Oligomeric liquid crystals

Abstract

The work presented in this Thesis is concerned with the synthesis and characterisation of liquid crystalline dimers and trimers. The role of the alkyl spacer and the mesogenic groups are shown to have a critical influence on the mesogenic behaviour of these oligomers. Chapter 1 provides a general account of the liquid crystal phase together with some structure-property relationships and the experimental techniques used to characterise their liquid crystalline behaviour.

Chapter 2 introduces the reader to order parameters and distribution functions which provides a background for the technique of nuclear magnetic resonance spectroscopy, NMR, as used to determine the orientational order parameters within the liquid crystal phase.

In Chapter 3 the odd-even behaviour of some methylene linked cyanobiphenyl dimers has been examined alongside that of analogous ether linked dimers by NMR spectroscopy using anthracene-d₁₀ as a solute. The odd-even behaviour of these dimers is shown to depend critically on molecular geometry. Dimers containing both an oxy and a methylene link have been similarly examined. A smectic phase, exhibited by odd dimers containing a methylene link, is characterised in 1,7-bis(4'-cyanobiphenyl-4-yl)heptane, using a variety of techniques. The diminished odd-even effect of a homologous series of carbonate linked cyanobiphenyl dimers is reported in Chapter 4.

Chapter 5 details the use of deuterium NMR spectroscopy to determine the order parameters of the specifically deuteriated mesogenic groups in two short length cyanobiphenyl terminated liquid crystal trimers whose mesogenic groups are predicted to be ordered to different extents. (DX184256)

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