The thickness of the surface layer in polymer‐aligned liquid‐crystal cells

Abstract— Existing experimental evidence, such as scanning tunneling microscopy (STM) or second‐harmonic generation (SHG), shows that the liquid‐crystal molecules are strongly fixed at the polymer surface. The nematic phase in the bulk is uniaxial, which shows that the molecules are free to rotate around one axis in the bulk of the material. Therefore, a transition layer where the molecules gradually gain freedom (or lose bond orientational order) must exist. New equations relating the thickness of this surface layer to the optical properties of untwisted liquid‐crystal cells of different thickness were derived. By comparing our equations with experimental observations, order‐of‐magnitude estimates for the thickness of the surface layer have been obtained. We found that the surface‐layer thickness is in the 0.1–1.0‐μm range.