Improved liquid crystals for vertical alignment applications

Abstract

Liquid crystals with a large negative dielectric anisotropy are difficult to align vertically on silicon oxide surfaces and sometimes even on polyimides. An interesting method has been found to generate high quality vertical alignment by doping the host liquid crystal with materials that have a cyanogroup along their long molecular axis. The effect is explained by considering both long range and short range interactions between liquid crystal and the alignment layer. Using this method we propose a way to design new liquid crystal mixtures with large negative dielectric anisotropy that have improved aligning ability for applications requiring vertical alignment. The method also allows for increased birefringence.

Silicon oxides as alignment surfaces for vertically-aligned nematics in photonic devices

“…These interactions determine the liquid crystal pretilt and polar anchoring energy of the cell. This affects crucial electrooptic factors [4,5], such as threshold voltage and response time of the device [6,7], which may be modified by varying different manufacturing process parameters [8][9][10][11].…”

Liquid-crystal anchoring transitions on aligning substrates processed by a plasma beam

“…Different alignment behavior of the NLC materials is attributed to the Van der Waals (VdW) interaction and order electricity. The competing effects between the VdW and dipole-to-dipole interactions are considered in [37] to explain why vertical alignment of NLC with (1) in the presence of the polar term proportional to w 1 = 0. There is a metastable state separated from the equilibrium structure by the energy barrier in the regions labeled by subscript B.…”

VAN LCOS Microdisplays: A Decade of Technological Evolution

“…This comes down to the requirement that the dielectric anisotropy must be large enough. Increasing the dielectric anisotropy may however affect the quality of the vertical alignment of the liquid crystal [16]. This can be alleviated by adding small amounts of liquid crystal materials that have a positive anisotropy [16].…”