Thin film polarizer based on photo-curable chromonic liquid crystalline solutions

Lyotropic chromonic liquid crystals (LCLCs) form a columnar discotic liquid crystalline (LC) phase in aqueous solution due to the disc-like or plank-like molecular shape of chromonic dyes and their ionic peripheries. Such columnar structures in the chromonic columnar N phase can be coated on a glass substrate, and aligned in one direction by applying external forces. The resulting thin crystalline film (TCF) can absorb a polarized light parallel to the molecular axis while transmitting a polarized light parallel to the columnar axis, which constructs an E-polarizer. Although the concept of the coatable polarizer known, it has not been commercially successful due to numerous problems mainly originated from the use of aqueous solution. It is extremely difficult to coat the aqueous solution on most of substrates, especially on plastic substrates. Large volume shrinkage occurs during the crystallization process generating unfavorable defects. Also, weak adhesion becomes an important issue when a TCF is applied to a flexible substrate. In this presentation, we demonstrate a novel preparation method of coatable polarizer from a photo-curable organicbased LCLC solution. Lyotropic LC solutions were prepared by dissolving amino-functional chromonic dye in acrylic acid containing photoinitiator and crosslinking agents. The solution was shear-coated with subsequent UV irradiation to provide a thin film polarizer. The coating processibility of this organic-based solution was outstanding, particularly on a plastic substrate. The maximum polarization efficiency was measured to be > 98 %. The resulting thin film polarizer showed excellent film characteristics, such as good adhesion strength to various substrates, superior surface hardness, good solvent resistance and decent thermal stability.