【作者】 彭增辉；

【导师】 宣丽；

【作者基本信息】 中国科学院研究生院（长春光学精密机械与物理研究所） ， 凝聚态物理， 2005， 博士

【摘要】 和传统的阴极射线管(CRT)显示器相比,液晶显示器(Liquid crystal display, LCD)具有环保、节能、易于平板化和便携性等性能优势,越来越受到人们的青睐。2003 年中国大陆地区LCD 的销量已经达到207 万台,首次超过了CRT 显示器的市场销售量,预计此后以每年20%左右的速率递增。LCD 的生产属于高技术领域,它的生产工艺需要不断研发和更新,才能跟上迅猛发展的高技术产品的需求。大多数液晶显示器件都需要取向膜来控制器件内液晶初始的均匀排列。目前LCD 生产中最不尽人意的工艺就是液晶的取向工艺。工业上常用的取向方法是定向摩擦高分子膜法,它有着易于大规模生产等技术优势,但是摩擦过程中会产生静电和尘埃,它们容易造成液晶器件的损伤和瑕疵。光控取向法是一种非常具有应用前景的取向方法,它利用线性偏振紫外光(LPUV)辐照光敏聚合物薄膜,使薄膜具有表面张力的各向异性,从而实现诱导液晶分子取向。光控取向是一种非接触式的取向方法,完全避免了现有摩擦取向法存在的灰尘沾染和电荷累积等问题,还可以进行微区取向控制,制作多畴宽视角显示器。从1992 年Schdat M.等人提出光控取向方法至今已经有十余年时间,但这种方法始终没有实用化。其原因为光控取向的稳定性差,取向效果也不如摩擦法。这主要是由于人们多采用光敏高分子作为成膜材料,光敏基团在空间位置上受到高分子主链的阻隔,定向光化学反应程度低。基于这种问题,本文提出了如下的解决方案:1)降低成膜光敏材料的分子量,即使用光敏小分子单体成膜,增加光敏基团碰撞、反应的机会,以期提高反应程度、稳定性和取向度;2)将光敏基团直接构建于有序的自组装膜体系中,在LPUV 辐照下可使薄膜中高效地、定向地发生环加成反应,使取向膜获得高取向度和高稳定性。围绕上述思路开展了如下工作:1)合成了三种可进行光二聚反应的光敏小分子单体,LPUV 辐照制作了光控取向膜;用紫外-可见光谱法和红外光谱法分析了薄膜中的光化学反应,发现小分子的光反应程度可达到50%以上,至少比光敏高分子高出5 倍;薄膜的偏振红外光谱证实,经过LPUV 辐照后薄膜出现了明显的各向异性;将小分子光控取向膜制成液晶器件,在偏光显微镜下观察看到均匀一致的液晶取向;并且热稳定性达到100℃左右,接近实用化要求。2)制备了含肉桂酸、香豆素基团的自组装单层膜;采用接触角的方法监测自组装反应的动力学过程;紫外-可见光谱证实了自组装单层膜在石英基板表面形成;自组装单层膜经LPUV 辐照后能诱导液晶均匀取向,而且热稳定性可达130℃,热稳定性进一步提高。3)合成了含有光敏双键的双季铵盐,在水溶液状态下将它和聚乙烯基苯磺酸钠沉积生成layer-by-layer 自组装多层膜,紫外-可见光谱证实这是一个逐层均匀的沉积;在LPUV 照射下,自组装膜中的光敏双键按照偏振方向发生[2+2]环加成反应,形成取向膜,用二向色性值评价的分子取向度高于高分子及小分子光控取向膜的水平;实验证明用自组装多层膜制成的液晶器件亮暗态均匀,静态对比度约为100,达到实用化器件的水平。更多还原

【Abstract】 Compared to conventional CRT displays, Liquid crystal displays (LCD) have many advantages, such as environmental protection, low power, flatness and portability. The statistic result of Display Search showed that the sell of LCD was 2.07 million sets in 2003 in the mainland of China, and the number was larger than the quantity of CRT displays. LCD manufacture is a high-tech region, technology must be developed and refreshed, so that it can keep up with the requirement of LCD market. In the region of LCD research and manufacture, most of LCD need alignment layers that can give liquid crystals a preference alignment direction. In the industry of LCD, rubbing alignment method has been widely used because its process can be easy to carry out. Photoalignment technique is another important alignment method, its mechanism was: a photosensitive solid film becomes anisotropy when it was irradiated by linear polarized ultraviolet (LPUV), the anisotropic film would have the ability to induce liquid crystal to alignment. Photoalignment is an un-contacted alignment method, so it can avoid the shortcomings of rubbing method, such as particle contamination and static charge buildup. Moreover, photoalignment is particularly useful in multi-domain applications; by this technique the LCD will have large view-angle. In 1992, Schdat M. had already given photoalignment method, but the method with superiority has not been applied in the LCD industry now. The reason may be as follow: the stability of photoalignment layer is not good, and alignment result is worse than that of rubbing treatment. The photosensitive materials are always polymer, when the photochemical reaction carries out, the backbone of polymer probably can obstruct the photosensitive group, which make the reactivity ratio of the film to be low. To resolve these problems, we give some new schemes: 1) A photosensitive monomer was used as film-formed material, a high reaction ratio would be obtained; 2) A photosensitive self-assembled film was introduced to photoalignment systems, because of self-assembled film is an ordered system, the photosensitive group was easy to react, this means the reaction would be complete and efficient. The content of the thesis mainly included three parts: 1) Three kinds of low molecular photosensitive monomers were synthesized, and they were used to fabricate photoalignment layer of nematic liquid crystals by photocycloaddition. The UV and IR spectroscopic studies of the monomer films showed that the photoreaction ratio of monomer (about 50%) was higher than the corresponding photosensitive polymer (about 10%, PVCi). The polarized IR spectra proved that obvious anisotropic absorption was displayed in the irradiated photosensitive film. With polarizing microscopy method, we found that these kinds of photoalignment films exhibited good alignment ability, and the stability of the photoalignment film could reach about 100℃. 2) A photosensitive self-assembled monolayer was fabricated that contained photo-cycloadditable groups, such as, coumarin and cinnamate. The reaction process were detected by contact angle method because the IR absorption of monolayer was very weak. The photosensitive self-assembled monolayer promote uniform alignment of nematic liquid crystals by LPUV, and it thermal stability could reach about 130℃. 3) A cationic bolaform amphiphiles was synthesized that had two photosensitive double bonds, and can be polymerized by ultraviolet. A layer-by-layer self-assembled deposition film was prepared in aqueous solution by using this material and poly (sodium 4-styrenesulfonate). The UV-Vis. spectra proved that the multilayers film was uniform and layer-by-layer. When LPUV irradiated the film, the photopolymerizable double bond underwent [2+2] cycloaddition, and the production of the reaction distributed along the polarized direction of incident LPUV. Polarized UV-Vis. spectra indicated that the irradiated self-assembled multiplayer film was anisotropic, and the dichromic ration is about 0.09, it is higher than the spin-coating method of photosensitive polymer or monomer. We used this anisotropic film as alignment layer of nematic liquid crystals, and obtained a uniform and stability alignment result, the static contrast ratio is about 100, which is very close to application of liquid crystal device. This thesis is an instance that the photochemical material was used in the physics region of liquid crystals, the route that was from photosensitive monomer, self-assembled monolayer film to self-assembled multiplayer film was undergone, by this logical research method photoailgnment of liquid crystal was extended and consummated.更多还原