On the biaxiality of smectic C and ferroelectric liquid crystals

Abstract

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_min 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.

Keywords:

• smectic C
• ferroelectric liquid crystals
• electric permittivities
• biaxiality
• biaxial order parameters
• refractive indices
• negative dielectric LC materials
• displays

Acknowledgements

I wish to thank all of the collaborators with whom I have conducted this work, but in particular Professors Peter Raynes, John Goodby and Carl Brown and Drs Paul Dunn and Mike Hird for their innumerable and invaluable contributions. More recently, I’d like to acknowledge Professor Helen Gleeson and Dr Mamatha Nagaraj for reintroducing me to biaxiality through our work on bent-core phases. Particular gratitude is expressed to Ms Vikki Minter for the viscosity and dipole moment measurements, and Dr Nagaraj for the theoretical dipole moments.

Additional information

Funding

This work was supported by the EPSRC [grant number EP/L015188/1].