Optical and electro-optic properties of polymer-stabilized blue phase liquid crystal cells with photoalignment layers

Abstract

A comparative study of the optical and electro-optic properties of polymer-stabilized blue phase liquid crystal (PS-BPLC) cells with photoalignment layers and rubbing alignment layers is performed. The optical microscope (OM) images of the photoaligned and rubbing-aligned cells depict that they have uniform PS-BPLC textures, while the post-processed OM images of the two cells reveal that the former has a more uniform PS-BPLC texture than the latter. The relatively uniform PS-BPLC texture in the photoaligned cell is verified by the reflective spectra of the two cells. The voltage-dependent transmittance curves and time-dependent transmittance curves of another two photoaligned and rubbing-aligned cells with in-plane-switching (IPS) electrodes indicate that the contrast ratio of the former is 41% larger than that of the latter, and the operation voltage (response time) of the former is 11 (10) % smaller than that of the latter. This result arises from the fact that the photoaligned cell with the IPS electrodes exhibits a relatively uniform PS-BPLC texture and relatively weak voltage-shielding effect. Therefore, the photoalignment can improve the electro-optic properties of PS-BPLC cells with alignment layers. The photoaligned and rubbing-aligned cells have no thermal hysteresis in low voltage regions due to the uniform surface alignment layers, and exhibit very low voltage-induced hysteresis in high voltage regions owing to no thermal hysteresis. Briefly, uniform surface alignment layers can eliminate the thermal hysteresis of PS-BPLC cells, suppressing their voltage-induced hysteresis. In other words, the hysteresis of PS-BPLC cells with alignment layers is independent of alignment methods as long as the alignment layers have strong surface anchoring energy.