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  • 1
    Electronic Resource
    Electronic Resource
    X-ray diffraction study of a Langmuir monolayer of C21H43OH (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2257-2270 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the structure of a monolayer of C21H43OH on water, in the region near close packing, by grazing incidence in-plane x-ray diffraction. For all temperatures studied the isotherms in the πa plane show a kink, signaling a phase transition. Along an isotherm, and for pressures above the kink, we observe that the transverse structure factor has one peak which has constant position, width, and intensity; below the kink the diffraction peak shifts to smaller scattering vector (larger separation) and the amplitude decays as the surface pressure decreases, but the width of the peak remains constant. We rationalize these observations in terms of the influence on the transverse structure factor of gauche configurations in the amphiphile tails, with the kink representing the point at which the last of the gauche configurations is squeezed out of the chain. Along an isobar which is at higher pressure than the kink pressures of all isotherms crossed, the transverse structure factor has a single peak above a transition temperature and two peaks below that temperature; for π=30 dyn/cm the transition temperature is in the range 16.3〈T〈21.3 °C. We interpret this observation, by comparison with the properties of the lamellar crystalline n-paraffins, as a hexagonal-to-pseudohexagonal structural transition analogous to the crystal rotator II-to-rotator I transition. Our results imply that the hydrocarbon tails of the amphiphile molecules dominate the properties of the monolayer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455068
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray reflection study of adsorption of a fluorosurfactant from an organic solution (1994)
    s.l. : American Chemical Society
    Langmuir 10 (1994), S. 2866-2868 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00021a005
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  • 3
    Electronic Resource
    Electronic Resource
    The validity of approximations made in differential anomalous X-ray scattering (1995)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 679-683 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Approximations of weighting-factor functions are used when determining coordination numbers from differential anomalous scattering (DAS) experiments. The accuracy of two single-value approximations for the weighting functions are tested using non-interacting hard-sphere models of systems that have been studied previously with DAS. The first approximation is an average of the weighting-factor function over the experimental wavevector range. The second is the weighting-function value at the wavevector that is related to a peak position in the corresponding differential radial distribution function (dRDF). It was found that the first approximation introduced up to 10% error into calculated coordination numbers. The second weighting-factor approximation introduced minimal error into the coordination-number calculations and is simple to use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767395004156
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  • 4
    Electronic Resource
    Electronic Resource
    Strategies for supercritical CO2 fractionation of polydimethylsiloxane (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 55 (1995), S. 773-778 
    Details
    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: The fractionation of polydimethylsiloxane (PDMS) using supercritical CO2 was studied to determine the parameters of pressure and temperature required to separate specific molecular weights. On a laboratory scale, we show that this fractionation method can quickly provide gram quantities of the polymer with a polydispersity of around 1.2 for molecular weights in excess of 200 kg/mol. This technique has obvious applications in the preparation of PDMS for surface-related uses. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070550514
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