Almost Critical Behavior of the Anchoring Energy at the Interface between a Nematic Liquid Crystal and a SiO Substrate

The anchoring energy at the interface between the nematic liquid crystal 4-n-pentyl-4?-cyanobiphenyl (5CB) and a glass plate treated by oblique evaporation of SiO is studied by measurement of the torque exerted on the surface by the nematic subject to an orienting magnetic field. The anchoring energy is sharply reduced as the clearing temperature is approached. The experiment provides the first direct evidence of a strong reduction of the surface order parameter for this system in the anisotropic phase.