I. Hirosawa et al., The relationship between pretilt angle of liquid crystal and optical anisotropy of alignment film, MOLEC CRYST, 368, 2001, pp. 4333-4339
We investigated the relationship between the pretilt of liquid crystal and
the optical anisotropy of three kinds of polyimide films (PI-A, PI-B and PI
-C) rubbed under various conditions. The optical anisotropy of the rubbed f
ilms was detected by reflection ellipsometry, and was characterized accordi
ng to anisotropic dielectric constants, the tilt of the principal dielectri
c axis and the thickness of the molecular oriented layer. The optical aniso
tropy of the rubbed PI-A and PI-C films was largely dependent on the rubbin
g condition. A monotonic decrease in pretilt was observed as the difference
between the ordinary and extraordinary dielectric constants of the molecul
ar oriented layers. In the case of PI-B, the optical anisotropy is changed
very little when rubbing conditions were changed. The correlation between t
he optical anisotropy in PI-B and pretilt was unclear. It was concluded tha
t the influence of molecular orientation on pretilt is strongly dependent o
n the polyimide type.