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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，我们研究了液晶分子的光诱导取向机理。紫外线(UV)照射产生的不稳定聚合物碎片残留在聚酰亚胺薄膜中。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来去除。发现液晶单分子膜的面内各向异性与聚酰亚胺薄膜的面内各向异性成正比，聚酰亚胺薄膜在线偏振紫外光(LPUVL)照射后被清洗。比例系数约为75%。这一结果表明，与LPUVL曝光的聚酰亚胺薄膜接触的LC分子的取向是由聚酰亚胺与LC分子之间的短程相互作用引起的。我们还基于主链结构中含有偶氮苯的聚酰胺酸(Azo-PAA)的光致异构化反应研究了LC分子的光诱导取向机理。我们测定了LPUVL辐照的偶氮PAA薄膜的面内分子有序性，以及通过热亚胺化得到的聚酰亚胺(Azo-PI)薄膜的面内分子有序性。我们发现，光致各向异性在面内分子取向上很小，但热亚胺化后光致各向异性显著增加，即偶氮-PI膜的面内分子有序性远大于偶氮-PAA膜。研究发现，液晶单分子膜的面内分子序数与偶氮-PI膜的分子序数基本相等。这一结果清楚地表明，液晶取向是由聚酰亚胺与液晶分子之间的短程相互作用引起的。此外，我们还证实了非偏振紫外光的斜角照射可以诱导偶氮-PI主链结构的倾斜排列，这也导致了液晶的倾斜均匀排列。我们成功地产生了~3°的预倾角。