  The rich mesophase polymorhism and the phase sequence of board-like colloids
depends critically on their shape anisometry. Implementing extensive Monte
Carlo simulations, we calculated the full phase diagram of sterically
interacting board-like particles, for a range of experimentally accessible
molecular dimensions/anisometries of colloids of this shape. A variety of self
organized mesophases including uniaxial and biaxial nematics, smectic, cubatic
and columnar phases have been identified. Our results demonstrate clearly that
the molecular anisometry influences critically not only the structure and the
symmetry of the mesophases but also, and perhaps more interestingly, the phase
sequence among them. New classes of phase sequences such as nematic-nematic
and, for the first time, a direct transition from a discotic and a biaxial
nematic to an orthogonal smectic A phase have been identified. The molecular
geometry requirements for such a phase behavior have been located.
