Study of the physics and chemistry of liquid crystal displays

Abstract

The study of Liquid Crystal Displays (LCDs) was divided into two aspects, physical and chemical. The chemical study was concerned with the surface coating of transparent electrodes for LCDs devices. Comparison was made between rubbing of conduction transparent glass plate with woolen cloth and treating the surface with poly(vinyl alcohol) mixed with a coupling agent, tetraethoxysilane or sodium silicate. The results show no significant difference. A cell of LCDs consists of two treated transparent glass plates seperated by two 10 micrometers spacers. The cell was then filled with mixed liquid crystals containing a dichroic dye. Either a parallel or a 90 degrees twisted cell was obtained, depending on the rubbing direction of the treated surface of the glass plate. Physical tests were made to obtain the response time, stability and contrast of color with and without an electric field (on and off state). Appropriate conditions were first found, e.g., strength and frequency of applied electric field, by measuring the light absorption in the visible region. In addition, in order to avoid region of reverse twist, which destroys the homogeneity of LCDs, a study was made to find the concentration of chiral compound in liquid crystal giving rise to a suitable pitch for LCDs.