THE INFLUENCE OF THE SHAPE AND THE INCOMPATIBILITY OF MOLECULAR MOIETIES ON THE STRUCTURE OF SMECTIC MESOPHASES

For selected compounds with perfluorinated chains the structure of sme ctic phases was investigated by X-ray diffraction measurements. For ro d-like compounds with only one terminal perfluorinated chain the incom patibility of the hydrocarbon and the fluorocarbon moieties leads to a segregation of both parts which can be considered as microphase separ ation. For swallow-tailed compounds the structure of smectic phases de pends on the position and the length of the perfluorinated chains. If the steric interaction dominates an antiparallel packing of the molecu les within the smectic layers is favoured. If the incompatibility of t he hydrocarbon and fluorocarbon moieties is of importance the smectic layers are distorted and at lower temperatures the layer structure is transformed into a columnar structure.