Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 2 (2000), S. 191-198 
    ISSN: 1292-895X
    Keywords: PACS. 61.10.Eq X-ray scattering (including small-angle scattering) - 61.30.-v Liquid crystals - 82.70.Dd Colloids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We report small-angle X-ray scattering experiments performed in both the isotropic and nematic phases of aqueous V2O5 suspensions. We show that the scattering in the isotropic phase can be well described in the whole accessible q-range by only considering the form factor of non-interacting ribbons. We investigate the influence of concentration and pH on the dimensions of V2O5 ribbons and show that these parameters do not have any significant effect, as long as the system stays well within the chemical stability domain of the ribbons. We then show that nematic single domains display an anisotropic small-angle scattering pattern, even at scattering vectors small compared to that at which a characteristic correlation peak is observed. This feature is expected for a nematic phase, but was rarely observed. We finally try to describe this scattering within the framework of theories developed for the structure factor of a nematic polymer, and we reach the conclusion that chain ends are certainly important to understand this pattern.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 592-596 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The smart thermo-optical systems studied here are based on the unusual thermoreversible sol-gel transition of zirconyl chloride aqueous solution modified by sulfuric acid in the molar ratio Zr/SO4:3/1. The transparency to the visible light changes during heating due to light scattering. This feature is related to the aggregates growth that occurs during gelation. These reversible changes can be controlled by the amount of chloride ions in solution. The thermoreversible sol-gel transition temperature increases from 323 to 343 K by decreasing the molar ratio Cl/Zr from 7.0 to 1.3. In this work the effect of the concentration of chloride ions on the structural characteristics of the system has been analyzed by in situ SAXS measurements during the sol-gel transition carried out at 323 and 333 K. The experimental SAXS curves of sols exhibit three regions at small, medium and high scattering vectors characteristics of Guinier, fractal and Porod regimes, respectively. The radius of primary particles, obtained from the crossover between the fractal and Porod regimes, remains almost invariable with the chloride concentration, and the value (4 Å) is consistent with the size of the molecular precursor. During the sol-gel transition the aggregates grow with a fractal structure and the fractal dimensionality decreases from 2.4 to 1.8. This last value is characteristic of a cluster-cluster aggregation controlled by a diffusion process. Furthermore, the time exponent of aggregate growth presents values of 0.33 and 1, typical of diffusional and hydrodynamic motions. A crossover between these two regimes is observed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 727-732 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Aqueous suspensions of vanadium pentoxide (V2O5) ribbons, also called Zocher phases, are known to display a lyotropic nematic phase. In this paper, it is shown how the small-angle X-ray scattering (SAXS) technique can provide useful information on the building blocks and their organization in this phase. SAXS experiments were performed either on unoriented samples or on samples aligned by a magnetic field or by shear flow. The scattering is comparable to that of the other classic lyotropic nematic phases displayed by stiff organic rod-like particles such as the tobacco mosaic virus. Scattering studies show that the building blocks have a ribbon shape, that their thickness is 9 (1) Å and indirectly that their width is several 100 Å. Their length is known to be around a few thousand Å and therefore could not be measured by SAXS. By following the average distance between the ribbons as a function of concentration, it is shown that the swelling of the phase is one-dimensional at large concentrations and two-dimensional at low concentrations. Finally, estimates of the nematic order parameter of a single domain sample and of samples sheared in a Couette cell have been obtained.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 12 (1999), S. 541-546 
    ISSN: 1434-6036
    Keywords: PACS. 61.10.Eq X-ray scattering (including small-angle scattering) – 61.30.-v Liquid crystals – 64.70.Md Transitions in liquid crystals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Aqueous suspensions of V2O5 ribbons are one of the very few examples of mineral liquid crystals. In the concentrated regime, we show that these ribbons organize in a biaxial nematic gel phase. A Couette shear cell was used to produce a well oriented sample for in situ synchrotron X-ray scattering studies. We observed two perpendicular anisotropic sections of reciprocal space, which proves the biaxial symmetry of the nematic order. The thermodynamic and flow properties of the biaxial nematic are well described by hard-core theories. We suggest the use of a shear geometry to produce and investigate single domains of other biaxial nematics, reported but still questioned in the literature.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 47 (1996), S. 1545-1565 
    ISSN: 1572-8943
    Keywords: cocoa butter ; fat crystallization ; DSC ; fat polymorphism ; fat structure ; fats ; lard ; milk fat ; triacylglycerols ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal behavior of three ural fats (displaying very different composition), cocoa butter (CB)2, lard, and a stearin obtained from anhydrous milk-fat (AMF) fractionation, were studied by both DSC and X-ray diffraction as a function of temperature (XRDT). To perform temperature explorations between −30
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 5 (1994), S. 79-89 
    ISSN: 1042-7147
    Keywords: Copolymers bropylene-7 methyl 1-6 octadiene ; Sulfonation ; Ionomers aggregation state ; Mechanical properties ; 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
    Notes: Polypropylene ionomers have been prepared by sulfonation of copolymers of propene and 7 methyl, 1-6 octadiene, followed by neutralization to cesium salts. Both WAXS and SAXS were used to study the morphology of the samples, while their thermal properties were studied by DSC and their mechanical properties by DMTA. The sulfonation process is shown to cause a further drop in crystallinity in addition to the effect of comonomer incorporation. Ion clustering is observed when the extent of sulfonation is high enough, the limit being dependent on the copolymer composition. The ion pairs which are not incorporated into the cluster cause a small-angle upturn in the WAXS pattern. The mechanical properties are strongly affected by the drop in crystallinity, but may be partly recovered due to ion clustering. No disruption of the ion clusters is observed before thermal decomposition of the polymer.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...