A nuclear magnetic resonance study of orientational ordering in thermotropic liquid crystals
A nuclear magnetic resonance study of orientational ordering in thermotropic liquid crystals
The work presented in this thesis is concerned with the study of orientational ordering in thermotropic liquid crystals by means of Fourier Transform Nuclear Magnetic Resonance spectroscopy. Particular emphasis has been placed on a detailed study of the 4-n-alkoxy-4'-cyanobiphenyl (n-OCB) homologous series; a range of liquid crystals which find extensive applications in liquid crystal display devices. Thus in Chapter 2 we present a study of selected members of the n-OCB series in the nematic phase. The orientational ordering along the flexible alkyl chain is determined by deuterium NMR spectroscopy and the experimental results compared with theoretical predictions. The conformational probabilities are calculated and a predictive theory is developed which is used to anticipate the behaviour of other members in the n-OCB series. Chapter 3 is concerned with a study of field-induced orientational ordering in the pretransitional region. We again employ deuterium NMR to study the behaviour of the first four members of the n-OCB series in the isotropic phase. An analysis similar to that presented in Chapter 2 is carried out and results for the isotropic and nematic phases are compared. In Chapter 4 we present a study of solute alignment in the n-OCB homologous series. Fully deuteriated para-xylene(d10)is employed as a solute and the liquid crystal solvents consist of the first twelve members of the series. We are then able to investigate in detail the effect of increasing the chain length on orientational ordering. The structure of para-xylene is known and we are able to calculate both the major order parameter and the biaxiality as a function of temperature for this solute. Chapter 5 is also concerned with solute aligment in liquid crystals but the ten solvents used now vary radically in their structures. Fully deuteriated para-xylene is again used as a solute and the results in Chapters 4 and 5 are compared. The anomalous behaviour observed for the solute in the smectic phases of the solvents HAB and 5-0-5 has been interpreted by the adoption of a two-site model in which the solute interacts preferentially with the core or chain regions of the solvent. A test of this model by simultaneous measurement of the ordering in both the solute and solvent shows good agreement with similar studies using different solutes. Finally a study of the orientational ordering of para-xylene in the binary mixtures PCH7/EBBA and ZLI-1132/EBBA is presented. A model has been proposed to account for the results obtained which, although capable of fitting the observed data, still needs to be validated experimentally.
University of Southampton
1987
Sachdev, Harpreet Singh
(1987)
A nuclear magnetic resonance study of orientational ordering in thermotropic liquid crystals.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The work presented in this thesis is concerned with the study of orientational ordering in thermotropic liquid crystals by means of Fourier Transform Nuclear Magnetic Resonance spectroscopy. Particular emphasis has been placed on a detailed study of the 4-n-alkoxy-4'-cyanobiphenyl (n-OCB) homologous series; a range of liquid crystals which find extensive applications in liquid crystal display devices. Thus in Chapter 2 we present a study of selected members of the n-OCB series in the nematic phase. The orientational ordering along the flexible alkyl chain is determined by deuterium NMR spectroscopy and the experimental results compared with theoretical predictions. The conformational probabilities are calculated and a predictive theory is developed which is used to anticipate the behaviour of other members in the n-OCB series. Chapter 3 is concerned with a study of field-induced orientational ordering in the pretransitional region. We again employ deuterium NMR to study the behaviour of the first four members of the n-OCB series in the isotropic phase. An analysis similar to that presented in Chapter 2 is carried out and results for the isotropic and nematic phases are compared. In Chapter 4 we present a study of solute alignment in the n-OCB homologous series. Fully deuteriated para-xylene(d10)is employed as a solute and the liquid crystal solvents consist of the first twelve members of the series. We are then able to investigate in detail the effect of increasing the chain length on orientational ordering. The structure of para-xylene is known and we are able to calculate both the major order parameter and the biaxiality as a function of temperature for this solute. Chapter 5 is also concerned with solute aligment in liquid crystals but the ten solvents used now vary radically in their structures. Fully deuteriated para-xylene is again used as a solute and the results in Chapters 4 and 5 are compared. The anomalous behaviour observed for the solute in the smectic phases of the solvents HAB and 5-0-5 has been interpreted by the adoption of a two-site model in which the solute interacts preferentially with the core or chain regions of the solvent. A test of this model by simultaneous measurement of the ordering in both the solute and solvent shows good agreement with similar studies using different solutes. Finally a study of the orientational ordering of para-xylene in the binary mixtures PCH7/EBBA and ZLI-1132/EBBA is presented. A model has been proposed to account for the results obtained which, although capable of fitting the observed data, still needs to be validated experimentally.
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Published date: 1987
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Local EPrints ID: 460757
URI: http://eprints.soton.ac.uk/id/eprint/460757
PURE UUID: 87e46b9d-66ca-4e69-8df4-e029b1751d3e
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Date deposited: 04 Jul 2022 18:29
Last modified: 04 Jul 2022 18:29
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Author:
Harpreet Singh Sachdev
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