IR properties of cholesteric-nematic liquid crystals
Dispersions of cholesteric-nematic liquid crystals in polymers have been of interest because of the possibilities for wider technical applications. Bistable properties of such dispersions make them suitable for storage modes.
In this paper, IR transmission of a mixture of the cholesteric liquid crystal (TM74A) and the nematic liquid crystal (E7), and polymer dispersion of the mixture are reported. Cholesteric-nematic sample cells were prepared by capillary method and polymer dispersed cholesteric-nematic liquid crystals sample cells by SIPS and TIPS method on ITO coated glass substrates. Results show that the mixture has two stable states: planar state and local conic state, in the near infrared region (4500-4000 cm-1) when applied field is zero. Difference in transmission between the focal conic state and planar state changes with increasing weight ratio of the cholesteric liquid crystal (TM74A). Maximum bistability is at 87.62:12.38 percent weight ratio.
Bistable mixture was dispersed in the polymer polyvinylpyrrolidone (PVP). Results show that the dispersion is bistable at the weight ratio 86:14 [86% (E7:TM74A), 14% PVP] of thickness 47 μm in the IR region.