  A simple model for functionalized disordered porous media is proposed and the
effects of confinement on self-association, percolation and phase behavior of a
fluid of patchy particles are studied. The media is formed by a randomly
distributed hard-sphere obstacles fixed in space and decorated by a certain
number of off-center square-well sites. The properties of the fluid of patchy
particles, represented by the fluid of hard spheres each bearing a set of the
off-center square-well sites, are studied using an appropriate combination of
the scaled particle theory for the porous media, Wertheim's thermodynamic
perturbation theory, and the Flory-Stockmayer theory. To assess the accuracy of
the theory a set of computer simulations have been performed. In general,
predictions of the theory appear to be in a good agreement with computer
simulation results. Confinement and competition between the formation of bonds
connecting the fluid particles, and connecting fluid particles and obstacles of
the matrix, give rise to a re-entrant phase behavior with three critical points
and two separate regions of the liquid-gas phase coexistence.
