Binary Smectic Systems Including Trinuclear Pyrimidines with and without Nematic Gap

Abstract

Phase diagrams of binary mixtures are presented in which one component has been selected from among four trinuclear isomeric pyrimidines forming a nematic or smectic A, phase, and the second one from cyanocompounds forming an A d smectic phase. Depending on the molecular structure of pyrimidine, mixtures were obtained that show or show not a nematic gap between the A, and A d smectic regions. In the latter case it was found that the relation = f(x) has two independent branches in different ranges of the concentration JC. The measured spacing of the smectic layers in such mixtures points to the possibility of the pyrimidine monolayer being transformed into a bilayer.

From the discovery of the partially bilayer smectic A phase to blue phases in polar liquid crystals

“…Only the first pyrimidine 26 having dipole moment 6.5 D (dipoles of CN group and pyrimidine ring are pointing in the same direction) gave mixtures with the nematic gap. [175] Two other pyrimidines with dipole moments 1.97 D probably form heterocomplexes; they exhibit the phase diagrams characteristic of a direct transition between SmA d and SmA 1 phases as observed by Nguyen et al in single molecules where the dipoles of the polar groups were pointing in the opposite direction. [60] In The molar mixing volumes were measured for 4DBT-8OCB mixtures by dilatometric method.…”