ELECTROCHIRALLY CONTROLLED BISTABLE SURFACE SWITCHING IN NEMATIC LIQUID-CRYSTALS

We present an electrically controlled bistable surface switching for nematic liquid crystals, in cells with the usual display geometry. The surface bistability is controlled by means of an electrochiral effect, by doping a nematic with chiral ions. The alternate transient commutation between the two surface states is related to the sign of an applied pulsed electric field. The threshold behavior allows a writing surface time of 32-mu-s for a field of 21 V/ 1.3-mu-m. In the birefringence mode, the optical texture response time is 0.3 ms. The effect, comparable with the one used with ferroelectric smectic liquid crystals, could be used to realize high definition video passive matrix displays.