SANS STUDIES OF FLUID-PHASE TRANSITIONS IN POROUS-MEDIA

The study of binary fluid phase transitions in porous media has receiv ed a great deal of attention, both theoretically and experimentally, o ver the past few years. The preferential wettability of the internal s urfaces by one of the fluids introduces a randomness that has led to c onsideration of Random Field Ising Models. However, in certain cases s uch as Vycor glass, the confinement in the pores plays a dominant role . A different limit is obtained in the case of aerogels which have int ernal mass fractal density correlations. We discuss the theory of scat tering by binary fluid concentration fluctuations in both these types of porous solid and recent studies of the scattering from water/lutidi ne critical and near-critical mixtures in these systems.