The Study Of Mixed Polyimide Alignment Layer For Cholesteric Bistable Liquid Crystal Displays

With the development of display technology, many new display technologies come to the fore for its unique advantages. Cholesteric bistable LCD can maintain the display without applying the drive voltage continually. Because it has the characteristics that the electric field is removed, the focal conic state or plane states can still maintain. This display mode has low power consumption, high-contrast, low-cost. So it can be made as curly flexible displays. Has a broad application prospects in the field of e-books, e-paper and electronic tags display. Due to its outstanding advantages, such as abrasion resistance, thermal stability, good electrical properties, polyimide (Polyimide, PI) material are widely applied to the cholesteric bistable liquid crystal display, to make the liquid crystal molecules have a certain orientation.Contrast with the planar state, the focal conic state can make the liquid crystal system in a higher energy state, which was stated as the metastability in the thermodynamic. Therefore, the focal conic state has played a key role in the stability of the cholesteric bistable display. It decides the performance is good or bad. If dealing the surface of the glass substrate with special alignment treatment, the "anchoring" effect will be formed on the substrate surface; their strength will directly affect the stability of the focal conic state. The surface energy of the substrate with the liquid crystal molecule and the pretilt angle can directly affect the display effect. Studying deeply to anchoring effect, surface energy and pretilt angle has important theoretical significance and application value. Specific researching works were done as following:1. Using mixed vertical and horizontal polyimide (PI) to adjust the anchoring energy and surface pretilt angle. We will coat the glass substrate with different concentrations of the vertical and horizontal ratio of the polyimide, and then make liquid crystal cells. The photoelectric characteristic curve of the liquid crystal cell is measured with a photoelectric characteristics measuring device. And using the formula derivation we can obtain the optical delay. We use Origin software fitting linear optical delay voltage curve. Finally we can calculate anchoring energy. Found that the anchoring energy is increased with the increasing of the concentration of vertical polyimide.2. By measuring the water contact angle of the sample surface with a reading microscope and a digital camera, establish tension balance, and then get the results of solid interface surface tension, and then get the surface energy. Found that surface energy will decrease with increasing V-PI., and the larger polar anchoring energy is, the more better stability the focal conic texture has.3. Using the crystal rotation method to measure the pretilt angle of liquid crystal molecules (the angle between the major axis of liquid crystal molecules and the substrate). Found that the pre-tilt angle is increased with the frictional strength or the increase of the concentration of vertical polyimide.