ELECTROHYDRODYNAMICS IN NEMATICS SUBJECT TO PARALLEL ELECTRIC AND MAGNETIC-FIELDS

Under parallel electric and magnetic fields, electrohydrodynamic insta bilities in nematic liquid crystals having negative dielectric anisotr opy are predicted to exhibit a strong dependence of roll spacing on ap plied magnetic field. We report studies of the parallel magnetic field dependence of the threshold electric field for instabilities and the roll wavelength at threshold. The threshold electric field exhibits fa scinating re-entrant behaviour not predicted by theory. We describe qu alitatively new mechanisms for the creation and destruction of the con vecting state at higher magnetic fields.