Magnetic resonance studies of flexible molecules in liquid crystals
Magnetic resonance studies of flexible molecules in liquid crystals
This thesis is concerned with the investigation of flexible solutes dissolved in uniaxial liquid crystals and liquid crystals themselves using the techniques of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy. A resume of the salient features of the various mesophases is presented in Chapter 1 together with a discussion of the characterisation of the orientational order in both ideal and real systems. Theories of orientational ordering of rigid molecules in uniaxial liquid crystals and a consideration of its extension to flexible molecules are also reviewed. In the second chapter it is shown how electron resonance and nuclear magnetic resonance spectroscopy maybe employed to probe the orientational properties of liquid crystals. The background theory related with molecular reorientation and spin relaxation of a spin probe in uniaxial mesophases is also described. In Chapter 3 the extension of the molecular field theory of uniaxial mesophases for rigid molecules to allow for its flexibility is outlined. This theory is used to calculate the orientational order along the n-octane and n-heptane solutes dissolved in uniaxial mesophases. These calculations are compared with the DMR results for fully deuteriated n-octane-d18 and n-heptane-d16 dissolved in the nematic phases of Phase V and E5. In the fourth chapter the orientational order of fully deuteriated n-octane-d18 and n-heptane-d16 are compared with that of doxyl substituted n-octane and n-heptane dissolved in the nematic phase of HAB. This study is extended to the spin labelled odd membered n-alkanes 4-doxyl-n-heptane, 6-doxyl-n-unde cane, 6-doxyl-n-pentadecane and 9-doxyl-n-heptadecane to probe the smectic A phase of HAB. Both the static and dynamic aspects involved with these n-alkane spin probes are discussed by analysing the angular dependence of the electron resonance linewidths in the smectic A phase of HAB. The linewidths observed in 0-terphenyl and the isotropic phase of HAB are analysed and discussed. In Chapter 5 the molecular field theory developed for biaxial rigid solutes at infinite dilution in a uniaxial mesophase composed of biaxial molecules is outlined. From this theory the biaxiality SXX -Syy of the ordering matrix for a rigid solute is calculated and is compared with the observed biaxiality of flexible solutes containing a benzene ring with different alkyl chain length dissolved in HAB. In Chapter 6 the influence of the alkyl chain on the fourth rank order parameter P4 of the rigid core of the nematogenic molecule is predicted with the aid of the model developed in Chapter 3. These predictions are compared with those of the Maier-Saupe theory for rigid molecules.
University of Southampton
1982
Viloria, Francisco René
(1982)
Magnetic resonance studies of flexible molecules in liquid crystals.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis is concerned with the investigation of flexible solutes dissolved in uniaxial liquid crystals and liquid crystals themselves using the techniques of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy. A resume of the salient features of the various mesophases is presented in Chapter 1 together with a discussion of the characterisation of the orientational order in both ideal and real systems. Theories of orientational ordering of rigid molecules in uniaxial liquid crystals and a consideration of its extension to flexible molecules are also reviewed. In the second chapter it is shown how electron resonance and nuclear magnetic resonance spectroscopy maybe employed to probe the orientational properties of liquid crystals. The background theory related with molecular reorientation and spin relaxation of a spin probe in uniaxial mesophases is also described. In Chapter 3 the extension of the molecular field theory of uniaxial mesophases for rigid molecules to allow for its flexibility is outlined. This theory is used to calculate the orientational order along the n-octane and n-heptane solutes dissolved in uniaxial mesophases. These calculations are compared with the DMR results for fully deuteriated n-octane-d18 and n-heptane-d16 dissolved in the nematic phases of Phase V and E5. In the fourth chapter the orientational order of fully deuteriated n-octane-d18 and n-heptane-d16 are compared with that of doxyl substituted n-octane and n-heptane dissolved in the nematic phase of HAB. This study is extended to the spin labelled odd membered n-alkanes 4-doxyl-n-heptane, 6-doxyl-n-unde cane, 6-doxyl-n-pentadecane and 9-doxyl-n-heptadecane to probe the smectic A phase of HAB. Both the static and dynamic aspects involved with these n-alkane spin probes are discussed by analysing the angular dependence of the electron resonance linewidths in the smectic A phase of HAB. The linewidths observed in 0-terphenyl and the isotropic phase of HAB are analysed and discussed. In Chapter 5 the molecular field theory developed for biaxial rigid solutes at infinite dilution in a uniaxial mesophase composed of biaxial molecules is outlined. From this theory the biaxiality SXX -Syy of the ordering matrix for a rigid solute is calculated and is compared with the observed biaxiality of flexible solutes containing a benzene ring with different alkyl chain length dissolved in HAB. In Chapter 6 the influence of the alkyl chain on the fourth rank order parameter P4 of the rigid core of the nematogenic molecule is predicted with the aid of the model developed in Chapter 3. These predictions are compared with those of the Maier-Saupe theory for rigid molecules.
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Published date: 1982
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Local EPrints ID: 459902
URI: http://eprints.soton.ac.uk/id/eprint/459902
PURE UUID: 5e333ebe-d4f6-41d4-a92f-c2783ff357f7
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Date deposited: 04 Jul 2022 17:24
Last modified: 04 Jul 2022 17:24
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Author:
Francisco René Viloria
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