Cholesteric-nematic liquid crystal dispersions in the visible region

Abstract

Cholesteric-Nematic Dispersions (CND) that selectively reflect light in the visible regime have been fabricated. The Nematic E48 and Cholesteric TM74A at different weight ratios were mixed and sandwiched between ITO-coated glass plates using the capillary technique. The chiral system was then characterized through optical microscopy, UV-VIS spectrophotometry and electro-optic tests. Three textures have been verified – the homeotropic, focal conic and planar textures. The CND in the planar state displayed different bright colors in the 400-760 nm visible range and exhibited thermochromic properties near room temperature (~28 °C). A decrease in the minimum transmitted wavelength was observed as the TM74A concentration increased. Bistability properties, i.e., two states at zero field, were also verified for the selective reflection wavelength range. The electro-optic response of the system was verified. Shown is an increase in V_trans, voltage needed for the CND to be transparent, as the concentration of TM74A increases for the region where selective reflection occurs. The E48-TM74A CND sample exhibits thermochromic properties and maybe utilized for temperature sensing/detection near ambient conditions.