Study On The Alignment Of Ferroelectric Liquid Crystals

The requirement of data transmitting in the era of multimedia and network will be 103～106 times as that of today. The commercialized liquid crystal display (LCD) will face an austere problem that the response speed of the nematic liquid crystal (NLC) can't satisfy the requirement of a large number of the data transmission. Therefore, the urgent and principle task of the researchers in the LC field is to research and develop a high responsive speed LCD. The responsive speed of the surface stable ferroelectric liquid crystal (SSFLC) is 102～103 times faster than that of the NLC. Therefore, the SSFLCD is popularly considered as the most promising LCD in the next century. But its application isn't extensive as expected because until now we have not made some breakthroughs of the critical technologies, such as the stabilization of alignment, the elimination of irretrievable zigzag defects, and the realization of continuous grayscales for the display of image. To solve the said problems, the alignment and the electro-optic character of the FLC were investigated in the paper. Based on the arrangement state of NLC on the baseplate surface, we analyzed the effects of rubbing alignment on the LC molecular arrangements. The experimental results indicate that the alignment degree of NLC molecules on the alignment film surface is only half of that in the bulk. Therefore, the alignment of NLC molecules on the alignment film surface is different from that in the bulk. And the rubbed film only provides a preferred alignment for NLC instead of a high order. According to the arrangement state of NLC on the baseplate surface, we can speculate that the alignment degree of FLC molecules on the alignment film surface is also not high, and there are not molecular layer structures. It leads to a bigger stress in the interfacial layers of a FLC device, which must be one of the critical factors that cause the alignment defects often occurring during the preparation of FLC device. As we slowly decrease the temperature, the stress in interfacial layers is eliminated because the layer structures on the surface is progressively identical to those in the bulk due to heat-induced de-adhering movement of FLC molecules. As a result, we obtain a uniform alignment. We profoundly analyzed the forming mechanism of the zigzag defect. And by controlling the anchoring strength and the pretilt angle of the alignment films, we obtained the uniform chevron shaped layer alignment of the FLC. But due to the tip and tilt zigzag in the chevron shaped layer structure, both the effective rotation conical angle and contrast ratio are small when it is drove. In our experiment, we applied a low frequency electric field, which changed the chevron shaped layer structure to a quasi-bookshelf layer structure. As a result, the effective rotation conical angle when drove is improved greatly, and the contrast ratio is improved a factor of 2. In order to achieve the continuous electro-optical (E-O) character, the body anchoring action of the polymer network had been introduced. Not only the stability of the alignment of the FLC was greatly improved, but also the V-shaped E-O character without threshold was observed. With the scanning electro microscope (SEM) and the polarized optic microscope, the orienting of the polymer network formed in FLC was investigated. Its saturation voltage is 5V, which combined with the thin film transistor (TFT) will realize a continuous grey level display. On the basis of the continuous theory of the Sc* phase, we theoretically studied the mechanism of the V-shaped continuous E-O characteristics, and clarified that the addition of the network anchoring energy changed the system energy state distribution. As a result, the freedom energy curve with two minima changed to a monotonous one, which must be the reason for the V-shaped continuous E-O characteristics without a threshold voltage. Finally, a FLC material which has continuous E-O character without adding polymer network was studied. The materials has not SA phase and are formed from the direct N*-Sc* phase transition. The stability of the layer arrangement of this material was very difficult to be controlled. After we controlled the rubbing strength to realize a uniform alignment and applied a DC voltage during the N*-Sc* phase transition, the alignment of the stable mono-domain was achieved. In addition, half V shaped E-O character without threshold was observed. The contrast radio of the FLC device was more than 100. Meanwhile, its saturation voltage is only 3V. In this paper, we exploringly investigated the alignment stability of the representative FLC material. And we obtained a FLC device with low saturation voltage and continuous E-O characteristics. This work fills up the blank of the domestic FLC field, and has great significance for people to open up the field of the high-speed respond LCD, to perfect the FLC alignment technology and to realize its application in the display industry.