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

液晶分子的均匀排列通常是通过聚合物表面诱导排列技术来实现的。然而，传统的摩擦技术存在一个严重的问题，即摩擦过程中会产生静电电荷和灰尘。为了在聚酰亚胺表面实现静电无尘，研究了一种新型液晶对准技术。将聚酰亚胺表面暴露在343 K的单向流动水中，然后进行热固化，得到了LC的均匀排列。在热亚酰化后，将聚酰亚胺表面暴露于水流的情况下，表面诱导的排列效应并不充分。水流作用下聚酰亚胺前驱体表面产生的局部链取向以及热亚酰化对链取向的放大是“水流摩擦”的可能机理。界面增强和频生成（ISFG）方法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。采用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。聚苯乙烯肉桂酸酯和聚乙烯醇作为聚合物。在两个ISEG光谱中，观察到5CB的cn -拉伸带的吸收带。在（PVCi /5GB）界面，cn -拉伸的吸光度带出现在2225 cm^<-1>处，这与5CB体态ET-IR光谱中的cn -拉伸带吻合较好。然而，在（PVA/ 5CB）界面，cn -拉伸带被筛选100 cm^<-1>至低频。这表明PVA与5CB的分子间相互作用比PVCi与5GB的分子间相互作用大得多。

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.