Phase Separation of Asymmetric Binary Hard-Sphere Fluids: Self-Consistent Density Functional Theory

The fundamental-measure free-energy density functional for general inhomogeneous hard-sphere fluids predicts phase separation in bulk binary mixtures with large size ratios, $\frac{R_2}{R_1}\gtrsim 4$ when the packing fractions for the two species are comparable, in qualitative agreement with recent experiments on "nearly hard sphere" colloidal particles. These results open the way, using the same free-energy functional, for studying external field effects (e.g., sedimentation and confining walls) on the entropically driven demixing transition, as encountered in real experiments on colloids.