Structure property relations of novel liquid-crystalline materials

Howell, Owen Torridon (1991) Structure property relations of novel liquid-crystalline materials. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The work contained in this thesis covers a wide range of new and sometimes novel liquid-crystalline materials. Chapter 1 gives a basic grounding in the fields of liquid crystals covered in this thesis. The following chapters describe the synthesis and study of novel liquid-crystalline materials. In chapter 2 the hydrogen bonding of benzoic acid groups has been utilised to synthesise molecules that can be considered as models for `trimeric' liquid crystals. This is because only the central core is a mesogenic sub-unit the other rigid units are phenyl or 4-methyloxyphenyl which on their own cannot be considered mesogenic units yet their presence does not result in the loss of liquid crystallinity. The pronounced odd-even effect seen in their transition temperatures shows that the terminal groups play a role in the liquid crystallinity of these materials. In chapter 3 the phenyloxyalkyloxybenzoic acids where converted into salts in order to study their lyotropic behaviour. Various salts were studied, however only tetralkylammonium salts where one of the alkyl chains was long showed lyotropic liquid crystalline behaviour when a lamellar phase was observed. In chapter 4 dimeric liquid crystals with a branched central spacer chain are investigated. The mesophase behaviour of the homologous series of 1,6-bis(4-n-alkylanilinebenzylidene-4')-3-methyl-adipoates, was compared with the equivalent unbranched series the 1,6-bis(4-n-alkylanilinebenzylidene) adipoates. As would be expected a fall in the clearing temperatures is seen as a result of the chain branching. The formation of smectic phases often promoted by the branching of terminal alkyl chains, here is also adversely affected.

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