Molecular field theories for biaxial liquid crystals

This thesis consists of five studies on the applications of the molecular field theory to model systems of biaxial molecules which form biaxial and uniaxial nematic and smectic A phases. The first study extends the original theory for biaxial nematic phases of D2h symmetry to allow the phase symmetry to be C2h. In the second study, a dipolar interaction is introduced to the original model of biaxial nematic phases formed from V-shaped molecules to explain a disagreement between theory and experiment. This leads to the stabilisation of the novel polar biaxial nematic phase. In the third study, we introduce molecular flexibility at a simplified level into an existing model of V-shaped molecules to investigate its effects on the stability of the biaxial nematic phases. The fourth study aims to explain and predict various effects of magnetic field on the uniaxial nematic to isotropic phase transition for a system of rigid V-shaped molecules. In the fifth study, we develop a model for biaxial smectic A phases. The theory is simplified by using several approximations which facilitates the calculations.