LIQUID-CRYSTAL ALIGNMENT ON POLYMER-FILMS - CHANGES OF THE PRETILT ANGLES DUE TO THE THERMAL-TREATMENT OF POLYALKYLENE PYROMELLITIMIDES

Two polyimides have been cured at different temperatures and some samp les further annealed at different temperatures after rubbing. It is fo und that the pretilt angles on these films increase with increasing cu ring temperature and/or increasing curing time. There is a further inc rease in the preiilt angle after annealing, but this effect is depende nt on the structure of the polyimide as well as the pretreatment condi tions of the sample. All these observations can be explained by consid ering the change in the alignment of the polyimide and thus the induce d in-plane order of the liquid crystalline layer.