Cholesteric thermo-reversible liquid-crystal gels: Phase behaviour and electro-optical response

Thermo-reversible gels of a chiral nematic liquid-crystal (LQ with 12-hydroxyoctadecanoic acid (HOA) were cast in a light-reflecting planar configuration by choosing a processing temperature higher than the sol-gel temperature but lower than the onset-temperature for the chiral nematic-isotropic transition in the gel. The choice of processing temperature is dictated by the quasi-ternary phase diagram of the system, which displays a 3-phase region at which an isotropic liquid is in equilibrium with a fibrillar solid and a chiral nematic mesophase. Planar configurations of the gels produced show a significant broadening of the reflection band with respect to the neat LC-material indicating a distribution of the cholesteric pitch within the gel. Visco-elasticity, electro-optical activity and zero electric field bistability of gelled films has been utilized in building a reflective bistable chiral nematic cell with improved shock-resistance that holds the promise of being produced via a continuous processing route.