EQUILIBRIUM PHASE-TRANSITIONS IN A POROUS-MEDIUM

Static critical phenomena of a three-dimensional Ising model confined in a porous medium made by spinodal decomposition have been studied us ing large-scale Monte Carlo simulations. We thus examine the influence of the geometry of Vycor-like materials on phase transitions. No surf ace interactions (preference of the Vycor-like material for one phase above the other) are taken into account. We find that the critical tem perature depends on the average pore size D as T-c(D)=T-c((infinity))- c/D. The critical exponents are independent of pore size: we find nu=0 .8+/-0.1, gamma=1.41-0.1, beta=0.65+/-0.13. No divergence is observed for the specific heat, indicating alpha less than or equal to 0. All d ata for all pore sizes can be collapsed well with the scaling function for the magnetic susceptibility chi L(-gamma/nu) = <(chi)over tilde>( tL(1/nu)), where t=T/T-c(D)-1. These critical phenomena are consistent with those computed for the randomly site-diluted Ising model. Experi mental realizations of our numerical experiments are discussed.