| In this thesis, we study both static and dynamic critical behavior of fluids embedded in porous media. First, we address the issue of the static critical behavior of fluids confined in random porous structures taking a mean-field approach. It is based on a lattice-gas formalism that incorporates effects of both fluid confinement and interaction between the fluid and the porous medium. We arrive at a new mean-field equation of state and use it to predict a variety of thermodynamic properties in these systems. We derive the dependence of the phase diagram on temperature, porosity and the strength of the fluid-pore interaction. We predict the existence of systems having the same porosity and critical temperature, but different fluid-pore interactions. In comparisons with adsorption isotherms generated by Monte Carlo computer simulation methods, the simulation data show good agreement with the mean-field predictions.; In order to develop a phenomenologically appealing simulation method of calculating transport coefficients in near-critical fluids, we propose a new relaxation method that proves advantageous over other existing methods near criticality. We describe this method in detail and show that we see critical slowing down at the correct critical temperatures for both homogeneous and confined fluids. Using this method, we also calculate the critical exponent for the collective diffusion constant for model B systems, a result that is the first calculation of this exponent using relaxation dynamics methods. The value of this exponent calculated (y = −1.97 ± 0.09) is in excellent agreement with its value found using Monte Carlo simulations in an equilibrium ensemble. Next, we study near-critical diffusion of dilute binary fluids embedded in porous media. We analyze the relaxation of the solute at the critical point of the solvent and successfully explain simulation results obtained for random structures. Finally, we arrive at the equation governing the flux of the solute in a near-critical membrane diffusion experiment and show that it is possible to have selective diffusion in the presence of more than one solute, a phenomenon that can be applied to separation processes. |
