Alignment and alignment dynamics of nematic liquid crystals on Langmuir-Blodgett mono-layers

TL;DR

This study investigates how nematic liquid crystals align on Langmuir-Blodgett monolayers of stearic and behenic acids, revealing metastable states, transition dynamics, and effects of temperature on alignment.

Contribution

It provides new insights into the alignment behavior and transition mechanisms of nematic liquid crystals on specific monolayer surfaces.

Findings

Metastable splay-bend alignment forms during filling

Transition to homeotropic alignment occurs over time

Heating induces reversible anchoring transition

Abstract

Mono-layers of stearic and behenic acids deposited with the Langmuir-Blodgett technique, were used as aligning films in nematic liquid crystal cells. During the filling process the liquid crystal adopts a deformed quasi-planar alignment with splay-bend deformation and preferred orientation along the filling direction. This state is metastable and transforms with time into homeotropic once the flow has ceased. The transition is accompanied by formation of disclination lines which nucleate at the edges of the cell. The lifetime of the metastable splay-bend state was found to depend on the cell thickness. On heating, anchoring transition from quasi-homeotropic to degenerate tilted alignment in form of circular domains takes place near the transition to the isotropic phase. The anchoring transition is reversible with a small hysteresis.