Friction as the fundamental factor controlling the pretilt angle of homeotropic liquid crystal cells: A microrubbing investigation

Abstract

The variation of a pretilt angle on polyimide films, which are rubbed using a tiny metal ball (1–8mm diameter), is evaluated. During the rubbing process, a vertical load and a frictional force are simultaneously measured, and the relationship between the pretilt angle and frictional work is investigated under the various rubbing conditions such as the vertical load, the number of rubbings, the moving speed, and the ball diameter. Particularly, the dominant factor affecting the variation of the pretilt angle is explored. We propose that the averaged frictional work can be expressed as the sum of contributions of elastic and plastic deformations. It is clarified that the frictional work of plastic deformation is the most fundamental and most important factor for controlling the pretilt angle under the various rubbing conditions.