CARBON-13 NMR STUDIES OF LIQUID CRYSTALS

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High resolution, proton decoupled {sup 13}C nmr are observed for a series of neat nematic liquid crystals, the p-alkoxyazoxybenzenes, and a smectic-A liquid crystal, diethylazoxydibenzoate in a magnetic field of 23 kG. The (uniaxial) order parameters S = <P{sub 2}(cos{theta})> are found to be about 0.4 and 0.9 for the nematic and smectic-A phase respectively at the clearing points. The order parameter increases with decreasing temperature in the nematic phase but is constant, or nearly so, with temperature in the smectic-A phase. In the nematic series studied, the ordering exhibits an even-odd alternation along the series and qualitative agreement with ... continued below

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124 p.

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Allison, Stuart June 1, 1975.

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High resolution, proton decoupled {sup 13}C nmr are observed for a series of neat nematic liquid crystals, the p-alkoxyazoxybenzenes, and a smectic-A liquid crystal, diethylazoxydibenzoate in a magnetic field of 23 kG. The (uniaxial) order parameters S = <P{sub 2}(cos{theta})> are found to be about 0.4 and 0.9 for the nematic and smectic-A phase respectively at the clearing points. The order parameter increases with decreasing temperature in the nematic phase but is constant, or nearly so, with temperature in the smectic-A phase. In the nematic series studied, the ordering exhibits an even-odd alternation along the series and qualitative agreement with a recent theory due to Marcelja is found. In both phases, the spectra show that the molecule rotates rapidly about its long axis. Tentative conclusions about molecular conformational motion and {sup 14}N spin relaxation are presented for both nematic and smectic-A phases. In the smectic-A phase, the sample is rotated about an axis perpendicular to H{sub 0} and the resulting spectra are discussed. The theory of observed chemical shifts in liquid crystals is treated in an appendix. Equations are derived which relate the nmr spectra of liquid-crystals to the order parameters. A model for the smectic-C phase due to Luz and Meiboom and Doane is described and lineshapes are determined on the basis of this model for special cases. Experiments on smectic-C liquid crystals are currently underway for comparison with the theory. Also treated in an appendix is the dependence of the order parameters on the molecular potential which give rise to the various degrees of order in the different liquid crystalline phases. To a good approximation the functional dependence of the order parameters on the molecular potential is shown to be a simple one in the limit of small tilt angle in the smectic-C phase.

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124 p.

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  • Related Information: Designation of Academic Dissertation: Masters; Academic Degree: M.S.; Name of Academic Institution: UC Berkeley

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  • Report No.: LBL-4506
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 937062
  • Archival Resource Key: ark:/67531/metadc900954

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  • June 1, 1975

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  • Sept. 27, 2016, 1:39 a.m.

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  • Sept. 30, 2016, 7:21 p.m.

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Allison, Stuart. CARBON-13 NMR STUDIES OF LIQUID CRYSTALS, thesis or dissertation, June 1, 1975; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc900954/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.