Morphological, optical and dielectric behavior of chiral nematic liquid crystal mixture: Study on effect of different amount of chirality

Abstract

We report the effect of chiral concentration on temperature dependent helical pitch of a chiral nematic liquid crystal system. The phase behaviour, optical and dielectric properties of binary mixtures of a nematic liquid crystal 4-pentyl-4′-cyano-biphenyl and a chiral liquid crystal cholesteryl oleyl carbonate in five different ratios was investigated. The study shows that by introducing optimum chirality into the molecule of nematogen leads to improved thermochromism performance and creation of new mesophases. The blue phase appeared in mixtures in large temperature window, including room temperatures. Many fold enhancement in the photoluminescence intensity was observed with an increase in chiral concentration. We have noticed considerable periodic alternation of temperature dependent refractive index in the visible spectral region, which is resulted by small pitch and more prominent chirality especially in the mixture of 30% nematic and 70% chiral composition. The dielectric loss decreased in mixtures particularly in lower frequency region.