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

Thermo-reversible gels of a chiral nematic liq.-crystal (LC) with 12-hydroxyoctadecanoic acid (HOA) were cast in a light-reflecting planar configuration by choosing a processing temp. higher than the sol-gel temp. but lower than the onset-temp. for the chiral nematic-isotropic transition in the gel. The choice of processing temp. is dictated by the quasi-ternary phase diagram of the system, which displays a 3-phase region at which an isotropic liq. is in equil. 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. Viscoelasticity, electrooptical activity and zero elec. 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. [on SciFinder (R)