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 rod-like and plate-like hard parallelepipeds is determined for aspect ratios $\kappa =5$ 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 $\kappa =15$, but to be unstable against demixing into two uniaxial nematics for $\kappa =5$. We find that the phase diagram for $\kappa =15$ is qualitatively similar to that of the binary mixture, regardless the amount of polydispersity, while for $\kappa =5$ a sufficient amount of polydispersity stabilizes the biaxial phase. This provides some clues for the design of an experiment in which this long searched biaxial phase could be observed.

4 pages, 5 eps figure files, uses RevTeX 4 style