The liquid-crystalline phase behavior of a fluid of biaxial hard particles (spheroplatelets) is studied using a scaled particle calculation of the fluid configurational entropy combined with a cell description of translational order. If translational ordering is ignored, the density versus particle biaxiality phase diagram displays a cusp-shaped biaxial-nematic phase intervening between two uniaxial nematic phases. The location of the crossover from rodlike to platelike uniaxial-nematic behavior is in agreement with previous bifurcation-analysis results. The density discontinuity at the isotropic-nematic transition decreases as this crossover is approached from both the rodlike and platelike sides, becoming vanishingly small at the crossover point itself. When the possibility of translational order is considered, the phase diagram displays three distinct smectic-A phases, in addition to the two uniaxial nematic phases, and only a small remnant of the biaxial-nematic phase. One of the three smectic phases has in-layer orientational order, while the other two have in-layer isotropic order.

• Received 13 May 1991

DOI:https://doi.org/10.1103/PhysRevA.44.3742