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  • 1
    Electronic Resource
    Electronic Resource
    A novel experimental procedure for removing ambiguity from the interpretation of neutron and x-ray reflectivity measurements: "Speckle holography'' (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 732-738 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The analysis of neutron or x-ray reflectivity data to obtain density profiles close to surfaces is akin to the notorious phaseless Fourier problem, well known in many fields such as crystallography. It is a difficult problem because a highly nonlinear transform relates the density profile to the data; this results in the existence of several very different solutions, which are also hard to find. A novel experimental procedure is presented, the analogue of astronomical speckle holography, which is designed to eliminate the ambiguity problems inherent in traditional reflectivity measurements. The theoretical basis of this procedure is explained, and it is illustrated with a simple example using both simulated and real experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349629
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Multilevel structure of reinforcing silica and carbon (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 587-591 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Using small-angle x-ray (SAXS), neutron (SANS), x-ray diffraction and light scattering, we study the structure of colloidal silica and carbon on length scales from 4 Å 〈 q−1 〈 107 Å where q is the magnitude of the scattering vector. These materials consist of primary particles of the order of 100 Å, aggregated into micron-sized aggregates that in turn are agglomerated into 100 µ agglomerates. The diffraction data show that the primary particles in precipitated silica are composed of highly defective amorphous silica with little intermediate-range order (order on the scale of several bond distances). On the next level of morphology, primary particles arise by a complex nucleation process in which primordial nuclei briefly aggregate into rough particles that subsequently smooth out to become the seeds for the primaries. The primaries aggregate to strongly bonded clusters by a complex process involving kinetic growth, mechanical disintegration and restructuring. Finally, the small-angle scattering (SAS) data lead us to postulate that the aggregates cluster into porous, rough-surfaced, non-mass-fractal agglomerates that can be broken down to the more strongly bonded aggregates by application of shear. We find similar structure in pelletized carbon blacks. In this case we show a linear scaling relation between the primary and aggregate sizes. We attribute the scaling to mechanical processing that deforms the fractal aggregates down to the maximum size able to withstand the compaction stress. Finally, we rationalize the observed structure based on empirical optimization by filler suppliers and some recent theoretical ideas due to Witten, Rubenstein and Colby.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800001199
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of 2-phenylacetophenone (1993)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 406-408 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270192009442
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  • 4
    Electronic Resource
    Electronic Resource
    Morphology of titania coatings on silica gel (1997)
    Springer
    Catalysis letters 45 (1997), S. 165-175 
    Details
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Control of the hydrolysis and condensation of soluble precursors of titanium is shown to yield oxide coatings of well-defined morphology. A ``smooth'' coating, consisting of patches of titania on silica, causes only a small increase in the surface area, from 130 m2/g for the uncoated silica gel to 154 m2/g. On the other hand, the ``rough'' coating, which consists of 3 nm diameter titania particles dispersed over the silica surface, results in an increase in the BET surface area to 350 m2/g. The specific titania surface area was determined via isopropanol dehydration activity and was found to be comparable to the BET surface area indicating that the titania phase is responsible for the increase in surface area. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) provide definitive evidence for the coating morphology while X-ray photoelectron spectroscopy (XPS) was used to determine the dispersion of the titania. The supported titania maintains its surface area upon calcination at temperatures up to 873 K while unsupported titania looses much of its surface area. Also demonstrated in this work is a novel preparation method using titanium bis-ammonium lactato dihydroxide (TALH), a water soluble precursor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019096419053
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  • 5
    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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