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In this original review we briefly consider the novel azo-dye photo-aligning technology: history and the
perspectives for future applications in liquid crystal (LC) devices. The review describes the following items.
The brief introduction to the history of photoalignment and the basic classes of the photoaligning materials:
photosensitive polymers, azodyes and monolayers will follow with an introduction to the physical mechanisms of
the photo-aligning and photo-patterning technology. The advantages and drawbacks of various photo-aligning
materials are analyzed from the point of view of practical applications. The detail description of the diffusion
photo-aligning in azo-dye materials is provided. The characteristics of azo-dye photoaligning LC layers are
compared with those ones prepared by polyimide rubbing method.
The characterization of LC-surface interaction, such as pretilt angle and azimuthal anchoring energy is
discussed. The newly developed materials should have a controllable pretilt angle and anchoring energy, thus
enabling to develop a new generation of the LC devices: with low voltage, fast response and wide viewing angles.
The problem of image sticking can be considerably reduced due to the high anchoring energy of azo-dye
materials. Promising results, obtained for voltage holding Ratio (VHR) and residual DC voltage (RDC) in azodye
photo-aligning materials are also shown. This implies that the azo-dyes can be applied as aligning layers in
active matrix liquid crystal displays (AM-LCDs).
The possibility to use the photo-aligning layers for new types of liquid crystal displays such as FLCD, VAN-LCD,
&pgr;-BTN LCD, optical rewritable memory, microdisplays, and TN-LCD on plastic substrates is
demonstrated. The photoaligning of liquid crystal polymers (LCP) and the new classes of devices based on them
(optical retarders and compensators) is discussed. Special types of 3D LC alignment, LC alignment inside thin
micro tubes, and grating surface were concerned.
New superthin photo-aligned polarizers based on azo-dye layers were demonstrated. The polarizers are based
both on photo-aligned lyotropic LC as well as pure azo-dye layers. The polarizers can be patterned and put inside
LC display cell to serve as internal polarizers. Both color and neutral internal polarizers can be fabricated with the
thickness 0.3-0.7 &mgr;m. The electo-optic response of TN-LCD with internal polarizers is practically the same as in
case of usual external polarizers. New applications in transflective and 3D displays are envisaged.
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