Cellulose films as alignment layers for liquid crystals: Application of flow-induced molecular orientation

Surface alignment of liquid crystals on films formed by coating hydroxypropylcellulose (HPC) solutions was studied. The films were cast and sheared at various speeds and thicknesses of the coating. Films made from cholesteric solutions showed homogeneous surface alignment, with the strength of surface alignment weakly dependent on the coating speed for thin films. On the other hand, HPC films made from isotropic solutions displayed no characteristic features in a polarizing microscope. The coating thickness also affected the surface alignment because of evaporation. On 40 μm films, the 4-cyano-4′-n-pentylbiphenyl molecules align radially on the film surface, indicating that the random molecular orientation in the vicinity of the film surface.