DISKOTIC MULTIYNE LANGMUIR-BLODGETT-FILMS .1. STRUCTURAL-X-RAY AND OPTICAL MICROSCOPY INVESTIGATION

The type of the diskotic phases in monolayers, Langmuir-Blodgett (LB) films and bulk liquid-crystalline state is considered as resulting from steric factors and intermolecular interactions. The role-of the dipole-dipole and pi-pi interactions for the induction of various diskotic phases in spread and deposited thin layers is emphasized on the basis of the recent achievements in structural modification of diskotic films. The monolayer organization of a novel disklike mesogenic multiyne amphiphile is characterized by means of surface pressure/area and surface potential/area isotherms, The structure and the morphology of the deposited LB films are investigated by means of X-ray diffraction and optical microscopy. Depending on the packing density of the layers, characterized by the average transfer ratios, three types of films structures are established-crystalline, teared, and smectic nematic, D-SN The D-SN diskotic phase, experimentally induced in the thin films by means of the LB technique, exhibits a higher degree of molecular order than the nematic phase of the bulk disk-shaped amphiphile. Models are presented for the ''edge-on'' nematic in-plane molecular arrangement of the spread diskotic monolayers and the smectic nematic, D-SN-like, multilayer structure of the LB films deposited at transfer ratios close to unity. Unification of the notations of the diskotic phases is proposed.