In situ, spatially variable photoalignment of liquid crystals inside a glass cell using brilliant yellow

The ability to control the alignment of liquid crystals (LCs) is a prerequisite for all LC applications such as LC displays, LC polarization gratings, and even for liquid crystal elastomer actuators. Out of the many alignment techniques available, photoalignment, i.e., spin-coating a thin layer of a photosensitive organic material and exposing it to polarized light, proves to be an attractive method. This method allows the non-contact and complete control over the alignment by just controlling the polarization state of the light exposure. We present a method to in situ align (in-plane) the nematic liquid crystals with a single-step exposure with the photoalignment technique. For this method, we have used the commercially available azo-dye, Brilliant Yellow (BY), which is photoaligned with linearly polarized 450 nm light. An in-house built, digital micromirror device (DMD) based projection setup allows the spatial structuring of the light, thereby enabling the pixel-by-pixel photoalignment of BY, and hence of LCs. This setup makes it possible to project computer-generated patterns on the substrate, thereby aligning the LCs in bulk in any arbitrary pattern. The photoalignment of BY is done in presence of LCs, i.e., after filling the LCs inside the glass cell. The achieved alignment is stable and rewritable. To the authors' knowledge, this is the first demonstration of in situ, spatially varying photoalignment of liquid crystals inside the glass cell with single-step exposure and with commercially available chemicals.