Liquid crystal photoalignment technique: Basics, developments, and flexible/stretchable device applications

The liquid crystal photoalignment technique is a non-contact approach to establishing liquid crystal alignment using light irradiation, with the advantages of being non-polluting and non-electrostatic, and allowing facile microdomain orientation, compared with the rubbing alignment method. This review covers three categories of photoalignment under polarized light irradiation: photoisomerization, photodegradation, and photo-crosslinking. Photosensitive materials, such as azobenzene, polyimide, and cinnamate, are also introduced. Nonpolarized photoalignment technique is also presented. This review also summarizes the methods of controlling pretilt angle and increasing photosensitivity and several applications of the photoalignment technique. The photoalignment technique has considerable promise and value for liquid crystal displays, spatial filters, and flexible/stretchable devices.