Self-Consistent Explanation of the Untwist Alignment of Ferroelectric Nematic Liquid Crystals with Decreasing Cell Thickness and Deviation of the Surface Easy Axis Experimented upon Using the Brewster Angle Reflection Method

Abstract

The huge dielectric constant of ferroelectric nematic liquid crystals (FNLCs) seems to bring about a difficulty of molecular alignment control in exchange for a potential device application. To obtain a satisfactory level of uniform molecular alignment, it is essential to understand how the molecules near the alignment surface are anchored. In this study, bulk molecular alignment with an anti-parallel rubbing manner, which has not yet been investigated extensively, is explained using a conventional torque balance model introducing a polar anchoring function, and it is shown that the disappearance of the bulk twist alignment with decreasing cell thickness can be explained self-consistently. To validate this estimation for a room-temperature FNLC substance, the Brewster angle reflection method was attempted to confirm the surface director’s deviation from the rubbing direction caused by the polar surface anchoring.

Evaluation of polar alignment structure and surface anchoring energy in ferroelectric nematic liquid crystals by renormalized transmission spectroscopic ellipsometry

“…21) The torque balance equation considering polar anchoring is detailed in our previous paper. 26) The polar direction of each FNLC molecule in the vicinity of the top and bottom substrate tends to align parallel to the rubbing direction so as to couple with the surface polarity. It should be noted that, because of the inherent polarity of the FNLCs, the surface anchoring energy is assumed to be predominantly polar anchoring energy.…”