Effect of Linking and Terminal Polar Groups on Liquid Crystal Alignment

Abstract

We observed the alignment of liquid crystals with polar linking and terminal groups on a glass substrate covered with an aminosilane coupling agent by using a polarizing microscope. The liquid crystals used were two types of cyanobiphenyl compounds, 5CB having a cyano group as a terminal substituent and ME7N having a terminal cyano group and an ester linking group between the two phenylene rings. For 5CB the director aligned perpendicular to the amino-covered substrate resulting in a monodomain, while ME7N exhibited a number of domains. In each domain the director aligned parallel to the substrate. These results suggest that the interaction between the polar groups in the liquid crystal and those on the substrate surface plays an important role in the liquid crystal alignment.