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Investigation of photoinduced alignment mechanism of liquid crystal molecules using polyimide alignment layers

使用聚酰亚胺取向层研究液晶分子的光诱导取向机制

基本信息

批准号：
13450003
负责人：
SAKAMOTO Kenji
金额：
$ 4.74万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

We have investigated the photoinduced alignment mechanism of liquid crystal (LC) molecules based on the photo-decomposition reactions of polyimide. Unstable polymer fragments produced by ultraviolet (UV) irradiation remain in the polyimide film. We found that the unstable polymer fragments can be removed by a few minutes of ultrasonic cleaning. The in-plane anisotropy of the LC monolayer was found to be proportional to that of the underlying polyimide film, which was washed after irradiation of linearly polarized UV light (LPUVL). The proportionality factor was about 75%. This result suggests that the alignment of the LC molecules in contact with the LPUVL-exposed polyimide film is induced by a short-range interaction between the polyimide and LC molecules.We have also investigated the photoinduced alignment mechanism of LC molecules based on the photo-isomerization reactions of polyamic acid (Azo-PAA) containing azobenzene in the backbone structure. We determined the in-plane molecular order of the Azo-PAA film irradiated with LPUVL, as well as that of the polyimide (Azo-PI) film obtained by thermally imidizing it. We found that the photoinduced anisotropy in the in-plane molecular orientation was small, but it increased significantly after thermal imidization ; i.e. the in-plane molecular order of the Azo-PI film was much greater than that of the Azo-PAA film. The in-plane molecular order parameter of the LC monolayer was found to be almost equal to that of the underlying Azo-PI film. This result clearly shows that the LC alignment is induced by a short-range interaction between the polyimide and LC molecules. In addition, we confirmed that inclined alignment of the Azo-PI backbone structure can be induced by oblique angle irradiation of un-polarized UV light, and that this also induces tilted homogeneous LC alignment. We succeeded in generating the pretilt angle of 〜3°.

基于聚酰亚胺的光分解反应，研究了液晶分子的光诱导取向机理。由紫外线（UV）照射产生的不稳定的聚合物片段保留在聚酰亚胺膜中。我们发现，不稳定的聚合物碎片可以通过几分钟的超声波清洗去除。发现LC单层的面内各向异性与下面的聚酰亚胺膜的面内各向异性成比例，该聚酰亚胺膜在线性偏振UV光（LPUVL）照射后被洗涤。比例系数约为75%。这一结果表明，液晶分子与LPUVL暴露的聚酰亚胺膜接触的取向是由聚酰亚胺和液晶分子之间的短程相互作用引起的。我们还研究了基于主链结构中含有偶氮苯的聚酰胺酸（Azo-PAA）的光致异构化反应的液晶分子的光致取向机制。我们测定了经LPUVL辐照的Azo-PAA薄膜以及热亚胺化后得到的聚酰亚胺（Azo-PI）薄膜的面内分子有序度，发现Azo-PI薄膜的面内分子取向的光致各向异性很小，但热亚胺化后明显增加，即Azo-PI薄膜的面内分子有序度远大于Azo-PAA薄膜。发现LC单层的面内分子有序参数几乎等于下面的Azo-PI膜的分子有序参数。该结果清楚地表明，液晶取向是由聚酰亚胺和液晶分子之间的短程相互作用引起的。此外，我们证实，倾斜排列的Azo-PI骨干结构可以诱导由斜角照射的非偏振光的紫外光，这也诱导倾斜均匀的LC排列。我们成功地产生了0.3 °的预倾角。