A Combined Method Based on Rubbing and UV-Irradiation for Preparing Stable Alignment-Layers with High Pretilt Angles

Abstract

A novel two-step method combining rubbing and UV-irradiation based on ladderlike polysilsesquioxanes (LPS) containing cinnamate and azobenzene side chains was developed to obtain alignment layers which features a high surface pretilt angle and good stability. At the first step, a low pretilt angle of 1–3° was generated by rubbing and at the second step, an increased pretilt angle of about 11° was obtained through further UV-irradiation. The polarized optical micrograph and the conoscopic picture prove that good LC alignment state with a stable high pretilt angle can be obtained by in situ photo-crosslinking of the cinnamate side-chains through proper UV-irradiation. The high pretilt angle arises from the photo-induced tautomerization of azobenzene side chains and that is confirmed by AFM study. In particular, the annealing test near the clearing point indicates the high stability of the high pretilt state, which heralds their potential application in LCD such as producing a patterned alignment layer for improving view angle.