Phase transitions in a solution of rodlike macromolecules of two different sizes

Phase equilibria for a solution of long rigid rods of diameters D_i and lengths L_i (i = 1,2) are studied analytically using Gaussian trial functions. The conditions on the molecular size parameters for a nematic—nematic phase transition to be possible are determined, and found to be satisfied everywhere except in a closed domain in the diameter ratio—length ratio plane. Information on the relative ordering of the two components is also provided.