X-ray reflectivity study of smectic wetting and prewetting at the free surface of isotropic liquid crystals.
We study the structures of free-surface-wetting layers above the isotropic to smectic-A transition of three liquid-crystal compounds that show different kinds of growth of the wetting film as the bulk transition is approached: layer-by-layer, continuous, and continuous with prewetting. The smectic-A surface phase of the layer-by-layer compound consists of well-defined layers and possesses a sharp boundary to the isotropic bulk phase, whereas in the two continuous compounds sinusoidal density oscillations with a continuously decaying amplitude are found. In the continuous case with prewetting, the wetting film below the prewetting transition does not show an essential difference to the continuous case without prewetting.
Lucht
R
R
Institute of Physical Chemistry, University Marburg, D-35032 Marburg, Germany.
Marczuk
P
P
Bahr
C
C
Findenegg
G H
GH