Is the binary hard-sphere mixture a good reference system for sterically stabilized colloids?

The relevance of the hard-sphere mixture model as a starting point for the study of sterically stabilized colloids is discussed. Two physical situations are distinguished: true molecular solvent-colloid mixtures, and pseudobinary mixtures of two supramolecular objects. For the former, the limitation of the hard-sphere mixture model are recalled. Its potential use as a reference system for perturbation treatments is then analyzed. The accuracy of the latter is tested numerically. This study shows that the hard-sphere mixture is, in general, not a good reference system for sterically stabilized colloids in molecular solvents. For pseudobinary mixtures, the potential of mean force between the bigger solutes induced by the smaller ones is considered. The influence of a very short-range heteroattraction is discussed.