Novel Method to Control Liquid Crystal Orientation based on Water Flow-induced Molecular Alignment

液晶（LC）分子的均匀排列通常通过聚合物表面的表面诱导排列技术产生。然而，传统的摩擦技术涉及一个严重的问题，即在通过摩擦的机械摩擦期间产生静电荷和灰尘。在这项研究中，一种新的液晶取向技术进行了研究，以实现静电荷和灰尘的聚酰亚胺表面上。在聚酰亚胺热固化前，将聚酰亚胺表面暴露于343 K的单向流动的水中，可获得均匀的液晶取向，但在聚酰亚胺热固化后暴露于水流中，表面诱导取向效应不明显。水流作用下聚酰亚胺前驱体表面的局部链取向及其热亚胺化对链取向的放大是“水流摩擦”的一种可能机制。界面增强和频产生（ISFG）技术是一种二阶非线性光学技术，是研究表面和界面的有力工具。用ISEG方法研究了4-氰基-4 '-戊基联苯（5CB）在聚合物/ 5CB界面上的行为。使用聚（肉桂酸乙烯酯）和聚（乙烯醇）作为聚合物。在两个ISEG光谱中，观察到归因于5CB的CN伸缩带的吸收带。在（PVCi /5GB）界面处，CN-伸缩的吸收带出现在2225 cm-1处<-1>，这与本体状态的5CB的ET-IR光谱中的CN-伸缩带非常一致。然而，在（PVA/ 5CB）界面处，CN-伸缩的带被筛分100cm-1<-1>至较低频率。这一结果表明，PVA和5CB之间的分子间相互作用远大于PVCi和5GB的情况。

The uniform alignment of liquid crystal (LC) molecules is generally produced by a surface-induced alignment technique of a polymer surface. However, the conventional rubbing technique involves a serious problem that an electrostatic charge and dust are generated during mechanical friction by rubbing. In this study, a novel liquid crystal alignment technique was investigated in order to realize electrostatic charge-and dust-free on the polyimide surface. A uniform alignment of LC was obtained by using the polyimide surface which was exposed to unidirectionally flowing water at 343 K before imidization by thermal cure.The surface-induced alignment effect was not sufficient in the case of exposing the polyimide surface to the water flow after the thermal imidization. The local chain orientation on the polyimide precursor surface induced by exposing to the water flow and its amplification of the chain orientation by the thermal imidization is a possible mechanism of "water flow rubbing".Interface enhanced sum-frequency generation (ISFG) method is a second-order nonlinear optical technique, which is a powerful tool to study the surface and the interface. The ISEG method was used for investigating 4-cyano-4'-pentylbiphenyl (5CB) behavior at the (polymer / 5CB) interface. Poly (vinyl cinnamate) and poly (vinyl alcohol) were used as polymer. In both ISEG spectra, the absorbance bands attributed to the CN-stretching bands of 5CB were observed. At the (PVCi /5GB) interface, the absorbance band of CN-stretching appeared at 2225 cm^<-1>, which was in good agreement with CN-stretching band in the ET-IR spectrum of 5CB in the bulk state. However, at the (PVA/ 5CB) interface, the band of CN-stretching was sifted 100 cm^<-1> to lower frequency. This results indicate that the intermolecular interaction between PVA and 5CB is much larger than the case of PVCi and 5GB.