Short chiral pitch and blue phase stability in cholesteric liquid crystal mixtures by adding achiral benzoic acid derivative

Cholesteric liquid crystal (CLC) is anticipated to have applications such as blue light and ultraviolet (UV) light blocking for human skin owing to its selective wavelength reflection against incident sunlight through several hundred nanometres of a periodic helical twist structure. In this study, we investigated short chiral pitch control and enlargement of the blue phase (BP) temperature range by adding an achiral constituent of 4-n-octylbenzoic acid (8 BA) into CLC mixtures composed of three kinds of cholesteryl compounds: cholesteryl chloride, cholesteryl pelargonate and cholesteryl palmitate. Hydrogen bonding dependence of chiral pitch and BP temperature range were also investigated for achiral dopant (8 BA) and CLC mixture through temperature-dependent Fourier-transform infrared analysis. It was found that 40 wt% of 8 BA within the CLC mixture selectively reflected UV and blue light over 360–400 nm with a decrease of chiral pitch. It was also found that the BP temperature range increased by 15.6°C owing to hydrogen bond dimers composed of 8 BA molecules in the CLC mixture.