Phase behavior of near-critical fluids confined in periodic gels

Experiments show that the coexistence region of a vapor-liquid system or binary Liquid mixture is narrowed dramatically when the fluid is confined in a dilute porous medium such as a silica aerogel. We propose a simple model of the gel as a periodic array of cylindrical strands and study the phase behavior of an Ising system confined in this geometry. Our results suggest that the coexistence region should widen out at lower temperatures and that the narrowness observed near the critical point may be a fluctuation-induced effect.