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

点击翻译按钮获取中文摘要

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.