Enhancement by polydispersity of the biaxial nematic phase in a mixture of hard rods and plates

Abstract

The phase diagram of a polydisperse mixture of uniaxial rodlike and platelike hard parallelepipeds is determined for aspect ratios κ=5 and 15. All particles have equal volume, and polydispersity is introduced in a highly symmetric way. The corresponding binary mixture is known to have a biaxial phase for κ=15, but to be unstable against demixing into two uniaxial nematics for κ=5. The phase diagram for κ=15 is qualitatively similar to that of the binary mixture, regardless of the amount of polydispersity, while for κ=5 a sufficient amount of polydispersity stabilizes the biaxial phase. This provides clues for designing an experiment to observe this long searched biaxial phase.