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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 2512-2519 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4581-4586 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dynamic storage and loss moduli of dilute solutions of linear poly(2-vinylpyridine) with molecular weights ranging from 3.0×104 to 1.0×106 have been measured under conditions where the polymer can be charged by protonation. A pronounced maximum is exhibited in the reduced moduli occurring at a concentration which is independent of molecular weight and measurement frequency. No change in the polyion hydrodynamic interaction upon dilution is observed, as determined from Zimm model fits of the reduced modulus vs frequency at finite polymer concentrations. The origin of the viscoelasticity maximum is explained in terms of an electrostatically driven polyion coil expansion and contraction resulting in the scaling of the relaxation spectrum by the longest relaxation time τ1.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2635-2642 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Viscosities of dilute solutions of linear poly(2-vinyl pyridine) with molecular weights ranging from 3.0×104 to 1.0×106 have been measured under conditions where the polymer can be charged by protonation. By employing weakly acidic solvents, large reduced viscosities typical of polyelectrolytes in low-salt solutions are observed. They exhibit a pronounced maximum occurring at a concentration which is independent of molecular weight. Separate pH titrations are used to calculate polyion charge density and electrostatic screening lengths. The origin of the viscosity maximum is explained by consideration of changing electrostatic persistence lengths on dilution, resulting in polyion coil expansion and contraction. Investigations of limiting conditions of low charge density and full electrostatic screening with basic and high acid or salt solutions reveal expected normal polymer behavior in concentration extrapolations to the intrinsic viscosity.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7653-7663 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Viscosities and diffusion coefficients of dilute solutions of molecular weight matched cyclic and liner poly(2-vinyl pyridine) samples with molecular weights ranging from 2.8×104 to 1.0×105 have been measured under conditions where the polymer can be charged by protonation. Limiting conditions of high charge density and full electrostatic screening with high acid concentration solutions show expected normal polymer behavior in extrapolations to the intrinsic viscosity and infinite dilution diffusion coefficients. By employing weakly acidic solvents, large reduced viscosities, typical of polyelectrolytes in low salt solutions are observed. A pronounced maximum in reduced viscosity occurs at a concentration which is independent of molecular weight and topology. Values of the reduced viscosity are lower for the cyclic samples over all concentrations investigated. Independent pH titrations are used to calculate polyion charge density and electrostatic screening lengths. Possible origins of the viscosity maxima are explored.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2780-2784 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new data-acquisition and averaging system is described which rapidly digitizes and averages periodic signals of known frequency. Each acquisition channel has a programmable gain input amplifier, track and hold amplifier, 12 bit analog to digital converter, 4K by 32 bit memory buffer, and an arithmetic logic unit which adds the converter output directly to the contents of the current memory location. In the present implementation, two channels are used in parallel with a common sampling clock at rates up to 1.35 MHz. With real time "add to memory'' capability, signal averaging can be continued to any desired degree in order to improve the signal-to-noise ratio and reject contributions from harmonics and asynchronous frequencies. This type of acquisition system is most suitable where a periodic signal of known frequency is applied to an experimental device and the system's response, at the same frequency, must be accurately determined. The phase resolution of better than ±0.001° which this system provides, is particularly important for analysis of a "drive and response'' experiment of this type.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 2049-2056 
    ISSN: 0887-6266
    Keywords: cyclic block copolymer ; theta conditions ; light scattering ; micellization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A unique diblock copolymer ring and its linear triblock copolymer precursor composed of polystyrene and polydimethylsiloxane have been characterized by static and dynamic light scattering in dilute solution. The measurements were carried out with cyclohexane as the solvent over a temperature range of 12-35°C. Cyclohexane has the useful property that it is nearly isorefractive with the PDMS so that the PDMS block segments are invisible to the light-scattering technique and it is a theta solvent for polystyrene at 34.5°C. The block polymers in this work contain 35.1 wt % of styrene as determined by proton NMR. In the linear triblock polymer, the polystyrene is the center block with PDMS blocks on each side. Static light scattering measurements give 4.31 × 104 for the average molecular weight of the whole polymer. Light scattering also shows that the apparent theta temperature for the linear triblock is shifted by 15°C to a value of 20°C at which point the second virial coefficient drops sharply and phase separation begins to induce aggregation. The diblock ring, however, shows a strongly positive second virial coefficient and no aggregation even at 12°C which is the limit of these experiments. The diffusion coefficients of cyclic diblock (Dc) and linear triblock copolymer (D1) are measured by dynamic light scattering. The ratio of diffusion coefficients of cyclic and linear copolymers at 14.9°C and 30°C are Dc/Dl = 1.13 and 1.107 respectively. These compare well with prediction of 1.18 for this ratio from consideration of the hydrodynamics of matched linear and cyclic polymer chains. Dynamic light scattering quantitatively confirms that the linear copolymer experiences a solvent quality change near 20°C but the cyclic polymer remains in good solvent over the entire experimental temperature range. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 1990-04-01
    Print ISSN: 0024-9297
    Electronic ISSN: 1520-5835
    Topics: Chemistry and Pharmacology , Physics
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  • 8
    Publication Date: 1991-03-15
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 9
    Publication Date: 1990-01-01
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 10
    Publication Date: 1991-11-15
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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