Influence of the type of phase sequence and polymer-stabilization on the physicochemical and electro-optical properties of novel high-tilt antiferroelectric liquid crystalline materials

Artikel i vetenskaplig tidskrift, 2019

Antiferroelectric liquid crystal (AFLC)mixtures with two types of phase sequence, isotropic - smectic A* - smectic C* - smectic CA* and isotropic - smectic CA*, respectively, have been formulated from components having biphenyl benzoate rigid cores, a non-chiral terminal chain with either alkoxy groups as well as perfluorinated parts on one side, and a chiral chain with different structures on the other side. The properties of the mixtures have been examined by means of polarized optical microscopy, differential scanning calorimetry, as well as UV–Vis-NIR spectrophotometry, and their electrooptic performance have been characterized in device cells, before and after polymer-stabilization of the structures. For all mixtures we observed unusually broad temperature ranges of the smectic CA* phase, extending from at least −30 °C to about +70 °C or more, molecular tilt angles of 42–44°, helical pitches of several micrometers, and a spontaneous polarization of about 200 nC/cm2. The polymer network has a profound impact on the relaxation to the anticlinic state, especially in the mixtures with a direct smectic SmCA*- isotropic phase transition. A symmetric electrooptic response, with both on and off response times of about 140 μs, was obtained in cell gaps of 1.5 μm, which is, to our knowledge, unique among contemporary available high tilt AFLC material systems.