Characterisation of porous media by the virtual capillary condensation method

A computational methodology for the calculation of pore size distribution from three-dimensional digitally represented porous media of any pore morphology is described in this work. The methodology consists of two steps: simulation of capillary condensation for a given porous medium by the Volume of Fluid (VOF) method, and then evaluating the equivalent pore size distribution from the calculated dependence of the fraction of filled pore volume on the liquid–vapour interface curvature radius. The methodology is first demonstrated on the example of capillary condensation in a single ink-bottle pore and then used for the evaluation of pore size distribution in three classes of porous media with qualitatively different microstructure: model Vycor glass represented by Gaussian porous media; model nanoparticle assemblies; and model open-cell solid foams created by colloidal templating. The relationship between the shape of the pore-size distribution and the morphological features of the porous medium is discussed, and the mean pore radius evaluated by the virtual capillary condensation method is compared with the equivalent hydraulic radius in each case. The two radii are shown to be correlated, but the correlation coefficient is different, and therefore characteristic, for each class of porous media.