38.2: Azodye Aligning Layers for Liquid Crystal Cells

Abstract

AbstractThe photo‐induced alignment of liquid crystal onto a photochemical stable azo dye film is studied for the liquid crystal display (LCD) applications. The photo‐aligning of azo dye takes place due to the pure reorientation of the molecular absorption oscillators perpendicular to the UV‐light polarization. The order parameters S= −0.4 (80% of the maximum absolute value Sm= −0.5) was measured at the wavelength of 372 nm from the polarized absorption spectra. The temperature stable pretilt angle of 5.3° was obtained by a two‐step exposure of azo‐ dye film using normally incident polarized light followed by oblique non‐polarized light. The azimuthal anchoring energy of the photo‐aligned substrate was Aɛ> 10−4 J/m2, which is of the same magnitude as the anchoring of the rubbed PI layer. VHR value of the photo‐aligned LC cell was also found to be very high (98–99%) at room temperature and more than 95% at T=80°C. The thermal stability of the photo‐aligned azo‐dye layers is sufficiently high, while UV‐stability has to be improved e.g. by polymerization. The bright perspectives for the new LCD aligning technology are envisaged.