Surface effects and director profiles in liquid crystal-polymer structures with spatially varying surface conditions
Surface effects and director profiles in liquid crystal-polymer structures with spatially varying surface conditions
Photorefractive effects have been observed in both pure liquid crystals and polymers such as PVK, but also in certain hybrid structure of both liquid crystal and polymer layers. These effects are only apparent for certain combinations of liquid crystals and polymer surface layer, suggesting the cause to be surface-mediated at the interface between the two, and not due to bulk effects in the liquid crystal or the polymer. This thesis presents characterisation and analysis of such hybrid structures and discusses a hypothesis for the underlying mechanism, supported by experimental and theoretical investigation.
A system developed for characterisation of the molecular alignment in samples has been shown to be valid for molecular angles 0-16.3° and 48.8-90° from the surfaces. The Crystal Rotation Method (CRM) found that for some polymer-liquid crystal combinations, such as LC1294-PVK, the surface “damage” is due to applying electric field and light illumination.
A mathematical model for liquid crystal reorientation under a spatially varying field is presented, based on the Landau De-Gennes theory and is used to simulate photorefractive gratings in liquid crystal cells with varying thickness and grating size. It has been found that the grating spacing to cell thickness ratio governs the penetration of electric field into the liquid crystal bulk. These simulations are useful for predicting the conditions for highest diffraction efficiency.
University of Southampton
Gilchrist, Graham
3b427fc1-57c3-44a1-b3b0-4c5498b26b04
2007
Gilchrist, Graham
3b427fc1-57c3-44a1-b3b0-4c5498b26b04
Gilchrist, Graham
(2007)
Surface effects and director profiles in liquid crystal-polymer structures with spatially varying surface conditions.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Photorefractive effects have been observed in both pure liquid crystals and polymers such as PVK, but also in certain hybrid structure of both liquid crystal and polymer layers. These effects are only apparent for certain combinations of liquid crystals and polymer surface layer, suggesting the cause to be surface-mediated at the interface between the two, and not due to bulk effects in the liquid crystal or the polymer. This thesis presents characterisation and analysis of such hybrid structures and discusses a hypothesis for the underlying mechanism, supported by experimental and theoretical investigation.
A system developed for characterisation of the molecular alignment in samples has been shown to be valid for molecular angles 0-16.3° and 48.8-90° from the surfaces. The Crystal Rotation Method (CRM) found that for some polymer-liquid crystal combinations, such as LC1294-PVK, the surface “damage” is due to applying electric field and light illumination.
A mathematical model for liquid crystal reorientation under a spatially varying field is presented, based on the Landau De-Gennes theory and is used to simulate photorefractive gratings in liquid crystal cells with varying thickness and grating size. It has been found that the grating spacing to cell thickness ratio governs the penetration of electric field into the liquid crystal bulk. These simulations are useful for predicting the conditions for highest diffraction efficiency.
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Published date: 2007
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Local EPrints ID: 466333
URI: http://eprints.soton.ac.uk/id/eprint/466333
PURE UUID: 3ca29743-5211-40f1-9707-768d428464d3
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Date deposited: 05 Jul 2022 05:11
Last modified: 16 Mar 2024 20:38
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Author:
Graham Gilchrist
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