Surface and bulk order parameters of a nematic liquid crystal

The measurements of the anisotropy of the refractive index have been made for heptyl-cyanobiphenyl (7CB) at the surface as well as in the bulk by the interferometric method. Using these data, order parameters S̄ at the surface and S in the bulk were calculated. The results show that S̄ is slightly larger than S in the nematic temperature region. S becomes zero in the isotropic region; nevertheless, the order parameter at the surface, S̄, still has a finite value even at temperatures above the clearing point.