Liquid crystal alignment layer polyimides and nematic LC pretilt angles

The LC pretilt angles (Θp′s) could be controlled by the polyimide structures and (or) the LCD processes under a certain rubbing condition. Θp was increased by introducing alkyl side chains and (or) other non-polar groups to the polyimide. On another hand, Θp was decreased by modifying the AL polyimide surface with O2 plasma or deep-UV exposure. A polar polymer provides a smaller Θp than a non-polar polymer. The electronic interaction between LC molecules and the AL surface would decrease the Θp while the steric repulsion by the side chains would increase the Θp. Thus the AL polyimide and its process can be designed so as to obtain a desired pretilt angle.