On the molecular requirements for the stabilisation of thermotropic biaxial ordering in rod-plate nematics

A nematic consisting of rod-Eke and plate-like molecular species is expecte d to exhibit phase biaxiality over a range of concentrations. Phase separat ion, however, prevents the achievement of such concentrations in mixtures o f conventional, low molar mass, thermotropic calamitic and discotic mesogen s. We present a theoretical study of the molecular requirements for phase b iaxiality in three types of rod-plate nematics, namely in (i) binary mixtur es of hard rods and discs, (ii) mixtures of rods and discs exhibiting molec ular association, either by direct rod-disc interaction or through selectiv e interactions with a third molecular species and (iii) single component sy stems with interconverting rod-like and plate-like conformations.