27.1: Invited Paper: New Developments in Liquid Crystal Photo-Aligning by Azo-Dyes
特邀報告：液晶圖片偶氮染料的新發展
V. G. Chigrinov, H.S. Kwok
Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Hirokazu Takada, Haruyoshi Takatsu
Corporate R&D Division, Dainippon Ink and Chemicals Incorporated, Japan
Abstract
摘要
Liquid crystal photo-alignment using azo-dyes is reviewed. This alignment method is very different from previously reported ones, such as photo-crosslinking, photo degradation and photo-isomerization. It will be shown that this photo-aligning method can provide a controllable pretilt angle and strong anchoring energy of the liquid crystal cell, as well as high thermal and UV stability. The application of this method to the alignment and fabrication of various types of liquid crystal displays is also discussed.
液晶光配向使用偶氮染料已經復習過了。此對應方法與如先前的報道是非常不同的，例如光交聯，光降解和光異構化。它將會這個照片調心的方法中顯示，可以提供一個可控的預傾角和強錨定能的液晶單元，以及高熱和UV穩定性。在此方法中，對不同類型的液晶顯示器的取向和制造中的應用進行了討論。
1. Introduction
介紹
The field of liquid crystal (LC) photo-alignment is very rapidly developing and a vast amount of the new materials, techniques and LCD prototypes based on photo-alignment (PA) technology have appeared recently. However, despite these potential advantages, the application of PA to LCD production is still limited to the laboratory. Large scale deployment of PA is hampered by the lack of a good material and by long term stability, not to mention the la ck of suitable mass production scale equipment. The effect of LC photoalignment is a direct consequence of the appearance of the photo-induced optical anisotropy and dichroic absorption in thin amorphous films, formed by molecular units with anisotropic absorption properties.
液晶（LC）領域光配向發展非常迅速，基于光配向 （PA）科技的大量新材料，科技和LCD原型最近也都相繼出現。然而，盡管有這些潛在的優勢，PA到LCD生產的應用仍然僅限于實驗室。
The first publication on LC photo-alignment appeared in 1988, which discussed the application of a reversible cis-transisomerization of the azo-benzene molecular layers [2]. The optical control of LC alignment was made by changing the wavelength of the non-polarized light illumination [2].Later it was shown that the alignment of a liquid crystal medium could be made by illuminating a dye doped polymer alignment layer with polarized light [3]. LC molecules in contact with the illuminated area were homogeneously aligned perpendicular to the direction of the laser polarization and remained aligned in the absence of the laser light. Subsequently, LC photo-alignment was also achieved using cinnamoyl side-chain polymers [4,5] and polyimide aligning agents [6]. More recently, a new class of azo-dyes have also been studied with excellent results [10,11]. In this paper, we shall review the physical mechanism of this alignment process and report some new results related to the processing conditions using these azo-dyes. In particular, we discuss the conditions where the light dosage is greatly reduced, to less than 50mJ/cm2. Applications of this new PA material to various types of LCD will also be reviewed. #p#分頁標題#e#
最近，一類新的偶氮染料也被研究出來了，而且具效果很好。在本文中，我們將回顧這個校準過程的物理機制和相關的加工條件下使用這些偶氮染料報告中的一些新的結果。特別是，光劑量大大降低，低于50mJ/cm2。這種新的PA材料應用于各種類型的LCD也將進行考察。
2. Results
結果
2.1  Azo-dye aligning layers
Photo-alignment can generally be classified into four categories according to their mechanism.
根據光取向的機制，光取向大致可以分為四類。
They are (i) photochemically reversible cis-trans isomeriz ation in azo-dye containing polymers, monolayers and pure dye films [12,13]; (ii) photochemical crosslinking in preferred directions of polymer precursors, such as cinnamoyl side-chain polymers [4,5]; (iii) photodegradation and orientational bond breaking in polyimide materials [14,15]; and (iv) pure reorientation of the azo-dye chromophore molecules or azo-dye  molecular solvates due to the diffusion under the action of polarized light [10,11]. Recently the method of repeated cis-trans photoisomerization reaction resulting in the reorientation of the backbone structure of polyamic acid contained azobenzene units was reported [16,17].
最近，據報道，順反光致異構化反應的方法導致了包含偶氮單位的聚酰胺酸主體結構的再定位。
We believe that the method (iv) with pure diffusion reorientation of the azo-dye chromophore molecules or azo-dye molecular solvates is the most promising one for large scale applications. In this case the azo- dye molecules, are tending to align their long axes perpendicular to the UV-light polarization resulting in anisotropic dichroism or birefringence of the PA film [18]. Actually the photo-aligned azo-dye molecules produce a very smooth and uniform structure with the thickness of several nanometers controlled by the concentration of the azo-dye in an organic solvent e.g. N,N-dimethylformamide (DMF) [11].
實際上，照片對齊偶氮染料分子產生一個非常光滑，均勻的結構，由偶氮染料的濃度控制在有機溶劑中，例如幾納米的厚度N，N-二甲基甲酰胺（DMF）[11]。
The change of the azo-dye concentration between 0.4 and 1.3  http://ukthesis.org/ygsslwdx/  wt/wt % concentration results in the thickness variation of the photo-alignment layer between 3 and 12 nm [19].
偶氮染料的濃度在0.4和1.3％濃度的變化導致了3至12納米的光取向層的厚度變化。