Depression of the nematic-isotropic phase transition temperature at nanopatterned surfaces

A spatially varying herringbone pattern with an easy axis alternating in angle between 0 and psi and having a period of 200 nm was scribed into a polyimide-coated substrate. The depression of the nematic-isotropic transition temperature for a nematic layer at the patterned surface relative to its value at a uniformly rubbed surface was investigated as a function of psi for 15 < psi < 88 degrees. It was found that the depression of the transition temperature increases with psi, up to approximately 7 mK at psi=88 degrees. A simple model was developed that includes not only elasticity, but also anchoring effects at the polyimide. The model, which is used to calculate the thickness of the nematic layer, indicates that anchoring-rather than elastic-effects play the dominant role in the depression of the layer's transition temperature.