Zenithal Anchoring Angle and Anchoring Strength on Oxidized Silane Plates

Abstract

Silane coated surfaces are chemically modified by using the post-discharge of an oxygen and nitrogen cold plasma, to produce alignment layers. These oxidized surfaces yield uniform nematic cells, provided that they are previously rubbed unidirectionally. Depending on the oxygen concentration arriving to the sample surface, the zenithal anchoring orientation may be tuned from planar to homeotropic, and tilted in-between. We measure the zenithal anchoring strength in the planar region, for 4-n-pentyl-4′ -cyanobiphenyl (5CB), as a function of the oxygen concentration and of temperature. The anchoring strength is found roughly independent of the oxygen concentration, with an extrapolation length ∼ 100 nm for ΔT=1.5K.