THE PRESSURE OF A FLUID CONFINED IN A DISORDERED POROUS MATERIAL

Using the Green-Bogoliubov method, we derive an expression for the the rmodynamic pressure or grand potential density for a molecular model o f a fluid confined in a disordered porous matrix. The expression is eq uivalent to the virial equation derived previously via the replica met hod [Rosinberg et al., J. Chem. Phys. 100, 5172 (1994)] but differs fr om an expression recently derived from the condition of mechanical equ ilibrium. It is concluded that the condition of mechanical equilibrium does not yield information about the thermodynamics of these systems. The thermodynamic pressure can be obtained from experiment indirectly by integrating the Gibbs adsorption isotherm and, in principle, by di rect measurement. (C) 1995 American Institute of Physics.