We study fluid-fluid phase separation in a colloid-polymer mixture adsorbed
in a colloidal porous matrix close to the \theta -point. For this purpose we
consider the Asakura-Oosawa model in the presence of a quenched matrix of
colloidal hard spheres. We study the dependence of the demixing curve on the
parameters that characterize the quenched matrix, fixing the polymer-to-colloid
size ratio to 0.8. We find that, to a large extent, demixing curves depend only
on a single parameter f, which represents the volume fraction which is
unavailable to the colloids. We perform Monte Carlo simulations for volume
fractions f equal to 40% and 70%, finding that the binodal curves in the
polymer and colloid packing-fraction plane have a small dependence on disorder.
The critical point instead changes significantly: for instance, the colloid
packing fraction at criticality increases with increasing f. Finally, we
observe for some values of the parameters capillary condensation of the
colloids: a bulk colloid-poor phase is in chemical equilibrium with a
colloid-rich phase in the matrix.Comment: 26 pages, 8 figures. In publication in Molecular Physics, special
volume dedicated to Luciano Reatto for his 70th birthda
