9 February 2007 Liquid crystal photoalignment: history and future
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Abstract
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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V. G. Chigrinov, H. S. Kwok, Hirokazu Takada, Haruyoshi Takatsu, "Liquid crystal photoalignment: history and future", Proc. SPIE 6487, Emerging Liquid Crystal Technologies II, 64870F (9 February 2007); doi: 10.1117/12.714853; https://doi.org/10.1117/12.714853
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