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Mossbauer Studies of Liquid Crystals

Mossbauer studies of glassy nematic [4-6], cholesteric [7, 8] and smectic [9-12] liquid crystals allow the determination of characteristic Debye temperatures, order parameters, intramolecular and lattice contributions to the nuclear vibrational anisotropy, and molecular orientation [13] in the liquid crystal states. For example, Bekeshev et al. have shown from In/ versus temperature data at very low temperatures that MBBA [A -(/7-methoxybenzylidene)-/7-bu-tylaniline] and some liquid-crystalline di-substituted derivatives of ferrocene have weak intermolecular bonds that result in the appearance of additional degrees of free-... [Pg.760]

Besides NQR spectroscopy and the study of nuclear quadrupole interaction effects in broad-line NMR spectroscopy, paramagnetic electron resonance 6°1, Mossbauer spectroscopy, and the study of perturbed angular correlation of y-rays, are suitable methods for studying nuclear quadrupole interactions in solids. Indirect methods are also available for acquiring information about the nuclear quadrupole couplinjg constant from the liquid state (particularly NMR spectroscopy in liquids and in liquid crystals in some cases gives information about this constant). By microwave spectroscopy, the nuclear quadrupole interaction may be studied in the gaseous phase (see the paper by Zeil). We shall deal here only with the aspect of NQR spectroscopy in solids since this method has the broadest applicability to chemical problems in comparison with the other methods mentioned. [Pg.4]

Equation (1.10) indicates that the probability of zero-phonon emission decreases exponentially with the square of the y-ray energy. This places an upper limit on the usable values of Ey, and the highest transition energy for which a measurable Mdssbauer effect has been reported is 155 keV for Os. Equation 1.10 also shows that/increases exponentially with decrease in which in turn depends on the firmness of binding and on the temperature. The displacement of the nucleus must be small compared to the wavelength X of the y-ray. This is why the Mossbauer effect is not detectable in gases and non-viscous liquids. Clearly, however, a study of the temperature dependence of the recoil-free fraction affords a valuable means of studying the lattice dynamics of crystals. [Pg.10]

Recently, Deacon, Price, and coworkers reported the synthesis and study of polymers containing triphenyl and tributyltin as side chains and of polystannanes produced using the Wurtz polymerization [59]. The polystannanes were characterized employing Mossbauer spectroscopy. The polystannane shown below exhibits some liquid-crystal behavior. The products have weight average molecular weights of 2.5 10. The coordination number for tin is 4 with the tin present as a distorted tetrahedral geometry (4). [Pg.304]

Mossbauer spectroscopy is a nondestructive technique which probes a specific element which may occupy one or more crystallographic sites, may have one or more electronic configurations, and may or may not carry a magnetic moment. The absorbers may be in the form of single crystals, powders, foils, surfaces, or frozen solutions solutions or liquids can not be studied. The influence of temperature, pressure, applied magnetic field, and electromagnetic irradiation is easily studied by Mossbauer spectroscopy. [Pg.270]

Studies of molecular mobility in various microregions of polymeric liquid crystals were made by Kosova et al. [25]. Estimates of characteristic Debye temperatures and mean square vibrational amplitudes of the label molecules ferrocene (F) and ferrocene aldehyde (FA) were used to determine the rigidity of regions in both the vitreous and liquid crystal phases of poly l-[2-(4 -cyano-4-biphenyloxy)undecyloxycarbonyl]ethylene (CBO-II-PM). Mossbauer spectra obtained in these studies are shown in Fig. 1. [Pg.762]


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Mossbauer studies

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