Density Functional Theory Model for Adsorption-Induced Deformation of Mesoporous Materials with Nonconvex Pore Geometry
Adsorption of fluids in nanoporous media causes mechanical stresses which results in deformation. This phenomenon is ubiquitous and its magnitude depends on the pore size and geometry. Adsorption and adsorption-induced deformation are typically modeled in slit-shape or convex (cylindrical or spherical) pores. However, many porous materials are composed of spherical grains, so that the pores are formed by the intergranular spaces between the convex solid surfaces. Here we present a first theoretical study of adsorption-induced deformation in non-convex pores, in particular we studied the templated mesoporous carbons. The model is based on classical density functional theory within the local density approximation applied to the description of hard sphere interactions. We predict the adsorption isotherms and solvation pressure isotherms for nitrogen adsorption in CMK-3 carbons. The shape of adsorption isotherm matches the shape of experimental isotherm. The predicted solvation pressure isotherms are qualitatively different from the solvation pressure isotherms in cylindrical pores. We attribute this difference to formation of liquid bridges between the adjacent rods. Our results suggest that adsorption-induced deformation in materials with non-convex pores cannot be predicted within the existing models. These results may shed some light on understanding adsorption-induced deformation of consolidated granular media.