Anchoring properties of photoaligned azo-dye materials

Abstract

The photoinduced alignment of a liquid crystal ͑LC͒ on films of azo dyes was studied for the liquid crystal display applications. In order to improve the alignment stability of the photoaligned dye ͑SD-1͒, the azo-dye derivative with polymerizable terminal groups was synthesized ͑SDA-1͒. The films of SDA-1 exhibit good photoalignment properties and ultraviolet stability after thermal polymerization. We investigated the anchoring coefficient for polar and azimuthal energy for both azo-dyes SD-1 and SDA-1 using a differential method developed by us. The polar and azimuthal anchoring strengths of azo-dye aligning materials are comparable with those of usual polyimide aligning materials. The electro-optic response of a 90°twisted LC cell remains almost the same after heating up to 200°C, i.e., the anchoring energy remains considerably high.

Diffusion model of photoaligning in azo-dye layers

“…The thermal and uv stability of the photoaligned azo-dye layers is high and can be considerably improved after thermopolymerization of azo-dyes layers [20]. The azo-dye layers exhibit a sufficiently high anchoring energy of liquid crystal with the substrate, which makes them one of the most attractive photoaligning materials for LCD technology [21].…”

Novel Photoaligned Twisted Nematic Liquid Crystal Cell

“…close to the twist angle usually measured in photo-aligned TN LC cells [1][2][3]. The twisted LC alignment occurs because the azo-dye layer supports the LC orientation perpendicular to the UV light polarization, i.e.…”

“…The photo-aligning technique has been widely recognized as a promising technology for the new generations of liquid crystal displays (LCDs), which can replace usual rubbing technology [1][2][3]. Azo-dye materials provide a perfect uniform alignment of nematic LC with a pretilt angle up to 5 0 , strong anchoring energy both in azimuthal and polar directions, high voltage holding ratio and long term stability to UV and IR light.…”

Breaking planar liquid crystal anchoring to form controllable twist disclination loops

“…This substrate has 'strong' anchoring. The flat substrate was spin coated with SD1 [7], an azo-dye which was photoaligned by exposure to linearly polarized UV light of intensity 6 mW/cm 2 for 5 minutes. Since this substrate has 'weak' anchoring, compared to the PI coated curved substrate, the anchoring will break on this substrate as shown below.…”