Homogeneous instability under free convection in a tilted nematic sample

Abstract

Exact calculations on homogeneous instability (HI) threshold under free convection in a tilted nematic sample are presented. Inclusion of the effect of secondary flow leads to HI threshold value in close agreement with the experimental result for MBBA. Effects of stabilizing and destabilizing magnetic fields on the HI threshold are studied. Calculations are extended to HBAB where it is shown that under the joint action of the stabilizing effect of free convection and the destabilizing effect of magnetic field, HI may occur in the sample. At high enough values of destabilizing field it may be possible to observe a mode (involving net secondary flow) of HI which is generally unfavorable. The presence of secondary flow may lead to a loss of scaling for materials which show a divergence of twist viscosity near the nematicsmectic A transition.