On the phase separation of a binary fluid in a porous medium

Our investigations of the phase diagram of a symmetric binary fluid in equi librium with a porous matrix show that moderate changes in the properties o f the matrix or in the matrix-fluid interaction lead to drastic modi cation s of the phase diagram of the fluid. Thus our results con rm on a qualitati ve basis recent experimental data. The phase diagrams that we have obtained show a wide variation and can be classified in terms of archetypes of syst ems of two order parameters. These different types can be characterised in terms of the loci where the lambda -line of the demixing transition interse cts the first-order liquid-vapour coexistence curve. Results are based on t he optimised random phase approximation and on grand-canonical Monte Carlo simulations.