Hydroxypropylcellulose films as alignment layers for liquid crystals

Homogeneous surface alignment of liquid crystals (5CB) is observed for films formed by coating with aqueous solutions of hydroxypropylcellulose (HPC) for high coating speeds and thin coating thicknesses. On the other hand, for films formed with isotropic ethanol solutions of HPC, 5CB molecules retain the flow-induced alignment created at the formation of the 5CB droplet. The microstructures responsible for the homogeneous surface alignment are not confirmed in the morphological measurement of the film surface with an atomic force microscope, although large grooves corresponding to the banded texture perpendicular to the coating direction exist on the films formed with liquid crystalline solutions of HPC. The possibility of highly oriented HPC molecules in the coating flow is pointed out using the Doi model. These results suggest that the now-induced anisotropic orientation of HPC molecules is responsible for the homogeneous surface alignment of 5CB.