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  • 1
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Forced Rayleigh scattering, a relatively recently developed optical technique, is used to measure tracer diffusion coefficients in polymer-solvent mixtures near the system glass transition temperature, Tg. The technique has a wider range of potential application than has yet been realized, and so is presented in some detail. The objectives were to obtain data necessary to scrutinize free volume theory, and to understand so-called anomalous, non-Fickian diffusion effects observed by others in polymer-solvent mixtures near Tg. Data on dye tracer diffusion coefficients in the systems polyvinyl acetate-toluene, polystyrene-toluene, and polystyrene-tri-m-tolyl phosphate were obtained over a polymer concentration range from infinite dilution to 96 wt. %. Small molecule diffusion coefficients are seen to vary by as much as nine orders of magnitude (10-14 to 10-5 cm2/s) over this concentration range. The data are in reasonable accord with expectations based on the Duda-Vrentas version of free-volume theory.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 15 (1969), S. 735-744 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model is presented to account for reduced mass transfer to drops falling through a continuous phase which contains a surface active agent. The fluid flow patterns are essentially laminar. The reduction in mass transfer is said to be due to a reduction in available interfacial transfer area and to changes in both velocity and pattern of internal circulation. These are shown to be functions of contact time and can be characterized. Experimental values agreed with the theoretically predicted ones with a deviation of less than 10%.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 1 (1995), S. 291-296 
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Deoxycholic acid is an important physiological bile acid. The binding of bile salts with metal ions has received more attention due to its clinical significance. In this study, a series of copper and zinc deoxycholate complexes were synthesized. EXAFS and FTIR spectroscopic techniques were used for characterization. The results indicated that both the carboxyl and hydroxyl groups of deoxycholic acid are binding to the Cu (or Zn) ion to form a new complex. There are six oxygen atoms surrounding the metal ion with the average bond lengths of Cu-O and Zn-O are 1.95 and 2.06 Å respectively. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 1807-1812 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymeric catenanes have been made from poly(2,6-dimethyl-1,4-phenylene oxide) crosslinked in the presence of several, paucidisperse poly(dimethylsiloxane) cyclics of varying degrees of polymerization. The fraction of cyclic threaded or captured by the polymer network increases as the degree polymerization of the cyclic increases in good agreement with the crude estimates of Frisch and Wasserman. Thermal analysis and electron micrographs reveal microphone separation in all of the polymeric catenanes; with PDMS domain size around 10-50 μ. Most of the catenanes exhibit a lower tensile strength to break than the pure crosslinked PPO.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1303-1308 
    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: In this paper we examine a conventional approach to correlate the fatigue crack growth rate with fracture mechanics parameters such as stress intensity factor or elastic energy release rate. To simulate a complex loading history we grow a fatigue crack in a vicinity of a hole in a single edge notched specimen under tension-tension. It is found that the correlation between the crack speed and stress intensity factor, etc. may exist only for limited experimental conditions. In general, fatigue crack growth is inseparable from the evolution of the damage zone preceding the crack, and damage evolution parameters should enter constitutive equations of fatigue crack growth. The essential role of the damage zone in determining the crack trajectory and speed is demonstrated.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 59 (1996), S. 511-520 
    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 dynamic FT-IR method was used to determine the individual curing temperature ranges of the isoimide-imide isomerization and crosslinking reactions of an acetylene-terminated polyisoimide prepolymer. The individual curing temperature ranges of these two types of chemical reactions for the polyisoimide system using differential scanning calorimetry (DSC) were totally overlapped. Using dynamic FT-IR spectroscopy, the curing temperature ranges of the isomerization and crosslinking reactions were clearly separated. The isomerization reaction began at lower temperatures than the crosslinking reaction and was complete when only half of the crosslinking reaction had occurred. The temperature width, ΔT1/2, was twice as great for the crosslinking reaction compared with the isomerization reaction. Activation energies from dynamic FT-IR spectroscopy can be obtained for the two separate reactions, however, for the reactions considered here, the activation energies were similar, 26 kcal/mol for the isomerization reaction and 23 kcal/mol for the crosslinking reaction. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 2629-2649 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The technique of forced Rayleigh scattering has been used to measure the tracer diffusion coefficient, Dt, for two photochromic dyes, azobenzene and Aberchrome 540, in polystyrene / toluene solutions, as a function of polymer concentration (79-90% by weight) and temperature (-15-+60°C). The dye diffusivity can be scaled quantitatively to the solvent diffusivity, permitting direct application of the Vrentas-Duda free volume predictions for binary systems. However, the scaling factors are not in agreement with the model assumptions. The temperature and concentration dependence of Dt above the solution glass transition temperature, Tgs, is in good agreement with the model, without any freely adjustable parameters. The value of Dt at Tgs is a very strong function of concentration, increasing by a factor of 103 as the polymer concentration is reduced from 90 to 80%; this is also in quantitative agreement with the model. It is demonstrated that the temperature dependence of Dt exhibits a distinct break in the vicinity of Tgs, with both the existence and the character of the break in qualitative agreement with the extension of the Vrentas-Duda approach to glassy solutions. However, a fundamental difficulty in the calculation of the polymer contribution to the solution free volume at temperatures well below the bulk polymer Tg is exposed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2005-2017 
    ISSN: 0887-6266
    Keywords: FTIR spectroscopy ; acetylene-terminated polyisoimide ; acetylene-terminated polyimide ; isoimide-imide isomerization ; cross-linking reaction ; thermal curing process ; flexibility effect ; cross-linking effect ; rate constant ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interrelationship between the cross-linking and isoimide-imide isomerization reactions of oligomeric isoimides and imides was investigated using FTIR spectroscopy. It was found that cross-linking of the acetylene units of Thermid IP-600 retarded the local rearrangement of the isoimide to imide conversion of Thermid IP-600 compared with an aniline-terminated analog, decreasing the rate constant by a factor of about 2. The increased flexibility of both the isoimide (Thermid IP-600) and imide (Thermid FA-700) oligomers increased the cross-linking rate of the acetylene end groups by a factor of 4 and 2, respectively, over that of the more rigid imide oligomer (MC-600). With increasing conversion of the isoimide to imide linkages in Thermid IP-600, the kinetic parameters, Eα and in A, for the cross-linking reaction of this oligomer became the same as those for the oligomeric imide, Thermid MC-600. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1075-4261
    Keywords: cholelithiasis ; gallstone ; bile salts ; periodic precipitation ; fractal precipitation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: This is the first observation that both chaotic and periodic patterns are formed in metal ions-deoxycholate-gel systems. It is an in vitro model for approximating the conditions present during gallstone formation. The experimental results suggest that a nonlinear scientific concept such as the “butterfly effect” should be considered in understanding gallstone formation. This effect suggests that a butterfly flapping its wings in Beijing today may lead to a thunderstorm in New York months later. Applying this concept to biology, minor changes in the local chemical environment within biological systems may lead to large variations in the structure and morphology of gallstone through changes in the behavior of biological mineralization process. © 1997 John Wiley & Sons, Inc. Biospect 3: 195-205, 1997
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 9 (1986), S. 119-123 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The quartz crystal microbalance (QCM) has a wide range of applications in surface physics and surface chemistry. We present result obtained by combining the high areal density sensitivety of the QCM with surface sensitive spectroscopies like Auger electron spectroscopy (AES) and ion surface scattering (ISS). One type of experiments deals with measurements of sputtering yield variations during ion profiling of metal-metal interfaces, situated at the surface of the QCM, as a function of varying surface composition. A new method for online measurements of angular distributions of sputtered particles from a solid surface, by utilizing the QCM's as collectors of the ejected particles, is the subject of the other type of experiment.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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