Vertical alignment of liquid crystals on polymer films containing renewable cardanol moieties

Abstract

Liquid crystal (LC) alignment behaviors of poly(methyl methacrylate) derivative films containing different amounts of plant-based and renewable cardanol moieties were studied for the first time. The poly(methyl methacrylate) derivatives containing the cardanol moieties (HCP#) were prepared using 2-hydroxy-3-cardanylpropyl methacrylate (HCPM) and methacrylate (MMA) as monomers. These polymer films exhibited good optical transparency in the visible light region. The LC cells made from the polymer having 100mol% of 2-hydroxy-3-cardanylpropyl methacrylate (HCP100) as the alignment layer showed vertical LC alignment having a pretilt angle of about 90°, while those made from HCP# films having smaller than 69mol% of 2-hydroxy-3-cardanylpropyl methacrylate exhibited random planar LC alignment behavior. The vertical LC alignment behavior on the HCP100 film was ascribed to the hydrophobic HCP100 surface generated by the nonpolar cardanol groups in the polymers. The thermal stability of the LC cell made from UV irradiated HCP100 film (HCP100C) was enhanced compared with HCP100 due to the formation of the cross-linked structure of the unsaturated hydrocarbon in the cardanol group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using the HCP100 as a LC alignment layer. This can give the basic idea for the design of LC alignment layers based on renewable cardanol resource containing polymer films.