Self-colored crosslinked cholesteric liquid crystalline solid films of hydroxypropyl cellulose

Solutions of lyotropic cholesteric liquid crystalline hydroxypropyl cellulose (HPC) in water were self-colored due to the selective reflection of visible light, depending on the solution concentration. It was attempted to apply colored coatings of the liquid crystalline aqueous HPC solutions. HPC solid films were cast from the liquid crystalline solutions at different conditions and the color of the films was controlled. The cast films were chemically crosslinked. The crosslinked cast films were self-colored blue, yellow, or orange, but not red. Circular dichroism study of the cast films revealed that some films exhibited the peak wavelength in the red region of visible light. Scanning electron microscopy also showed that some films had the cholesteric pitch corresponding to the red region of visible light. However, colorimetry of the films indicated that no red films were prepared. This may be due to the highly varied distribution of the pitch. Some problems for applying the HPC liquid crystalline solution as colored coatings still remained open.