of the kinetic factors in controlling the morphology in reactive modifier-epoxy systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00544684
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  • 15
    Electronic Resource
    Electronic Resource
    Fluorene-based polymers-preparation and applications (2000)
    Springer
    Journal of materials science 11 (2000), S. 111-116 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper briefly reviews our work on the syntheses and applications of a family of fluorene-based polymers. We have found that fluorene as a monomer offers a number of advantages, the most significant being its ability to impart solubility while maintaining a high degree of delocalization. An improved Pd-catalyzed polymerization procedure has enabled the preparation of a large variety of fluorene homopolymers and copolymers. Unlike PPV and related materials, LED devices with fluorene polymers in a conventional configuration appear to have electrons as the majority carrier and their performance is markedly improved when modified with an appropriate polymeric hole transporting layer. An optimized green-emitting device exhibits very high luminance (10 000 cd m-2) at very low bias (〈 7 V) and high efficiency (∼10 lm W-1), attributable in part to the high hole mobility of fluorene-based polymers. Applications of these materials to other electronic devices, such as field effect transistors and photocells, are in progress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008917128880
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  • 16
    Electronic Resource
    Electronic Resource
    Reaction-induced phase separation in a semiinterpenetrating network of reactive ternary blends (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 781-788 
    Details
    ISSN: 0887-624X
    Keywords: DGEBA epoxy ; polycarbonate (PC) ; PMMA ; reactions ; IPN ; ternary polymer blends ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Morphology and reaction mechanisms were probed on a model reactive ternary blend system of polycarbonate (PC), poly(methyl methacrylate) (PMMA), and diglycidylether of bisphenol-A (DGEBA) epoxy by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Molecular interactions/reactions between the components in the blends after heating treatments are discussed. It was found that reactions took place among the components and that an interpenetrating network was built. The possible reaction mechanisms and the resulting structures after the heating treatments were probed. In the blends, PC and DGEBA reacted to form a network, while PMMA remained free. The semiinterpenetration, however, did not result in a network interlocked into a homogeneous state. The single Tg of the heated ternary DGEBA/PC/PMMA blends actually did not reflect a homogeneous interpenetrating network. Due to relatively small PMMA domains, the ternary blend network exhibited a single Tg. Upon etching the PMMA domains from the blend by acetone, a clearly interpenetrating network of reacted PC and epoxy was exposed and confirmed. The reactions leading to such a morphology are discussed with experimental evidence. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Morphology and glass transition behavior of polycarbonate-phenoxy system: Effects of trans-reactions in domain interface regions (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 97-103 
    Details
    ISSN: 0887-624X
    Keywords: phenoxy ; polycarbonate (PC) ; exchange reactions ; morphology ; polymer blends ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Effects of trans reactions on the morphology, glass transition, and phase behavior in a classical blend system of a poly(hydroxyl ether bisphenol-A) (phenoxy) with bisphenol-A polycarbonate (PC) were investigated by differential scanning calorimetry (DSC) and optical microscopy. Although two Tgs were observed in the as-prepared PC/phenoxy blends, an apparently single, but broadened, Tg was found in the blends after heating at high temperatures, typically 200-250°C for short times. The optical microscopy results indicated that same scales of heterogeneity did exist in post-heated PC/phenoxy blends as well as unheated blends. Explanations were provided. After heating-induced interchange reactions (—OH and carbonate), randomly linked polymer chains might form at the numerous interfaces of the mutually occluded/included micro-domains. The majority of the chains in the micro-domains are forced to relax in coordinated motion modes after heating, thus showing a single Tg. A mechanism of trans reactions in interfacial regions was briefly discussed in supplement to earlier reports in the literature. © 1997 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Thermal—electrical finite element modelling for radio frequency cardiac ablation: Effects of changes in myocardial properties (2000)
    Springer
    Medical & biological engineering & computing 38 (2000), S. 562-568 
    Details
    ISSN: 1741-0444
    Keywords: Finite element ; RF ablation ; Cardiac ablation ; Temperature-controlled ; Power-controlled ; Bio-heat equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Finite element (FE) analysis has been utilised as a numerical tool to determine the temperature distribution in studies of radio frequency (RF) cardiac ablation. However, non of the previous FE analyses clarified such computational aspects as software requirements, computation time or convergence test. In addition, myocardial properties included in the previous models vary greatly. A process of FE modelling of a system that included blood, myocardium, and an ablation catheter with a thermistor embedded at the tip is described. The bio-heat equation is solved to determine the temperature distribution in myocardium using a commercial soft-ware application (ABAQUS). A Cauchy convergence test (∈=0.1°C) was performed and it is concluded that the optimal number of elements for the proposed system is 24610. The effects of changes in myocardial properties (±50% electric conductivity, +100%/−50% thermal conductivity, and +100%/−50% specific heat capacity) in both power-controlled (PCRFA) and temperature-controlled RF ablation (TCRFA) were studied. Changes in myocardial properties affect the results of the FE analyses of PCRFA more than those of TCRFA, and the maximum changes in lesion volumes were −58.6% (−50% electric conductivity), −60.7% (+100% thermal conductivity), and +43.2% (−50% specific heat).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02345754
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  • 19
    Electronic Resource
    Electronic Resource
    Skin impedance measurements using simple and compound electrodes (1992)
    Springer
    Medical & biological engineering & computing 30 (1992), S. 97-102 
    Details
    ISSN: 1741-0444
    Keywords: Compound electrode ; Electrode configuration ; Skin impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract We have studied the effect of the electrode configuration on the measurement of body impedance and found that the electrode configuration greatly affects the impedance measurement using the four-electrode method. We studied the characteristics of the compound electrode and found that the compound electrode provides the four-electrode method in a compact form. A new method of measuring the skin impedance using simple electrodes at low frequencies was developed. At high frequencies where the effect of internal tissue impedance is not negligible, we used the compensation method using compound electrodes, because they measure the voltage right under the skin. At 50 kHz, we measured the real part of the skin impedance of less than 80 Ω on the thorax. We propose a simple instrument which can measure accurate skin impedance at various frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02446200
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  • 20
    Electronic Resource
    Electronic Resource
    Morphology and properties of an epoxy alloy system containing thermoplastics and a reactive rubber (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1664-1673 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A novel approach for toughening thermosetting epoxy matrices using both thermoplastics and liquid reactive rubbers as modifiers has been investigated. The network structure of the modified epoxy systems was characterized using dynamic mechanical analysis, and the morphology of the multiphase structure was examined using scanning electron microscopy (SEM). To investigate the continuity of the phase domains, the constituents in the phase domains were positively identified using solving etching and RuO4 staining techniques for transmission electron microscopy (TEM). The fracture toughness of the modified and basic epoxy samples was measured using compact tension (CT) specimens. Quite limited toughness improvement was achieved for the epoxy modified with only the PSu thermoplastic, or the liquid rubber by itself. However, the fracture toughness was found to increase dramatically when a proper combination of both the liquid reactive rubber and thermoplastic was simultaneously incorporated into the epoxy. Toughening by using dual modifiers resulted in maximum improvement of fracture toughness with minimal compromises in processability and Tg depression by rubbers.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760342204
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