Kazukiyo Nagai

We review the important features of LC orientation for the alignment layer, namely, production method, alignment mechanisms, and required properties. Photoalignment, which could eliminate the disadvantages of the rubbing method is explored. Applicable materials and techniques for photoalignment are also examined. Many materials for photoalignment layers have been proposed, but polyimide‐based materials are commonly used because of their transparency and insulation properties, which are needed for optical electronic devices. Furthermore, photoisomerization, photodimerization, and photodecomposition as photoalignment methods are reviewed, and specific photoreactive groups and alignment mechanisms are used to induce LC alignment. In summary, polyimides cause photodecomposition and have the following disadvantages; (1) requirement of relatively short‐wavelength ultraviolet (UV) irradiation, (2) difficulty in reorienting polymer chains owing to their rigid polymer matrix, and (3) low‐photo reactivities. The solutions for each disadvantage are already proposed, but the required properties should be determined during material design. Polyimide‐based materials introduced with the azobenzene and cinnamate groups are proposed and found to have the ability of fulfilling the required properties. The mechanism of polyimide photodecomposition is not fully understood. It likely has the advantage in terms of LC alignment stability because of the absence of E/Z isomerization. Therefore, the alignment mechanism and availabilities should be further explored.

In this study, the water vapor sorption of four types of alginate, namely, alginic acid (Alg), Na‐Alg, Ca‐Alg, and NH₄‐Alg, were measured, and the effect of differences in counter cations on water vapor solubility and crystallization mechanism associated with the arrangement of hydrogen bonds generated during humidification was investigated. The sorption amounts in the high‐humidity region can be arranged as follows: Na‐Alg > NH₄‐Alg > Ca‐Alg > Alg. All samples formed a (C)‐type double helix structure before and after the sorption based on the results of Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction. The counter cation affects the arrangement of the hydrogen bonds in this structure. Only Ca‐Alg possessed a pseudocrosslinking among the (C)‐type double helix structures due to the divalent Ca²⁺ ions, which induced variations in the crystal arrangement behavior of the other three samples before and after sorption. Cases I–III show a case of how the orientation is aligned with a new hydrogen bond and classified for each sample.

This study aimed to determine the solubility and temperature dependence of methanol and ethanol vapor caused by the difference in the substituents of polyhedral oligomeric silsesquioxane (POSS)‐containing polymethacrylate membranes and the spacer length between the backbone and POSS backbone. Vapor sorption of methanol and ethanol was measured at 25°C, 35°C, and 45°C for three kinds of POSS‐containing polymer membranes, namely, poly(methacryl isobutyl POSS), poly(methacrylate isobutyl POSS), and poly(methacryl phenyl POSS). The primary structures of the three POSS‐containing polymer chains were columnar. The solubility of alcohol vapor on the POSS‐containing polymer membranes followed the mechanism of solid adsorption and not the general dissolution diffusion. The sorption amount at all three temperatures was related to the surface area of the cylindrical primary structure and the solid adsorption property of the alcohol molecule of the POSS substituent. The sorption amount increased because of the large surface area and adsorption property of alcohol molecules. Although a typical glassy polymer shows exothermic mixing and a rubbery polymer displays endothermic mixing, the sample with the POSS substituent of isobutyl group exhibited an unusual behavior of endothermic mixing despite being a glassy polymer.