Non-symmetric liquid crystal dimers

Blatch, Andrew (1997) Non-symmetric liquid crystal dimers. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The work presented in this thesis examines the relationship between the structure of several novel series of dimeric liquid crystals and the occurrence of liquid crystalline behaviour. The lengths and parity of the terminal alkyl chains and flexible alkyl spacers are shown to have a critical influence on the phase behaviour of these compounds. Chapter One introduces the reader to the liquid crystal phase and outlines the experimental techniques used to characterise its structure. A novel family of symmetric azobenzene dimers is presented in Chapter Two, the α-ω-bis(4-n-alkyl azobenzene-4'-oxy)alkanes. The phase behaviour of these compounds is compared to the analogous symmetric Schiff's base dimers. In Chapter Three, non-symmetric azobenzene dimers are reported where the lack of symmetry derives solely from differences in the terminal alkyl chain lengths. These compounds are compared to the Schiff's base/cyanobiphenyl non-symmetric dimers which exhibit the intercalated and interdigitated smectic phase arrangements.

It had been suggested that these fascinating molecular arrangements could result from purely excluded volume or space filling constraints. The X-ray diffraction data of the non-symmetric azobenzene dimers, however, indicated that these materials formed the monolayer smectic A phase arrangement. In Chapter Four, four new families of non-symmetric dimers are presented, based on the cyanobiphenyl, Schiff's base, cinnamoate, biphenyl and azobenzene moieties, in order to further the understanding of the molecular requirements necessary to stabilise the intercalated and interdigitated smectic phase arrangements. Only the compounds containing the polar cyano group were found to form the intercalated and interdigitated phases, enhancing the view that some sort of specific interaction is needed in order to stabilise these molecular arrangements.

This record has no associated files available for download.