Combination of small angle scattering and three-dimensional stochastic reconstruction for the study of adsorption-desorption processes in Vycor porous glass

We study sorption and transport processes in dry and wet (preadsorbed with CH2Br2) Vycor glass by combining small angle scattering and three-dimension al (3D) stochastic reconstruction methods. Three-phase systems of solid, co ndensate, and void space, are generated for the first time, by the combinat ion of the above methods. The resulting 3D images can visualize the evoluti on of the adsorption process and show how sorption alters the pore space ch aracteristics of the material. Desorption is modeled in this system with th e additional employment of an invasion percolation algorithm to account for the hysteresis effect caused by the inaccessible regions of the porous mat rix. It is found that desorption is simulated very well provided that the m ain mechanism for hysteresis depends only on the topology of the pore space and not on thermodynamic effects. Based on a random-walk procedure, Knudse n transport properties of the reconstructed images are also determined for different degrees of saturation, providing very good agreement with experim ental relative permeability data. Thus, relative permeability reflects pure ly the pore accessibility properties of the material and may assist in disc erning their exact contribution to the equilibrium sorption hysteresis loop . (C) 2000 American Institute of Physics. [S0021-9606(00)70422-3].