Mesophase behaviour of binary mixtures of bent-core and calamitic compounds

摘要

The mesophase behaviour of binary mixtures of bent-core and calamitic liquidcrystals is presented. The nematogenic 4,6-dichloro-1,3-phenylenebis[4'-(10-undecen-1-yloxy)-1,1'-biphenyl-4-carboxylate] (I) was thebanana-shaped component. As the calamitic compound ethyl4'-(9-decen-1-yloxy)-1,1'-biphenyl-4-carboxylate (II), similar to one arm ofthe bent-core molecule, was used which exhibits smectic phases in a widetemperature range. A total of 6 mixtures with different compositions wereprepared and studied by polarising optical microscopy, differential scanningcalorimetry and X-ray diffraction on non-oriented samples. In the mixtures anematic phase is not concomitant with smectic A phase, and the temperaturerange of both phases highly depends on the concentration of the comprisingcompounds. Lowered melting temperatures have been observed for all mixtureswith respect to that of the pure compounds. Unforeseen finding is the inductionof a monotropic SmC phase in mixtures with lowest concentration of thebent-core compound. Semi-empirical quantum-chemical calculations have also beenperformed. Based on the calculated molecular conformation, as well as oncollected X-ray diffraction data, a model for a possible self-assembly of thebanana-shaped and calamitic compounds is proposed.