Characterization of Nematic Phase of Banana Liquid Crystal

Abstract

We report the first detailed optical and electrical characterizations of the nematic (N) phase of a banana liquid crystal, i.e., pretilt angle, and optical and dielectric anisotropies, and point out the difference from those of rodlike molecules. The pretilt angle measurements using a conventional crystal rotation method show that the pretilt angle is very small (less than 1°) even in cells with a polyimide film yielding a high pretilt angle like 8° for calamitic molecules. We also measured the birefringence Δn in the N phase as a function of temperature and estimated the orientational order parameter S. The medium shows a small negative dielectric anisotropy in the N phase and the anisotropy becomes large in the B2 phase mainly because of the tilt of the molecules from the layer normal.