Study on the molecular orientation of liquid crystals induced by the various alignment layers in LCD and flexible display

Abstract

Liquid crystals, which determine the characteristics of liquid crystal display, are organic materials that possess an intermediate phase, or mesophase, between the solid and isotropic liquid phases. The surface alignment of liquid crystal (LC) molecules is of great importance in the fabrication of liquid crystal displays (LCDs). Liquid crystal displays (LCD) are light-controlling devices which rely on the optical properties of liquid crystal materials to control the transmission of light from an external source. In recent years, there has been significant research investment in the development of a flexible display technology. Flexible flat panel display technologies offer many potential advantages, such as very thin profiles, lightweight and robust display systems, the ability to flex, curve, conform, roll, and fold a display for extreme portability, high-throughput manufacturing, wearable displays integrated in garments and textiles, and ultimate engineering design freedom. A liquid crystal display using plastic substrates is the most promising device for the flexible display since the relevant technologies have been well established in recent years. The successful operation of the LC-based display requires uniform alignment of liquid crystal molecules on substrate, which is currently achieved by confining the liquid crystal between liquid crystal alignment layers formed on surface of ITO layer. Due to the liquid-like properties of liquid crystals, relatively little external energy provided by alignment layer is required to produce large changes in the molecular orientation. Also, the interaction between liquid crystal and alignment layer at the boundary is a critical importance on electro-optic properties of liquid crystal. Usually, liquid crystal alignment is induced by the rubbing method. The rubbed polymer surface has optical anisotropies caused by the orientation of polymer molecules and microgrooves, which is responsible for the LC alignment. Howeve...