Surface rheology of rubbed polyimide film in liquid crystal display

The rheological properties of polyimide film surfaces have an important influence on contrast reduction during the in-plane switching mode of liquid crystal displays. To clarify these properties, the slight difference of deviation angles of liquid crystal directors from the rubbing direction were measured during prolonged exposure to alternating electric fields. The results indicate that the data can be well described using the Kelvin-Voigt model. The relation between the in-plane shear modulus G and the strain at the polyimide surface was also investigated based on the torque balance between the energy density of the electric field and the elastic energy density of the polyimide surface. It was found that much smaller G than bulk polyimide materials existed on the polyimide surface in liquid crystal display. (C) 2014 Optical Society of America