Liquid crystal aligned on the apparent isotropic surface in the liquid crystal cell: optical characterization

The liquid crystal alignments in the liquid crystal cell composed of the bare glass and indium tin oxide (ITO) regions are investigated based on birefringence. The experimental results by the proposed methods of circularly and linearly polarized light agree with the observation through the polarized optical microscope. The results show that the liquid crystal in the region of the bare glass is optical anisotropic and the liquid crystal director is almost parallel to the long side of the liquid crystal cell, while the liquid crystal in the region of ITO is isotropic. No other chemical components were found on the bare glass and ITO surfaces by the x-ray energy dispersive spectrometer, and the numerous random scratches on the bare glass were observed through the atomic force microscope. The self-consistent explanations for the different approaches and characteristic results are obtained. It is concluded that the bulk stress on the bare glass, rather than the local stress accompanied with the scratches, resulted in the liquid crystal alignment. Compared with the anisotropy of the bulk stress on the full bare glass, which formed during the preparation, the local stress on the scribed bare glass of the liquid crystal cell is isotropic. The scratch orientations are random, which cause the averaged local stress isotropic. The bulk stress on the long side is more significant than that on the short side of the cell. As a result, the liquid crystal director is almost parallel to the long side of the liquid crystal cell. The direction of the liquid crystal in the region of ITO is random, and the liquid crystal in that region is not birefringent.