Dichroic dye dependent electro-optic and thermal behavior of ZnO nanoparticles induced homeotropically aligned nematic liquid crystal cells

Abstract The present study investigates the electro-optical (EO) and thermal behavior of homeotropically aligned liquid crystal (HALC) cells doped with zinc oxide (ZnO) nanoparticles (NPs) and varying concentrations (0.0625 wt%, 0.125 wt%, 0.25 wt% and 0.5 wt%) of an orange azo dichroic dye. The prepared series of dye doped NPs induced HALC sample cells are referred as S1, S2, S3 and S4 corresponding to 0.0625 wt%, 0.125 wt%, 0.25 wt% and 0.5 wt% dye concentrations respectively. The cells were examined using polarized optical microscopy for their morphology which confirmed the homeotropic alignment (HA) of liquid crystal (LC) induced from ZnO NPs. The uniform optical textures across the temperature range of 20 °C–60 °C confirm thermal stability of the sample cells even under the applied voltages. Further, voltage–transmittance (V–T) analysis reveals a decrease in the threshold and operating voltages by 7.50% and 5.0% respectively with increasing dye content from 0.0625 wt% to 0.5 wt% at particular temperature. Additionally, the contrast ratio showed a notable improvement up to 47% with increasing dye content. Despite thermal variations from 20 °C–60 °C, all cells exhibited consistent OFF-state opacity and ON-state saturation transmittance, shows stable switching integrity. Overall, the results establish that ZnO NPs are responsible for inducing stable HA, while the azo dye serves to modulate the EO responses. The consistent EO performance and thermal stability of dye doped NPs induced HALC cells highlight their strong potential for the use in high temperature and energy efficient display applications.