P-103: Photo-Alignment of Liquid Crystals by Azodyes

• Published in: SID International Symposium Digest of technical papers 2003-05, Vol.34 (1), p.617-619
• Main Authors: Umanskii, Boris A., Novoseletskii, Nikolai V., Torgova, Sofia I., Dorozhkina, Galina N.
• Format: Article
• Language: English
• ISSN: 0097-966X; 2168-0159
• DOI: 10.1889/1.1832351

In this paper the photo‐induced alignment of liquid crystals by azo‐dyes was investigated in spin‐coated films of individual azo‐dyes and azo‐dyes incorporated in polymer. It was studied the photo‐induced optical anisotropy (POA) properties of different azodyes; the influence of azo‐dye molecular structure with different terminal and lateral substituents on the POA properties and on the aligning ability of LC. The inclined LC alignment was controlled by two‐steps irradiation: 1) with normal linearly polarized light and 2) with oblique non‐polarized light. It was shown that the type and the quality of the LC alignment as well as the value of pretilt angle depend on the exposure time to the nonpolarized light, on the nature of the solvent for spin‐coating process and on the treatment of the orienting layers. The correlation between POA of azo‐dyes and their aligning capability was explored. It was shown that it has nonlinear character: even small anisot‐ropy gives a good LC alignment. Moreover, photo‐aligning azo‐dye layers have a good thermostability and are stable under weak UV irradiation as well. In this case all the main parameters of these films, such as optical anisotropy, pretilt angle and degree of ordering are practically independent of temperature.