FREQUENCY VARIATION OF PERIODIC DISTORTION THRESHOLDS IN A NEMATIC LIQUID-CRYSTAL

Investigations are reported on the electric held induced orientational transitions in the bend Freedericksz geometry under the action of a s tabilizing magnetic held. When the magnetic field is strong enough, th e deformation above electric threshold is periodic with the periodicit y disappearing at a higher voltage. The alignment does not remain home otropic below threshold and the sample exhibits pretransitional biaxia lity. Every transition is discontinuous and accompanied by hysteresis. The expected form of scaling appears to hold for all the observed thr esholds. The thresholds and the direction of the wave vector are frequ ency dependent, showing that the instability mechanism involves electr ical conductivity.