Influence of the molecular structure of calamitic compounds with trifluoromethoxy terminal group on the induction of the smectic a phase. Part I

For the liquid crystalline mixtures of compounds with positive and negative dielectric anisotropies, the induction of the liquid crystal smectic A phase can be observed. This effect can be very favourable for definite specific purposes. The main aim of this work is to determine the influence of the molecular structure of compounds with a polar trifluoromethoxy (-OCF3) group on the induction strength of the orthogonal smectic A (SmA) phase. In order to reach this target, the phase diagrams of the mixtures were established using the polarised optical microscope observations. The presence of a triple bond, phenyl and cyclohexyl rings as well as fluorine atoms in the core and the length of terminal alkyl chains of the tested compounds were considered. The length of the rigid core has the greatest effect on the induction strength of the SmA phase, while the length of the alkyl chain (3-5 carbon atoms) has relatively minor influence. Explaining the correlation between the molecular structure and the induction strength, the dipole moments and the polarisability of the molecules should be taken into account. For shorter molecules, changes in the molecular structure have more significant influence on the temperature and concentration range of the orthogonal SmA phase.