Vertical alignment of liquid crystals with negative dielectric anisotropy on an inorganic thin film with a hydrophilic surface

The vertical alignment of liquid crystals having negative dielectric anisotropy on an amorphous silicon O_xide (a-SiO_x) thin film is the consequence of the anisotropic interaction between liquid crystals and a-SiO_x thin films. To investigate the mechanism of the vertical alignment, we changed the physicochemical characteristics of alignment layers by controlling the composition, since the anisotropic interaction depends on the nature of both liquid crystals and an alignment layer. The variation of composition gives rise to a change in the polarizability, which is a simple measure of induced-dipole strength at the surface of the alignment layer. There is a critical transition point from planar to vertical alignment of liquid crystals, and it is the long-range van der Waals interaction that is responsible for the vertical alignment. The competition between long-range van der Waals interaction and short-range dipolar interaction were investigated and analyzed in terms of the interfacial energy between liquid rystals and an alignment layer.