Phase behavior of colloidal rod-sphere mixtures

We investigate the depletion induced phase separation in mixed suspensions of colloidal spheres with diameter s and colloidal rods with length L and diameter D. Using an extension of the free volume method developed by one of us [H.N.W. Lekkerkerker and A. Stroobants, Physica A 195, 387 (1993), we calculate the phase diagrams for L≤σ and various L/D ratios. For long thin rods, the volume fractions of rods needed to induce phase separation scale as D2/Lσ . Good agreement with recent experimental results is obtained