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Title: Photoisomerising effects in chiral liquid crystal systems
Author: Remnant, Anna Marie
ISNI:       0000 0001 3513 6918
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2002
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Photoisomerising liquid crystals are added to smectic and chiral nematic systems. The consequences of dye addition to the phase sequence and switching properties of the host material are described. The effect of ultra violet illumination, causing a shape changing photoisomerisation of the dye molecules, on these mixtures is explored. The photoisomerisation of the azobenzene molecules, used as dyes, is to change the straight trans isomer that is very compatible with the liquid crystalline phase to the bent cis isomer that is less compatible. This conversion is caused by illumination by ultra violet, the reverse isomerisation can be caused thermally or by illumination by infra red wavelengths. Organosiloxane liquid crystals produce stable ferroelectric semectic C* liquid crystalline phases that have a tilt angle close to 45° and a high spontaneous polarisation. The effect of monomesogenic and bimesogenic dye addition was to add a smectic A phase to the sequence, which showed a large electroclinic, effect and aided the alignment of the ferroelectric phase. The bimesogenic dye acted as a template for the monomesogenic host molecules, inducing an anticlinic antiferroelectric arrangement. The effect of ultra violet illumination was to reversibly reduce the phase transition temperatures, the spontaneous polarisation and the tilt angle of the mixtures indicating a reduction in the order of the system. Azobenzene dyes were added to chiral nematic bimesogens mixtures with a high flexoelectric coefficient. The effect of ultra violet was to reduce the phase transition temperatures and the helical pitch. The response time and tilt angle were unchanged. The results indicate a reduction in the order parameter but no measurable change of the flexoelectric constants.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ferroelectric