High Optical Quality Films of Liquid Crystalline Cellulose Derivatives in Acrylates

Cholesteric liquid crystals based on polymers are attractive because of their film-forming properties. However, their optical properties (sharpness and directionality of the selective reflection) are usually lower than low molar mass compounds because of a polydomain structure and an angular distribution of the helix axes. In this work, cholesteric films made of liquid crystalline cellulose derivatives with improved optical properties are prepared. The careful choice of the solvent, hydrogen bond influencing additives, the synthetic realization of a very high degree of substitution on the cellulosic polymer, and the use of mechanical stirring in combination with a tuned substrate treatment and film-preparation method and subsequent polymerization allow the fabrication of free standing cholesteric films of high optical quality. They show selective reflection with a half width of only 25 nm and nearly only perpendicular reflection. In addition, a method is developed by which fluorescent dyes can be introduced into the films after their preparation.