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  • 1
    Electronic Resource
    Electronic Resource
    Small-Angle Scattering from Polymeric Mass Fractals of Arbitrary Mass-Fractal Dimension (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 29 (1996), S. 134-146 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Debye equation for polymer coils describes scattering from a polymer chain that displays Gaussian statistics. Such a chain is a mass fractal of dimension 2 as evidenced by a power-law decay of −2 in the scattering at intermediate q. At low q, near q ∼ 2π/Rg, the Debye equation describes an exponential decay. For polymer chains that are swollen or slightly collapsed, such as is due to good and poor solvent conditions, deviations from a mass-fractal dimension of 2 are expected. A simple description of scattering from such systems is not possible using the approach of Debye. Integral descriptions have been derived. In this paper, asymptotic expansions of these integral forms are used to describe scattering in the power-law regime. These approximations are used to constrain a unified equation for small-angle scattering. A function suitable for data fitting is obtained that describes polymeric mass fractals of arbitrary mass-fractal dimension. Moreover, this approach is extended to describe structural limits to mass-fractal scaling at the persistence length. The unified equation can be substituted for the Debye equation in the RPA (random phase approximation) description of polymer blends when the mass-fractal dimension of a polymer coil deviates from 2. It is also used to gain new insight into materials not conventionally thought of as polymers, such as nanoporous silica aerogels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889895011605
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Interpenetrating and pseudo-interpenetrating polymer networks of polyethylacrylate and zeolite 13X (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 673-677 
    Details
    ISSN: 0887-624X
    Keywords: polyethylacrylate ; interpenetrating polymer networks ; zeolite 13X ; pseudo IPN ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Free radical polymerization of liquid ethylacrylate in the presence of zeolite 13X yielded PIPNs without crosslinker and IPNs if the crosslinker ethylene glycol dimethacrylate was present. We studied these materials both unextracted as well as partially extracted with a variety of solvents using DSC, SEM as well as Small Angle X-ray Scattering (SAXS). These studies suggest that in the composites polyethylacrylate chains entered the internal pores of the zeolite. These chains had an extended state and did not exhibit a bulk glass transition, a similar behavior to that previously reported for polystyrene/zeolite 13X composite. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Nano-structured, semicrystalline polymer foams (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 3063-3072 
    Details
    ISSN: 0887-6266
    Keywords: nano-structured foams ; semicrystalline polymers ; small-angle scattering ; platelet model ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Semicrystalline polymers gelled from thermally quenched semidilute solutions can, in some cases, be supercritically dried to produce nano-structured foams of exceedingly high specific surface area. This article investigates the nano-morphology of these semicrystalline foams. The common morphological feature that these systems display in small-angle scattering can be described by uncorrelated lamellar platelets. The morphological details, which can be obtained using microscopy and small-angle scattering, indicate that these low-density systems occupy a morphological niche between polymeric crystallites from dilute solutions, and spherulitic crystals derived from concentrated solutions and melts. Because these crystalline morphologies occur in concentration ranges between dilute and concentrated, they may offer simple insight into the mechanisms available for distortion of ideal, dilute-solution-derived crystallites as polymer concentration is increased. Several mechanisms for the observed distortions are proposed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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