The area of liquid crystals has received a substantial research effort over the last century, particularly when the beneficial applications such as Liquid Crystal Displays (LCDs) were realised and developed. The changes to the molecular structure of liquid crystals can have a significant effect upon their mesomorphism and ferroelectric properties. Most of the research in liquid crystal for display applications concentrates on the design and synthesis of novel mesogenic cores to which straight terminal alkyl or alkoxy chains are attached. However, little is known about the effects upon the mesomorphism and ferroelectric properties of varying the terminal chains. The synthesis and mesomorphic properties of a systematic range of ortho difluoroterphenyls with a bulky terminal chain are detailed. The bulky terminal chain consists of either a tertiarybutyl group or a trimethylsilyl unit, each separated from the core by a short (dimethylene) chain, with the other terminal chain being either octyloxy or heptyl. Unusually for liquid crystals with bulky terminal chains, the smectic phase stability (particularly smectic C) is upheld by more than the nematic phase stability, and in most cases the smectic C phase stability is actually higher than comparable analogues with conventional unbranched terminal chains. It is postulated that the surprisingly high smectic C phase stability results from a phase separation effect due to the incompatibility of the spherical bulky group and the conventional unbranched terminal chain, hence implying that the smectic 'layers' are well defined, and such definition of the layers bodes well for bookshelf geometry in ferroelectric mixtures. Two mono- and four trifluoroterphenyls with a bulky terminal chain were prepared in this work to study the effect on the mesomorphic behaviour of varying the degree of fluoro substituents upon the multi-ring system. Two chiral ortho difluoro-substituted terphenyl compounds were prepared also in this work for future ferroelectric mixtures.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:550475 |
| Date | January 2010 |
| Creators | Radini, Ibrahim Ali M. |
| Contributors | Hird, Michael |
| Publisher | University of Hull |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hydra.hull.ac.uk/resources/hull:4924 |
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