We present a Monte Carlo simulation study of the phase diagram of an off-lattice molecular model of f fluid in a disordered porous material. The model consists of a Lennard-Jones 12-6 fluid confined in a rigid matrix of spheres and the size parameters are representative of methane in a silica xerogel. The fluid phase diagram shows effects of confinement, wetting, and matrix disorder. Our results provide evidence of two fluid phase transitions. The primary transition is analogous to the bulk vapor-liquid transition while the second transition has its origins in the wetting properties of the fluid in the more confined regions of the matrix.

• Received 23 January 1996

DOI:https://doi.org/10.1103/PhysRevE.54.R29