Homogeneous instability in shear flow 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) is studied as a function of magnetic field strength and field orientation when the field is applied obliquely in a plane normal to the initial orientation of the nematic director. For general orientations of the field, the HI threshold can vary in magnitude when the sign of flow is reversed. Out of the four main situations possible, shear flow is studied in some detail. Calculations are extended to a non-flow aligning nematic (NFAN) in which HI is known to be possible under the action of sufficiently strong destabilising fields. The possibility of crossover between two uncoupled modes is investigated as a function of shear rate and field orientation. The case of negative diamagnetic susceptibility anisotropy is briefly discussed.