Anchoring transitions of liquid crystals on SiO x

Anchoring transitions were observed of nematic liquid crystal (LC) mixtures on obliquely evaporated SiO _x by varying the relative abundance of two components in the mixture. Of these two components, one has a longitudinal cyano group and another has lateral cyano groups. It was also found that both temperature and SiO _x thickness variations are able to shift the anchoring transitions. The anchoring on SiO _x has two origins: long‐range van der Waals potential and short‐range surface interactions. Since the two origins have opposite preference in LC director orientation the observed transition is caused by the change of their relative strength. Thermal absorption–desorption of molecules on SiO _x surface is important in determining the strength of short‐range interactions, whereas the layer thickness and optical properties of SiO _x are dependent on the van der Waals potential. Based on previous work by de Gennes we propose a model to describe the observed phenomenon.