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  • 1
    Electronic Resource
    Electronic Resource
    The time-dependent stress-optical behavior of polycarbonate in the glass transition region (1991)
    Springer
    Rheologica acta 30 (1991), S. 419-429 
    Details
    ISSN: 1435-1528
    Keywords: Polycarbonate ; stress-optical coefficient ; glass transition ; KWW equation ; creep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The mechanical and stress-optical behavior of Bisphenol-A polycarbonate was investigated in the glass-transition region. For this purpose, optical creep experiments were carried out in shear and elongation on a tensile tester specially designed for use on a microscope state. A Kohlrausch Williams Watts equation (KWW) with a temperature-independent parameter β could successfully be applied to the curves describing the time-dependent values of the stress-optical coefficient for several temperatures. The temperature dependence of the corresponding retardation time could be established and described by the WLF equation. For variable stresses the time-dependent birefringence is obtained from a generalized linear stress-optical rule as modeled according to linear superposition. The time-temperature superposition principle was applied to all measurements. With the dynamic moduli some deviations were observed at the transition from the rubbery plateau to the α relaxation. The strain-optical coefficient was found to decrease with increasing time and strain. The strain dependence was found to be independent of temperature at constant stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396528
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  • 2
    Electronic Resource
    Electronic Resource
    The peculiar rheo-optical behavior of bisphenol A-polycarbonate and polymethylmethacrylate (1991)
    Springer
    Rheologica acta 30 (1991), S. 329-340 
    Details
    ISSN: 1435-1528
    Keywords: Flow birefringence ; stress-optical coefficient ; polarizability ; polycarbonate ; polymethylmethacrylate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The rheological and stress-optical behavior of the melts of several grades ob bisphenol-A-polycarbonate (PC) and polymethylmethacrylate (PMMA) is investigated. Pertinent flow birefringence measurements are carried out in a remodelled cone-plate apparatus [1]. The shear stress in the polymer melt is calculated from the dynamic moduli, which are determined separately. It is shown that the linear stress optical rule is obeyed. In this way, the stress-optical coefficient C of the melt can be determined. The low-Mw polycarbonates all behave as Maxwellian fluids. The main stress direction does not deviate significantly from 45°. In the temperature range from 160° to 260°C the stress-optical coefficients of the different grades lie between 3 and 4×10−9 Pa−1 and show a weak temperature dependence. The stress-optical coefficient of PMMA is about a factor of 100 lower and shows a peculiar temperature-dependence, changing its sign at 144°C. The results are discussed in terms of the anisotropy of the polarizability of the polymer chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00404193
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of the birefringence distributions in compact discs of polycarbonate (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 813-820 
    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: The birefringence distributions in injection-molded Compact Discs (CD) are determined in radial and tangential cross-sections and interpreted in terms of the process. The influence of processing conditions is discussed in several examples. It is shown that despite the high birefringence level the retardation of a beam of normal incidence is almost zero due to several compensation mechanisms. One optical axis is almost perpendicular to the surface. The medium, however, is biaxial with the preferential directions depending on the distance from the surface and the radial position. In contrast to a parallel beam, zero retardation cannot be achieved with a convergent beam in injection-molded polycarbonate disks for that reason.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760301403
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  • 4
    Electronic Resource
    Electronic Resource
    Gapwise density distributions in injection-molded poly(methylmethacrylate) (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 383-392 
    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: Residual density distributions are determined in injection-molded poly(methyl-methacrylate) (PMMA) with the aid of a quantitative Schlieren optical technique. The gapwise distributions typically show a maximum beneath the surface. The height of the maximum as well as the level in the core vary with distance from the gate of the mold. The density distributions and the influence of the molding parameters are explained by the pressure course measured in the cavity and the process of vitrification of the sample during molding. The magnitudes of the variations of the gapwise distributions agree with the average density variations measured in a density gradient column. Residual stresses do not contribute significantly to the determined distributions. The density maximum is found closer to the surface than the maximum in birefringence that is induced by the shear flow during filling. The magnitude of the density variations is less than predicted by the pseudocompressibility, as determined in samples vitrified under constant pressure.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330703
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  • 5
    Electronic Resource
    Electronic Resource
    Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. II. Effects of sectioning (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1051-1060 
    Details
    ISSN: 0887-6266
    Keywords: birefringence ; polycarbonate ; molecular orientation ; cooling stresses ; effects of sectioning ; stress relief ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Birefringence distributions in cross-sections of quenched polycarbonate disks are investigated. The effects of the introduction of new surfaces by sectioning are studied by using different cross-section widths, by quenching rod-shaped specimens, and by measuring the birefringence with oblique incident light. The experimental results are confirmed by numerical calculations of stress distributions in rods with varying aspect ratios. Stress release by appropriate sectioning is used to distinguish between stress and orientation contribution to birefringence. It is found that cutting cross-sections leads to a major stress redistribution in the width direction. This does not affect the birefringence measurement, but the decrease of the stress level in the long direction needs to be taken into account. The molecular orientation in the quenched samples cannot be explained only by the effect of transient thermal stresses above the glass transition. There is another orientation contribution, most likely related to stress relaxation below Tg. © 1993 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310815
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  • 6
    Electronic Resource
    Electronic Resource
    Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. I. Free quenching (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1041-1049 
    Details
    ISSN: 0887-6266
    Keywords: birefringence ; polycarbonate ; molecular orientation ; cooling stresses ; free quenching ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The residual birefringence distributions in polycarbonate disks quenched in a liquid bath under various conditions are determined. Unbalanced distributions of approximately parabolic shape are obtained in the cross-sections in general. A systematic influence of the initial quench temperature on the imblance of the birefringence distributions is observed, with higher initial temperatures leading to a strong shift of birefringence in the positive direction. The systematic variation of the birefringence distribution with quenching conditions is interpreted in terms of a stress and an orientation contribution. The distributions are predicted correctly by a numerical program making use of the linear stress-optical rule with a different stress-optical coefficient above and below the glass-transition temperature. The contribution of molecular orientation is distinguished experimentally from the stress contribution by annealing experiments. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310814
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of the density distributions in quenched polycarbonate specimens by a quantitative schlieren optical technique (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 83-90 
    Details
    ISSN: 0887-6266
    Keywords: polycarbonate quenched, Schlieren optical technique for density distribution measurement in ; density distribution in quenched polycarbonate, Schlieren optical study of ; glassy polymers, Schlieren optical technique for measurement of density distributions in ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new technique for the determination of spatial density distributions is described. The density is derived from the refractive index gradient as determined with a quantitative Schlieren optical technique. The advantages of this technique are a high spatial resolution and sensitivity. Gapwise profiles can be measured without slicing the sample so that more reliable data are obtained quickly. This is demonstrated for the gapwise density distributions in quenched polycarbonate specimens. It is shown that the density distribution is determined by a competition between the local cooling rate variation and the cooling stress distribution. The residual density is predominantly determined by the coolant temperature. The density in the core is higher than at the surface for high coolant temperatures, whereas for low coolant temperatures the density in the core is lower than at the surface. The observed effects are explained semiquantitatively by a simple model using calculated cooling stresses and cooling rates.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090300108
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular orientation induced by cooling stresses. Birefringence in polycarbonate: III. Constrained quench and injection molding (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 595-605 
    Details
    ISSN: 0887-6266
    Keywords: injection molding ; polycarbonate ; birefringence ; molecular orientation ; residual stresses ; constrained quench ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Residual stress and birefringence distributions are determined in polycarbonate samples obtained by quenching in a specially designed apparatus and by injection molding. The molecular orientation is distinguished from the thermally and pressure-induced residual stresses. The birefringence in the quenched samples is found to be positive and almost constant, independent of the quench temperature, but varying strongly with initial quench temperature between 150 and 180°C. The residual stress level, as determined by layer removal and sectioning, is very low. The birefringence distribution is mainly due to a tensile equibiaxial orientation induced by transient cooling stresses built up above Tg. The samples which are injection-molded with a high injection speed and without packing pressure display the same birefringence distribution as the quenched samples, apart from a local maximum beneath the surface due to the shear flow during filling. Apart from the flow during filling and packing, the frozen-in molecular orientation in injection-molded samples is also induced by transient thermal stresses present during vitrification. The birefringence from thermally induced orientation was found to be of comparable magnitude to that from flow-induced orientation. For a correct prediction of molecular orientation the thermal strains above Tg must therefore be included in simulation programs. Because of the low level of thermal stresses, the application of a packing pressure will lead to tensile stresses at the surface in general. © 1994 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090320401
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  • 9
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    The Very Long-Term Volume Recovery of Polycarbonate:  Is Self-Retardation Finite? (1996)
    American Chemical Society
    Details
    Publication Date: 1996-01-01
    Print ISSN: 0024-9297
    Electronic ISSN: 1520-5835
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society
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  • 10
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    Three-Dimensional Flow-Through Protein Platform (2009)
    American Chemical Society
    Details
    Publication Date: 2009-07-01
    Print ISSN: 0003-2700
    Electronic ISSN: 1520-6882
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society
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