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  • 1
    Electronic Resource
    Electronic Resource
    Determination of the kinetic parameters for the polymerization of a polyurethane using an improved method of differential scanning calorimetry (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 46 (1992), S. 571-580 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: The kinetic parameters for the polymerization reactions of two polyurethane systems were determined by using an improved method of differential scanning calorymetry (DSC). The calculated activation energy, reaction order, and Arrhenius prefactor show good correlation with the experimental results. The method used here shows several improvements as respects to other DSC methods: the three kinetic parameters can be calculated directly; it is more accurate than other DSC methods; and it requires only one heating rate, during the calorimetric experiments, to determine the activation energy.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070460402
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  • 2
    Electronic Resource
    Electronic Resource
    Activation energy for urethane-linkage formation. An improved calculation from the differential scanning calorimetry data (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 1579-1592 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Differential scanning calorimetry (DSC) has been utilized in several studies on polymerization kinetics, at different heating rates. However, there are several factors affecting the precision of kinetic parameters. In this work, the activation energy of urethane-bond formation between 2,6-tolylene diisocyanate and diethylene glycol is reported, the latter being in excess in order to minimize problems such as thermal transitions and incomplete reaction in the final step. The DSC technique was applied at different heating rates. Both the equal conversion and equal conversion rate options of the method are discussed. The latter appears to be a more adequate option for the system studied here. The results obtained show a good agreement with the model used.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280623
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  • 3
    Electronic Resource
    Electronic Resource
    Ceramic thin films deposited on Si(100) by laser ablation: Application as buffer layers for YBa2Cu3O7 films (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 2 (1993), S. 99-103 
    Details
    ISSN: 1057-9257
    Keywords: Buffer layers ; Laser ablation ; Superconducting films ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Ceramic thin films of yttria-stabilised zirconia (YSZ), SrTiO3(STO) and CeO2 have been deposited on Si(100) substrates by laser ablation. The films have been characterized by X-ray diffractometry, field emission scanning electron microscopy and secondary ion mass spectrometry (SIMS). The effects of the oxygen partial pressure during deposition and the substrate temperature were studied. All the films have preferential orientation: (h00) and (hh0) for STO and (hhh) for CeO2 and YSZ. The films show a low density of particulates and a very smooth surface. SIMS profiles indicate a low interdiffusion between film and silicon. One of the applications of these materials is their use as a buffer layer for the growth of YBCO on silicon. Because both materials are highly reactive, it is necessary to put a barrier between YBCO and silicon. For this purpose we used the ceramic films previously deposited in order to obtain superconducting YBCO films. The deposited YBCO films present good superconducting properties with zero resistance at temperatures between 80 and 85 K.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860020113
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  • 4
    Electronic Resource
    Electronic Resource
    Study of crosslinking density in polydimethylsiloxane networks by DSC (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 55 (1995), S. 1317-1327 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 calorimetric study for estimating crosslinking densities of polydimethylsiloxane (PDMS) networks is presented. It involves the experimental determination of the heat capacities of the polymer with (Cip) and without (C0p) crosslinking. The theoretical basis of the method is described as well as the procedure used for the determination of the Cps. The crosslinking densities of PDMS networks, determined by absorbency (swelling) measurments, using the Flory-Rehner equation, and by the method described here, are compared. The PDMS, obtained by the anionic synthesis of octamethylcyclotetrasiloxane, was analyzed by gel permeation chromatography and infrared spectroscopy. Separate samples of the polymer were further crosslinked at different network densities. The Cps and the thermal stabilities were determined by DSC and TGA, respectively. The results indicate that the crosslinking density ratios of the polymer networks calculated by the relation ΔCip/C0p are in reasonable agreement with those obtained from absorbency measurements. The crosslinking density can also be obtained from heat capacity measurments if the density of the network is known at the temperature that ΔCp is obtained. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070550905
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  • 5
    Electronic Resource
    Electronic Resource
    Enhancement and inhibition of luminol chemiluminescence by phenolic acids (1995)
    New York : Wiley-Blackwell
    Journal of Bioluminescence and Chemiluminescence 10 (1995), S. 175-184 
    Details
    ISSN: 0884-3996
    Keywords: Luminol ; enhanced chemiluminescence ; phenolic acid ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: We explored the behaviour of a series of phenolic acids used as enhancers or inhibitors of luminol chemiluminescence by three different methods to determine if behaviour was associated with phenolic acid structure and redox character. All the phenolic acids inhibited chemiluminescence when hexacyanoferrate(III) was reacted with the phenolic acids before adding luminol. The redox character of these compounds was clearly related to structure. When hexacyanoferrate(III)-luminol-O2 chemiluminescence was initiated by phenolic acid-luminol mixtures some phenolic acids behaved as enhancers of chemiluminescence, and others as inhibitors. We propose a mechanism to explain these findings. We found direct relationships between the redox character of the phenolic acids and the enhancement or inhibition of the chemiluminescence of the luminol-H2O2-peroxidase system and we propose mechanism to explain these phenomena.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bio.1170100306
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  • 6
    Electronic Resource
    Electronic Resource
    Phenol derivatives as enhancers and inhibitors of luminol-H2O2-horseradish peroxidase chemiluminescence (1998)
    New York : Wiley-Blackwell
    Journal of Bioluminescence and Chemiluminescence 13 (1998), S. 75-84 
    Details
    ISSN: 0884-3996
    Keywords: luminol ; enhanced chemiluminescence ; phenol ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Systematic studies on phenol derivatives facilitates an explanation of the enhancement or inhibition of the luminol-H2O2-horseradish peroxidase system chemiluminescence. Factors that govern the enhancement are the one-electron reduction potentials of the phenoxy radicals (PhO•/PhOH) vs. luminol radicals (L•/LH-) and the reaction rates of the phenol derivatives with the compounds of horseradish peroxidase (HRP-I and HRP-II). Only compounds with radicals with a similar or greater reduction potential than luminol at pH 8.5 (0.8 V) can act as enhancers. Radicals with reduction potentials lower than luminol behave in a different way, because they destroy luminol radicals and inhibit chemiluminescence. The relations between the reduction potential, reaction rates and the Hammett constant of the substituent in a phenol suggest that 4-substituted phenols with Hammett constants (σ) for their substituents similar or greater than 0.20 are enhancers of the luminol-H2O2-horseradish peroxidase chemiluminescence. In contrast, those phenols substituted in position 4 for substituents with Hammett constants (σ) lower than 0.20 are inhibitors of chemiluminescence. On the basis of these studies, the structure of possible new enhancers was predicted. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Assay of cholinesterase using a proenhancer of the luminol-H2O2-horseradish peroxidase reaction (1995)
    New York : Wiley-Blackwell
    Journal of Bioluminescence and Chemiluminescence 10 (1995), S. 285-289 
    Details
    ISSN: 0884-3996
    Keywords: Cholinesterase ; luminol ; pro-enhancer ; chemiluminescence ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: 2-Naphthyl acetate acts as a pro-enhancer of the luminol-H2O2-horseradish peroxidase reaction. Cholinesterase hydrolyses the bound acetyl group and produces 2-naphthol, and this compound is an enhancer of the chemiluminescent reaction. We studied the kinetics of chemiluminescent emission and the influence of 2-naphthyl acetate and cholinesterase enzyme concentration. The cholinesterase concentration versus chemiluminescence intensity maximum was linear for cholinesterase between 0 and 181 μU/mL, with a detection limit of 8 μU/mL and a relative standard deviation of 9.5% (n = 3), for a sample containing 90.67 μU/mL of cholinesterase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bio.1170100505
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  • 8
    Electronic Resource
    Electronic Resource
    Kinetic salt effects on the outer sphere electron transfer reaction between hexacyanoferrate(II) and 4-pyridinecarboxylatopentammine cobalt(III) (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 1083-1091 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study is made of the kinetic salt effects upon the outer-sphere electron transfer reaction between hexacyanoferrate(II) and 4-pyridinecarboxylatopentaamminecobalt(III). The observed salts effects are analyzed, taking into account the possible association of the reactants with the ions of the supporting electrolyte, though no conclusive results could be obtained. A correlation has been established between the logarithm of the observed second-order rate constants and the logarithm of the rate constants for a related innersphere electron transfer reaction. From this correlation the conclusion can be drawn that the observed salt effects in concentrated electrolyte solutions are mainly due to the effects on the electron transfer step. © John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550241206
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