Alignment of nematic liquid crystals on mixed Langmuir-Blodgett mono-layers

TL;DR

This study investigates how mixed Langmuir-Blodgett mono-layers of stearic and behenic acids influence the alignment and dynamics of nematic liquid crystals, revealing composition-dependent metastable states and irreversible anchoring transitions.

Contribution

It provides new insights into the effects of mixed mono-layer compositions on nematic liquid crystal alignment and the associated transition dynamics.

Findings

Metastable orientation lifetime depends on mono-layer composition.

Transition between anchoring states is irreversible in mixed mono-layers.

Cooling induces a quasi-planar nematic state that relaxes to homeotropic alignment.

Abstract

Mono-layers of stearic and behenic acids and mixtures of them in different proportions, deposited with the Langmuir-Blodgett technique, were used to study the alignment and the alignment dynamics in nematic liquid crystal cells. A relaxation process from a splay-bend flow induced metastable orientation to the homeotropic one occurs. The lifetime of the metastable state was found to depend on the mono-layer composition. The transition between the homeotropic and the conical anchoring was found to be irreversible in the case of the mixed aligning mono-layers: on cooling from the isotropic phase a quasi-planar nematic state (schlieren texture) appears. It is stable in a range of a few degrees below the clearing point and, on decreasing the temperature, relaxes to the homeotropic state in form of expanding domains.