Liquid Crystals: Electro-Optical Modes and Applications

Kapitel i bok, 2015

Ferroelectric liquid crystals are particular because they have vector properties: There is a local polarization P everywhere in the volume. This leads to an electrooptic effect that depends on the sign of the applied field E.For a polarization to appear, the structure has to be chiral, and the common representative for this kind ofmaterial is smectic C*, the chiral form of smectic C. Antiferroelectric liquid crystals also have a local polarization, but this polarization is already cancelled on the molecular level as the P vectors of adjacent smecticlayers are antiparallel to each other. While the smectic C* phase is not ferroelectric per se, it may, togetherwith surfaces, form a ferroelectric structure. This led to the first manufactured bistable liquid-crystal displays,demonstrating several attractive electrooptic properties like in-plane switching, broad viewing angle, andhigh speed. Several nematic devices have been elaborated in the last decade that feature one or several of theseproperties. Their principles will be explained after the presentation of the ferroelectric and antiferroelectricdevices. Finally, some nondisplay applications will be discussed.