  We study various manifestations of structural crossover in the properties of
a binary mixture of hard-spheres. For homogeneous mixtures that are
sufficiently asymmetric, there is a crossover line in the phase diagram such
that for thermodynamic states that lie on one side, the decay of the three bulk
pair correlation functions is oscillatory with a common wavelength
approximately equal to the diameter of the smaller spheres, and for states on
the other side, the common wavelength is approximately the diameter of the
bigger spheres. Using density functional theory we show that structural
crossover manifests itself in the intermediate range decay of i) the one-body
density profiles of a hard-sphere mixture adsorbed at planar walls, ii) the
effective (depletion) potential between two big hard-spheres immersed in the
same binary mixture and iii) the solvation force, or excess pressure, of the
same mixture confined between two planar hard-walls. We determine exactly the
structural crossover line for a one-dimensional binary mixture of hard-rods and
present evidence, based on density functional theory calculations and
Monte-Carlo simulations, for structural crossover in homogeneous binary
mixtures of hard-disks in two dimensions. By considering a multicomponent
mixture of hard-spheres, with an appropriate bimodal distribution of diameters,
we argue that structural crossover should still occur in the presence of
polydispersity and that our results could be relevant to colloidal mixtures
where correlation functions can be measured using real-space techniques.
