Photogeneration of High Pretilt Angles of Nematic Liquid Crystals by Non‐Polarized Light Irradiation of Azobenzene‐Containing Polymer Films

Abstract

A vertical‐alignment (VA) cell of nematic liquid crystals (LCs) was prepared using photoirradiated thin films of a poly(methacrylate) with mesogenic moieties of 4‐trifluoromethoxyazobenzene as the side chains. Optical anisotropy was generated by oblique irradiation of the azobenzene‐containing polymer films with non‐polarized UV light, followed by annealing treatment to enhance the photodichroism, which displayed thermal stability. The combination of oblique exposure to non‐polarized UV light and subsequent annealing treatment brought about high pretilt angles of nematic LCs so that a photoaligned VA LC cell was fabricated. The photopatterned LC cell exhibited electro‐optical properties with excellent optical quality when a voltage was applied even after heating at 100 °C for several hours.

Surface-Mediated Photoalignment of Discotic Liquid Crystals on Azobenzene Polymer Films

“…It is worth noting that the perpendicular irradiation of the pMAzCN film with linearly polarized light resulted only in azimuthal reorientation of the p -cyanoazobenzenes, while the oblique nonpolarized light irradiation regulated both their azimuthal and polar angles. , The azimuthal order level of the aligning film was not an important factor for the surface-mediated DLC orientation. The overall experimental results suggest that the following two prerequisites must be fulfilled for optimum generation of DLC photoalignment: first, three-dimensional orientation of the azobenzene side chains should be achieved by oblique nonpolarized light irradiation, as illustrated in Figure B, and second, their photoaligned states should be stable to external stimuli, particularly to solvents for spin-coating the DLC solution and heat for generating the N D phase.…”

“…DLC Cell between Two pMAzCN Films. Our first attempt to control the orientation of discotic liquid crystals (DLCs) was by fabricating antiparallel LC cells with pMAzCN films in a manner similar to that for conventional CLC cells . C 8 OBzTp in its isotropic phase at 250 °C was placed between two pMAzCN films which had been exposed to oblique nonpolarized light before the fabrication of the DLC cell.…”

Enhancement of the Photoalignment Stability of Block Copolymer Brushes by Anchor Segments

“…Polarized UV/Vis analysis is widely used to determine the degree of alignment of surface polymer brushes . A sample was prepared by coating P(MMA‐NPAMI) 232 ‐b‐PMAz6Me 157 onto a PMMA substrate, denoted by P(MMA‐NPAMI) 232 ‐b‐PMAz6Me 157 /PMMA.…”

Photochromic Cholesteric Liquid Crystals via Arylazopyrazole Functionalization of Hydroxypropyl Cellulose

“…In our system, the AAP is not simply bonded to the mesogen, but it is part of this rod-like structure, so a change in the photoswitch's shape, interaction strength, or twisting power may affect this smaller length scale of order and propagate differently across higher levels of cholesteric organization [40]. Additionally, some azopolymer systems experience photo-induced domain reorientation, depending on the number of Z isomers, their molecular interactions, and the steric hindrance of the liquid crystalline order [20,25]. So, as we increase the DS of AAP HPC, we may not simply be adding more photoisomerizable groups that influence the twisting powers of the mesogen and cholesteric helix, but instead could be changing the sterics on these length scales, thereby altering the domain-level order.…”