Magnetic resonance studies of solutes dissolved in liquid crystals
Magnetic resonance studies of solutes dissolved in liquid crystals
Three important themes run through this thesis. The first is that nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy provide powerful techniques for studying the orientational ordering of liquid crystals. Secondly, that solute molecules can be introduced in low concentrations to mimic the macroscopic alignment of the host molecules, without significantly perturbing the mesophase. Finally, careful choice of the solute can provide useful properties not readily determined for liquid crystals molecules themselves. Following a general introduction to both liquid crystals and magnetic resonance spectroscopy, Chapter 2 describes the construction of a deuterium NMR probe head which allows the sample to be rotated with respect to the magnetic field. Preliminary studies were undertaken to measure the tilt angle in some smectogens to test the goniometer probe. In Chapter 3 a theory is presented which predicts the variation in the biaxiality of the Saupe ordering matrix with the major order parameter. When the theory is compared with experimental results there is reasonably good but not perfect agreement. This discrepency may be because the temperature dependence of the orientational ordering is studied at constant pressure and most theories of liquid-crystalline behaviour assume the volume to be constant. To investigate this, high pressure NMR experiments were carried out, with pressures up to 2 kbars. A theory for the variation of the orientational ordering along a flexible liquid crystal chain is described in Chapter 4. These theoretical predictions are compared with experimental results of the order parameters for different positions within a chain of n-alkanes dissolved in mesogenic phases obtained using deuterium NMR. Chapter 5 explains that one of the important properties of the tilted smectic phases is the angle made by the director with the layer normal. Using an ESR spin probe technique the tilt angle of one of the first ferroelectric liquid crystals to be synthesised has been determined as a function of temperature in the smectic A, C, I and G phases. These results are compared to those extracted from the layer spacing determined by X-ray diffraction of the pure liquid crystal. The final chapter describes an ESR study of a spin probe, synthesised by incorporating an oxazolidine ring into a liquid crystal molecule. The temperature dependence of the hyperfine splitting was measured throughout the nematic and smectic A phases. However, the determination of the order parameter, from the hyperfine splitting, requires the angle between the molecular long axis and the axis orthogonal to the oxazolidine ring. This was obtained from an angular variation to the oxazolidine ring. This was obtained from an angular variation study of the linewidths in the smectic A phase and was found to be 30o. (D82539)
University of Southampton
1987
Smith, Stephen William
(1987)
Magnetic resonance studies of solutes dissolved in liquid crystals.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Three important themes run through this thesis. The first is that nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy provide powerful techniques for studying the orientational ordering of liquid crystals. Secondly, that solute molecules can be introduced in low concentrations to mimic the macroscopic alignment of the host molecules, without significantly perturbing the mesophase. Finally, careful choice of the solute can provide useful properties not readily determined for liquid crystals molecules themselves. Following a general introduction to both liquid crystals and magnetic resonance spectroscopy, Chapter 2 describes the construction of a deuterium NMR probe head which allows the sample to be rotated with respect to the magnetic field. Preliminary studies were undertaken to measure the tilt angle in some smectogens to test the goniometer probe. In Chapter 3 a theory is presented which predicts the variation in the biaxiality of the Saupe ordering matrix with the major order parameter. When the theory is compared with experimental results there is reasonably good but not perfect agreement. This discrepency may be because the temperature dependence of the orientational ordering is studied at constant pressure and most theories of liquid-crystalline behaviour assume the volume to be constant. To investigate this, high pressure NMR experiments were carried out, with pressures up to 2 kbars. A theory for the variation of the orientational ordering along a flexible liquid crystal chain is described in Chapter 4. These theoretical predictions are compared with experimental results of the order parameters for different positions within a chain of n-alkanes dissolved in mesogenic phases obtained using deuterium NMR. Chapter 5 explains that one of the important properties of the tilted smectic phases is the angle made by the director with the layer normal. Using an ESR spin probe technique the tilt angle of one of the first ferroelectric liquid crystals to be synthesised has been determined as a function of temperature in the smectic A, C, I and G phases. These results are compared to those extracted from the layer spacing determined by X-ray diffraction of the pure liquid crystal. The final chapter describes an ESR study of a spin probe, synthesised by incorporating an oxazolidine ring into a liquid crystal molecule. The temperature dependence of the hyperfine splitting was measured throughout the nematic and smectic A phases. However, the determination of the order parameter, from the hyperfine splitting, requires the angle between the molecular long axis and the axis orthogonal to the oxazolidine ring. This was obtained from an angular variation to the oxazolidine ring. This was obtained from an angular variation study of the linewidths in the smectic A phase and was found to be 30o. (D82539)
This record has no associated files available for download.
More information
Published date: 1987
Identifiers
Local EPrints ID: 461887
URI: http://eprints.soton.ac.uk/id/eprint/461887
PURE UUID: e3854936-1c21-408a-939c-09d041cdae3e
Catalogue record
Date deposited: 04 Jul 2022 18:57
Last modified: 04 Jul 2022 18:57
Export record
Contributors
Author:
Stephen William Smith
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics