Alignment properties of the surface of peeled off and flipped anisotropic liquid crystal polymer film

Abstract
The alignment of liquid crystals (LC) can be arranged using specially prepared alignment layers. In the case of layer-by-layer deposition of a polymerizable LC, the upper surface of the preceding layer plays the role of the alignment layer. We succeeded in separating the film of the polymerizable LC RM257 aligned on the azo dye surface from the substrate and using its opposite side to align the next LC layer. The "Brilliant yellow" azo dye as photoalignment layer was irradiated by linearly polarized light with subsequent coating of RM257 layer, followed by its UV-curing. Then, a drop of UV-polymerizable glue was applied to the surface of the polymer film and the second substrate was attached. After fixing the UV glue, the resulting sandwich was mechanically separated. In the process of substrate separation, the azo dye remains on the mother substrate, and the oriented polymerized film of RM257 is transferred to the second substrate. The resulting alignment surface provides high-quality orientation of LC materials – both uniform and with a complex spatially periodic distribution of the LC director typical for diffraction optical elements. This approach eliminates transmission losses associated with the azo dye absorption, significantly improves the adhesion of the film, and allows for transferring the aligned film onto various substrates.

Keywords: photoalignment, alignment, polymer liquid crystal, RM 257, laser holography, diffractive optical element (DOE)