Usami Kiyoaki

We have investigated the effect of alkyl-amine vapor treatment on pretilt angle generation by photo-alignment films of polyimide containing azobenzene in the backbone structure (Azo-PI). By performing alkyl-amine vapor treatment in preparing photo-alignment Azo-PI layers, the controllable range of the pretilt angle was extended at least up to 38° without appearance of threadlike disclination loops. We found that such a high pretilt angle was induced by the photo-alignment layers with a high inclination angle and narrow orientation distribution of the Azo-PI backbone structure in the out-of-plane direction.

<p>Photo-alignment efficiency of polyimides containing azobenzene in the backbone structure (Azo-PIs) is significantly enhanced by performing a simple alkylamine vapor treatment on the precursor (polyamic acid: Azo-PAA) films prior to photo-alignment. This is due to the efficient photo-induced rotation of Azo-PAA backbone structures in the amine-treated films, which are swollen by absorbing alkylamine molecules. In this study, we have examined the relationships between the amine vapor treatmen t time and the thickness of the amine-treated Azo-PAA film, and also between the amine vapor treatment time and the photo-induced in-plane anisotropy of the Azo-PAA and Azo-PI films.</p>

<p>By performing alkyl-amine vapor treatment in preparing photo-alignment layers of polyimides containing azobenzene in the backbone structure (Azo-PIs), the controllable range of the pretilt angle of liquid crystals can be extended at least to 38 without appearance of threadlike disclination loops. In this study, we have investigated the relationship between the average inclination angle of the Azo-PI backbo ne structure and the pretilt angle. We found that the pretilt angle increases with increas ing average inclination angle of the Azo-PI backbone structure.</p>

Recently, we succeeded in improving the controllable range of the pretilt angle of liquid crystal with defect-free alignment by using amine-vapor-treated photoalignment layers of polyimides containing azobenzene in the backbone structure (Azo-PI). The molecular orientation of the Azo-PI photoalignment layers with and without the amine vapor treatment was determined by measuring polarized infrared absorption spectra as a function of the angle of incidence. We found that the average inclination angle of the Azo-PI backbone structures in the amine-vapor-treated film was much higher than that in the untreated film.

We have succeeded in controlling the pretilt angle of liquid crystal (LC) molecules over the whole range from 0 to 90 degrees by using photo-aligned polyimide films. The polyimide contains azobenzene in the backbone structure (Azo-PI) and has side-chains. The photo-alignment treatment was linearly polarized light irradiation at normal incidence followed by oblique angle irradiation of unpolarized light, and it was performed on the corresponding polyamic acid (Azo-PAA) film. By curing the Azo-PAA films, the photo-aligned polyimide films were obtained. The pretilt angle of LC molecules induced by the photo-aligned polyimide films increased as the side-chain content in Azo-PI increased.