Reentrant Nematic and Injected Smectic Behaviour in Binary Mixtures Including Those of Terminally Non-Polar Compounds

Abstract

Some new examples of injected smectic behaviour for binary mixtures of strong terminally polar mesogens (CBs, PCHs, BCOs, and CCHs) with a range of terminally non-polar esters are presented. Variations in the strength of the injected behaviour are discussed. Examples of S _B as well as S_A injection occur.

Studies of mixtures of terminally non-polar 4,4″-dialkyl-2″-fluoro-p-terphenyls (I) with cyano-substituted mesogens are also described and provide an example of injection of S _A and S _E phases.

Of greater interest is the observation that binary mixtures consisting solely of hom-ologues of (I) can exhibit reentrant nematic behaviour, providing further evidence that reentrant phenomena are not a special feature of terminally polar mesogens and their mixtures. An isomeric mixture of two compounds of structure (I) also gives an interesting case of an injected S _c phase, and enhanced S _c properties are recorded for other mixtures of homologues of (I).

Mixtures involving alkyl/alkoxy analogues of (I) also provide examples of S _c phase injection or enhancement, and in one case some evidence for injected S_I, behaviour.

Keywords:

• mixtures of terminally non-polar mesogens
• reentrant nematics
• injected S_A phases
• injected S_c phases
• lateral fluoro-substitution