Morphology of Fluids Confined in Physically Reconstructed Mesoporous Silica: Experiment and Mean Field Density Functional Theory

Three-dimensional
physical reconstruction of the random mesopore
network in a hierarchically structured, macroporous–mesoporous
silica monolith via electron tomography has been used to generate
a lattice model of amorphous, mesoporous silica. This geometrical
model has subsequently been employed in mean field density functional
theory (MFDFT) calculations of adsorption and desorption. Comparison
of the results with experimental sorption isotherms for nitrogen at
77 K shows a good qualitative agreement, with both experiment and
theory producing isotherms characterized by type H2 hysteresis. In
addition to the isotherms, MFDFT provides the three-dimensional density
distribution for the fluid in the porous material for each state studied.
We use this information to map the phase distribution in the mesopore
network in the hysteresis region. Phase distributions on the desorption
boundary curve are compared to those on the adsorption boundary curve
for both fixed pressure and fixed density, revealing insights into
the relationship between phase distribution and hysteresis.