Studies of Electro-Optic and Thermal Behaviour of Azo Dye Doped Vertically Aligned Liquid Crystal

Abstract

The performance of liquid crystal (LC) display devices significantly depends on the usage of an optimized concentration of dopant. Thus, in the present study, vertically aligned liquid crystals (VALCs) display cells were prepared using dispersion of zinc oxide (ZnO) nano particles into host nematic liquid crystal (NLC) without any surface treatment. Further, the sample mixture was doped with fixed concentration of 0.5% of azo dye. Both the sample cells were analyzed and compared for morphological, electro-optical (E-O) and thermal behaviour. Results show the improvement in voltage-transmittance characteristics with lowering of threshold and operating voltage, however the contrast ratio (CR) for dye doped sample cell was found to be degraded. This degradation may be possibly due to much lower transition temperature at this concentration of dye, which further might because of higher OFF state and lesser ON state transmittance due to disturbance in intrinsic LC order. As, the thermal study showed the doping of 0.5% of azo dye reduced the transition temperature to 410 for dye doped VALC from 680 of VALC sample. Hence, these results indicate that a control amount of dichroic dye is a crucial measure for an adequate performance of VALC display.