Studies Of V-shape Electric-optic Characteristics Of Polymer Stabilized Ferroelectric Liquid Crystals

Surface stabilized ferroelectric liquid crystal displays (SSFLCDs) have shown great promise in applications for its high contrast ratio, wide viewing angle and fast switching speed. However, it has some drawbacks to hinder its development. Among them, the most serious problems are that it lacks gray scale capability for the bistability and sensitive to mechanical shock.Beginning with the basic issues of FLCDs, the key SSFLCDs layer structure and relationships between electro-optical characteristics and the molecular alignments were studied. According to disadvantages of SSFLCDs mentioned above, the novel polymer network stabilized ferroelectric LCDs (PNSFLCDs) was put forward in this dissertation which a small amount of diacrylate mononer was doped into FLC.With the scanning electron microscope (SEM) and polarized microscope, the structures of polymer network under different forming conditions were investigated. Meantime, the effects of polymer network to the ferroelectric liquid crystal molecules orientation was studied systematically. The experimental results exhibit that the polymer network formed in the FLC cell was anisotropic and fibrils-like, and affect the FLC alignments greatly. The conventional Chevron layer structure was changed into quasi-bookshelf layer structure which appears the uniform striped texture typically. The striped texture was explained by the smectic C* elastic free energy theory successfully.On the basic of understanding the FLC orientation, the electro-optical characteristics of PNSFLCDs were studied in detail. The results shows that if the monomers are UV polymerized under an AC electric field, the formed anisotropic polymer network can improve not only the FLC orientation to exhibit good uniform texture without any defects but also its E-0 characteristics performing low threshold voltage and good contrast ratio. Especially, the new PNSFLCDs exhibits a novel "V" shape E-0 curve without threshold which can make grayscales available.Utilizing the smectic C* continuum theory, the polymer network energy model and FLC molecular orientation model which were designed, the "V"shape E-O curve in the PNSFLCDs cell has been studied theoretically. And we confirmed that the key point to produce the "V" shape E-0 characteristics is the combination of bookshelf layer structure and the molecular twist orientation near the aligning surface. The concept of network field is bring out firstly in this paper which can be used not only in the FLC system but also in the other polymer network stablilized systems. Another FLCD model to realize gray scale capability梩wisted FLCDs (TFLCDs) was put forward firstly in this dissertation which exhibits good "V" shape E-O characteristics in our experiments. Following the former way, TFLCD' s E-O characteristics were also explained with smectic C* continuum theory. And the theory simulated results fit the experiments results well. Furthermore, we utilized the bulk anchoring effect of the polymer network to overcome the problem of slow respond speed of TFLCD successfully.It' s very significant to discover the thresholdless "V" shape E-0 characteristics. This performance can solve the problem of lackness for gray scale capability for the bistability in the SSLCDs. Furthermore, If this novel electro-optical characteristics is combined with thin film transistor (TFT) driving scheme, we will obtain large screen, high resolution, wide viewing angle and full color visual LC display. Therefore, this characteristic has shown great potential for science studies and manufacture applications.