Liquid crystal orientation induced by Van der Waals interaction

It has been discovered that liquid crystal alignment on an inorganic surface such as SiO2 depending on the dielectric anisotropy of the liquid crystal materials. The liquid crystals with positive dielectric anisotropy tend to align parallel or parallel with a tilt to the SiO2 substrates, while the liquid crystals with negative dielectric anisotropy tend to align perpendicular or perpendicular with a tilt to the SiO2 substrates. The pretilt angle of liquid crystals with positive dielectric anisotropy aligned by single evaporation of SiO2 tends to be at a complementary angle to that of liquid crystals with negative dielectric anisotropy. Van der Waals interaction is responsible for such orientation when all the other types of interactions between liquid crystal molecules and surfaces are absent or negligible. In addition, this work provides a simple and reliable method for high quality homeotropic and tilted homeotropic liquid crystal alignment.