Control of high pretilt angle for nematic liquid crystal using in situ photoalignment method on homeotropic alignment layer

Pretilt angle generation and liquid crystal (LC) aligning capabilities for nematic (N) LC using an in situ photoalignment method with obliquely polarized UV exposure of the polyimide (PI) surface for homeotropic alignment were studied. The high pretilt angle of 30° for NLC with obliquely polarized UV exposure for 10-20 min on the PI surface can be achieved. The exposure energy of UV used was 15.5 mW/cm² at 365 nm. The pretilt angle generated in NLC using the in situ photoalignment method was higher than that generated using a conventional photoalignment method on a homeotropic alignment layer. Lastly, we suggest that the generation of pretilt angle in NLC with obliquely polarized UV exposure during imidization of the polymer for homeotropic alignment is a promising method to generate a high pretilt angle.