Photoalignment of LCs

A vast amount of investigations on photoalignment of LCs has been reported during the past one and a half decades. Irradiation with LPL induces photo-induced anisotropy, in which molecules are generally oriented to an unexcitable direction, namely, perpendicular to the electric vector of the polarization direction. This effect is called photoinduced optical anisotropy (Seki, 2004 Natansohn and Rochon, 2002 Ichimura, 2000). 

Figure 8.5, Photoalignment of chromonic LC/silica nanohybrid. Chemical struc-ture of the component and a scheme of B67 columns on a photoaligned PPLC film. See color insert.

To describe the physical mechanisms of LC photoalignment with a special emphasis on the most useful photosensitive materials and preparation procedures suitable for the purpose. 

Progress in the application of LC photoaligning for LCDs has stimulated many fundamental studies of its mechanism. However, an adequate explanation of the photoalignment phenomenon is still absent. Several publications have appeared recently and provide only a qualitative explanation of the phenomenon of photoalignment. A more adequate explanation of the process is still in progress, taking into account both photochemical and non-photochemical transformations in photosensitive layers under the action of polarized or non-polarized, but directed, light. 

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