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  • Conference proceedings  (1)
  • FT-IR spectroscopy  (1)
  • Living polymers gels  (1)
  • hydrogen bonded structures  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    Dielectric properties of solutions of antimony (III) halides in methanol (1993)
    Springer
    Journal of solution chemistry 22 (1993), S. 1063-1071 
    Details
    ISSN: 1572-8927
    Schlagwort(e): Antimony trihalides ; methanol ; dielectric properties ; hydrogen bonded structures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The complex permittivities obtained by time domain reflectometry (TDR) measurements in the frequency range 0.1–15 GHz are reported for solutions of SbF3, SbCl3 and SbBr3 in methanol at 25°C. By increasing the concentration of the solutes, a marked increase of the main relaxation time and of the static permittivity of methanol is observed. These effects have been attributed to the ability of antimony (III) halides to strengthen the hydrogen bonding in methanol and to promote the shift of the dynamic equilibria among the various populations of hydrogen bonded methanol aggregates toward those characterized by a parallel orientation of neighboring dipoles. A second relaxation, occurring at low frequencies, was attributed to the rotational dynamics of the solvated solute molecules.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00647729
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  • 2
    Digitale Medien
    Digitale Medien
    Sol-gel transition in worm-like micelles (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 771-781 
    Details
    ISSN: 0392-6737
    Schlagwort(e): Neutron scattering techniques (including small-angle scattering) ; Gels and sols ; Brillouin and Rayleigh scattering ; Conference proceedings
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Summary The statical and dynamical properties of lecithin/H2O/cyclohexane cylindrical reverse micelles are investigated as a function of lecithin volume fraction, ϕ, and temperature at fixed water/lecithin ratio,w 0. The viscosity data are well fitted by the Cates model when the breathing mode of micelles is taken into consideration, overlapping with the breaking and reforming mechanisms. We present some results from Brillouin-scattering experiment, performed across the sol-gel transition. In order to explain the experimentally observed ϕ-dependence of the hyperacoustic parameters, a mechanical model was developed from which the ϕ-dependence of the micelle size distribution was obtained. From a comparison with the viscosity data the entanglement length was estimated. Furthermore some new results from an incoherent quasi-elastic neutron scattering experiment are presented. The whole body of the experimental results suggests for a sol-gel transition triggered by topologic phenomena. When the lecithin volume fraction increases, the kinetic equilibrium between the breaking and reforming mechanisms of the micelles shifts the mean micelle length towards higher values and the entanglement of the micelles becomes highly favourable. The obtained results are discussed and compared with other findings in literature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02456723
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  • 3
    Digitale Medien
    Digitale Medien
    About entangled networks of worm-like micelles: a rejected hypothesis (1996)
    Springer
    Colloid & polymer science 274 (1996), S. 809-818 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Living polymers gels ; reverse micelles ; SANS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract We report new results from small-angle neutron scattering ond 12-cyclohexane/lecithin/water micellar solutions performed as a function of the water content (w 0), temperature (T) and dispersed phase volume fraction (ϕ). The data from dilute samples are interpretable in terms of the existence of giant cylindrical reverse micelles and are well fit with a core-shell model (that provides the micelle structure and dimensions) with values of 28 and 45 Å for the inner core and the outer shell radii, almost independent on temperature and concentration. Such a result could appear consistent with the current idea that worm-like micelles are living polymers. On the contrary, the appearance of a sharp interference maximum at high concentrations (ϕ〉0.15) suggests arguments against the current hypothesis of an entangled network of giant flexible cylinders. Further arguments against the current hypothesis are given by the close similarity between the above described results and those from free of water micelles (for sure not cylinders). All the data are well fitted in terms of a unique model taking into account the micellar form factor plus a hard sphere structure factor. The data analysis suggests a micellar size distribution determined by the competition between concentration and interaction effects on which temperature plays not a minor role. Following our results, the current hypothesis of a gel structure in terms of an entangled network can be assumed as wrong and some caution has to be taken in assuming wormlike micelles as living polymers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00654738
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  • 4
    Digitale Medien
    Digitale Medien
    Study of lecithin reverse micelles by FT-IR spectroscopy (1997)
    Springer
    Colloid & polymer science 105 (1997), S. 220-223 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Lecithin ; giant micelles ; organogels ; FT-IR spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract FT-IR spectra of water/lecithin/deuterated cyclohexane microemulsions as a function of water/lecithin molar ratioR (R=[water]/[lecithin]) at various lecithin volume fractions (φ) have been recorded. After elimination of the spectral contributions due to the deuterated cyclohexane and normalization, the band parameters of the CO and PO4 vibrational modes due to lecithin have been found dependent only uponR. This behaviour has been interpreted in terms of a progressive structural modification of the water/lecithin interface superimposed to the progressive hydration of CO and PO4 groups. Moreover, no correlation between the CO and PO4 band parameters and the formation of gel-like micellar solutions has been found. This and other spectral features allow us to raise some doubts on the current structural picture of gel-like micellar solutions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01188954
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