Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618036
Title: Unusual particle motions in the liquid crystal phases
Author: Oh, Ji Young
ISNI:       0000 0004 5353 1278
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2014
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Abstract:
The motions of particles dispersed in liquid crystals can be influenced by the application of an electric field, the effect depending on the field frequency and field amplitude. Sandwich cells under the application of electric field are widely used as the tool in order to investigate the fundamental research relating to electro-optic display technology. Therefore, the aim of this experimental work is to find and investigate novel motion of the particles dispersed in the liquid crystal phases, held within a sandwich cell. For the liquid crystal–particle systems in the sandwich cells in this thesis, the particle shapes, temperature and cell geometry are all shown to have an influence on the regime of the particle’s motions, with different phenomena observed using three different phases of liquid crystals. The experiments are designed to find and investigate the novel motion of the micron sized silica particles in the liquid crystal phases. In the chiral nematic phase, spherical particles are shown to exhibit linear motion, which is related to the electrophoretic mobility. Such spherical particles are also observed to show circular motion which is found to have a field dependency that can be related to Quincke rotation. A maximum frequency for motion occurs which is found to possibly be related to the effect of the ion diffusion in the liquid crystal-particle composite system. The direction of the circular motion is found to be independent of the handedness of the chiral nematic material. In the isotropic phase of a chiral nematic liquid crystal, the spherical particles do not exhibit any linear motion, which shows the system does not follow the traditional electrophoresis observed in normal isotropic liquids. The circular motion of the spherical particle that is observed in the isotropic phase is analysed in terms of the Quincke rotation and again shows the Maxwell relaxation time. The electric-field induced motion of elongated particles in four different nematic systems is examined. In this case of planar aligned systems, linear motion is observed, in which the velocity shows a minimum for particles of the same length as the cell gap. A novel field-induced defect texture appears in the homeotropic device containing a nematic liquid crystal of negative dielectric anisotropy. Interestingly, the motion of the particle is found to be strongly coupled with the defects formed.
Supervisor: Gleeson, Helen; Dierking, Ingo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.618036  DOI: Not available
Keywords: Liquid crystal
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