To achieve control over optical properties of liquid-crystalline materials, alignment control of anisotropic molecules is important. Conventionally, a surface rubbing treatment has been widely used to induce molecular alignment, because it is easy, versatile, and practical. However, this method has some drawbacks, such as static electricity generation, and contamination by dust. To overcome these problems, an alternative photochemical alignment method has been developed. This method can induce molecular alignment without direct contact, however, it requires high intensity polarized light and specific photo-reactive compounds added that limit molecular design.<br/>Recently we have proposed a new photo-alignment method that does not require polarized light, or specific photo-reactive dyes to be added. When monomers are photo-polymerized with a photomask, thus causes molecular diffusion at the border of irradiated and un-irradiated areas, and the molecules become aligned in this region. We hypothesize that this diffusion causes shear stress to the molecules and results in molecular alignment. However, the precise mechanism of how this molecular diffusion aligns molecules still remains unclear.<br/>In this study, to examine molecular alignment behavior from shear stress caused by molecular diffusion, we compared molecular alignment induced by masked photo-polymerization and the alignment induced by mechanically shearing randomly aligned polymer films. We used (6-[4-(4’-cyanobiphenyl)oxy]hexyl acrylate and 4-[(6-Acryloyloxy)hexyloxy]-4'-cyanobiphenyl as anisotropic monomers. The photoinitiator Irgacure 651 was added to each monomer mixture, and were photopolymerized through a mask to induce molecular alignment. Randomly aligned films were also prepared by photo-polymerization without a mask, and the films were sandwiched between two glass plates and sheared. We compared the optical properties of these films, and discuss general molecular alignment behavior during masked photo-polymerization.

Alignment of liquid-crystalline polymers by shear stress induced by masked photo-polymerization

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.