Use of Ellipsometry in a Study of the Surface Order in the Isotropic Phase of a Liquid Crystalline Polyacrylate

Abstract

Pretransitional order at the free surface of the isotropic phase of a liquid crystalline side-group polyacrylate was studied by reflection ellipsometry. A large shift of the Brewster angle φ_B to higher values was observed when the temperature approached the isotropic-nematic transition point, indicating a boundary layer of large thickness together with negative anisotropy of the dielectric constant. To describe the profile of the reflecting layer, a model function for the dielectric constant assuming uniaxial symmetry of the layer and exponential decay of the anisotropy was used, taking into account a roughness of the surface. The data are well represented by fits to this model, leading to negative values of the nematic order parameter at the surface.