PHASE-SEPARATION OF ASYMMETRIC BINARY HARD-SPHERE FLUIDS - SELF-CONSISTENT DENSITY-FUNCTIONAL THEORY

It was recently shown (Phys. Rev. Lett. 1994, 72, 3831) that the ''tes t-particle-self-consistent'' fundamental measure free energy density f unctional for general inhomogeneous hard-sphere fluids (J. Chem. Phys. 1993, 98, 8126) predicts phase separation in bulk binary mixtures wit h large size ratios, R(2)/R(1) > similar to 4, when the packing fracti ons for the two species are comparable, in qualitative agreement with recent experiments on ''nearly hard-sphere'' colloidal particles. Thes e preliminary calculations are focused on the spinodals and not on the equilibrium coexistence curve, which is much harder to calculate. To prepare the necessary tools for undertaking the complete thermodynamic calculation, the present paper provides a full description of this se lf-consistent density functional for mixtures and clears many fine poi nts in the theory. It also gives a more detailed presentation of the r esults relevant for phase separation. These results should be useful f or studying external field effects (e.g., sedimentation and confining walls) on the entropically driven demixing transition, as encountered in real experiments on colloids.