Depletion forces and packing models

In binary colloidal suspensions, due to the depletion forces, large spheres tend to pack together so as to make entropy maximum. Based on the complexities of depletion forces and phase behaviors in binary mixtures, two packing models, named nucleation and non-nucleation packing, are proposed in this Letter. Numerical results show that, when the volume fraction is small, the nucleation is possible. As a result, the large spheres tend to pack into a larger and larger cluster. However, when the volume fraction is very large in a way, the hard-spheres will proceed in the non-nucleation packing fashion. The numerical results also show that differences between the two packing models decrease with the decrease of volume fraction.