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 result 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 nonconvex 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 the adsorption isotherm matches the shape of the experimental isotherm. The predicted solvation pressure isotherms are qualitatively different from the solvation pressure isotherms in cylindrical pores. We attribute this difference to the formation of liquid bridges between the adjacent rods. Our results suggest that adsorption-induced deformation in materials with nonconvex pores cannot be predicted within the existing models. These results may shed some light on understanding the adsorption-induced deformation of consolidated granular media.