Physics of Ferroelectric Fluids: The Discovery of a High-Speed Electro-Optic Switching Process in Liquid Crystals

Abstract

The fluid-like internal viscosity for collective molecular motion has as yet resisted attempts of obtaining fast response of liquid crystals towards applied electric fields. In a chiral smectic C liquid crystal, which is ferroelectric and may thus permit a very strong action by an external field, there is, however, a certain collective molecular motion distinguished by a large optic effect and very low internal friction, which should be very fast if it can be acted upon in a proper way. This requires suppression of the director helix, characteristic of the medium in the bulk, which can be achieved in suitably prepared samples. The resulting new electro-optic effect exhibits high-speed response, threshold behaviour, and bistability; attributes which suggest a variety of novel light control applications. Compared to present-day liquid crystal devices, the response speed has been increased by about ten-thousand times, which means that the applications of liquid crystals have been extended into the Megaherz frequency domain. This is not an absolute limit: though very few ferroelectric liquid crystals are available today, synthesis efforts towards new suitable compounds should permit to further raise the attainable speed.