Homogeneous Instability in Free Convection of Nematics—Effect of an Oblique Magnetic Field

Abstract

Using the continuum theory of uniaxial nematics, the homogeneous instability (HI) threshold of a flow aligning nematic (FAN), under free convection in a tilted sample whose boundaries are maintained at different temperatures, is studied as a function of strength and orientation of a magnetic field which is applied obliquely in a plane normal to the initial orientation of the nematic director. For a general field orientation, the HI threshold changes in magnitude when the sign of the temperature difference is reversed. Calculations are extended to a non-flow aligning nematic (NFAN) in which HI is possible under the action of a sufficiently strong destabilising field. The possibility of crossover between the field thresholds of two uncoupled modes is investigated as a function of the field orientation as well as the sign and magnitude of the temperature difference applied between the two plates. The case of nematics with negative diamagnetic anisotropy is briefly discussed.