*Macromolecules * **25**, 3227
(1992)

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

## S. Immerschitt, W. Stille, and G. Strobl

### Fakultät für Physik, Universität Freiburg, 79104 Freiburg,
Germany

#### 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.