  Comprehensive calculations were performed to predict the phase behaviour of
large spherical colloids mixed with small spherical colloids that act as
depletant. To this end, the free volume theory (FVT) of Lekkerkerker et al.
[Europhys. Lett. 20 (1992) 559] is used as a basis and is extended to
explicitly include the hard-sphere character of colloidal depletants into the
expression for the free volume fraction. Taking the excluded volume of the
depletants into account in both the system and the reservoir provides a
relation between the depletant concentration in the reservoir and in the system
that accurately matches with computer simulation results of Dijkstra et al.
[Phys. Rev. E 59 (1999) 5744]. Moreover, the phase diagrams for highly
asymmetric mixtures with size ratios q . 0:2 obtained by using this new
approach corroborates simulation results significantly better than earlier FVT
applications to binary hard-sphere mixtures. The phase diagram of a binary
hard-sphere mixture with a size ratio of q = 0:4, where a binary interstitial
solid solution is formed at high densities, is investigated using a numerical
free volume approach. At this size ratio, the obtained phase diagram is
qualitatively different from previous FVT approaches for hard-sphere and
penetrable depletants, but again compares well with simulation predictions.
