Effects of Humidity and Surface on Photoalignment of Brilliant Yellow*

Controlling and optimizing the alignment of liquid crystals is a crucial process for display applications. Here, we investigate the effects of humidity and surface types on photoalignment of an azo-dye brilliant yellow (BY). Specifically, the effect of humidity on the photoalignment of BY was studied at the stage of: substrate storage before coating; during the spin-coating process; between film coating and exposure; and after exposure. Surprising results are the drastic effect of humidity during the spin-coating process, the humidity annealing to increase the order of the BY layer after exposure, and the dry annealing to stabilize the layer. Our results are interpreted in terms of the effect of water on the aggregation or crystallization of BY. The type of surface studied had minimal effects. Thin BY films (3nm thickness) were sensitive to the hydrophilicity of the surface while thick BY films (30nm thickness) were not affected by changing the surface. The results of this paper allow optimization of the photoalignment of BY for liquid crystal display applications as well a better understanding of the BY photoalignment mechanism.