On the nematic-nematic phase transition in mixtures composed of sheet-shaped palladium organyls and apolar organic solvents

The three sheet-shaped palladium organyls la-e exhibit lyotropic nematic properties in apolar organic solvents. The occurrence of two nematic lyomesophases was verified by the investigation of the orientational properties of these liquid crystalline systems. In cells with obliquely deposited SiOx layers, the director of the high temperature phase N-2 is aligned in a homogeneous, planar manner. In the low temperature phase N-1, a different orientational pattern is observed. The specific pattern type depends on the deposition conditions of the SiOx layers. In samples homeotropically aligned in the N-2 phase, the director is tilted away from the cell normal after the transition into the N-1 phase. These changes of orientation are reversible. The experimental observations presented here support our proposed model for the structural change at the nematic-nematic phase transition.