On the biaxiality of smectic C and ferroelectric liquid crystals

Ferroelectric liquid crystals (FLCs) were a major topic for research in the 1980s and 1990s, to which George Gray and his research family played a fundamental role in developing the field. The famous symbiotic relationship between the chemists at Hull University and device physicists at the Royal Signals and Radar Establishment (RSRE) continued throughout this period, providing the basis for the τV<inf>min</inf> mode of FLC operation. The principal of this mode relies on the dielectric biaxiality inherent to the smectic C and ferroelectric smectic C* liquid crystal phases. As with nematics before, new materials and device physics developed hand-in-hand, allowing materials to be formulated with addressing times of 12μs at voltages below 30 V. After reviewing the material physics behind these devices, new measurements of the biaxial refractive indices and permittivities are presented, from which the biaxial order parameter C is determined.