Effects of Photopatterning Conditions on Azimuthal Surface Anchoring Strength

TL;DR

This study investigates how photopatterning conditions like layer thickness, light intensity, and aging influence the alignment quality and surface anchoring strength of liquid crystals on azo-dye coated substrates.

Contribution

It provides a detailed analysis of how various photopatterning parameters affect azimuthal surface anchoring strength, offering guidelines for optimizing liquid crystal alignment.

Findings

Optimal BY layer thickness is 5-8 nm.

Anchoring coefficient W increases with irradiation dose and light intensity.

Aging of non-irradiated coatings reduces anchoring strength.

Abstract

Spatially varying alignment of liquid crystals is essential for research and applications. One widely used method is based on the photopatterning of thin layers of azo-dye molecules, such as Brilliant Yellow (BY), that serve as an aligning substrate for a liquid crystal. In this study, we examine how photopatterning conditions, such as BY layer thickness (b), light intensity (I), irradiation dose, and age affect the alignment quality and the strength of the azimuthal surface anchoring. The azimuthal surface anchoring coefficient, W, is determined by analyzing the splitting of integer disclinations into half-integer disclinations at pre patterned substrates. The strongest anchoring is achieved for b in the range of 5-8 nm. W increases with the dose, and within the same dose, W increases with I. Aging of a non-irradiated BY coating above 15 days reduces W. Our study also demonstrates that sealed photopatterned cells filled with a conventional nematic preserve their alignment quality for up to four weeks, after which time W decreases. This work suggests the optimization pathways for photoalignment of nematic liquid crystals.