A study of orientational ordering in thermotropic liquid crystals by nuclear magnetic resonance

The work presented in this thesis is concerned with the study of orientational ordering in thermotropic liquid crystals by means of Fourier Transform Nuclear Magnetic Resonance spectroscopy. Chapter 1 is concerned with an introduction to the properties of liquid crystals and NMR spectroscopy. In Chapter 2 we present a study of the orientational order for the members of the α,ω-bis-(phenyloxy)alkane (BPO-n) homologous series dissolved in a range of liquid crystals. The experimental and theoretical calculated order parameters for different segments in the molecules are compared. Chapter 3 is a conformational study for the central C-C bond of 1,2-bis-(phenyloxy)ethane in liquid crystal and isotropic phases. The result is compared with previous studies of similar compounds with different terminal groups. Chapter 4 presents studies of the orientational order of binary mixtures. The observation of the reentrant diphasic behaviour for the binary mixtures of phenol and 152 is compared with the theoretical prediction using a theory of binary mixtures including scalar interactions. A study for the binary mixtures of hexafluorobenzene and Phase V is carried out, and the experimental results are compared with the theoretical data obtained from the theory of binary mixtures including scalar interactions. Chapter 5 is concerned with a study of field-induced orientational ordering of the isotropic phases in the isotropic and biphasic regions for binary mixtures. The result is understood using a layer-structure model.