PHASE-DIAGRAM OF ONSAGER CROSSES

Onsager crosses are hard nonconvex bodies formed by rigidly connecting three elongated rods, equally thick but not necessarily equally long, to form perpendicular crosses. We study the phase behavior of systems of such particles, focusing on their ability to form spatially homoge neous orientationally ordered phases with a symmetry lower than that o f the standard uniaxial nematic. We treat these systems in the Onsager , second virial coefficient, approximation. We apply bifurcation analy sis to build up a global picture of the phase diagram, which is then r efined using approximate numerical calculations. Finally, we generaliz e the Gaussian approximation for the nematic orientational distributio n function, to deal with the more ordered phases encountered here, and compare with the results from the previous techniques to see whether it is feasible to reliably predict the phase diagrams from a computati onally cheaper technique. [S1063-651X(98)01211-2].