Azo Dye Materials for the Alignment of Liquid Crystals

In this paper, the photo-induced alignment of liquid crystal on an azo dye film is discussed for the liquid crystal display (LCD) applications. This is a non-contact technique to align the liquid crystals so that the dust particles and static charges generated by the rubbing process can be eliminated. To prepare for the photo-alignment layer, the azo dye film is exposed to a linearly polarized or non-polarized light. As a result of the dipole absorption, the photo-induced molecular distribution is non-uniform and has an angular dependence. Consequently, since the dispersion forces between the dye and the liquid crystal molecules dominate, the induced orientation of the liquid crystal molecules is possible. The oblique incidence of the light exposure will also favour a non-zero pretilt angle. We find that the order parameter associated with the aligned liquid crystal medium is high, and very good contrast has been measured in the Twist Nematic (TN) LCD.