NEMATIC AND SMECTIC SURFACE ORDER IN THE ISOTROPIC-PHASE OF LOW MOLAR-MASS AND POLYMERIC LIQUID-CRYSTALS

Pretransitional surface ordering phenomena, as they occur in the isotr opic phase of liquid crystals upon approaching the clearing point, wer e studied by variable angle ellipsometry and X-ray reflectivity measur ements. Ellipsometric data obtained for two phenylcyclohexanes indicat e a logarithmic divergence of the thickness of a nematic boundary laye r with homoeotropic orientation, which corresponds to a complete wetti ng behaviour. Data can be represented by a model based on a Landau-de Gennes approach. An investigation of a LC-side group polyacrylate show ed a boundary layer with planar orientation. The thickness, which incr eases on approaching the clearing point, is clearly larger than in the case of the low molar mass samples. In X-ray reflectivity studies on a film of a LC-side group polymer boundary layers with smectic order w ere detected. They possess a remarkable stability and exist also at la rger distances from the clearing point. A stepwise procedure in the da ta analysis enables a detailed, complete characterization.