Abstract
This paper describes thermally enhanced in‐plane and out‐of‐plane reorientation of mesogenic groups in copolymer liquid‐crystal (CPLC) films that have a photo‐cross‐linkable 4‐(4′‐methoxycinnamoyl)biphenyl (MCB) side group and a 4‐methoxybiphenyl (4MB) side group. The side groups are cross‐linked by irradiation with linearly polarized ultraviolet (LPUV) light and subsequent annealing. Due to axis‐selective photo‐cross‐linking, a small negative optical anisotropy is observed for all CPLCs after exposure to LPUV light. When the composition of the 4MB comonomer is less than 45 mol‐%, thermal treatment in the liquid‐crystalline temperature range causes in‐plane reorientation of the film and results in an in‐plane order parameter of 0.71. In contrast, when the composition of the 4MB is increased, out‐of‐plane reorientation is generated. Three‐dimensional molecular reorientation and inclined out‐of‐plane reorientation are achieved by adjusting the exposure angle.
Angular dependence of UV absorption spectrum of film 3. The inset shows a conoscope observation of the film. The film was annealed at 130 °C for 10 min.
magnified imageAngular dependence of UV absorption spectrum of film 3. The inset shows a conoscope observation of the film. The film was annealed at 130 °C for 10 min.