Antiferroelectric liquid crystals with 45° tilt - a new class of promising electro-optic materials

Abstract

Antiferroelectric liquid crystals with a tilt angle of 45 degrees have very interesting optical properties, which seem to have been overlooked so far - perhaps because such materials have hardly been available. We have prepared a four-component mixture of partially fluorinated compounds with a SmC_a* phase in the interval between 27.4°C and 121.6°C, in which the tilt angle θ saturates at 45 degrees for T≤80°C, and we investigate the optical properties, theoretically and experimentally. One of the surprising features of 45 degree materials is that they permit a remarkably high contrast by virtue of an excellent dark-state, in spite of the fact that AFLC materials are notoriously difficult to align. This is because a 45° AFLC turns out to be (negatively) uniaxial instead of biaxial. We describe these properties and propose a number of potentially interesting new applications, including a polarizer-free display mode and a three-level “phase-only” modulator.

Keywords:

• uniaxial antiferroelectric liquid crystal
• 45° tilt
• Sm C_a*
• AFLC dielectric tensor
• new electro-optic modes