Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

The liquid crystal (LC) alignment properties of a series of polystyrene derivatives containing various fluorinated side chain terminal moieties, such as 4-fluorophenoxymethyl, 3,4,5-trifluorophenoxymethyl, pentafluorophenoxymethyl, and 4-trifluoromethoxyphenoxymethyl groups, were investigated. These polymers could induce homeotropic and/or homogeneous planar LC alignment on their surfaces by changing the LC molecules and rubbing conditions. For example, when a positive (MJ001929 from Merck) and negative dielectric anisotropic LC mixture (MLC-7026-000 from Merck) were used, homeotropic LC alignment was observed in the LC cells made from unrubbed films of pentafluorophenoxymethyl- and 4-trifluoromethoxyphenoxymethyl-substituted polystyrenes with a smaller surface energy, whereas random planar LC alignment was observed in those made from the other polymers with a larger surface energy. On the other hand, homeotropic LC alignment behavior was observed in all the LC cells made from unrubbed films of all the polystyrene derivatives when 5CB was used as the LC material.