Polymer stabilized highly tilted antiferroelectric liquid crystals - the influence of monomer structure and phase sequence of base mixtures

Abstract

Polymer stabilization offers unique opportunities for improving features of liquid crystals. In particular, it influences the static and dynamic performance of antiferroelectric liquid crystals (AFLCs) due to the stabilization of surface-stabilized geometry of such self-assembling materials forming anticlinic structures. The main advantages of polymer-stabilized AFLCs consist of a significant decrease of the electro-optical switching time, and a lower sensitivity to mechanical shock and temperature changes in working devices. This work experimentally analyzes the effect of functionality of selected mesogenic monomers on the properties of new developed high-tilted AFLC mixtures with different phase sequences, before and after polymer stabilization. It was found that tetrafunctional monomers (especially those with non-chiral terminal chains) reduce the thermal stability of antiferroelectric phase and increase helical pitch at low temperatures before polymerization. However, they reduce values of the tilt angle and spontaneous polarization and simultaneously flatten the temperature dependence after polymerization to a greater extent than bifunctional monomers. Tetrafunctional monomers improve electro-optical characteristics of tested AFLC mixtures after polymer stabilization. On the other hand, polymer-stabilized materials based on bifunctional monomers and LC mixtures with direct SmCA* - Iso phase transition show acceptable electro-optical performance in device cells. Most importantly, the obtained results confirm definite advantages of using mixtures with direct SmCA* - Iso phase transition when designing new polymer-stabilized AFLC materials with appropriate features in effects based on surface-stabilized geometry.