Light scattering by fluctuations within a nematic wetting layer in a isotropic phase of a liquid crystal

Abstract

Wetting of a solid surface by a homeotropically oriented nematic layer in the isotropic phase of the liquid crystal CB8 is examined by static light scattering experiments under evanescent illumination. For angles of incidence between the critical angle of total internal reflection and a larger second critical angle, an enhanced off-specular scattering is observed, which can be attributed to orientational fluctuations within the surface layer. In contrast to the scattering of the isotropic bulk there is a marked dependence on the scattering vector component parallel to the interface. The effect is observable only within a range of 0.4 K above the clearing point. The second critical angle gives experimental access to the order parameter S(0) at the interface. By combination of the scattering data with ellipsometric measurements, the thickness of the layer at a temperature close to the clearing point is estimated to d = 6.9 nm. This value is comparable to the isotropic bulk correlation length xi(ni) = 5.6 nm determined by conventional light scattering.