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" Electron spin resonance studies of solute-solvent interaction in liquid crystalline solvents "
M. A. M. Morsy
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Latin Dissertation
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English
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| Record Number
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1113284
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TLpq304081067
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| Main Entry
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M. A. M. Morsy
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| Title & Author
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Electron spin resonance studies of solute-solvent interaction in liquid crystalline solvents\ M. A. M. Morsy
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| College
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King Fahd University of Petroleum and Minerals (Saudi Arabia)
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| Date
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1993
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| student score
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1993
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| Degree
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Ph.D.
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| Page No
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219
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| Abstract
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An extensive study of interactions between nitroxide spin probes and liquid crystalline solvent molecules has been carried out. The solvents studied are the pentyl (5CB), hexyl (6CB), heptyl (7CB), and octyl (8CB) members of the p-n-alkyl-p-cyanobiphenyl series. From analysis of the ESR spectra anisotropic ordering, line shapes, and relaxation times for PD-Tempone nitroxide radical in the different liquid crystals were obtained. The effect of the molar structure of the branched and unbranched nonane solutes on the nematic-to-isotropic transition temperature (T) in the studied solvents have been investigated. Also, ESR measurements on solutions of nonmesomorphic solutes in the nematic liquid crystalline solvents systems have been carried out to determine their phase diagrams. The results show that both the hyperfine splitting and the g-value depend on the ordering matrix parameter. However, the g-value is also related to the conformational properties of the liquid crystal molecules. Based on the g-values determined, 5CB and 7CB fall into one category and 6CB and 8CB into another. Moreover, hyperfine splitting values were used to arrive at values for the order parameter of the spin probe at different temperatures. Also the order parameter values were used to explain the odd behavior exhibited by 6CB. The line width analysis of PD-Tempone spectra at different temperatures in the nematic and isotropic phases of 5CB was carried out to examine the different factors affecting the relaxation mechanism of PD-Tempone. Our analysis shows anisotropy in both the nematic and isotropic phases, orientational-fluctuation on either sides of the nematic-to-isotropic transition, and the ordering potential in the nematic phase to be the main factors influencing the relaxation mechanism of PD-Tempone. By using n-nonane, 3,3-diethylpentane (tetraethyl methane), t-propyltin, and t-butyltin solutes, impurity-liquid crystalline solvent interactions were studied. Promising results obtained in this part support the solvents' classification suggested in the previous part and point to the semiflexible nature of the alkyl-tails of the liquid crystal molecules. The results suggest that the ability of the solute to disturb the order of the liquid crystalline solvents depends on the molecular structure of the solute as well as the chain length of the semiflexible alkyl-tail on the liquid crystal solvent molecule. Also, these ESR studies allowed the detection of a slight curvature in the coexistence lines in the reduced temperature (T*(=T/TNI)) versus solutes' mole fractions (x2) phase diagrams at low x2 values.
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Chemistry
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Chemistry
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Organic chemistry
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Pure sciences
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