Liquid Crystalline Polymer Stabilized FLCDs with Conventional Rubbed Polyimide Films or with Photo Alignment Films of Poly(vinyl Cinnamate)

Abstract

Polymer stabilized SSFLCDs have been successfully fabricated. A liquid crystalline polymer network in a device cell is formed by the photo-cure of UV photo-currable liquid crystalline monomers that are doped in an FLC, where both the rubbed polyimide (PI) and non-rubbed but linearly polarized UV irradiated poly(vinyl cinnamate) (PVCi) films are utilized as surface FLC molecular alignment. The actual monomers adopted is acrylate with a mesogenic side chain. The PVCi is one of the photo alignment polymer. The fabrication process of these SSFLC cells is as follows; first the photo-cure is done on a monomers and initiators doped LC medium at the temperature where this material takes SmA phase and then the cell is cooled down to room temperature, at which the medium takes SmC* phase. The layer structure of the liquid crystalline polymer stabilized (LC-PS) FLC cells has been investigated by X-ray diffraction measurement. As the experimental results, it is found that the formed polymer network suppresses the formation of a chevron layer structure, resulting in the formation of a quasi-bookshelf layer structure; the only C1-uniform state is spontaneously formed without giving a high surface pretilt angle; and a fairly good memory state with an excellent contrast ratio and a low threshold voltage are obtained for a low concentration of doped monomers (2 ∼ 3 wt%) in particular with photo-alignment layers of PVCi; and furthermore, in a cell with a higher concentration of doped monomers (4 wt%) an excellent electroclinic like behavior (called the quasi-electroclinic effect) is obtained.