STRUCTURAL-CHANGES IN DISCOTIC SAMPLES DURING TRANSITION FROM CRYSTALTO DISCOTIC MESOPHASE AS REVEALED BY ELECTRON-MICROSCOPY AND DIFFRACTION

Classical methods of structural analysis cannot be applied to liquid c rystals because higher order reflections disappear during the transiti on from crystal to liquid crystal due to the reduction in long range o rientational and translational correlations. However, in order to rela te physical properties to the molecular architecture, it is essential to have information about molecular positions and orientations in the crystalline state as well as in the liquid crystalline state. In this work, the transition from crystalline to liquid crystalline phase is c arefully monitored and the relationship between the original lattice a nd the new molecular positions found using electron diffraction. In ad dition to this, a new high resolution electron-microscopic technique i s described in which the positions of molecules in the crystalline and the quenched discotic phase are directly imaged and the defects obser ved in the crystalline and LC phase compared and quantitatively analys ed.