Two transitions between isotropic and nematic phases in confined liquid crystals.

The molecular mean-field theory for the nematic-isotropic (N-Iso) phase transition in the vicinity of the surface is derived. We have shown that the nematic order parameter in liquid crystal near the surface is generally different from that in the bulk. It is never equal to zero if the anisotropic interaction with the surface is present. At the same time, transition from the phase with large nematic order parameter at the surface to the phase with small nematic order parameter at the surface is possible on heating. This surface transition always happens at higher temperatures than N-Iso phase transition related to the bulk. The theoretical prediction was well reproduced experimentally.