POLYMORPHISM AND CHEVRON LAYER STRUCTURE OF AN ANTIFERROELECTRIC LIQUID-CRYSTAL STUDIED BY X-RAY-DIFFRACTION

We report X-ray diffraction experiments performed on an antiferroelect ric compound exhibiting a very rich polymorphism (S-IA-S-C*A-S-C*FI1 -S-CFI2-S-C* -S-C* alpha-S-A) The structural study of the unknown pha ses only allows us to exclude some phenomenological models. The use of oriented planar samples prepared between solid glass plates generate by cooling from the Sa phase a chevron structure of tilted layers alre ady well characterized for the Sc phase. The extensive analysis of the evolution of the chevron structure through the numerous smectic-smect ic phase transitions provides some original information in three disti nct areas: fundamental data on the important physical parameters in th e chevron structure formation, detection of the smectic-smectic phases transition by small change of the chevron structure. and information on the local molecular order induced by the alignment layer (interacti on with a rubbed polymer).