BEHAVIOR OF BIAXIAL NEMATICS IN THE PRESENCE OF ELECTRIC AND MAGNETIC-FIELDS - EVIDENCE OF BISTABILITY

The behaviour of a biaxial nematic liquid crystal in the presence of electric and magnetic fields is discussed. In terms of the values of the magnetic susceptibilities and the dielectric permittivities, each biaxial nematic compound can be classified to belong to one of thirty-six different states. These states can be grouped together into three different classes, denoted by us as type A, B and C. The states belonging to each class exhibit a different qualitative behaviour in the presence of perpendicular electric and magnetic fields. While type A biaxial nematics always exhibit the same stable configuration in the presence of the fields, type B and C biaxial nematics exhibit two possible stable equilibrium configurations. Which of these is stable is determined by the magnitudes of the applied fields. The exchange of stability for type B systems can be modelled as a second order transition, while the exchange of stability for type C systems is of first order. In addition, the latter type can develop a bistable behaviour if certain conditions for the magnitudes of the electric and magnetic fields are fulfilled.