Influence of the molecular structure of compounds with terminal isothiocyanate group on the induction of the smectic A phase: Part II

The influence of the structure of compounds having terminal isothiocyanate group in binary mixtures with compounds having terminal alkyl chains on the induction of the smectic A phase is shown. Compounds with a triple bond in the molecular core exhibit a weaker induction of a SmA phase than compounds without it. Molecular lengths, dipole moments and polarisabilities of investigated compounds were calculated. Dielectric spectroscopy studies were done for the chosen system to show that single compounds have the opposite signs of the dielectric anisotropy, while the mixture with maximum temperature of SmA-N phase transition in the nematic phase has a positive dielectric anisotropy. In addition, the dielectric spectroscopy results confirm that the SmA phase is indeed nucleated in the mixture. It has been concluded that there is a competition of different factors, like the shape of molecules, their polarity and polarisability affecting the induction of SmA phase. The shape of a molecule appears to be a crucial factor here since it determines the distance between molecules and influences the contribution of dispersion forces.